Increased contraction to noradrenaline by vasopressin in human renal arteries

OBJECTIVE

Arginine vasopressin (AVP) not only acts directly on blood vessels through vasopressin V1 receptor stimulation but also may modulate adrenergic-mediated responses in animal experiments. The aim of the present study was to assess whether subpressor concentrations of AVP could contribute to an abnormal adrenergic contractile response of human renal arteries.

METHODS

Renal artery rings were obtained from 27 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension.

RESULTS

AVP (10(-10) mol/l) and the vasopressin V1 receptor agonist [Phe2, Orn8]-vasotocin (10(-10) mol/l) produced a leftward shift of the concentration-response curve to noradrenaline (half-maximal effective concentration decreased from 1.1 x 10(-6) mol/l to 3.1 x 10(-7) mol/l). The enhancement of noradrenaline-induced contractions was inhibited by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)AVP (10-8 mol/l) and unaffected by endothelium removal or pretreatment with the inhibitor of nitric oxide (NO) synthase NG-monomethyl-l-arginine (l-NMMA). The vasopressin V2 receptor agonist 1-desamino-8-D-arginine vasopressin (dDAVP) (10(-10)-10(-8) mol/l) did not modify contractile responses to noradrenaline. In the presence of the dihydropyridine calcium antagonist nifedipine (10(-6) mol/l), vasopressin failed to enhance the contractile response to noradrenaline.

CONCLUSIONS

The results demonstrate that subpressor concentrations of vasopressin potentiate the contractile effects of noradrenaline without intervention of the NO system. The effects appear to be mediated by vasopressin V1 receptor stimulation, which brings about an increase in calcium entry through dihydropyridine-sensitive calcium channels.

Relaxation induced by milrinone and rolipram in human penile arteries and veins

We studied the relaxant effects of milrinone, an inhibitor of phosphodiesterase 3, and rolipram, an inhibitor of phosphodiesterase 4, on contracted human penile dorsal artery and deep dorsal vein. Vascular rings from 12 multi-organ donors were suspended in organ baths for isometric recording of tension. Both milrinone and rolipram inhibited (100%) the contraction induced by noradrenaline and shifted the relaxation-response curves to the cAMP forming agents prostaglandin E(1) and forskolin to the left. The findings indicate that the cAMP pathway appears to be a main determinant of relaxation in human penile vessels.

U-46619-induced potentiation of noradrenergic constriction in the human saphenous vein: antagonism by thromboxane receptor blockade

OBJECTIVE

We investigated the potentiating effect of U-46619, a synthetic analogue of thromboxane A(2) (TXA(2)), on the adrenergic responses in human saphenous vein.

METHODS

Saphenous vein rings were obtained from 35 patients undergoing coronary artery bypass surgery. The rings were suspended in organ bath chambers for isometric recording of tension.

RESULTS

U-46619 (10(-10)-3 x 10(-7) mol/l) produced concentration-dependent and endothelium-independent contractile responses. U-46619 (10(-10) mol/l) potentiated the contractions elicited by electrical stimulation and potassium chloride, and produced leftward shifts of the concentration-response curve for noradrenaline. The TXA(2) receptor antagonist SQ-30741 (10(-8) mol/l) prevented the potentiation evoked by U-46619. The dihydropyridine calcium antagonist nifedipine (10(-6) mol/l) did not affect the potentiation of electrical stimulation and noradrenaline induced by U-46619, but abolished the potentiation of U-46619 on KCl-induced contractions.

CONCLUSIONS

U-46619 facilitates sympathetic neurotransmission and potentiates constrictor effects of noradrenaline in human saphenous veins through stimulation of TXA(2) receptors. These effects are independent of calcium entry through dihydropyridine calcium channels.

Low level of circulating activated protein C is a risk factor for venous thromboembolism

The levels of circulating activated protein C (APC) reflect in vivo protein C activation. The aim of this study was to determine whether a low APC level is an independent risk factor for venous thromboembolism (VTE). We measured APC in 160 patients with a history of VTE and without recognized thrombophilic defects, and in 199 healthy individuals. The mean (+/- SD) APC level was lower in patients (0.99 +/- 0.44 ng/ml) than in controls (1.19 +/- 0.41 ng/ml) (p < 0.0001), and showed a different distribution in the two groups. Thirty-eight patients (23.7%) had APC levels below the 5th percentile of the control group (<0.69 ng/ml) and 57 patients (35.6%) had APC levels below the 10th percentile (<0.77 ng/ml). APC levels <0.69 ng/ml increased the risk of a single or recurrent episode of VTE 4.2-fold (95% confidence interval, 2.0-9.0) or 6.9-fold (2.6-17.9). respectively, and APC levels <0.77 ng/ml increased these risks 3.4-fold (1.9-6.2) or 5.1-fold (2.3-11.2), respectively, compared with controls. Familial studies revealed that in some cases the low APC phenotype seems to be hereditary. We conclude that a low level of circulating APC in individuals without any of the most recognized thrombophilic defects is a prevalent, independent risk factor for VTE, and that it predisposes to recurrent VTE.

Inhibition of nitric oxide activity by arginine analogs in human renal arteries

BACKGROUND

Plasma levels of endogenous guanidine compounds are increased in various pathologic conditions, including chronic renal failure. In the present study we tested the effects of some of these compounds on basal and stimulated nitric oxide activity in human renal arteries.

METHODS

Rings from human renal arteries were obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ baths for isometric recording of tension. We then studied the effects of N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetrical dimethylarginine [ADMA]), aminoguanidine (AG), and methylguanidine (MG) on artery rings under basal and stimulated conditions.

RESULTS

In precontracted arteries, L-NMMA (1 micromol/L to 1 mmol/L) and ADMA (1 micromol/L to 3 mmol/L) caused concentration- and endothelium-dependent contractions (median effective concentrations [EC50] = 13.3 micromol/L and 17.5 micromol/L, respectively; Emax = 15+/-4% and 17+/-4% of the response to 100 mmol/L KCl, respectively). Aminoguanidine (0.01 to 3 mmol/L) and MG (0.01 to 3 mmol/L) produced endothelium-independent contractions (Emax = 9+/-3% and 16+/-2% of the response to 100 mmol/L KCl, respectively). L-arginine (1 mmol/L) but not D-arginine (1 mmol/L) prevented the contractions by L-NMMA and ADMA, but did not change contractions induced by AG and MG. In precontracted arteries, the relaxation to acetylcholine was decreased but not abolished by L-NMMA and ADMA. The remaining relaxation was reduced by charybdotoxin (0.1 mol/L) and tetraethylammonium (1 mmol/L).

CONCLUSIONS

The results demonstrate that L-NMMA and ADMA reduce basal and stimulated nitric oxide activity in human renal arteries. An increase in the plasma concentrations of methylarginines associated with renal disease should be considered as a risk factor for endothelial dysfunction and abnormal vasomotor tone in human renal arteries.

Increased activation of protein C, but lower plasma levels of free, activated protein C in uraemic patients: relationship with systemic inflammation and haemostatic activation

Chronic renal failure (CRF) courses with both systemic inflammatory reaction and haemostatic activation. We explored the relationship of these processes with plasma levels of free, activated protein C (APC) and complexes of APC with its inhibitors in patients with CRF under conservative treatment. Plasma concentrations of inflammatory cytokines [tumour necrosis factor alpha (TNFalpha) and interleukin 8], acute-phase proteins (C-reactive protein, fibrinogen, alpha1-anti-trypsin and von Willebrand factor), and markers of haemostatic activation (thrombin-anti-thrombin complexes, plasmin-anti-plasmin complexes, and fibrin and fibrinogen degradation products) were higher in patients than in controls. Inflammatory and haemostatic markers were significantly and positively correlated. Total plasma APC and APC:alpha1-anti-trypsin (alpha1AT) complexes were 44% and 75% higher in patients than in controls (P = 0.0001), whereas free APC was 20% lower (P < 0.015). No significant difference was observed in APC:protein C inhibitor (PCI) complexes between both groups. The free/total APC ratio was significantly lower in patients than in controls (P < 0.0001). Total plasma APC and APC:alpha1AT were positively correlated with activation markers of haemostasis and acute-phase proteins, whereas free APC was inversely correlated with plasma levels of creatinine, acute-phase proteins and fibrin degradation products (FnDP). Systemic inflammation and activation of haemostasis are interrelated processes in CRF. APC generation was increased in response to elevated thrombin production, but the inflammatory reaction, associated with increased synthesis of alpha1AT, reduced its anticoagulant effect. Lower free plasma APC in CRF may be pathogenically associated with atherothrombosis, a major cause of death in this disease.

[PSA:alpha 1-antichymotrypsin ratio/total PSA in the diagnosis of prostatic cancer in the range of total PSA from 4 to 10 ng/ml]

OBJECTIVE

To evaluate the usefulness of the ratio PSA:alpha-1-antichymotrypsin/total PSA (C/T) in the diagnosis of prostate cancer in the range of total PSA between 4 and 10 ng/mL.

MATERIAL AND METHODS

By using home-made ELISAs we have determined plasmatic concentrations of total PSA and complex PSA:alpha-1-ACT in 300 patients with total PSA between 4-10 ng/mL. All samples were obtained before any manipulation that could interfere the PSA levels.

RESULTS

By prostatic biopsy 85 patients (28.3%) were diagnosed of prostate cancer (CaP) and 215 (71.6%) of benign prostatic hyperplasia (BPH). The mean values of the complex PSA:alpha-1-ACT (4.2 ng/mL in the BPH patients vs 5.0 ng/mL in the CaP patients) and of the C/T ratio (0.70 vs 0.82, respectively) showed significant differences between both groups (p = < 0.0001). The total PSA did not show differences (6.1 ng/mL vs 6.0 ng/mL; p = 0.79). From all three parameter evaluated, the ratio C/T had the biggest area under the ROC (0.884) and statistically significant differences in comparison with total PSA (0.490; p = < 0.001) and the complex PSA:alpha-1-ACT (0.696: p = < 0.001). Therefore, by using a ratio C/T > 0.62 to decide the performance of a biopsy, 27% of the patients with BPH could have avoided this procedure with a 100% sensitivity. Increasing the ratio to 0.68 the specificity is 47% and the sensitivity is 95.2%. Rectal examination did not have influence on the cut-off, sensitivity, specificity and area under the ROC of the ratio C/T.

CONCLUSIONS

Our results confirm that the ratio C/T improve the diagnostic capacity of the total PSA between 4-10 ng/ml. Moreover, the rectal examination does not influence the selection of ratio C/T cut-off suggestives of CaP neither the diagnostic efficacy.

Endothelin-1-induced potentiation of adrenergic responses in the rabbit pulmonary artery: role of thromboxane A(2)

To examine whether low concentrations of endothelin-1 potentiate the vasoconstrictor response to adrenergic stimulation, we recorded the isometric response of rings of rabbit pulmonary artery to electrical stimulation and noradrenaline. Endothelin-1 (10(-10) M) potentiated the contractions induced by electrical stimulation and noradrenaline. The endothelin ET(B) receptor antagonist (2,6-dimethylpiperidinecarbonyl-gamma-methyl-Leu-N(in)-[Methoxycarbonyl]-D-Trp-D-Nle) (BQ-788, 10(-6) M), but not the endothelin ET(A) receptor antagonist cyclo(D-Asp-Pro-D-Val-Leu-D-TRP) (BQ-123, 10(-6) M), inhibited the potentiating effects of endothelin-1. Pretreatment with the cyclooxygenase inhibitor indomethacin, the thromboxane synthase inhibitor furegrelate and the thromboxane receptor antagonist [1S-[1alpha,2alpha(Z),3alpha,4alpha]]-7-[3-[[[[(1-oxoheptyl)amino]acetyl]amino] methyl]-7-oxabicyclo-[2.2.1]hept-2-yl]-5-heptenoic acid (SQ-30741) (all at 10(-5) M) prevented the potentiation induced by endothelin-1 on adrenergic stimulation. The Ca(2+) channel antagonist nifedipine (10(-6) M) did not affect the potentiation induced by endothelin-1. The results indicate that endothelin-1 potentiates the responses to electrical stimulation and noradrenaline by activating endothelin ET(B) receptors. This potentiation depends on the production of cyclooxygenase-generated factors, probably thromboxane A(2).

Inhibition of neuroeffector transmission in human vas deferens by sildenafil

Sildenafil (0.1 - 30 microM), a cyclic GMP phosphodiesterase 5 (PDE 5) inhibitor, induced inhibition of electrically evoked contractions of ring segments of human vas deferens from 34 vasectomies. Zaprinast (0.1 - 100 microM), another PDE 5 inhibitor, and the nitric oxide (NO) donor sodium nitroprusside (SNP) (0.1 - 100 microM) had no effect on neurogenic contractions. The inhibition induced by sildenafil was not modified by the inhibitor of guanylate cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) (1 - 30 microM) but it was abolished by the K(+) channel blockers tetraethylammonium (TEA, 1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM). Sildenafil, zaprinast and SNP did not affect the contractions induced by noradrenaline. SNP (10 microM) caused elevation of cyclic GMP levels that was potentiated by sildenafil (10 microM) and zaprinast (100 microM). ODQ (10 microM) inhibited the increase in cyclic GMP. Sildenafil inhibits adrenergic neurotransmission in human vas deferens. The inhibition is not related to accumulation of cyclic GMP but is probably due to activation of prejunctional large-conductance Ca(2+)-activated K(+) channels.

Contractile effects of arginine analogues on human internal thoracic and radial arteries

OBJECTIVES

Plasma levels of endogenous guanidino-substituted analogues of L -arginine are increased in various pathologic conditions. In the present study we determined the effects of some of these compounds on basal and stimulated release of nitric oxide in human internal thoracic and radial arteries.

METHODS

Rings of human internal thoracic and radial arteries were obtained from 16 multiorgan donors. The rings were suspended in organ baths for isometric recording of tension.

RESULTS

N(G)-monomethyl L -arginine (10(-6) to 10(-3) mol/L) and N(G),N(G)-dimethyl L -arginine (10(-6) to 10(-3) mol/L) caused concentration- and endothelium-dependent contractions. Maximal force of contractions for N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine in the internal thoracic artery were 18.0% +/- 4.3% and 17.8% +/- 3.8%, respectively, of the contraction to 100 mmol/L KCl, and those found in the radial artery were 9.6% +/- 2.5% and 9.1% +/- 2.4%, respectively. Aminoguanidine (10(-5) to 3 x 10(-3) mol/L) and methylguanidine (10(-5) to 3 x 10(-3) mol/L) produced endothelium-independent contractions. L -Arginine (10(-3) mol/L) prevented the contractions by N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine but did not change contractions induced by aminoguanidine and methylguanidine. N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine inhibited, in a concentration-dependent manner, the endothelium-dependent relaxation to acetylcholine in the internal thoracic artery and had little attenuating effect in the radial artery; aminoguanidine and methylguanidine were without effect.

CONCLUSIONS

The results suggest that the contractions induced by N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine are due to inhibition of both basal and stimulated nitric oxide production, whereas aminoguanidine and methylguanidine do not affect the synthesis of nitric oxide. An increase in the plasma concentration of N(G)-monomethyl L -arginine and N(G),N(G)-dimethyl L -arginine is likely to represent a risk factor for abnormal vasomotor tone in conduit arteries used as coronary grafts.

Relaxation induced by cGMP phosphodiesterase inhibitors sildenafil and zaprinast in human vessels

BACKGROUND

Sildenafil is currently used in the treatment of erectile dysfunction. However, assessment of direct effects of sildenafil on coronary arteries and on arteries used as coronary grafts is unknown. This study was designed to investigate the effects of sildenafil on contracted human coronary, internal mammary, and radial arteries obtained from multiorgan donors. The observations were extended to forearm veins. Zaprinast was included in this study for comparison.

METHODS

Segments of left coronary, internal mammary, and radial arteries, and forearm veins were obtained from 16 multiorgan donors. Vascular rings were suspended in organ bath chambers and isometric tension was recorded. Then the effects of sildenafil, zaprinast, and sodium nitroprusside on precontracted vessels were studied.

RESULTS

Sildenafil (10(-8) - 3 x 10(-5) mol/L) caused concentration-dependent relaxation in the internal mammary arteries, radial arteries, and forearm veins. In the coronary arteries, sildenafil had a modest relaxant effect. In addition, sildenafil amplified the relaxation induced by sodium nitroprusside in all four vessels. Relaxation was unaffected by the inhibitor of nitric oxide synthase NG-monomethyl-L-arginine (10(-4) mol/L). Compared with zaprinast, sildenafil was eight to ten times more potent in terms of EC50 values.

CONCLUSIONS

The direct relaxant effects of sildenafil together with its synergistic interaction with nitric oxide donors should be considered in patients undergoing coronary bypass surgery, patients with low blood pressure, and patients receiving antihypertensive regimes.

Effects of sildenafil on human penile blood vessels

OBJECTIVES

To investigate the effects of sildenafil on human penile blood vessels and evaluate the interaction of sildenafil with neurogenic-mediated responses. Sildenafil is currently used in the treatment of erectile dysfunction.

METHODS

Penile dorsal arteries and deep dorsal veins were obtained from 14 multiorgan donors. Vascular rings were suspended in organ bath chambers, and the isometric tension was recorded. We then studied the effects of sildenafil on precontracted vessels and the neurogenic (noradrenergic and nitrergic) responses.

RESULTS

Sildenafil (10(-9) to 3 x 10(-6) M) caused concentration-dependent relaxation and amplified the relaxation induced by sodium nitroprusside. Relaxation was unaffected by the inhibitor of nitric oxide synthase N(G)-monomethyl-L-arginine (10(-4) M). Compared with zaprinast, sildenafil was 8 to 10 times more potent in terms of the median effective concentration (EC(50)) values. Electrical field stimulation of the vessels under resting tension caused frequency-dependent contractions that were attenuated in the presence of sildenafil. When penile vessels were contracted after blockade of norepinephrine release with guanethidine (10(-6) M), electrical stimulation induced frequency-dependent, nitric oxide-dependent relaxations that were enhanced by sildenafil.

CONCLUSIONS

These results indicate that the relaxation of human penile arteries and veins induced by sildenafil involves inhibition of noradrenergic contraction, enhancement of neurogenic nitric oxide-mediated relaxation, and inhibition of smooth muscle contraction.

Prostate-specific antigen complexed to alpha(1)-antichymotrypsin in the early detection of prostate cancer

OBJECTIVES

To study the usefulness of the complexed-to-total (C:T) prostate-specific antigen (PSA) ratio in the early detection of prostate cancer in patients with a total PSA value <4.0 ng/ml.

PATIENTS AND METHODS

Total PSA and PSA complexed to alpha(1)-antichymotrypsin were measured in plasma from 193 men with benign prostatic hyperplasia (BPH) and 34 with prostate cancer. The diagnosis was confirmed in 28 BPH and 16 prostate cancer patients by biopsy and in 165 BPH and 18 prostate cancer patients by histological study following transurethral prostatectomy or open prostatectomy.

RESULTS

The area under the receiver operating characteristic (ROC) curve was significantly greater for the C:T PSA ratio (0.908) than for total PSA (0.692) (p<0.001). Using a cut-off point of 0.83 for the C:T PSA ratio and regardless of the digital rectal examination (DRE) finding, 20 of the 34 prostate cancer patients would have been given a correct diagnosis (59% sensitivity) and in only 8 of the 193 BPH patients would a biopsy have been necessary (96% specificity). With a cut-off of 0.79, the sensitivity increased to 85% with a specificity of 92%. When the analysis was restricted to the 44 patients with abnormal DRE, the area under the ROC curve for the C:T PSA ratio was 0.919, and a cut-off point of 0. 78 gave a sensitivity of 87% and a specificity of 93%. Using a cut-off of 0.63, all prostate cancers were detected (100% sensitivity) and 54% of the negative biopsies would have been eliminated. For the 183 patients diagnosed following surgery, a cut-off of 0.82 gave a sensitivity of 72% and a specificity of 94%.

CONCLUSION

Our results show that the C:T PSA ratio significantly improves the clinical utility of the PSA assay for detecting prostate cancer in patients with total PSA < 4 ng/ml, increasing the sensitivity without significantly increasing the number of biopsies.

Effects of antidepressants in adrenergic neurotransmission of human vas deferens

OBJECTIVES

To evaluate the effects of sertraline, fluoxetine, and amitriptyline on the contractile responses of the human vas deferens muscle elicited by norepinephrine, electrical field stimulation, and KCl, because the therapeutic action of antidepressants may be accompanied by sexual dysfunction related to the contractility of the vas deferens smooth muscle.

METHODS

Ring segments of the epididymal part of the vas deferens were taken from 32 elective vasectomies and mounted in organ baths for isometric recording of tension. We then studied the effects of sertraline, fluoxetine, and amitriptyline on the neurogenic and agonist-induced contractile responses.

RESULTS

Amitriptyline caused concentration-dependent inhibition of neurogenic and norepinephrine-induced contractions. In contrast, only the highest concentration (10(-5) M) of sertraline and fluoxetine reduced the adrenergic contractions. The dihydropyridine calcium antagonist nifedipine (10(-6) M) completely prevented the inhibitory effect of sertraline and fluoxetine on neurogenic and norepinephrine-induced contractions but did not change the inhibition caused by amitriptyline. Sertraline, fluoxetine, and amitriptyline (all at 10(-5) M) attenuated contractions elicited by KCl and reduced contractions induced by CaCl(2) in KCl-depolarized preparations.

CONCLUSIONS

The results indicate that sertraline and fluoxetine inhibit vas deferens motility through inhibition of Ca(2+) entry, with no effect on the adrenergic receptors, and amitriptyline acts as an adrenoceptor antagonist and inhibitor of the entry of calcium.

Effects of some guanidino compounds on human cerebral arteries

BACKGROUND AND PURPOSE

Accumulation of endogenous guanidino-substituted analogues of L-arginine in chronic renal failure might contribute to some of the vascular and neurological disorders of this pathology. We tested the hypothesis that in human cerebral arteries, some guanidino compounds may increase vascular tone, through nitric oxide (NO) synthase inhibition, and impair endothelium-dependent relaxation.

METHODS

Rings of human middle cerebral artery were obtained during autopsy of 26 patients who had died 3 to 12 hours before. The rings were suspended in organ baths for isometric recording of tension. We then studied the responses to N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetrical dimethylarginine; ADMA), aminoguanidine (AG), and methylguanidine (MG).

RESULTS

L-NMMA (10(-6) to 3x10(-4) mol/L) and ADMA (10(-6) to 3x10(-4) mol/L) caused concentration- and endothelium-dependent contractions (median effective concentrations [EC(50)]=1.1x10(-5) and 1.6x10(-5) mol/L, respectively; E(max)=35. 5+/-7.9% and 43.9+/-5.9% of the response to 100 mmol/L KCl). AG (10(-5) to 3x10(-3) mol/L) and MG (10(-5) to 3x10(-3) mol/L) produced endothelium-independent contractions (E(max)=44.3+/-8.8% and 45.7+/-5.8% of the response to 100 mmol/L KCl, respectively). L-Arginine (10(-3) mol/L) prevented the contractions by L-NMMA and ADMA but did not change contractions induced by AG and MG. L-NMMA and ADMA inhibited endothelium-dependent relaxation induced by acetylcholine in a concentration-dependent manner; AG and MG were without effect.

CONCLUSIONS

The results suggest that the contractions induced by L-NMMA and ADMA are due to inhibition of endothelial NO synthase activity, whereas AG and MG do not affect the synthesis of NO. An increase in the plasma concentration of L-NMMA and ADMA associated with uremia is likely to represent a diminished release or effect of NO, and consequently, an increased cerebrovascular tone in uremic patients is highly conceivable.

Relaxant effects of antidepressants on human isolated mesenteric arteries

AIMS

The therapeutic action of tricyclic agents may be accompanied by unwanted effects on the cardiovascular system. The evidence for the effects on vascular and nonvascular smooth muscle comes from animal studies. Whether these studies can be extrapolated to human vessels remains to be determined. Therefore, the present study was designed to investigate the influence of amitriptyline, nortriptyline and sertraline on the contractile responses of human isolated mesenteric arteries to electrical field stimulation, noradrenaline and potassium chloride.

METHODS

Arterial segments (lumen diameter 0.8-1.2 mm) were obtained from portions of the human omentum during the course of 41 abdominal operations (22 men and 19 women), and rings 3 mm long were mounted in organ baths for isometric recording of tension. In some artery rings the endothelium was removed mechanically.

RESULTS

In precontracted artery rings amitriptyline, nortriptyline and sertraline (3x10(-7)-10(-4) m ) produced concentration-dependent relaxation that was independent of the presence or absence of vascular endothelium. Incubation with indomethacin (3x10(-6) m ) reduced the pD2 values thus indicating the participation of dilating prostanoid substances in this response. Amitriptyline and nortriptyline inhibited both the neurogenic-and noradrenaline-induced contractions. In contrast, only the highest concentration of sertraline reduced the adrenergic responses. Amitriptyline, nortriptyline and sertraline inhibited contractions elicited by KCl and produced rightward shifts of the concentration-response curve to CaCl2 following incubation in calcium-free solution.

CONCLUSIONS

These results indicate that amitriptyline and nortriptyline could act as adrenoceptor antagonists and direct inhibitors of smooth muscle contraction of human mesenteric arteries, whereas sertraline might principally exert its action only as direct inhibitor of smooth muscle contraction. This relaxant mechanism involves an interference with the entry of calcium.

Phase I clinical and pharmacologic study of 13-cis-retinoic acid, interferon alfa, and paclitaxel in patients with prostate cancer and other advanced malignancies

PURPOSE

Recent studies demonstrate that retinoids decrease expression of the anti-apoptotic protein bcl-2, enhance the effect of chemotherapy, and act synergistically with interferon alfa (IFNalpha) to inhibit tumor cell growth in vitro. A phase I trial of 13-cis-retinoic acid (CRA), IFNalpha, and paclitaxel (TAX) was conducted to determine the toxicity and recommended phase II dose of this combination. Pharmacodynamic studies were performed to determine whether CRA and IFNalpha could modulate bcl-2 expression in vitro and in patients.

PATIENTS AND METHODS

Twenty-two patients with prostate cancer or other advanced malignancies were treated with CRA/IFNalpha and escalating doses of TAX. The effect of CRA/IFNalpha on TAX pharmacokinetics was analyzed in both patients and human liver microsomes. The effect of CRA/IFNalpha on bcl-2 expression was assessed in vitro and in peripheral-blood mononuclear cells (PBMCs) by immunoblotting.

RESULTS

CRA 1 mg/kg on days 1 to 4, IFNalpha 6 MU/m(2) subcutaneously on days 1 to 4, and TAX 175 mg/m(2) on day 3 was well tolerated. Pharmacokinetic studies demonstrated that CRA/IFNalpha caused a 33% decrease in TAX clearance and a 23% decrease in the area under the concentration-time curve values of the TAX metabolite 6-alfa-hydroxytaxol (6-HT). CRA alone reduced conversion of TAX to 6-HT by 41% in human liver microsomes. CRA/IFNalpha decreased bcl-2 expression in vitro and in PBMCs.

CONCLUSION

CRA/IFNalpha and TAX is a well-tolerated regimen. CRA/IFNalpha increases TAX area under the concentration-time curve through an inhibitory effect of CRA on the metabolism of TAX to 6-HT. CRA/IFNalpha can modulate bcl-2 expression in vitro and demonstrates similar biologic activity in patients. Further studies will determine the activity of CRA/IFNalpha/TAX and validate the assessment of bcl-2 in PBMCs as a marker of tumor response.

Modulation of adrenergic contraction of dog pulmonary arteries by nitric oxide and prostacyclin

The aim of this work was to investigate the influence of endothelium-derived nitric oxide and prostaglandins on the contractile responses of isolated dog pulmonary arteries to electrical field stimulation and noradrenaline. Electrical field stimulation (1-8 Hz, 20 v, 0.25 ms duration, for 30 s) produced frequency-dependent contractions that were abolished by tetrodotoxin, guanethidine and, prazosin (all at 10(-6) M). Noradrenaline induced concentration-dependent contractions with an EC50, of 1.85 x 10(-6) M. The increases in tension induced by electrical stimulation and noradrenaline were of greater magnitude in arteries denuded of endothelium. In segments with endothelium, N(G)-nitro-L-arginine methyl ester (10(-4) M) or indomethacin (10(-5) M) had no effects on the basal tone, but significantly enhanced the neurogenic and noradrenaline-induced contractions. The potentiation by N(G)-nitro-L-arginine methyl ester of electrical stimulation-induced contractile responses was partially reversed by L-arginine (10(-4) M). In the presence of N(G)-nitro-L-arginine methyl ester together with indomethacin the electrical stimulation-induced contractile responses were higher than those obtained when only N(G)-nitro-L-arginine methyl ester or indomethacin was used. N(G)-nitro-L-arginine methyl ester and indomethacin did not influence neurogenic-induced contractile responses of endothelium-denuded arteries. The results suggest that endothelial cells of isolated dog pulmonary arteries depress the contractile response to electrical field stimulation of intramural nerves and that endothelium-derived dilator prostaglandins and nitric oxide may interact to inhibit contractile effects of adrenergic stimulation.

V2-receptor-mediated relaxation of human renal arteries in response to desmopressin

The effects of deamino-8-D-arginine vasopressin (desmopressin), a V2 receptor antidiuretic agonist, were studied in isolated rings from branches of renal arteries obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ bath chambers for isometric recording of tension. In precontracted rings with norepinephrine (10(-6) to 3 x 10(-6) mol/L), desmopressin (10(-11) to 3 x 10(-7) mol/L) caused endothelium-dependent relaxation (81%+/-4% reversal of the initial contraction in arteries with endothelium; 20%+/-4% in arteries without endothelium; P < .05). The relaxation to desmopressin in rings with endothelium was reduced significantly by indomethacin (10(-6) mol/L) and unaffected by the inhibitor of nitric oxide synthase NG-nitro-L-arginine methyl ester (10(-4) mol/L). Two V1 receptor antagonists (a peptidic and a nonpeptidic) had no effect on desmopressin-induced relaxation. However, V2 receptor antagonists (three peptidic and a nonpeptidic) reduced significantly (P < .05) the maximal response to desmopressin. The results of this study show that desmopressin exerts powerful endothelium-dependent relaxation of human renal arteries, probably through stimulation of V2-like receptors that may bring about the release of dilating prostaglandins.

Comparative effects of dilator drugs on human penile dorsal artery and deep dorsal vein

The present study was designed to characterize the response of human penile dorsal artery and deep dorsal vein to dilator drugs used in the diagnosis and treatment of erectile dysfunction with special emphasis on the effects on sympathetic neurotransmission. Ring segments of penile dorsal artery and deep dorsal vein were obtained from 20 multi-organ donors during procurement of organs for transplantation. The rings (3 mm long) were suspended in organ bath chambers for isometric recording of tension. We then studied the relaxant responses to prostaglandin E1 (PGE1), vasoactive intestinal peptide (VIP), papaverine (PV), sodium nitroprusside (SNP) and linsidomine chlorhydrate (SIN-1), and analysed the effects of these drugs on contractions induced by stimulation of perivascular sympathetic nerves. In artery and vein rings contracted by noradrenaline, all the drugs tested caused concentration-dependent relaxation. The order of potencies in terms of IC50 values (concentration of agonist causing 50% of the maximal relaxation) was PGE1=VIP>SNP>SIN-1=PV. Both arteries and veins contracted to electrical field stimulation (15 V, 0.5-2 Hz, 0.2 ms duration for 15 s) in a frequency-dependent manner. All relaxant drugs caused concentration-dependent inhibition of neurogenic contractions; the relative order of potencies was PGE1>VIP>SNP>SIN-1=PV. It is concluded that inhibition of sympathetic activity constitutes an effective relaxing mechanism in penile dorsal artery and vein. Modulation of sympathetic activity together with the direct effects on smooth muscle should be considered to evaluate adequately the efficacy of relaxant drugs to increase human penile blood supply.

Role of vasopressin on adrenergic neurotransmission in human penile blood vessels

We have used in vitro preparations of human penile dorsal artery and deep dorsal vein from 20 multiorgan donors to investigate whether subpressor concentrations of vasopressin facilitate noradrenergic transmission in penile blood vessels. Vasopressin constricted penile dorsal arteries (pD2, 9.38 +/- 0.18) and deep dorsal veins (pD2, 9. 40 +/- 0.14) by activating V1 receptors. Vasopressin (10(-11) and 3 x 10(-11) M) caused concentration-dependent potentiation of the contractions elicited by electrical stimulation (15 V, 0.5-2 Hz, 0.2 msec duration for 15 sec) and produced leftward shifts of the concentration-response curve for norepinephrine. The V1 receptor antagonist d(CH2)5Tyr(Me)AVP (3 x 10(-9)-10(-7) M) induced concentration-dependent inhibitions of potentiation caused by vasopressin. In contrast, the V2 receptor antagonist [d(CH2)5,D-Ile2, Ile4,Arg8]-vasopressin (10(-8)-10(-7) M) did not prevent the potentiation induced by vasopressin. The results demonstrate that vasopressin exerts powerful constrictor action in human penile arteries and veins by direct stimulation of V1 receptors. In addition, vasopressin strongly potentiates the contractions to norepinephrine and stimulation of perivascular adrenergic nerves. Consequently, the direct contractile effects of vasopressin together with its amplifying effects on adrenergic-mediated constriction should be taken into consideration in the overall regulation of penile erection and in those states characterized by increased plasma vasopressin levels.

Vasopressin receptors involved in adrenergic neurotransmission in the circular muscle of the human vas deferens

We studied the effects of vasopressin on the adrenergic responses of in vitro preparations of circular muscle from the vas deferens obtained from 28 men undergoing elective vasectomy. Vasopressin (3 x 10(-9)-3 x 10(-8) M) enhanced the phasic contractions elicited by electrical field stimulation and noradrenaline. This potentiation was blocked by the vasopressin V1 receptor antagonist d(CH2)5Tyr(Me)vasopressin (10(-6) M) but not by the vasopressin V2 receptor antagonist [d(CH2)5, D-Ile2,Ile4,Arg8]vasopressin (10(-6) M). The Ca2+ antagonist nifedipine (10(-6) M) did not affect the potentiation of electrical field stimulation induced by vasopressin and noradrenaline but reduced KCl-induced contractions and abolished the induction of phasic activity by vasopressin in the presence of KCl. The results demonstrate that vasopressin, in addition to its direct contractile effects, strongly potentiates contractions of human vas deferens elicited by adrenergic stimulation. Both the direct and indirect effects of vasopressin appear to be mediated by vasopressin V1 receptor stimulation and are independent of Ca2+ entry through dihydropyridine Ca2+ channels.