Characterisation of pomegranate juice effects on human corpus cavernosum

Pomegranate (POM) juice may benefit the erectile process, but the scientific evidence is lacking. This study evaluates the molecular characterisation and confirmation of POM's action on human corpus cavernosum (HCC) obtained from patients (n = 16) undergoing penile prosthesis implantation. After phenylephrine contraction, the relaxant effects of POM with various inhibitors in the presence and absence of palmitic acid (PA)-induced acute oxidative stress were investigated. Electrical field stimulation (EFS)- and acetylcholine (ACh)-induced relaxation were performed using organ bath preparation. Expression of neuronal nitric oxide synthase (nNOS), endothelial (eNOS), phosphodiesterase (PDE)-5A and cGMP levels were assessed in cells from ex vivo organ cultures of HCC, using RT-PCR, ELISA and immunohistochemistry techniques. POM induced marked relaxation of HCC (maximum response: 97.0 ± 3.1%) and reversed the PA-induced decrease of EFS (20 Hz). nNOS transcription was increased by 7-fold in POM-treated cells without influencing eNOS and PDE5A expressions. We conclude that POM induced marked relaxation of HCC via: (i) nNOS stimulation, and (ii) downstream relaxation stimulated by nNOS and cGMP and bypassing the NO and PDE5. This action provides a rationale for the therapeutic or preventative use of POM in men with erectile dysfunction who do not respond well to PDE5 inhibitors.

Adipose tissue-derived stem cell therapy for prevention and treatment of erectile dysfunction in a rat model of Peyronie's disease

Peyronie's disease (PD) is a localized connective tissue disorder that involves the tunica albuginea (TA) of the penis. While surgical correction remains the gold standard, the search for an effective and less invasive therapy continues. The objective of this study was to evaluate the effects of intratunical injection of adipose tissue-derived stem cells (ADSCs) for the prevention and treatment of erectile dysfunction in a rat model of PD. Twenty-four male Sprague-Dawley rats (300-350 g) were randomly divided into four groups: sham, PD, PD + ADSC (prevention) and PD + ADSC (treatment). All rats underwent penile injections into the TA with 50 μL vehicle (sham) or 0.5 μg transforming growth factor (TGF)-β1 (remaining groups). The ADSC groups received intratunical injections with 0.5 million rat-labelled ADSCs on day 0 (prevention) or day 30 (treatment). Forty-five days following TGF-β1 injection, rats underwent cavernous nerve stimulation (CNS) with total intracavernous-to-mean arterial pressure ratio (ICP/MAP) and total ICP recorded to measure response to therapy. Tissues were evaluated histologically and for mRNA expression of tissue inhibitors of metalloproteinases (TIMPs), matrix metalloproteinases (MMPs) and zymographic activity of MMPs. Statistical analysis was performed by analysis of variance followed by the Tukey test for post hoc comparisons. In both prevention and treatment groups, intratunical injection of ADSCs resulted in significantly higher ICP/MAP and total ICP in response to CNS compared with the PD group. Local injection of ADSCs prevented and/or reduced Peyronie's-like changes by decreasing the expression of TIMPs, and stimulating expression and activity of MMPs. This study documents the preventive and therapeutic benefits of ADSC on penile fibrosis and erectile function in an animal model of PD.

Effect of avanafil on rat and human corpus cavernosum

We compared the activity of a new phosphodiesterase-5 inhibitor (PDE5i) avanafil with sildenafil and tadalafil in human and rat corpus cavernosum (CC) tissues. The effect of avanafil with several inhibitors and electrical field stimulation (EFS) was evaluated on CC after pre-contraction with phenylephrine. With the PDE5i, sildenafil and tadalafil, concentration-response curves were obtained and cyclic guanosine monophosphate (cGMP) levels were measured in tissues. Avanafil induced relaxation with maximum response of 74 ± 5% in human CC. This response was attenuated by NOS inhibitor and soluble guanylate cyclase (sGC) inhibitor. Avanafil potentiated relaxation responses to acetylcholine and EFS in human CC and enhanced SNP-induced relaxation and showed 3-fold increase in cGMP levels. When compared with sildenafil, avanafil and tadalafil were effective at lower concentrations in human CC. In addition, Sprague-Dawley rats underwent in vivo intracavernosal pressure (ICP) and mean arterial pressure (MAP) measurements. Avanafil increased ICP/MAP that was enhanced by SNP and cavernous nerve (CN) stimulation in rat CC tissues. Also avanafil showed maximum relaxation response of 83 ± 7% in rat CC with 3-fold increase in cGMP concentration. Taken together, these results of our in vivo and in vitro studies in human and rat suggest that avanafil promotes the CC relaxation and penile erection via NO-cGMP pathway.

Animal models of catheter-induced intimal hyperplasia in type 1 and type 2 diabetes and the effects of pharmacologic intervention

Diabetes is a complex disorder characterized by impaired insulin formation, release or action (insulin resistance), elevated blood glucose, and multiple long-term complications. It is a common endocrine disorder of humans and is associated with abnormalities of carbohydrate and lipid metabolism. There are two forms of diabetes, classified as type 1 and type 2. In type 1 diabetes, hyperglycemia is due to an absolute lack of insulin, whereas in type 2 diabetes, hyperglycemia is due to a relative lack of insulin and insulin resistance. More than 90% of people with diabetes have type 2 with varied degrees of insulin resistance. Insulin resistance is often associated with impaired insulin secretion, and hyperglycemia is a common feature in both types of diabetes, but failure to make a distinction between the types of diabetes in different animal models has led to confusion in the literature. This is particularly true in relation to cardiovascular disease in the presence of diabetes and especially the response to vascular injury, in which there are major differences between the two types of diabetes. Animal models do not completely mimic the clinical disease seen in humans. Animal models are at best analogies of the pathologic process they are designed to represent. The focus of this review is an analysis of intimal hyperplasia following catheter-induced vascular injury, including factors that may complicate comparisons between different animal models or between in vitro and in vivo studies. We examine the variables, pitfalls, and caveats that follow from the manner of induction of the injury and the diabetic state of the animal. The efficacy of selected antidiabetic drugs in inhibiting the development of the hyperplastic response is also discussed.

Pressor responses to ephedrine are not impaired in dopamine beta-hydroxylase knockout mice

BACKGROUND AND PURPOSE

Ephedrine and amphetamine can cause substantial increases in systemic arterial pressure. However, the role of endogenous noradrenaline release in mediating the pressor response to ephedrine is controversial. Studies using pharmacologic agents to decrease the synthesis, storage, and release of catecholamines have supported both a direct and an indirect mechanism of action for ephedrine. The purpose of the present study was to determine if endogenous noradrenaline release is required for cardiovascular responses to ephedrine and amphetamine using a genetic mouse model.

EXPERIMENTAL APPROACH

Increases in systemic arterial pressure and heart rate in response to ephedrine and amphetamine were investigated and compared in dopamine beta-hydroxylase knockout (Dbh -/-) mice that cannot synthesize noradrenaline. Dbh +/- littermates have normal noradrenaline and adrenaline tissue levels, and served as controls in all experiments.

KEY RESULTS

In Dbh -/- mice the increases in systemic arterial pressure and heart rate in response to i.v. injections of ephedrine were not impaired whereas responses to amphetamine were markedly reduced, when compared with responses in Dbh +/- mice. The pressor response to tyramine was abolished whereas pressor responses to noradrenaline, phenylephrine, dopamine, and angiotensin II were similar in Dbh -/- and Dbh +/- mice.

CONCLUSIONS AND IMPLICATIONS

The present results in Dbh -/- mice provide support for the hypothesis that pressor responses to ephedrine are directly mediated whereas responses to amphetamine are dependent on the release of noradrenaline and suggest that Dbh +/- and Dbh -/- mice are useful for the study of direct and indirect mechanisms.

Gene and stem cell therapy for erectile dysfunction

Erectile dysfunction (ED) is defined as the inability to attain and/or maintain penile erection sufficient for satisfactory sexual performance. ED is a highly prevalent health problem with considerable impact on the quality of life of men and their partners. Although the treatment of ED with oral phosphodiesterase type V (PDE5) inhibitors is effective in a wide range of individuals, it is not efficacious in all patients. The failure of PDE5 inhibitors happens mainly in men with diabetes, non-nerve sparing radical prostatectomy, and high disease severity. Therefore, improved therapies based on a better understanding of the fundamental issues in erectile physiology and pathophysiology have recently been proposed. Here, we summarize studies on ED treatment using gene and stem cell therapies. Adenoviral-mediated intracavernosal transfer of therapeutic genes, such as endothelial nitric oxide synthase (eNOS), calcitonin gene-related peptide (CGRP), superoxide dismutase (SOD), and RhoA/Rho kinase and mesenchymal stem cell-based cell and gene therapy strategy for the treatment of age- and diabetes-related ED are the focus of this review.

Effect of combination endothelial nitric oxide synthase gene therapy and sildenafil on erectile function in diabetic rats

Erectile dysfunction associated with diabetes mellitus is caused in part by disordered endothelial smooth muscle relaxation, neuropathy, and a decrease in cavernosal nitric oxide synthase (NOS) activity. The purpose of this study was to determine whether a combination of sildenafil and adenoviral gene transfer of endothelial NOS (eNOS) could enhance the erectile response in diabetic rats. Five groups of animals were utilized: (1) age-matched control rats, (2) streptozotocin (STZ)-induced diabetic rats (60 mg/kg i.p.), (3) STZ-rats + sildenafil (2 mg/kg i.v.), (4) STZ-rats transfected with AdCMVbetagal or AdCMVeNOS, and (5) STZ-rats transfected with AdCMVeNOS +sildenafil (2 mg/kg i.v.). At 2 months after i.p. injection of STZ, groups 4 and 5 were transfected with the adenoviruses and 1-2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Cyclic 3',5'-guanosine monophosphate (cGMP) levels were assessed in the cavernosal tissue. STZ-diabetic rats had a significant decrease in erectile function as determined by the peak intracavernosal pressure (ICP) and total ICP (area under the erectile curve; AUC) after CNS when compared to control rats. STZ-diabetic rats+AdCMVeNOS had a peak ICP and AUC, which were similar to control animals. STZ-diabetic rats administered sildenafil demonstrated a significant increase in peak ICP at the 5 and 7.5 V settings, while the AUC was significantly increased at all voltage (V) settings. The increase in both ICP and AUC of STZ-diabetic rats transfected with AdCMVeNOS at all V settings was greater than STZ-diabetic rats transfected with AdCMVbetagal. STZ-diabetic rats transfected with AdCMVeNOS and administered sildenafil had a significant increase in total ICP that was greater than eNOS gene therapy alone. Cavernosal cGMP levels were significantly decreased in STZ-diabetic rats, but were increased after transfection with AdCMVeNOS to values greater than control animals. In conclusion, overexpression of eNOS and cGMP in combination with sildenafil significantly increased both the peak ICP and total ICP to CNS in the STZ-diabetic rat, which was similar to the response observed in control rats. Moreover, the total erectile response was greater in STZ-diabetic rats receiving eNOS gene therapy plus sildenafil than STZ-rats receiving sildenafil or eNOS gene therapy alone.

Antiproliferative effects of calcitonin gene-related peptide in aortic and pulmonary artery smooth muscle cells

Pulmonary hypertension is characterized by vascular remodeling involving smooth muscle cell proliferation and migration. Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are potent vasodilators, and the inhibition of aortic smooth muscle cell (ASMC) proliferation by NO has been documented, but less is known about the effects of CGRP. The mechanism by which overexpression of CGRP inhibits proliferation in pulmonary artery smooth muscle cells (PASMC) and ASMC following in vitro transfection by the gene coding for prepro-CGRP was investigated. Increased expression of p53 is known to stimulate p21, which inhibits G(1) cyclin/cdk complexes, thereby inhibiting cell proliferation. We hypothesize that p53 and p21 are involved in the growth inhibitory effect of CGRP. In this study, CGRP was shown to inhibit ASMC and PASMC proliferation. In PASMC transfected with CGRP and exposed to a PKA inhibitor (PKAi), cell proliferation was restored. p53 and p21 expression increased in CGRP-treated cells but decreased in cells treated with CGRP and PKAi. PASMC treated with CGRP and a PKG inhibitor (PKGi) recovered from inhibition of proliferation induced by CGRP. ASMC treated with CGRP and then PKAi or PKGi recovered only when exposed to the PKAi and not PKGi. Although CGRP is thought to act through a cAMP-dependent pathway, cGMP involvement in the response to CGRP has been reported. It is concluded that p53 plays a role in CGRP-induced inhibition of cell proliferation and cAMP/PKA appears to mediate this effect in ASMC and PASMC, whereas cGMP appears to be involved in PASMC proliferation.

Peroxynitrite does not impair pulmonary and systemic vascular responses

The effects of peroxynitrite (ONOO-) on vascular responses were investigated in the systemic and hindquarters vascular bed and in the isolated perfused rat lung. Intravenous injections of ONOO- decreased systemic arterial pressure, and injections of ONOO- into the hindquarters decreased perfusion pressure in a dose-related manner. Injections of ONOO- into the lung perfusion circuit increased pulmonary arterial perfusion pressure. Responses to ONOO- were rapid in onset, short in duration, and repeatable without exhibiting tachyphylaxis. Repeated injections of ONOO- did not alter systemic, hindquarters, or pulmonary responses to endothelium-dependent vasodilators or other vasoactive agonists and did not alter the hypoxic pulmonary vasoconstrictor response. Injections of sodium nitrate or nitrite or decomposed ONOO- had little effect on vascular pressures. Pulmonary and hindquarters responses to ONOO- were not altered by a cyclooxygenase inhibitor in a dose that attenuated responses to arachidonic acid. These results demonstrate that ONOO- has significant pulmonary vasoconstrictor, systemic vasodepressor, and vasodilator activity; that short-term repeated exposure does impair vascular responsiveness; and that responses to ONOO- are not dependent on cyclooxygenase product release.

Cardioprotection with sildenafil, a selective inhibitor of cyclic 3',5'-monophosphate-specific phosphodiesterase 5

The effects of sildenafil (Viagra), a specific inhibitor of phosphodiesterase 5, on ischemic myocardium was examined using an isolated rat heart model. Rats were pretreated with sildenafil at doses ranging from 0.001 mg to 0.5 mg/kg body weight. After 60 min, isolated hearts were subjected to ischemia for 30 min followed by 2 h of reperfusion. The results demonstrated that at 0.05 mg/kg (and to some extent at 0.01 mg/kg), sildenafil provided significant cardioprotection as evidenced by improved ventricular recovery, a reduced incidence of ventricular fibrillation and decreased myocardial infarction. At higher doses, it caused a significant increase in the incidence of ventricular fibrillation while at very low doses it had no effect on cardiac function. As expected, sildenafil increased cyclic 3',5'-monophosphate (cGMP) content in the heart. The results demonstrate for the first time that within a narrow dose range, sildenafil can protect the heart from ischemia/reperfusion injury, probably through a cGMP-signaling pathway.

Comparison of responses to novel nitric oxide donors in the feline pulmonary vascular bed

Pulmonary vascular responses to the novel diazeniumdiolate nitric oxide (NO) donors diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt, were investigated and compared in the intact-chest cat. Under conditions of controlled blood flow, when tone in the pulmonary vascular bed had been raised to a high steady level, intralobar injections of diethylamine/NO (0.3-10 microg), diethylenetriamine/NO (10-30 microg), spermine/NO (10-30 microg), sulfite/NO (10-30 microg), and angeli's salt (10-30 microg) caused dose-related decreases in lobar arterial pressure without changing left atrial pressure. In terms of relative vasodilator activity in the pulmonary vascular bed, the dose of the compounds that decreased lobar arterial pressure 4 mm Hg (ED(4) mm Hg) was significantly lower for diethylamine/NO compared to S-nitroso-N-acetylpenicillamine which was significantly less than diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt. The half-life of the vasodilator responses, as measured by 50% response recovery time, to diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt was similar for doses with similar magnitudes of vasodilation, while the half-life to S-nitroso-N-acetylpenicillamine was significantly less than the diazeniumdiolate NO donors. The present data demonstrate that the diazeniumdiolate NO donors diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt have potent but relatively short-lasting vasodilator activity in the pulmonary vascular bed of the cat.

Gene transfer of prepro-calcitonin gene-related peptide restores erectile function in the aged rat

Erectile dysfunction in the aging male is caused, in part, by inadequate relaxation of the corpora cavernosal smooth musculature. Calcitonin gene-related peptide (CGRP), a peptide neurotrasmitter localized in the corpora cavernosa, is down-regulated in the aging rat penis. We examined the hypothesis that this reduction in CGRP may contribute to decreased cavernosal smooth muscle relaxation. Therefore, we sought to determine whether adenoviral-mediated gene transfer of prepro-CGRP (AdRSVCGRP) could enhance erectile responses in aged rats. We found a significant decrease in CGRP concentrations and in cAMP and cGMP levels in aged rat cavernosal tissue compared to younger rats. Aged rats also had significantly lower erectile function as determined by cavernosal nerve stimulation compared to younger rats. Five days after transfection with AdRSVCGRP, these aged rats had an approximately threefold increase in cavernosal CGRP levels compared to animals transfected with adenoviruses encoding nuclear-targeted beta-galactosidase (AdRSV beta gal). The AdRSVCGRP-transfected animals also demonstrated an increase in CGRP mRNA and immunohistochemical localization of CGRP in the smooth muscle of the corpora cavernosa. In addition, cAMP levels in the corpora cavernosa were significantly increased, whereas cGMP levels remained unchanged. Adenoviral transduction efficiency of beta-galactosidase reporter gene was measured by chemiluminescence and was observed in cavernosal tissue 5 days after transfection with AdRSV beta gal. More importantly, 5 days after administration of AdRSVCGRP, a significant increase was observed in the erectile response to cavernosal nerve stimulation in the aged rat, similar to the response observed in younger rats. These data suggest that in vivo adenoviral gene transfer of CGRP can physiologically improve erectile function in the aged rat.

Differential responses to ATPgammaS in the mesenteric and hindlimb vascular bed of the cat

The mechanism by which the purinergic agonist adenosine 5'-O-(3 thiotriphosphate) (ATPgammaS) decreases vascular resistance was investigated in the mesenteric and hindlimb vascular beds of the cat. Injections of ATPgammaS into the hindlimb perfusion circuit elicited dose-dependent decreases in perfusion pressure while injections into the mesenteric circuit produced a biphasic response with an initial vasopressor response followed by a vasodepressor response. In the mesenteric vascular bed the pressor response to ATPgammaS was blocked by a P2X1 receptor antagonist. Also an inhibitor of nitric oxide synthase enhanced the vasoconstrictive responses to ATPgammaS. However, the vasodepressor response in the mesenteric bed was not altered by the adminstration of an alpha adrenergic receptor antagonist, a cyclooxygenase inhibitor, a P2Y1 receptor antagonist, or a K+ATP channel blocking agent. These data suggest that the vasopressor response to ATPgammaS in the mesenteric vascular bed of the cat is mediated via P2X1 receptor activation. The differential responses to ATPgammaS in the hindlimb and mesentery suggest differences in purinergic receptor distribution in the vascular system of the cat. In addition, the results suggest that prostaglandin synthesis, P2Y1 receptor activation, alpha receptor inhibition, and K+ATP channels activation play little to no role in mediating the vascular response to ATPgammaS in the mesentery of the cat.

Analysis of responses to hAmylin, hCGRP, and hADM in isolated resistance arteries from the mesenteric vascular bed of the rat

Responses to human calcitonin gene-related peptide (hCGRP) and human adrenomedullin (hADM) hAmylin were investigated in isolated mesenteric resistance arteries from the rat. The results of the present investigation show that hCGRP, hAmylin, and hADM induce dose-related vasodilator responses in isolated resistance arteries from the rat mesenteric vascular bed. Vasodilator responses to hCGRP and hAmylin were not altered after denuding the vascular endothelium, after administration of the nitric oxide synthase inhibitor L-NA, or after administration of the soluble guanylate cyclase inhibitor ODQ, suggesting that vasodilator responses to hCGRP and hAmylin are not mediated by the release of nitric oxide from the vascular endothelium and the subsequent increase in cGMP. Vasodilator responses to hCGRP, hAmylin, and hADM were not altered by the vascular selective K+(ATP) channel antagonist U-37883A. The role of the CGRP1 receptor was investigated and responses to hCGRP and hAmylin, but not hADM, were significantly reduced following administration of hCGRP-(8-37). Moreover, vasodilator responses to hCGRP and hAmylin, but not hADM, were significantly reduced by hAmylin-(8-37), suggesting that an hAmylin-(8-37)-sensitive receptor mediates responses to hCGRP and hAmylin in the rat mesenteric artery. These data suggest that hCGRP and hAmylin have direct vasodilator effects in the isolated mesenteric resistance artery that are mediated by hAmylin-(8-37)- and hCGRP-(8-37)-sensitive receptors.

L-NAME enhances responses to atrial natriuretic peptide in the pulmonary vascular bed of the cat

This study investigated the hypothesis that atrial natriuretic peptide (ANP) responses are mediated by particulate guanylate cyclase in the pulmonary vascular bed of the cat. When tone in the pulmonary vascular bed was raised to a high steady level with the thromboxane mimic U-46619, injections of ANP caused dose-related decreases in lobar arterial pressure. After administration of HS-142-1, an ANP-A- and ANP-B-receptor antagonist, vasodilator responses to ANP were reduced. The nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) enhanced ANP vasodilator responses, suggesting that inhibition of NO modulates ANP responses. L-NAME administration with constant 8-bromo-cGMP infusion attenuated the increased vasodilator response to ANP, suggesting that supersensitivity to ANP occurs upstream to activation of a cGMP-dependent protein kinase. In pulmonary arterial rings, ANP produced concentration-related vasorelaxant responses with and without endothelium. Methylene blue, L-NAME, or N(omega)-monomethyl-L-arginine did not alter ANP vasorelaxant responses. These data show that ANP supersensitivity observed in the intact pulmonary vascular bed is not seen in isolated pulmonary arterial segments, suggesting that it may only occur in resistance vessel elements. These results suggest that ANP responses occur through activation of ANP-A and/or -B receptors in an endothelium-independent manner and are modulated by NO in resistance vessel elements in the pulmonary vascular bed of the cat.

Vasodilator responses to ATP and UTP are cAMP dependent in the mesenteric vascular bed of the cat

BACKGROUND

This study was designed to examine the responses to and the mechanism by which purinergic agonists decrease vascular resistance in the mesenteric vascular bed of the cat.

METHODS AND RESULTS

Injections of ATP, UTP, and 2-MethylThioATP (2-MetSATP) into the mesenteric perfusion circuit elicited dose-dependent decreases in perfusion pressure while injections of beta,gamma-MethylATP (beta,gamma-MetATP) produced a biphasic response with an initial vasopressor response followed by a vasodilator response. The order of potency of the vasodilator response was 2-MetSATP > ATP > UTP > beta,gamma-MetATP. The vasodilator responses to ATP, UTP, 2-MetSATP, and beta,gamma-MetATP were increased in duration by the cAMP phosphodiesterase inhibitor, rolipram. However, vasodilator responses were not altered by the adminstration of a nitric oxide synthase inhibitor, a cGMP phosphodiesterase inhibitor, or a cyclooxygenase inhibitor. Treatment with PPADS, a P2X(1), P2Y(1), and P2Y(4) receptor antagonist, did not alter vasodilator responses to the purinergic agonists; however, the vasopressor component of the response to beta,gamma-MetATP was decreased.

CONCLUSIONS

These data suggest that ATP, UTP, 2-MetSATP, and beta,gamma-MetATP dilate the mesentary vascular bed in the cat by a cAMP dependent mechanism, and that nitric oxide or prostaglandin release, cGMP accumulation, or activation of P2X(1), P2Y(1), or P2Y(4) receptors play little or no role in mediating vasodilator responses to the purinergic agonists in this regional vascular bed. In addition, these results suggest that the pressor component of the response to beta,gamma-MetATP is mediated by the activation of P2X(1) receptors.

Analysis of vasodilator responses to novel nitric oxide donors in the hindquarters vascular bed of the cat

Controlled release of nitric oxide (NO*) may be useful in the treatment of a variety of vascular disorders. NO* donors of the diazeniumdiolate family with different rates of spontaneous NO* release have been synthesized. In the current study responses to seven diazeniumdiolate NO* donors (DEA/NO*, DETA/NO*, OXI/NO*, PIPERAZI/NO*, PROLI/NO*, SPER/NO*, and SULFI/NO*) were investigated in the hindquarters vascular bed of the cat. Intravenous injections of all NO* donors caused dose-dependent decreases in systemic arterial pressure and the rank order of potency was SNP > DEA/NO* > PIPERAZI/NO* > SPER/NO* > PROLI/NO* > OXI/NO*. Injections of all NO* donors into the hindlimb perfusion circuit caused dose-related decreases in hindquarters perfusion pressure that were similar to the order of potency in decreasing systemic arterial pressure. The rank order of the time required for the response to return to 50% of the maximal decrease in pressure (T(1/2)) and total duration of action of the NO* donors was SPER/NO* > PIPERAZI/NO* > DEA/NO* > OXI/NO* > DETA/NO* > PROLI/NO* > SULFI/NO*. After treatment with the NO* synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (100 mg/kg, i.v.), hindlimb vasodilator responses to the NO* donors were not significantly different, but vasodilator responses to acetylcholine were significantly reduced. After treatment with zaprinast (2 mg/kg, i.v.), a type V cyclic 3',5'-guanosine monophosphate-specific phosphodiesterase inhibitor, the duration of vasodilator responses to the NO* donors, as measured by T(1/2), was increased significantly, whereas the duration of the response to the beta2-adrenergic receptor agonist albuterol was unchanged. These data suggest that diazeniumdiolate NO* donors are endothelium-independent, directly stimulate soluble guanylate cyclase, and decrease vascular resistance by increasing cyclic 3',5'-guanosine monophosphate levels in the hindquarters vascular bed of the cat.

Increased Expression of Arginase II in Human Diabetic Corpus Cavernosum: In Diabetic-Associated Erectile Dysfunction

Nitric oxide (NO) is the principal mediator of penile erection. NO is synthesized by nitric oxide synthase (NOS). It has been well documented that the major causative factor contributing to erectile dysfunction in diabetic patients is the reduction in the amount of NO synthesis in the corpora cavernosa of the penis resulting in alterations of normal penile homeostasis. Arginase is an enzyme that shares a common substrate with NOS, thus arginase may downregulate NO production by competing with NOS for this substrate, l-arginine. The purpose of the present study was to compare arginase gene expression, protein levels, and enzyme activity in diabetic human cavernosal tissue. When compared to normal human cavernosal tissue, diabetic corpus cavernosum from humans with erectile dysfunction had higher levels of arginase II protein, gene expression, and enzyme activity. In contrast, gene expression and protein levels of arginase I were not significantly different in diabetic cavernosal tissue when compared to control tissue. The reduced ability of diabetic tissue to convert l-arginine to l-citrulline via nitric oxide synthase was reversed by the selective inhibition of arginase by 2(S)-amino-6-boronohexanoic acid (ABH). These data suggest that the increased expression of arginase II in diabetic cavernosal tissue may contribute to the erectile dysfunction associated with this common disease process and may play a role in other manifestations of diabetic disease in which nitric oxide production is decreased.

Evaluation of nitric oxide synthase and arginase in the induction of a Peyronie's-like condition in the rat

Peyronie's disease is an idiopathic, localized connective tissue disorder of the penis, involving the tunica albuginea of the corpus cavernosum and adjacent areolar space. Current proposals as to the origin of Peyronie's disease suggest that fibrosis and collagen changes of the tunica are the result of an inflammatory process following vascular trauma. Our laboratory and other investigators have recently proposed an animal model for the study of Peyronie's disease. When transforming growth factor-beta1 (TGF-beta1) was injected into the rat tunica albuginea, tissue fibrosis was observed at 6 weeks. Therefore, our aim was to assess arginase II, endothelial and inducible nitric oxide synthase isoforms, and nitrotyrosine levels--all factors involved in inflammatory reactions--in the cavernosal tissue of saline-injected and TGF-beta1-injected rats after 6 weeks in order to evaluate the roles these enzymes may play in the induction of a Peyronie's-like condition in the rat. To examine the expression of endothelial nitric oxide synthase (eNOS), iNOS, and arginase II protein, and mRNA in the corpus cavernosum, immunoblot analysis, and reverse transcriptase-polymerase chain reaction were performed. We also determined immunohistochemically the expression of nitrotyrosine, a marker of peroxynitrite formation, in the rat penis. After 6 weeks, iNOS protein and gene expression was up-regulated and eNOS protein and gene expression was down-regulated in the corpora cavernosa of the TGF-beta1-injected penises. Furthermore, arginase II protein expression as well as immunohistochemical localization of nitrotyrosine was significantly higher in the TGF-beta1-injected corpora cavernosa. These results suggest that iNOS is the key control element for peroxynitrite formation, arginase II expression, and eNOS down-regulation in the induction of a Peyronie's-like condition in the rat.

Direct effects of selective type 5 phosphodiesterase inhibitors alone or with other vasodilators on the erectile response in cats

PURPOSE

Zaprinast, dipyridamole and sildenafil were injected into the corpora cavernosa of cats to determine whether changes in the steady state level of cyclic guanosine monophosphate (cGMP) induced by inhibiting type 5 phosphodiesterase would cause an erectile response.

MATERIALS AND METHODS

Increases in intracavernous pressure, penile length and erectile response duration were determined after intracavernous injection of the type 5 cGMP specific phosphodiesterase inhibitors zaprinast, dipyridamole and sildenafil as well as combined zaprinast and prostaglandin E1 (PGE1), and zaprinast and sodium nitroprusside. Systemic arterial pressure was concurrently assessed in these experiments. All responses to phosphodiesterase inhibitors were compared to a control triple drug combination of 1.65 mg papaverine, 0.5 microg PGE1 and 25 microg phentolamine.

RESULTS

Each selective type 5 phosphodiesterase inhibitor caused dose related increases in intracorporeal pressure and penile length. However, none of the compounds was as effective as the control drug combination of papaverine, phentolamine and PGE1. Combining zaprinast with sodium nitroprusside led to further increases in pressure and erectile response duration that more closely resembled the control drug response. Combining zaprinast with PGE1 led to a response that was indistinguishable from the control response.

CONCLUSIONS

The results of these feline studies establish that administering a type 5 phosphodiesterase inhibitor without concomitant administration of a nitric oxide donor or stimulation of the cavernous nerves may have a direct effect on the erectile response. These data also suggest that combining a selective type 5 phosphodiesterase inhibitor with PGE1 may be highly effective local therapy for erectile dysfunction and an acceptable alternative to other current forms of treatment.

Pharmacotherapy for erectile dysfunction

Erectile dysfunction (ED) is defined as the consistent inability to obtain or maintain an erection for satisfactory sexual relations. An estimated 20-30 million men suffer from some degree of sexual dysfunction. The past 20 years of research on erectile physiology have increased our understanding of the biochemical factors and intracellular mechanisms responsible for corpus cavernosal smooth muscle contraction and relaxation, and revealed that ED is predominantly a disease of vascular origin. Since the advent of sildenafil (Viagra), there has been a resurgence of interest in ED, and an increase in patients presenting with this disease. A thorough knowledge of the physiology of erection is essential for future pharmacological innovations in the field of male ED.

Comparison of responses to siguazodan, rolipram, and zaprinast in the feline pulmonary vascular bed

The present study was undertaken to investigate and compare responses to the cyclic nucleotide phosphodiesterase inhibitors siguazodan (type III, guanosine 3',5'-cyclic monophosphate (cGMP)-inhibited adenosine 3',5'-cyclic monophosphate (cAMP)), rolipram (type IV, cAMP-specific), and zaprinast (type V, cGMP-specific) in the feline pulmonary vascular bed. When tone in the pulmonary vascular bed was raised to a high steady level with a constant infusion of the thromboxane mimic U46619 (9,11-dideoxy-11, alpha9alpha-epoxymethano prostaglandin F(2alpha)), intralobar injections of the three phosphodiesterase inhibitors caused dose-related decreases in lobar arterial pressure. In terms of relative vasodilator activity, rolipram was more potent at higher doses than siguazodan, which was more potent than zaprinast. The duration of the pulmonary vasodilator response to zaprinast was shorter than for siguazodan or rolipram. Furthermore, siguazodan and rolipram, but not zaprinast, decreased systemic arterial pressure when injected into the perfused lobar artery in the range of doses studied. The present data demonstrate that the three phosphodiesterase inhibitors have potent, long-lasting vasodilator activity in the pulmonary vascular bed of the cat. These data suggest that there is rapid turnover of cAMP and cGMP in the pulmonary circulation and indicate that phosphodiesterase enzyme types III, IV, and V may play an important role in the regulation of vasomotor tone in the feline lung.

L-163,491 is a partial angiotensin AT(1) receptor agonist in the hindquarters vascular bed of the cat

Responses to the nonpeptide angiotensin II agonist 5, 7-Dimethyl-2-ethyl-3-[[2'-([butyloxycarbonyl) aminosulfonyl]-5'-(3-methyoxybenzyl)-[1, 1'-biphenyl]-4-yl]methyl]-3H-imidazo[4,5-b]pyridine (L-163,491) were investigated and compared with responses to angiotensin II, angiotensin IV and norepinephrine in the hindquarters vascular bed of the cat under constant-flow conditions. Injections of L-163,491 into the hindquarter perfusion circuit caused dose-related increases in hindquarters perfusion pressure. In relative terms, angiotensin II was more potent than norepinephrine, which was more potent than angiotensin IV and L-163,491 in increasing hindlimb vascular resistance. The slope of the dose-response curve for L-163,491 was flat, while the apparent affinity of the compound for angiotensin AT(1) receptors was slightly greater than angiotensin IV. Responses to L-163,491 were inhibited by the angiotensin AT(1) receptor antagonist DuP 532 (2-propyl-4-pentafluoroethyl-1-[2'-(1H-tetrazol-5-yl)bipheny l-4-yl)me thyl]imidazole-5-carboxylic acid) and were not altered by the angiotensin AT(2) receptor antagonist PD123,319 (S(+)-1-[[4-(Dimethylamino)-3-methylphenyl]methyl]-5-(diphenylacetyl+ ++) -4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditribluoroacetate). However, the increase in hindlimb perfusion pressure in response to angiotensin II and angiotensin IV was significantly decreased following injection of L-163,491. These data suggest that the nonpeptide angiotensin analog L-163,491 has partial agonist activity, which is dependent on the stimulation of angiotensin AT(1) receptors in the hindquarters vascular bed of the cat.

Adenoviral gene transfer of endothelial nitric oxide synthase (eNOS) to the penis improves age-related erectile dysfunction in the rat

Nitric oxide (NO) is the principal mediator of penile erection. NO is synthesized by a variety of nitric oxide synthases (NOS). It has been demonstrated that a decrease in NOS activity, as observed in aging, is associated with a diminished erectile response. The objective of this study was to determine if adenoviral-mediated gene transfer of eNOS could reverse age-related erectile dysfunction in the rat. Two groups of animals were transfected with adenoviruses: (1) aged rats (60 weeks) with AdRSVbetagal; and (2) aged rats (60 weeks) with AdRSVeNOS. Five days after transfection, these study animals underwent cavernosal nerve stimulation (CNS) to assess erectile function and their responses were compared with young (20 weeks) control rats. Cross-sections of the rat penises transfected with AdRSVeNOS were examined after trichrome staining. Adenoviral transduction efficiency of beta-galactosidase reporter gene was measured by a galacto-light chemiluminescent reporter gene assay in cavernosal tissues of rats administered AdRSVbetagal. The transgene expression of eNOS was examined by RT-PCR in rats transfected with AdRSVbetagal and AdRSVeNOS. eNOS and iNOS protein levels were measured by Western blot analysis, and cGMP levels were assessed in cavernosal tissue by enzyme immunoassay. Adenoviral expression of the beta-galactosidase reporter gene was observed in cavernosal tissue for up to 30 days, with peak expression registered at 5 days after intracavernosal administration of AdRSVbetagal. Cross-sections of the rat penises transfected with the AdRSVeNOS revealed no pathological (morphological or histological) changes. Five days after administration of AdRSVeNOS, eNOS protein, mRNA and cGMP levels in the corpora cavernosa were significantly increased (P<0. 05), while iNOS protein levels remained unchanged (P>0.05). In conclusion, enhanced expression of eNOS employing an adenoviral vector significantly increased the erectile response to cavernosal nerve stimulation in the aged rat, similar to the response observed in younger rats. These data suggest that in vivo adenoviral gene transfer of eNOS can physiologically improve erectile function in the aged rat.

Vasodilator responses to ATP and UTP are not dependent on nitric oxide release, K+(ATP) channel activation, or the release of vasodilator prostaglandins in the hindlimb vascular bed of the cat

The effects of the purinergic agonists, ATP, ATPgammaS, UTP, and 2-Met-Thio AP, were investigated in the hindlimb vascular bed of the cat. Under constant-flow conditions, injections of the purinergic agonists into the perfusion circuit elicited dose-related decreases in perfusion pressure. The order of potency was 2-Met-Thio ATP > ATPgammaS > ATP > UTP. In contrast, injections of GTPgammaS, cAMP, UDP, and UMP had no effect. Vasodilator responses to ATP, ATPgammaS, UTP, and 2-Met-Thio ATP were increased in duration by the cAMP phosphodiesterase inhibitor rolipram, whereas the cGMP phosphodiesterase inhibitor zaprinast had no effect. Responses to the purinergic agonists were not altered by nitric oxide synthase inhibitors, K+(ATP) channel antagonists, cyclooxygenase inhibitors, or agents that interfere with the actions of the adrenergic nervous system. These data suggest that ATP, ATPgammaS, UTP, and 2-Met-Thio ATP dilate the hindlimb vascular bed by a direct cAMP-dependent mechanism, and that the release of nitric oxide, vasodilator prostaglandins, K+(ATP) channel opening, or an inhibitory effect on the adrenergic nervous system play little, if any, role in mediating or modulating responses to the purinergic agonists in the hindlimb circulation of the cat.

Analysis of responses of garlic derivatives in the pulmonary vascular bed of the rat

Allicin, an extract from garlic, has been shown to be a systemic and pulmonary arterial vasodilator that acts by an unknown mechanism. In the present experiments, pulmonary vascular responses to allicin (10-100 microg), allyl mercaptan (0.3-1 mg), and diallyl disulfide (0.3-1 mg) were studied in the isolated lung of the rat under constant-flow conditions. When baseline tone in the pulmonary vascular bed of the rat was raised to a high-steady level with the thromboxane A(2) mimic U-46619, dose-related decreases in pulmonary arterial pressure were observed. In terms of the mechanism of action of allicin vasodilator activity in the rat, responses to allicin were not significantly different after administration of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester, the K(ATP)(+) channel antagonist U-37883A, or the cyclooxygenase inhibitor sodium meclofenamate, or when lung ventilation was interrupted. These data show that allicin has significant vasodilator activity in the pulmonary vascular bed of the rat, whereas allyl mercaptan and diallyl disulfide produced no significant changes in pulmonary arterial perfusion pressure. The present data suggest that pulmonary vasodilator responses to allicin are independent of the synthesis of nitric oxide, ATP-sensitive K(+) channels, activation of cyclooxygenase enzyme, or changes in bronchomotor tone in the pulmonary vascular bed of the rat.

Vasorelaxant responses to endomorphins, nociceptin, albuterol, and adrenomedullin in isolated rat aorta

The endogenous peptides endomorphins 1 and 2 are newly discovered, potent, selective mu-opioid receptor agonists. In the present study, the effects of endomorphins 1 and 2 on vascular smooth muscle tone were investigated on isolated rings from rat aorta with and without endothelium. In rings precontracted with phenylephrine, endomorphins 1 and 2 at concentrations of 0.1 and 1.0 microM, nociceptin at concentrations of 1-100 microM, and adrenomedullin at concentrations of 0.01-1.0 microM induced concentration dependent relaxant responses. The endomorphins and nociceptin were less potent than adrenomedullin. No relaxation was induced by endomorphins 1 and 2 in aortic rings denuded of endothelium and precontracted with phenylephrine. The results of the present studies demonstrate that the endomorphins relax aortic vascular smooth muscle from the rat aorta by an endothelium-dependant mechanism.

A rat model of Peyronie's disease associated with a decrease in erectile activity and an increase in inducible nitric oxide synthase protein expression

PURPOSE

Our objective was to assess erectile function in saline-injected, transforming growth factor-beta 1 (TGF-beta1)-injected, and surgical injury rats after six weeks and to determine the role of nitric oxide in this rat model of Peyronie's disease.

MATERIALS AND METHODS

Fifty-four adult male CD rats were divided into three groups: 1) saline-injected (0.1 ml.) into the tunica albuginea; 2) TGF-beta1 (0.5 microgram.) injected into the tunica albuginea; and 3) surgical injury to the tunica albuginea. All groups underwent electrical stimulation of the cavernosal nerve and pharmacological stimulation with acetylcholine, an endothelium-dependent vasodilator, after six weeks. In a separate group of animals, aminoguanidine (5 mg./kg. i.v.), a specific iNOS inhibitor, was administered and cavernosal nerve stimulation was performed. Cavernosal tissue was homogenized and constitutive and inducible NOS enzyme activity were measured by L-arginine to L-citrulline conversion in the presence and absence of calcium after 2 days, 3 and 6 weeks in all three groups. Cross-sections of the rat penises were examined using Hart and trichrome stains.

RESULTS

Erectile function as measured by cavernosal nerve stimulation and acetylcholine injection was significantly lower (p <0.05) in the TGF-beta1-injected and surgical-injury rats when compared to the saline-injected rats. iNOS inhibition significantly increased (p <0.05) erectile responses to cavernosal nerve stimulation in the rat. iNOS was significantly higher (p <0.05) and constitutive NOS was downregulated (p <0.05) in the corpus cavernosum of the TGF-beta1-injected and surgical-injury rats after 6 weeks. The TGF-beta1-injected and surgical-injury rats exhibited thickening of the tunica albuginea, fragmentation of the elastic fibers, and collagen thickening around the neurovascular bundle.

CONCLUSIONS

We have shown that erectile function is significantly lower in the TGF-beta1-injected and surgical-injury rats after 6 weeks at a time when iNOS is upregulated and constitutive NOS is downregulated. Furthermore, iNOS inhibition causes a greater erectile response in the rat, suggesting that iNOS may alter the vascular tone in the penis. These data document a possible mechanism by which some men with Peyronie's disease suffer from erectile dysfunction.

Nitric oxide-mediated erectile effects of galantide but not galanin in vivo

The purpose of this study was to investigate the in vivo effects of intracavernosal injections of galanin and galantide (a specific galanin receptor antagonist) on penile erection in the anesthetized cat. Erectile responses to galanin and galantide were compared with responses to a standard triple drug combination [1.65 mg papaverine, 25 microg phentolamine, and 0.5 microg prostaglandin E(1) (PGE(1))]. Intracavernosal injections of galanin (3-100 nmol) and galantide (0. 1-3 nmol) induced penile erection in a dose-dependent manner. In terms of relative potency, galantide was approximately 100-fold more potent than galanin at increasing cavernosal pressure. The maximal increases in intracavernosal pressure in response to galanin and galantide were 83 and 95%, respectively, of the control triple drug combination. The total durations of erectile response caused by these peptides were significantly shorter (P<0.05) than those by the triple drug combination. The nitric oxide synthase inhibitor L-NAME (20 mg) significantly decreased the erectile response in the cat to galantide but not to galanin, while the K(+)(ATP) channel antagonist U-37883A (3 mg) had no effect on the erectile response to galanin nor galantide. The results of the present study demonstrate that galantide, a putative antagonist for the galanin receptor, has more potent agonist activity than galanin in increasing intracavernosal pressure in the cat. Moreover, these data suggest that galantide, but not galanin, causes penile erection by an NO/cGMP-dependent mechanism. This is the first study to demonstrate that galanin may play a role in the physiology of penile erection.

In vivo gene transfer of prepro-calcitonin gene-related peptide to the lung attenuates chronic hypoxia-induced pulmonary hypertension in the mouse

BACKGROUND

Calcitonin gene-related peptide (CGRP) is believed to play an important role in maintaining low pulmonary vascular resistance (PVR) and in modulating pulmonary vascular responses to chronic hypoxia; however, the effects of adenovirally mediated gene transfer of CGRP on the response to hypoxia are unknown.

METHODS AND RESULTS

In the present study, an adenoviral vector encoding prepro-CGRP (AdRSVCGRP) was used to examine the effects of in vivo gene transfer of CGRP on increases in PVR, right ventricular mass (RVM), and pulmonary vascular remodeling that occur in chronic hypoxia in the mouse. Intratracheal administration of AdRSVCGRP, followed by 16 days of chronic hypoxia (FIO(2) 0.10), increased lung CGRP and cAMP levels. The increase in pulmonary arterial pressure (PAP), PVR, RVM, and pulmonary vascular remodeling in response to chronic hypoxia was attenuated in animals overexpressing prepro-CGRP, whereas systemic pressure was not altered while in chronically hypoxic mice, angiotensin II and endothelin-1-induced increases in PAP were reduced, whereas decreases in PAP in response to CGRP and adrenomedullin were not changed and decreases in PAP in response to a cAMP phosphodiesterase inhibitor were enhanced by AdRSVCGRP.

CONCLUSIONS

In vivo CGRP lung gene transfer attenuates the increase in PVR and RVM, pulmonary vascular remodeling, and pressor responses in chronically hypoxic mice, suggesting that CGRP gene transfer alone and with a cAMP phosphodiesterase inhibitor may be useful for the treatment of pulmonary hypertensive disorders.

A novel right-heart catheterization technique for in vivo measurement of vascular responses in lungs of intact mice

The present study employed a new right-heart catheterization technique to measure pulmonary arterial pressure, pulmonary arterial wedge pressure, and pulmonary vascular resistance in anesthetized intact-chest, spontaneously breathing mice. Under fluoroscopic guidance, a specially designed catheter was inserted via the right jugular vein and advanced to the main pulmonary artery. Cardiac output was determined by the thermodilution technique, and measured parameters were stable for periods of </=3 h. Pressure-flow curves in vivo were curvilinear, with mean pulmonary arterial pressure increasing more rapidly at low pulmonary blood flows of 5-10 ml/min and less rapidly at higher blood flow rates. The pressure-flow relationship was shifted to the left by the nitric oxide synthase inhibitor nitro-L-arginine methyl ester (L-NAME) at higher blood flow levels, whereas the cyclooxygenase inhibitor sodium meclofenamate was without effect. The increase in pulmonary arterial pressure in response to acute hypoxia (fractional inspired O(2) 10%) was augmented by L-NAME but unaltered by sodium meclofenamate. The present results demonstrate that the right-heart catheterization technique can be used to measure pulmonary vascular pressures and responses in the mouse. This is, to our knowledge, the first report of a right-heart catheterization technique to measure pulmonary vascular pressures and responses in the intact-chest, spontaneously breathing mouse and should prove useful for the investigation of pulmonary vascular responses in transgenic mice.

Feline penile erection induced by transurethral administration of sodium nitroprusside

Nitric oxide (NO) is an important mediator in the relaxation of cavernosal smooth muscle. The aim of this study was to investigate the in vivo feline erectile response after transurethral administration of sodium nitroprusside (SNP), a NO donor drug. Erectile responses after administration of transurethral SNP were compared with those elicited by an intracavernosal control triple-drug combination (1.65 mg papaverine, 25 microg phentolamine, and 0.5 microg prostaglandin E1). SNP was administered via a 20-gauge Jelco intravenous catheter in a volume of 200 microl and changes in intracavernosal pressure, penile length, and systemic blood pressure were monitored. The control triple-drug combination was administered via a 30-gauge needle at the end of each experiment to serve as a control reference. Transurethral administration of SNP (1-4 mg) induced penile erection in a dose-dependent manner with minimal changes in systemic blood pressure. The maximum increase in intracavernosal pressure and penile length after transurethral administration of SNP (4 mg) was significantly less than after the intracavernosal injection of the control triple-drug combination (P<0.01). These data suggest that transurethral administration of SNP can induce an erectile response in cats with minimal side effects.

Distribution, functional role, and signaling mechanism of adrenomedullin receptors in the rat adrenal gland

Adrenomedullin (ADM) is a hypotensive peptide, highly expressed in the mammalian adrenal medulla, which belongs to a peptide superfamily including calcitonin gene-related peptide (CGRP) and amylin. Quantitative autoradiography demonstrated the presence of abundant [125I]ADM binding sites in both zona glomerulosa (ZG) and adrenal medulla. ADM binding was selectively displaced by ADM(22-52), a putative ADM-receptor antagonist, and CGRP(8-37), a ligand that preferentially antagonizes the CGRP1-receptor subtype. ADM concentration-dependently inhibited K+-induced aldosterone secretion of dispersed rat ZG cells, without affecting basal hormone production. Both ADM(22-52) and CGRP(8-37) reversed the ADM effect in a concentration-dependent manner. ADM counteracted the aldosterone secretagogue action of the voltage-gated Ca2+-channel activator BAYK-8644, and blocked K+- and BAYK-8644-evoked rise in the intracellular Ca2+ concentration of dispersed ZG cells. ADM concentration-dependently raised basal catecholamine (epinephrine and norepinephrine) release by rat adrenomedullary fragments, and again the response was blocked by both ADM(22-52) and CGRP(8-37). ADM increased cyclic-AMP release by adrenal-medulla fragments, but not capsule-ZG preparations, and the catecholamine response to ADM was abolished by the PKA inhibitor H-89. Collectively, the present findings allow us to draw the following conclusions: (1) ADM modulates rat adrenal secretion, acting through ADM(22-52)-sensitive CGRP1 receptors, which are coupled with different signaling mechanisms in the cortex and medulla; (2) ADM selectively inhibits agonist-stimulated aldosterone secretion, through a mechanism probably involving the blockade of the Ca2+ channel-mediated Ca2+ influx; (3) ADM raises catecholamine secretion, through the activation of the adenylate cyclase/PKA signaling pathway.

Structure-activity relationships of adrenomedullin in the circulation and adrenal gland

Adrenomedullin (ADM) is a recently discovered vasoactive peptide that has potent vasodilator activity in the pulmonary and peripheral vascular beds and has significant effects on endocrine function. ADM is a member of the CGRP/amylin superfamily of peptides based largely on the presence of the six-membered ring structure and C-terminal amidation that is highly conserved in this family. Proadrenomedullin is a 185 amino acid precursor with enzymatic cleavage sites for both ADM and a unique 20 amino acid peptide named proadrenomedullin N-terminal 20 peptide (PAMP). ADM and PAMP are found in a variety of organ systems, and plasma levels of the peptides are increased in pathophysiologic conditions. Both peptides have hypotensive and vasodilator activity in the pulmonary and regional vascular beds and have significant effects on the endocrine system, including the adrenal gland. ADM (15-52), which retains the six-membered ring structure, maintains the vasodilator activity of ADM, suggesting that the 14 amino acid N-terminal extension is not necessary for the full agonist activity. However, analogs, such as ADM-(22-52) and ADM-(40-52), which do not contain the six-member ring structure, lack agonist activity. Unlike the full-sequence peptide, hADM-(15-22) and ADM-(16-21), which contain the ring structure, increase systemic arterial pressure in the rat but not in the cat. The present review discusses the structure-activity relationship for the actions of ADM and related peptides and discusses the mechanisms which mediate responses to these widely distributed peptides.

Potentiation of erectile response and cAMP accumulation by combination of prostaglandin E1 and rolipram, a selective inhibitor of the type 4 phosphodiesterase (PDE 4)

PURPOSE

Phosphodiesterases (PDEs) are an important component of the signal transduction pathway during the erectile response. To determine the PDE isoforms in the corpora cavernosa in the cat and to establish the functional presence of PDE 4 in human cavernosal tissue, the erectile response to intracavernosal phosphodiesterase (PDE) inhibitors alone and the combination of PDE inhibitors and prostaglandin E1 (PGE1) was evaluated in the anesthetized cat. The in vitro formation of cAMP and cGMP in human cavernosal smooth muscle cells (HCSMCs) treated with PGE1 and rolipram in primary culture was also measured.

MATERIALS AND METHODS

In pentobarbital-anesthetized cats, increases in intracavernosal pressure, penile length, and duration of erectile response were determined after intracavernosal injections of (i) the type 3 cAMP-specific, cGMP-inhibitable PDE inhibitor, milrinone, (ii) the type 4 cAMP-specific PDE inhibitor, rolipram, (iii) the type 5 cGMP-specific PDE inhibitor, zaprinast, and (iv) the combination of rolipram and PGE1. Systemic arterial pressure was concurrently assessed in these experiments. All responses to PDE inhibitors were compared with a control triple-drug combination comprised of papaverine (1.65 mg.), PGE1 (0.5 microg.), and phentolamine (25 microg.). HCSMCs were incubated with PGE1 (3 microM) and rolipram (10 microM) individually or in combination up to 2 hours at 37C. The intracellular cAMP and cGMP was extracted by cold absolute ethanol and measured (pmol./10(6) cells) by a commercially available EIA kit.

RESULTS

Milrinone (3 to 100 microg.), rolipram (3 to 100 microg.), and zaprinast (3 to 100 microg.) induced dose-dependent increases in intracavernosal pressure and penile length (p <0.05) when administered intracavernosally. The maximum increase in cavernosal pressure in response to zaprinast was associated with no significant change in systemic arterial pressure. When rolipram was combined with PGE1 (0.1 microg.), the increases in intracavernosal pressure and the duration of erectile response were significantly higher (p <0.05) and longer (p <0.05) than those observed when rolipram alone was injected intracavernosally. PGE1 (3 microM) and rolipram (10 microM) produced significant increases (p <0.05) in the accumulation of intracellular cAMP levels in HCSMCs in primary culture above those of the baseline values while intracellular levels of cGMP did not change.

CONCLUSIONS

PDE inhibitors administered intracavernosally caused dose-dependent increases in cavernosal pressure in the cat. When a specific cAMP PDE inhibitor was combined with PGE1, the erectile response was enhanced and intracellular levels of cAMP were increased in HCSMCs in primary culture. These data suggest further exploration of the combination of various PDE inhibitors and PGE1 in the pharmacologic treatment of erectile dysfunction and provide functional evidence for the presence of PDE 4 isoenzyme in human penile cavernosal cells.

Role of AT(1) receptors and autonomic nervous system in mediating acute pressor responses to ANG II in anesthetized mice

Hemodynamic responses to angiotensin II and the role of AT(1) and AT(2) receptors and the autonomic nervous system in mediating acute responses to angiotensin II were investigated in anesthetized CD1 mice. Injections of angiotensin II caused dose-related increases in systemic arterial pressure that were antagonized by candesartan. Pressor responses to angiotensin II were not altered by PD-123,319 in doses up to 25 mg/kg iv. At the lowest dose studied (20 microgram/kg iv), the inhibitory effects of candesartan were competitive, whereas at the highest dose (100 microgram/kg iv) the dose-response curve for angiotensin II was shifted to the right in a nonparallel manner with inhibitory effects that could not be surmounted. The inhibitory effects of candesartan were selective and were similar in animals pretreated with enalaprilat (1 mg/kg iv) to reduce endogenous angiotensin II production. Acute pressor responses to angiotensin II were not altered by propranolol (200 microgram/kg iv), phentolamine (200 microgram/kg iv), or atropine (1 mg/kg iv) but were enhanced by hexamethonium (5 mg/kg iv). Increases in total peripheral resistance induced by angiotensin II were inhibited by the AT(1)-receptor antagonist but were not altered by AT(2)-, alpha-, or beta-receptor antagonists. These results suggest that acute pressor responses to angiotensin II are mediated by AT(1) receptors, are buffered by the baroreceptors, and are not modulated by effects on AT(2) receptors and that activation of the sympathetic nervous system plays little if any role in mediating rapid hemodynamic responses to the peptide in anesthetized CD1 mice.

Analysis of vasoconstrictor responses to histamine in the hindlimb vascular bed of the rabbit

Hemodynamic responses to histamine were investigated in the anesthetized rabbit. Intravenous injections of histamine induced dose-dependent decreases in systemic arterial pressure that were blocked by the H(1)-receptor antagonist pyrilamine but not the H(2) antagonist cimetidine. Injections of histamine and the H(1) agonist 6-[2-(4-imidazolyl)ethylamine]-N-(4-trifuormethylphenyl)-heptan ecardo xamide dimaleate (HTMT) into the hindlimb perfusion circuit increased hindlimb perfusion pressure, whereas the H(2) agonist dimaprit decreased perfusion pressure and the H(3)-receptor agonist R-(-)-alpha-methylhistamine did not alter perfusion pressure. Pyrilamine reduced hindlimb vasoconstrictor responses to histamine and HTMT but did not alter vasodilator responses to dimaprit. Cimetidine reduced the response to dimaprit but did not alter vasoconstrictor responses to histamine or HTMT. The H(3)-receptor antagonist thioperamide was without effect on responses to the histamine agonists. These data suggest the presence of H(1) and H(2) receptors and that histamine for the most part acts by stimulating H(1) receptors to produce vasoconstriction in the hindlimb vascular bed of the rabbit. Responses to histamine, HTMT, and norepinephrine were significantly enhanced by a nitric oxide synthase inhibitor at a time when vasodilator responses to dimaprit were unaltered and responses to acetylcholine were significantly reduced. Responses to histamine and the H(1) and H(2) agonists were not affected by the cyclooxygenase inhibitor meclofenamate or by ATP-sensitive K(+) channel, alpha-adrenergic, or angiotensin AT(1) receptor antagonists. The present data suggest that H(1) receptors mediate both systemic vasodepressor and hindlimb vasoconstrictor responses to histamine.

Gene transfer of endothelial nitric oxide synthase to the penis augments erectile responses in the aged rat

Nitric oxide (NO), a mediator involved in penile erection, is synthesized by the nitric oxide synthase (NOS) family of enzymes. It has been shown that NOS activity decreases with age. To determine whether adenoviral-mediated overexpression of endothelial NOS (eNOS) could enhance erectile responses, we administered a recombinant adenovirus containing the eNOS gene (AdCMVeNOS) into the corpora cavernosum of the aged rat. Adenoviral expression of the beta-galactosidase reporter gene was observed in cavernosal tissue 1 day after intracavernosal administration of AdCMVbetagal; 1 day after administration of AdCMVeNOS, transgene expression was confirmed by immunoblot staining of eNOS protein, and cGMP levels were increased. The increase in cavernosal pressure in response to cavernosal nerve stimulation was enhanced in animals transfected with eNOS, and erectile responses to acetylcholine and zaprinast were enhanced at a time when the erectile response to the NO donor sodium 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate was not altered. These results suggest that in vivo gene transfer of eNOS, alone or in combination with a type V phosphodiesterase inhibitor, may constitute a new therapeutic intervention for the treatment of erectile dysfunction.

Endothelial cell regrowth and morphology after balloon catheter injury of alloxan-induced diabetic rabbits

Neointimal thickening after catheter injury has been reported to be influenced by the integrity of the vascular endothelium. We have previously shown that neointimal thickening is significantly reduced in alloxan-induced diabetic New Zealand White rabbits after catheter injury compared with euglycemic rabbits. In the present study, it was hypothesized that endothelial cell regrowth, morphology, and endothelium-dependent vasoreactivity after catheter injury are improved in the diabetic rabbit (glucose >/=400 mg/dl) compared with the euglycemic rabbit. Two weeks after catheter injury, the percent endothelial regrowth was significantly increased in diabetic animals compared with euglycemic animals (32.1 +/- 2 and 15.6 +/- 1, respectively; P < 0.05). The endothelial cell morphology analyzed by scanning electron microscopy was also restored 2 wk after catheter injury in thoracic aortas from the diabetic animals compared with vessels from euglycemic animals. Endothelium-dependent relaxation to ACh in vessels from diabetic and euglycemic rabbits was attenuated 2 wk after injury, and, although improved by 4 and 8 wk, relaxation remained significantly depressed. These results suggest that endothelial cell regrowth and morphology in diabetic animals was improved compared with euglycemic animals; however, endothelium-dependent vasoreactivity remained impaired. Thus the attenuated neointimal thickening seen in the diabetic rabbit may be a function of the rate and degree of regrowth rather than the normalization of ACh-induced relaxation.

Gene transfer of endothelial nitric oxide synthase to the lung of the mouse in vivo. Effect on agonist-induced and flow-mediated vascular responses

The effects of transfer of the endothelial nitric oxide synthase (eNOS) gene to the lung were studied in mice. After intratracheal administration of AdCMVbetagal, expression of the beta-galactosidase reporter gene was detected in pulmonary airway cells, in alveolar cells, and in small pulmonary arteries. Gene expression with AdCMVbetagal peaked 1 day after administration and decayed over a 7- to 14-day period, whereas gene expression after AdRSVbetagal transfection peaked on day 5 and was sustained over a 21- to 28-day period. One day after administration of AdCMVeNOS, eNOS protein levels were increased, and there was a small reduction in mean pulmonary arterial pressure and pulmonary vascular resistance. The pressure-flow relationship in the pulmonary vascular bed was shifted to the right in animals transfected with eNOS, and pulmonary vasodepressor responses to bradykinin and the type V cGMP-selective phosphodiesterase inhibitor zaprinast were enhanced, whereas systemic responses were not altered. Pulmonary vasopressor responses to endothelin-1 (ET-1), angiotensin II, and ventilatory hypoxia were reduced significantly in animals transfected with the eNOS gene, whereas pressor responses to norepinephrine and U46619 were not changed. Systemic pressor responses to ET-1 and angiotensin II were similar in eNOS-transfected mice and in control mice. Intratracheal administration of AdRSVeNOS attenuated the increase in pulmonary arterial pressure in mice exposed to the fibrogenic anticancer agent bleomycin. These data suggest that transfer of the eNOS gene in vivo can selectively reduce pulmonary vascular resistance and pulmonary pressor responses to ET-1, angiotensin II, and hypoxia; enhance pulmonary depressor responses; and attenuate pulmonary hypertension induced by bleomycin. Moreover, these data suggest that in vivo gene transfer may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders.

Induction of penile erection by intracavernosal and transurethral administration of novel nitric oxide donors in the cat

PURPOSE

The effects of novel nitric oxide (NO) donors administered intracavernosally and transurethrally on erectile function in the anesthetized cat were evaluated.

MATERIALS AND METHODS

In pentobarbital-anesthetized cats, increases in intracavernosal pressure, penile length, and duration of erectile response were determined after intracavernosal and transurethral injections of novel NO donors (MAHMA/NO, PAPA/NO, DEA/NO, PIPERAZI/NO and PROLI/NO). All parameters were measured after administration of NO donors intracavernosally via a 30-gauge needle and urethrally via a Jelco i.v. catheter in a volume of 200 microliters. Systemic arterial pressure was also assessed in these experiments. All NO donors were compared with a triple-drug control combination comprised of papaverine (1.65 mg.), prostaglandin E1 (0.5 microgram.), and phentolamine (25 micrograms.).

RESULTS

MAHMA/NO, PAPA/NO, DEA/NO, PIPERAZI/NO and PROLI/NO induced dose dependent increases in intracavernosal pressure and penile length (p < 0.05) when administered intracavernosally. The increases in cavernosal pressure and penile length were comparable to those observed with the triple-drug control combination. The maximum increase in cavernosal pressure in response to PROLI/NO and PAPA/NO was associated with no significant change in systemic arterial pressure. Transurethral administration of PROLI/NO and PIPERAZI/NO induced dose-dependent increases in cavernosal pressure and penile length (p < 0.05). The response was similar to that of the triple-drug control combination, except that transurethral PROLI/NO and PIPERAZI/NO had no significant effect on systemic blood pressure.

CONCLUSIONS

NO donors caused dose-dependent increases in cavernosal pressure when administered intracavernosally and transurethrally. These data suggest further exploration of the use of NO donors for the treatment of erectile dysfunction.

Proadrenomedullin N-terminal 20 peptide (PAMP), acting through PAMP(12-20)-sensitive receptors, inhibits Ca2+-dependent, agonist-stimulated secretion of human adrenal glands

Proadrenomedullin N-terminal 20 peptide (PAMP) is a 20-amino acid hypotensive peptide expressed in the adrenal medulla. We investigated the localization and function of PAMP receptors in the human adrenal gland. Autoradiography showed the presence of [125I]PAMP-binding sites in both zona glomerulosa and adrenal medulla that were displaced by cold PAMP and PAMP(12-20) but not by other preproadrenomedullin-derived peptides. PAMP, but not PAMP(12-20), counteracted, in a concentration dependent manner, both aldosterone response of zona glomerulosa cells and catecholamine response of adrenal medulla cells to BAYK-8644, the selective agonist of voltage-activated Ca2+ channels, as well as to K+ and angiotensin II. PAMP(12-20) partially reversed this antisecretagogue effect of PAMP. Collectively, these findings suggest (1) that PAMP inhibits Ca2+-dependent, agonist-stimulated aldosterone and catecholamine secretion, acting via specific receptors and through a mechanism involving the impairment of Ca2+ influx; and (2) that PAMP(12-20) acts as a weak antagonist of PAMP receptors, thereby suggesting that both C- and N-terminal sequences of the PAMP molecule are required for this peptide to exert its antisecretagogue action on the human adrenal gland.

Responses to propofol in the pulmonary vascular bed of the rat

BACKGROUND

Although a great deal is known about responses to propofol, controversy remains about its mechanism of action. The present study was undertaken to investigate the direct effects of 2,6-diisopropyl phenol, disodium edetate, and its intralipid emulsion in the rat pulmonary vascular bed and to better understand the mechanisms involved in propofol-mediated responses.

METHODS

The effects of N omega-l-nitro-l-arginine benzyl ester (L-NABE), an inhibitor of nitric oxide synthase, of the cyclooxygenase blocker, meclofenamate, and the K + ATP channel antagonist, U-37883A, an ATP-sensitive potassium channel antagonist, on responses to propofol, acetylcholine, nitroglycerin, and isoproterenol were investigated in the isolated blood-perfused rat lung under low tone and high steady-state tone.

RESULTS

Propofol produced a dose-dependent decrease in pulmonary arterial perfusion pressure. L-NABE significantly reduced vasodilator responses to acetylcholine, whereas the nitric oxide synthase inhibitor had no significant effect on responses to propofol. Meclofenamate significantly reduced vasodilator responses to arachidonic acid without effecting responses to propofol. Responses to propofol were not significantly changed in the presence of U-37883A, whereas U-37883A reduced vasodilator responses to levcromakalim. Additionally, 2,6-diisopropylphenol in a pure preparation as well as an intralipid preparation similar to propofol emulsion had no significant effect while disodium edetate had a dose-dependent depressor effect under high steady-state tone.

CONCLUSION

Propofol has significant vasodilator activity in the pulmonary vascular bed of the rat but responses to propofol are not mediated or modulated by the release of nitric oxide, opening of K + ATP channels, or the release of vasodilator cyclooxygenase products.

Vasodepressor responses to [D-Ala2]-endomorphin 2 (TAPP) are mediated by an L-NAME-sensitive mechanism in the rat

Endomorphin 1 and 2 are newly discovered endogenous ligands for the mu-opioid receptor. We recently showed that endomorphin 1 and 2 have vasodepressor activity, and in this study, responses to a novel endomorphin analog [D-Ala2]-endomorphin 2 (TAPP) were investigated in the systemic vascular bed of the rat. Intravenous injections of TAPP, endomorphin 1, and endomorphin 2 decreased systemic arterial pressure in a dose-related manner. Decreases in systemic arterial pressure in response to TAPP were similar to vasodepressor responses to endomorphin 1 and 2 and were not altered by passage of time. Decreases in systemic arterial pressure in response to TAPP, endomorphin 1, and endomorphin 2 were attenuated by the opioid receptor antagonist naloxone (2 mg/kg, i.v.) when the vasodepressor response to the ORL1-receptor agonist nociceptin (orphanin FQ) was not altered. Decreases in systemic arterial pressure in response to TAPP, endomorphin 1 and 2, and acetylcholine were attenuated by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 50 mg/kg, i.v.) when decreases in systemic arterial pressure in response to nociceptin and calcitonin gene-related peptide (CGRP) were not altered. These results indicate that TAPP, endomorphin 1, and endomorphin 2 decrease systemic arterial pressure by a naloxone-sensitive mechanism and suggest that the vasodepressor response to TAPP, endomorphin 1 and 2, but not nociceptin, is mediated by the release of nitric oxide.

Adrenomedullin and calcitonin gene-related peptide (CGRP) interact with a common receptor of the CGRP1 subtype in the human adrenal zona glomerulosa

Frozen sections of normal adrenal glands, obtained from patients undergoing unilateral nephrectomy for kidney cancer, were labeled in vitro with human [125I]ADM(1-52). Autoradiography showed the presence of abundant ADM binding sites in the zona glomerulosa (ZG) and the outermost portion of the zona fasciculata, which were completely displaced by the addition of an excess of cold ADM(1-52). Calcitonin gene-related peptide (CGRP) and the non-selective ligand of the CGRP-receptor subtypes 1 and 2 CGRP(8-37) eliminated [125I]ADM(1-52) binding in the ZG, while the selective ligand of CGRP receptor subtype 2 [Cys(acm)2,7]-CGRP and CGRP(1-8) were ineffective. These findings confirm the presence of ADM binding sites in the human ZG, and provide the first morphological evidence that ADM and CGRP interact with a common receptor of the CGRP1 subtype.

Inhibitory effect of adrenomedullin (ADM) on the aldosterone response of human adrenocortical cells to angiotensin-II: role of ADM(22-52)-sensitive receptors

Human adrenomedullin (ADM) is a 52-amino acid hypotensive peptide, which possesses a disulfide bridge-formed six-membered ring in 16-21 position. The ring structure, and both the N- and C-terminal amino-acid sequences seem to play a key role in the vascular effects of ADM(1-52), and we have investigated whether the same is true for the inhibitory effect of this peptide on the aldosterone response of zona glomerulosa (ZG) cells to angiotensin-II (ANG-II). Autoradiography showed the presence of abundant [125I]ADM(1-52) binding sites in the ZG of human adrenals, which were displaced not only by cold ADM(1-52), but also by both ADM(13-52) and ADM(22-52); ADM fragments 1-12, 15-22 and 16-31 were ineffective. ADM(1-52) and ADM(13-52), but not other fragments, concentration-dependently inhibited ANG-II-stimulated aldosterone secretion of dispersed human adrenocortical cells. The aldosterone antisecretagogue actions of ADM(1-52) and ADM(13-52) were counteracted by ADM(22-52) in a concentration-dependent manner, while other ADM fragments were ineffective. In light of these findings the following conclusions could be drawn: (i) human ZG cells are provided with ADM(22-52)-sensitive receptors; (ii) the six-membered ring structure and the C-terminal, but not N-terminal, amino-acid sequence are both essential for ADM(1-52) to exert its antimineralocorticoid action; and probably (iii) the C-terminal sequence is needed for ADM(1-52) to bind its ZG receptors, while the ring structure is required for the receptor activation.

Vasodilator responses to the endomorphin peptides, but not nociceptin/OFQ, are mediated by nitric oxide release

The endomorphin peptides, endogenous ligands for the mu-opioid receptor, and nociceptin (orphanin FQ; OFQ), an endogenous ligand for the ORL1 receptor, have substantial vasodilator activity in the rat. The roles of nitric oxide, vasodilator prostaglandins, and the opening of K+ATP channels in mediating vasodilator responses to these novel agonists were investigated in the hindquarters vascular bed of the rat. Under constant-flow conditions, injections of the mu-selective agonists, endomorphin 1 and 2, PL017 ([N-MePhe3, D-Pro4]-morphiceptin), and DAMGO, and the ORL1 receptor agonist, nociceptin/OFQ, produced dose-dependent decreases in hindquarters perfusion pressure. Vasodilator responses to endomorphin 1, PL017, and DAMGO were attenuated by the nitric oxide synthase inhibitor L-NAME at a time when vasodilator responses to nociceptin/OFQ were not altered. Responses to endomorphin 1 and 2, PL017, DAMGO, and nociceptin/OFQ were not altered by the cyclooxygenase inhibitor sodium meclofenamate or the K+ATP channel blocker U-37883A. The results of these studies indicate that responses to endomorphin 1 and 2, PL017, and DAMGO are mediated in large part by the release of nitric oxide, while responses to nociceptin/OFQ are mediated by an L-NAME-insensitive mechanism. Moreover, these results demonstrate that responses to these peptides are not mediated by the release of vasodilator prostaglandins or K+ATP channel opening in the hindquarters vascular bed.

Analysis of the effects of candesartan on responses to angiotensin II in the hindquarters vascular bed of the cat

The effects of the nonpeptide angiotensin II (AngII) AT1 receptor blocker candesartan on responses to AngII were investigated in the hindquarters vascular bed of the cat. Under constant-flow conditions, injections of AngII into the hindquarters perfusion circuit elicited dose-dependent increases in perfusion pressure. Candesartan in a dose of 3 microg/kg intravenously (i.v.) decreased vasoconstrictor responses to AngII in a surmountable manner. At doses of 30 and 300 microg/kg i.v., candesartan shifted the dose-response curve to AngII to the right in an insurmountable manner, indicating an insurmountable blockade of AT1 receptors. The inhibitory effects of the larger doses of candesartan on responses to AngII were long in duration, and the AT1 receptor blocker had little effect on baseline pressures. Candesartan was without effect on vasoconstrictor responses to norepinephrine, U46619, PGF2alpha, vasopressin, BAY K8644; biphasic responses to endothelin-1; or on vasodilator responses to acetylcholine, albuterol, or levcromakalim. These results indicate that candesartan is a potent and selective angiotensin AT1 receptor blocker that can induce both surmountable and insurmountable AT1 receptor blockade and provide support for the hypothesis that there are "spare" AT1 receptors in the hindquarters vascular bed of the cat.

The influence of candesartan and PD123319 on responses to angiotensin II in the hindquarters vascular bed of the rat

The effects of the AT1 and AT2 receptor blockers candesartan and PD123319 on hemodynamic responses to angiotensin II (AngII) were investigated in the anesthetized rat. Injections of AngII caused dose-related increases in systemic arterial and in hindquarters perfusion pressure that were reduced by candesartan. The inhibitory effects of candesartan were insurmountable, and a vasodepressor or vasodilator response to AngII was not unmasked. The AT2 receptor antagonist PD 123319 had no effect on increases in systemic arterial and hindquarters perfusion pressure in response to AngII. The present results suggest that pressor responses to AngII are mediated by the activation of AT1 receptors, and that AT2 receptors do not appear to modulate hemodynamic responses to AngII in the anesthetized rat.