Regional differences in the functional and biochemical properties of endothelin receptor subtypes in the rabbit prostatic urethra

OBJECTIVE

To examine the regional differences in the functional (pharmacological) and biochemical properties of endothelin (ET) receptors in the rabbit prostatic urethra.

MATERIALS AND METHODS

The properties of ET receptors in 6-month-old male rabbit prostatic urethras were examined using isolated muscle-bath and radioligand receptor-binding techniques. Using plasma membrane suspensions, saturation and inhibition experiments with [(125)I]ET-1 and unlabelled agonists and antagonists (ET(A)-selective antagonist BQ123, and ET(B)-selective agonist sarafotoxin 6c, STX6c) were done to determine the ET receptor densities and their subtype specificities in the different regions of the urethra.

RESULTS

The ETs (ET-1 and ET-3) produced significant concentration-dependent contractile responses in the smooth muscle strips from the different regions of the urethra. Although the maximum contractile responses induced by ET-1 were similar in the different regions, the maximum contractile responses induced by ET-3 were greater in the distal region than in the proximal or middle regions, suggesting that the contractile response to ET-1 is more potent than that to ET-3 in all regions, and that there are region-specific differences in the responses to ET-3 but not ET-1. Moreover, the ET-3-induced contractile response was suppressed by BQ788 (a selective antagonist of the ET(B) receptor) suggesting that the ET(B) receptor subtype contributes to the contractile responses mediated by ET-3. The ET receptors were expressed in higher concentrations in the distal than in the proximal or middle regions. BQ123 and STX6c inhibited [(125)I]ET-1 binding in all regions with high and low affinity constants, indicating the presence of both ET(A) and ET(B) receptor subtypes. The proportions of high-affinity binding sites for BQ123, representing ET(A) receptors, were approximately 68%, 63% and 42% in the proximal, middle and distal regions, respectively. By contrast, the proportions of high-affinity binding sites for STX6c, representing ET(B) receptors, were approximately 27%, 35% and 52% in the proximal, middle, and distal regions, respectively. These data indicate the presence of regional differences in the densities and subtype specificities of ET receptor subtypes, and the existence of regional differences in the rabbit prostatic urethra.

CONCLUSION

The results suggest regional differences in ET(B) receptor subtypes that mediate contractile responses to ET-3, reflecting differences in the densities and specificities of the ET receptor subtypes in the rabbit prostatic urethra.

Central gene transfer of interleukin-10 reduces hypothalamic inflammation and evidence of heart failure in rats after myocardial infarction

The expression of proinflammatory cytokines increases in hypothalamus of rats with myocardial infarction (MI) and heart failure. We used central gene transfer of human interleukin (IL)-10, a potent antiinflammatory cytokine, to counter the effects of brain proinflammatory cytokines and examine their functional significance. Sprague-Dawley rats underwent coronary ligation to induce MI or sham surgery (SHAM). One week later, adenoviral vectors encoding human IL-10 (AdIL-10) or beta-galactosidase (betaGal) were injected (30 microL over 30 minutes) into lateral ventricle. One week after injection, there was abundant expression of human IL-10 in the brain of MI+AdIL-10 and SHAM+AdIL-10 rats. Compared with SHAM+betaGal, MI+betaGal had increased (P<0.05) IL-1beta and cyclooxygenase-2 mRNA and protein and nuclear factor kappaB activity in the hypothalamus, cyclooxygenase-2 fluorescence in perivascular cells of the paraventricular nucleus of hypothalamus, prostaglandin E(2) in cerebrospinal fluid, and Fra-like activity (indicating neuronal excitation) in paraventricular nucleus. Plasma norepinephrine levels, lung/body weight, right ventricle/body weight, and left ventricular end-diastolic pressure were increased and maximal left ventricular dP/dt was decreased. All of these findings were ameliorated in MI rats treated with AdIL-10. Hypothalamic tumor necrosis factor-alpha and circulating tumor necrosis factor-alpha and IL-1beta levels, also increased in MI+betaGal, were not affected by AdIL-10 treatment. Rat native IL-10 was not affected by MI or AdIL-10. AdIL-10 had no effects on SHAM rats. The results demonstrate that cardiovascular and autonomic mechanisms leading to heart failure after MI can be modulated by manipulating the balance between proinflammatory and antiinflammatory cytokines in the brain.

Preservation of coronary reserve by ivabradine-induced reduction in heart rate in infarcted rats is associated with decrease in perivascular collagen

We tested the hypothesis that chronically reducing the heart rate in infarcted middle-aged rats using ivabradine (IVA) would induce arteriolar growth and attenuate perivascular collagen and, thereby, improve maximal perfusion and coronary reserve in the surviving myocardium. Myocardial infarction (MI) was induced in 12-mo-old male Sprague-Dawley rats, which were then treated with either IVA (10.5 mg.kg(-1).day(-1); MI + IVA) or placebo (MI) via intraperitoneal osmotic pumps for 4 wk. Four weeks of IVA treatment limited the increase in left ventricular end-diastolic pressure and the decrease in ejection fraction but did not affect the size of the infarct, the magnitude of myocyte hypertrophy, or the degree of arteriolar and capillary growth. However, treatment reduced interstitial and periarteriolar collagen in the surviving myocardium of MI + IVA rats. The reduced periarteriolar collagen content was associated with improvement in maximal myocardial perfusion and coronary reserve. Although the rates of proliferation of periarteriolar fibroblasts were similar in the MI and MI + IVA groups, the expression levels of the AT(1) receptor and transforming growth factor (TGF)-beta(1) in the myocardium, as well as the plasma level of the ANG II peptide, were lower in treated rats 14 days after MI. Therefore, our data reveal that improved maximal myocardial perfusion and coronary reserve in MI + IVA rats are most likely the result of reduced periarteriolar collagen rather than enhanced arteriolar growth.

Increased cyclooxygenase-2 expression in hypothalamic paraventricular nucleus in rats with heart failure: role of nuclear factor kappaB

We investigated the role of nuclear factor kappaB (NF-kappaB) in the cytokine-mediated induction of cyclooxygenase-2 activity in the paraventricular nucleus of hypothalamus (PVN), a critical cardiovascular and autonomic center, in rats with heart failure (HF). Sprague-Dawley rats underwent coronary artery ligation to induce HF or sham surgery. HF rats were treated orally for 6 weeks with vehicle (tap water), the NF-kappaB inhibitor pyrrolidine dithiocarbamate (150 mg/kg per day), or the mineralocorticoid receptor antagonist eplerenone (30 mg/kg per day), which has been shown to reduce circulating proinflammatory cytokines in this model. Compared with sham surgery, HF rats had higher (P<0.05) levels of aldosterone, interleukin-1beta and norepinephrine in plasma and prostaglandin E2 in cerebrospinal fluid. In the PVN, NF-kappaB p50 precursor p105 mRNA increased, and mRNA for its inhibitor, IkappaB, decreased (P<0.05). Cyclooxygenase-2 mRNA and protein expression was increased in perivascular cells of the PVN. Both pyrrolidine dithiocarbamate and eplerenone reduced (P<0.05) p105 mRNA and increased IkappaB mRNA in PVN. Both also reduced (P<0.05) cyclooxygenase-2 mRNA and protein expression in PVN, cerebrospinal fluid prostaglandin E2, and plasma norepinephrine. Eplerenone, but not pyrrolidine dithiocarbamate, reduced plasma interleukin-1beta. Pyrrolidine dithiocarbamate and eplerenone had no effect on plasma aldosterone. The results suggest that activation of NF-kappaB is an intermediary step in cytokine-mediated induction of cyclooxygenase-2 in the PVN of HF rats. By enhancing access of prostaglandin E2 to hypothalamic neurons, this mechanism may contribute to augmented sympathetic nerve activity in HF.

Calcific Aortic Valve Stenosis in Old Hypercholesterolemic Mice

Background— Hypercholesterolemia and old age are clinical risk factors for development of aortic valve stenosis, and hypercholesterolemia is a putative therapeutic target. We tested the hypothesis that calcification and aortic valve stenosis would develop in genetically hypercholesterolemic old mice.

Methods and Results— Twenty-four low-density lipoprotein receptor–deficient apolipoprotein B-100–only ( LDLr −/− ApoB 100/100 ) mice were fed normal chow from weaning until age 20.1±0.5 months (mean±SE; range 17 to 22 months). Twenty-one age-matched (20.8±0.9 months, range 17 to 25 months) C57Bl/6 mice served as controls. Echocardiographic imaging was used to assess morphology and function of the aortic valve and left ventricle. A subset of 12 mice underwent invasive hemodynamic assessment of aortic valve function. Functionally significant aortic stenosis, with >75% reduction in valve area, occurred in 8 of 24 LDLr −/− ApoB 100/100 mice and in 0 of 21 controls ( P =0.01). In the subset that underwent catheterization, mice with echocardiographic evidence of aortic stenosis had a systolic transvalvular gradient of 57±6 mm Hg. In the group of all LDLr −/− ApoB 100/100 mice with aortic stenosis, left ventricular mass was increased by 67% ( P =0.001) and ejection fraction was decreased by 30% ( P =0.004) compared with LDLr −/− ApoB 100/100 without aortic stenosis. Von Kossa staining of the aortic valve demonstrated abundant mineralization in LDLr −/− ApoB 100/100 mice but not in control mice. Superoxide (oxyethidium fluorescence) was present in valve tissue from all 3 groups of mice and was more abundant in mice with aortic stenosis.

Conclusions— Hypercholesterolemic LDLr −/− ApoB 100/100 mice are prone to develop calcification and oxidative stress in the aortic valve, with functional valvular heart disease, mimicking the clinical syndrome. This discovery holds promise for elucidation of the pathophysiology of aortic valve disease mechanisms and for the design of effective nonsurgical treatment.

Novel effect of mineralocorticoid receptor antagonism to reduce proinflammatory cytokines and hypothalamic activation in rats with ischemia-induced heart failure

Blocking brain mineralocorticoid receptors (MRs) reduces the high circulating levels of tumor necrosis factor (TNF)-alpha in heart failure (HF) rats. TNF-alpha and other proinflammatory cytokines activate neurons in the paraventricular nucleus (PVN) of hypothalamus, including corticotropin-releasing hormone (CRH) neurons, by inducing cyclooxygenase (COX)-2 activity and synthesis of prostaglandin E2 by perivascular cells of the cerebral vasculature. We tested the hypothesis that systemic treatment with a MR antagonist would reduce hypothalamic COX-2 expression and PVN neuronal activation in HF rats. Rats underwent coronary ligation to induce HF, confirmed by echocardiography, or sham surgery, followed by 6 weeks treatment with eplerenone (30 mg/kg per day, orally) or vehicle (drinking water). Eplerenone-treated HF rats had lower plasma TNF-alpha, interleukin (IL)-1beta and IL-6, less COX-2 staining of small blood vessels penetrating PVN, fewer PVN neurons expressing Fra-like activity (indicating chronic neuronal activation), and fewer PVN neurons staining for TNF-alpha, IL-1beta, and CRH than vehicle-treated HF rats. COX-2 and CRH protein expression in hypothalamus were 1.7- and 1.9-fold higher, respectively, in HF+vehicle versus sham+vehicle rats; these increases were attenuated (26% and 25%, respectively) in HF+eplerenone rats. Eplerenone-treated HF rats had less prostaglandin E2 in cerebrospinal fluid, lower plasma norepinephrine levels, lower left ventricular end-diastolic pressure, and lower right ventricle/body weight and lung/body weight ratios, but no improvement in left ventricular function. Treatment of HF rats with anticytokine agents, etanercept or pentoxifylline, produced very similar results. This study reveals a previously unrecognized effect of MR antagonism to minimize cytokine-induced central neural excitation in rats with HF.

Severe feto-placental abnormalities precede the onset of hypertension and proteinuria in a mouse model of preeclampsia

Preeclampsia is a prevalent and potentially devastating disorder of pregnancy. Characterized by a sudden spike in blood pressure and urinary protein levels, it is associated with significant obstetric complications. BPH/5 is an inbred mouse model of preeclampsia with borderline hypertension before pregnancy. BPH/5 mice develop hypertension, proteinuria, and endothelial dysfunction during late gestation (after E14.5). We hypothesized that BPH/5 mice might exhibit early feto-placental abnormalities before the onset of maternal disease. All placental cell lineages were present in BPH/5 mice. However, the fetal and placental weights were reduced, with abnormalities in all the placental zones observed starting early in gestation (E9.5-E12.5). The fractional area occupied by the junctional zone was significantly reduced at all gestational timepoints. Markedly fewer CDKN1C-stained trophoblasts were seen invading the proximal decidual zone, and this was accompanied by reductions in Cdkn1c gene expression. Trophoblast giant cell morphology and cytokeratin staining were not altered, although the mRNA levels of several giant cell-specific markers were significantly downregulated. The labyrinth layer displayed decreased branching morphogenesis of endothelial cells, with electron microscopy evidence of attenuated trophoblast layers. The maternal decidual arteries showed increased wall-to-lumen ratios with persistence of actin-positive smooth muscle cells. These changes translated into dramatically increased vascular resistance in the uterine arteries, as measured by pulse-wave Doppler. Collectively, these results support the hypothesis that defects at the maternal-fetal interface are primary causal events in preeclampsia, and further suggest the BPH/5 model is important for investigations of the underlying pathogenic mechanisms in preeclampsia.

Age Related Changes in the Functional, Biochemical and Molecular Properties of α 1 -Adrenoceptors in the Rat Genitourinary Tract

PURPOSE

Because age related changes occur in the properties of alpha(1)-adrenoceptor in several mammalian tissues and alpha(1)-adrenoceptor antagonists are extensively used to treat lower urinary tract symptoms secondary to benign prostatic hyperplasia, we investigated age related changes in the functional, biochemical and molecular properties of alpha(1)-adrenoceptor in the rat genitourinary tract.

MATERIALS AND METHODS

The characteristics of alpha(1)-adrenoceptor in the ventral and dorsolateral prostate, and bladder base and dome of 3 and 22-month-old rats were determined using an isolated muscle bath, radioligand receptor binding and real-time reverse transcriptase-polymerase chain reaction techniques.

RESULTS

Old rats had significantly higher body weight, lower testosterone, a smaller ventral prostate and a larger bladder dome than young rats. Although there was no significant age dependent difference in the properties of alpha(1)-adrenoceptor in the bladder base and dome, total alpha(1)-adrenoceptor density, mRNA expression of all 3 alpha(1)-adrenoceptor subtypes (alpha(1A), alpha(1B) and alpha(1D)) and the maximum contractile responses to phenylephrine were significantly lower in the ventral and dorsolateral prostate of 22 vs 3-month-old rats.

CONCLUSIONS

Age related differences in the molecular, biochemical and functional properties of alpha(1)-adrenoceptors in the rat genitourinary tract may indicate potential differences in the response to alpha(1)-adrenoceptor antagonists with aging, ie a decrease in the therapeutic response in old vs young rats in the response to alpha(1)-adrenoceptor antagonists when used to treat lower urinary tract symptoms secondary to benign prostatic hyperplasia.

Vascular effects of a common gene variant of extracellular superoxide dismutase in heart failure

A common gene variant of human extracellular superoxide dismutase (ecSOD), in ∼5% of humans, is associated with increased risk of ischemic heart disease. The purpose of this study was to examine vascular effects of ecSOD with effects of the ecSOD variant (ecSODR213G) in rats with heart failure. Seven weeks after coronary artery ligation, we studied rats with heart failure and sham-operated rats. Adenoviral vectors expressing human ecSOD, ecSODR213G, or a control virus were injected intravenously. In the aorta from rats with heart failure, responses to acetylcholine (69 ± 4% relaxation, means ± SE) and basal levels of nitric oxide (NO) (vasoconstrictor responses to a NO synthase inhibitor) were greatly impaired, and levels of superoxide and peroxynitrite were increased. Gene transfer of ecSOD restored responses to acetylcholine (92 ± 2% relaxation) and basal levels of NO to normal and reduced levels of superoxide [from 2.3 ± 0.2 to 0.9 ± 0.2 relative light units per second per millimeter squared (RLU·s−1·mm−2)] and peroxynitrite (from 2.4 ± 0.2 to 0.9 ± 0.1 RLU·s−1·mm−2) in the aorta from rats with heart failure. Gene transfer of ecSODR213G produced little or no improvement. Responses to nitroprusside were not different among the groups. Expression of endogenous mRNA for SODs (CuZnSOD, MnSOD, and ecSOD) and endothelial NOS in the aorta was not different among the groups. In contrast to ecSOD, gene transfer of ecSODR213G in rats with heart failure has minimal beneficial effect on oxidative stress, endothelial function, or basal bioavailability of NO. We speculate that greatly diminished efficacy of ecSODR213G in protection against oxidative stress and endothelial dysfunction may contribute to increased risk of cardiovascular disease in humans with ecSODR213G.

A role for Akt in the rapid regulation of inflammatory and apoptotic pathways in mouse bladder

Akt is linked to both inflammatory and neoplastic pathways. Akt activation is dependent on the phosphatidylinositol-3 kinase (PI3K) signaling pathways. Upon phosphorylation by PI3K, Akt can phosphorylate nuclear factor kappa B (NF-kappaB) and members of the forkhead family of transcription factors, which includes AFX. Our goal is to examine the effect of Escherichia coli lipopolysaccharide (LPS) on early cellular signaling in inflammatory (NF-kappaB) and apoptotic pathways (AFX) in a mouse-bladder model and in T-24 urothelial cancer cells. Female C57BL/6 mice were given an intraperitoneal (IP) injection of LPS or LPS free water and sacrificed 0-120 minutes later. Bladders were harvested, and immunohistochemistry (IHC) and/or immunoblotting performed using antibodies to PI3K, inhibitor kappa B-alpha (IkappaB-alpha), and total and phosphorylated Akt, NF-kappaB and AFX. Levels of IkappaB-alpha and total and phosphorylated Akt and NF-kappaB were determined in T-24 cells treated with LPS for 0-120 minutes. Bladders and T-24 cells were treated with PI3K inhibitors in some experiments. Protein amounts in different samples were normalized to immunoreactive actin. Phosphorylated and non-phosphorylated species of Akt, NF-kappaB, and AFX were localized to the urothelium. IP LPS injection rapidly (within 30 minutes) increased Akt phosphorylation. IP LPS injection decreased IkappaB-alpha levels, and increased NF-kappaB and AFX phosphorylation. Wortmannin effectively blocked phosphorylation of Akt in LPS-treated mice, and also reduced phosphorylation of AFX and, to a lesser extent, NF-kappaB. After treatment with LPS, Akt and NF-kappaB phosphorylation was rapidly increased in T-24 cells. Akt phosphorylation, and to a lesser extent NF-kappaB phosphorylation, were blocked by LY-294,002. LPS/PI3K/Akt is a cellular signaling pathway which rapidly activates downstream pathways of inflammation and neoplasia in bladder urothelium.

The effects of chronic fluoxetine treatment on chronic mild stress-induced cardiovascular changes and anhedonia

BACKGROUND

Depression has a complex bidirectional association with heart disease. Previously we have shown notable cardiovascular changes in the chronic mild stress (CMS) rodent model of depression. Here we investigated the effects of a serotonin-specific reuptake inhibitor on a behavioral index of depression (anhedonia) and cardiac function in rats exposed to CMS.

METHODS

Male Sprague-Dawley rats were exposed to either 4 weeks of control conditions or CMS, consisting of unpredictable periods of mild stressors, while being treated concurrently with 4 weeks of daily fluoxetine (10 mg/kg, sc) or vehicle.

RESULTS

Chronic fluoxetine treatment prevented anhedonia in rats exposed to CMS, versus the CMS group treated with vehicle. However, treatment with fluoxetine in the CMS group only partially prevented specific cardiovascular changes associated with CMS, including elevated resting heart rate (HR), exaggerated pressor and HR responses to air jet stress, reduced cardiac output and stroke volume, and HR exaggerated responses to beta-adrenergic receptor blockade.

CONCLUSIONS

These findings provide evidence that 4 weeks of fluoxetine treatment can prevent behavioral responses and can partially prevent cardiovascular changes associated with CMS, providing insight into the role of serotonin in the link between depression and cardiovascular dysfunction.

Pacemaker activity in the upper urinary tract

Ureteral peristaltic activity begins with the origin of electrical activity at pacemaker sites. These sites are located in the proximal portion of the urinary collecting system. The 'atypical' smooth muscle cells at these sites fire 'pacemaker' potentials at a frequency higher than the 'driven' action potentials recorded from typical smooth muscle cells. In contrast to typical smooth muscle cells, these atypical pacemaker cells have less than 40% of their cellular area occupied by contractile filaments and demonstrate a sparse immunoreactivity for alpha-smooth muscle actin. Expression of c-Kit, a tyrosine kinase receptor, correlates with the onset of organized ureteral peristalsis in the embryo. Capsaicin-sensitive sensory afferents and the endogenous release of tachykinins and prostaglandins are involved in the maintenance of normal ureteral peristalsis.