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

Reactive Oxygen Species Are Central Mediators of Vascular Dysfunction and Hypertension Induced by Ethanol Consumption

Consumption of high amounts of ethanol is a risk factor for development of cardiovascular diseases such as arterial hypertension. The hypertensive state induced by ethanol is a complex multi-factorial event, and oxidative stress is a pathophysiological hallmark of vascular dysfunction associated with ethanol consumption. Increasing levels of reactive oxygen species (ROS) in the vasculature trigger important processes underlying vascular injury, including accumulation of intracellular Ca2+ ions, reduced bioavailability of nitric oxide (NO), activation of mitogen-activated protein kinases (MAPKs), endothelial dysfunction, and loss of the anticontractile effect of perivascular adipose tissue (PVAT). The enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase plays a central role in vascular ROS generation in response to ethanol. Activation of the renin-angiotensin-aldosterone system (RAAS) is an upstream mechanism which contributes to NADPH oxidase stimulation, overproduction of ROS, and vascular dysfunction. This review discusses the mechanisms of vascular dysfunction induced by ethanol, detailing the contribution of ROS to these processes. Data examining the association between neuroendocrine changes and vascular oxidative stress induced by ethanol are also reviewed and discussed. These issues are of paramount interest to public health as ethanol contributes to blood pressure elevation in the general population, and it is linked to cardiovascular conditions and diseases.

Hypertension and chronic ethanol consumption: What do we know after a century of study?

The influences of life habits on the cardiovascular system may have important implications for public health, as cardiovascular diseases are among the leading causes of shorter life expectancy worldwide. A link between excessive ethyl alcohol (ethanol) consumption and arterial hypertension was first suggested early last century. Since then, this proposition has received considerable attention. Support for the concept of ethanol as a cause of hypertension derives from several epidemiologic studies demonstrating that in the general population, increased blood pressure is significantly correlated with ethanol consumption. Although the link between ethanol consumption and hypertension is well established, the mechanism through which ethanol increases blood pressure remains elusive. Possible mechanisms underlying ethanol-induced hypertension were proposed based on clinical and experimental observations. These mechanisms include an increase in sympathetic nervous system activity, stimulation of the renin-angiotensin-aldosterone system, an increase of intracellular Ca²⁺ in vascular smooth muscle, increased oxidative stress and endothelial dysfunction. The present report reviews the relationship between ethanol intake and hypertension and highlights some mechanisms underlying this response. These issues are of interest for the public health, as ethanol consumption contributes to blood pressure elevation in the population.

Ethanol consumption alters the expression and reactivity of adrenomedullin in the rat mesenteric arterial bed

AIMS

Adrenomedullin (AM) is a peptide that displays cardiovascular protective activity. We investigated the effects of chronic ethanol consumption on arterial blood pressure, vascular reactivity to AM and the expression of AM system components in the rat mesenteric arterial bed (MAB).

METHODS

Male Wistar rats were treated with ethanol (20% vol/vol) for 6 weeks. Systolic, diastolic and mean arterial blood pressure were monitored in conscious rats. Vascular reactivity experiments were performed on isolated rat MAB. Matrix metalloproteinase-2 (MMP-2) levels were determined by gelatin zymography. Nitrite and nitrate generation were measured by chemiluminescence. Protein and mRNA levels of pre-pro-AM, CRLR (calcitonin receptor-like receptor) and RAMP1, 2 and 3 (receptor activity-modifying proteins) were assessed by western blot and quantitative real-time polymerase chain reaction, respectively.

RESULTS

Ethanol consumption induced hypertension and decreased the relaxation induced by AM and acetylcholine in endothelium-intact rat MAB. Phenylephrine-induced contraction was increased in endothelium-intact MAB from ethanol-treated rats. Ethanol consumption did not alter basal levels of nitrate and nitrite, nor did it affect the expression of MMP-2 or the net MMP activity in the rat MAB. Ethanol consumption increased mRNA levels of pre-pro-AM and protein levels of AM in the rat MAB. Finally, no differences in protein levels or mRNA of CRLR and RAMP1, 2 and 3 were observed after treatment with ethanol.

CONCLUSION

Our study demonstrates that ethanol consumption increases blood pressure and the expression of AM in the vasculature and reduces the relaxation induced by this peptide in the rat MAB.

Cyclic AMP-independent CGRP8-37-sensitive receptors mediate adrenomedullin-induced decrease of CaCl2-contraction in pregnant rat mesenteric artery

OBJECTIVES

We tested the hypothesis that adrenomedullin reduces calcium influx independent of potassium channels in depolarized endothelium-denuded mesenteric artery from pregnant rats.

RESULTS

Adrenomedullin reduced the CaCl(2)-induced contraction, while the receptor antagonist calcitonin gene-related peptide (CGRP)(8-37), but not adrenomedullin(22-52), reversed these effects. Adenylate cyclase inhibition by SQ22536 did not prevent adrenomedullin effects on CaCl(2)-induced contraction. Adrenomedullin did not inhibit depolarization-induced calcium entry to isolated vascular smooth muscle. Inhibition of myosin light-chain (MLC) phosphatase by calyculin A reversed the effects of adrenomedullin on contraction caused by submillimolar concentrations of CaCl(2), while adrenomedullin still inhibited contraction caused by higher concentrations of CaCl(2). However, the ratio of phosphorylated to total myosin phosphatase target 1, the regulatory subunit of MLC phosphatase, did not change with adrenomedullin, indicating a lack of MLC phosphatase activation. Interestingly, sodium fluoride, a nonspecific protein phosphatase inhibitor, completely blocked the effect of adrenomedullin on CaCl(2)-induced contraction. Adrenomedullin inhibited calcium mobilization from intracellular stores induced by thapsigargin.

CONCLUSION

Adrenomedullin inhibits CaCl(2)-induced contraction, without affecting calcium influx, through a CGRP(8-37)-sensitive receptor, but not using the cyclic adenosine monophosphate pathway, probably through activation of protein phosphatases. Inhibition of intracellular calcium release is an additional role played by adrenomedullin in calcium homeostasis in vascular smooth muscle.

Amylin and hypertension: association of an amylin -G132A gene mutation and hypertension in humans and amylin-induced endothelium dysfunction in rats

CONTEXT

Amylin has been linked to the development of hypertension in several pathological states related to hypertension and insulin resistance, although there is scant data regarding its potential mechanisms of action. The -132 G/A mutation located within an activator domain of the amylin gene's promoter was first identified in a small cohort of Spanish patients with type 2 diabetes.

OBJECTIVE

The objective of the study was to test the interference of amylin peptide with endothelium-dependent responses as an added potential mechanism for amylin-induced hypertension.

DESIGN

A total of 384 patients with type 2 diabetes and 207 healthy controls were subjected to clinical analysis and genetic screening for the -132 G/A mutation of the amylin gene. The effect of amylin on endothelium-dependent responses was analyzed in aortic rings and mesenteric microvessels from nondiabetic rats.

RESULTS

The prevalence of the mutation was 10.1 vs. 0.9% in the control population (P<0.001). Hypertension was higher in a diabetic population carrying the mutation than in diabetic noncarriers (74 vs. 57%; P<0.05). Diabetic carriers showed higher fasting amylin levels than diabetic noncarriers (11.4+/-7 vs. 8.2+/-3 pmol/liter; P<0.05). Preincubation with 20 pmol/liter amylin impaired the relaxant responses induced by acetylcholine in rat aorta and mesenteric microvessels. This effect was abolished in both vascular beds in the presence of 100 micromol/liter NG-nitro-L-arginine methyl ester.

CONCLUSIONS

We propose that amylin levels and hypertension may be linked by a novel mechanism involving the capacity of amylin to induce endothelial dysfunction by interfering with nitric oxide-mediated responses.

Vascular hyperresponsiveness to adrenomedullin during pregnancy is associated with increased generation of cyclic nucleotides in rat mesenteric artery

Cardiovascular adaptation is a hallmark of pregnancy. Here we report on vascular hyperresponsiveness to an endogenous vasodilator, adrenomedullin (ADM), during pregnancy. Intravenous administration of ADM dose dependently decreased the mean arterial pressure, and the decrease was significantly greater in pregnant compared with nonpregnant rats without affecting the heart rate. In endothelium-intact mesenteric artery precontracted by ED70 concentration of norepinephrine, the potency and efficacy of ADM in causing the vasodilation of mesenteric arterial rings from pregnant rats are significantly higher compared with nonpregnant females at diestrus. The magnitude of inhibition of concentration-dependent response to ADM by the inhibition of either soluble guanylate cyclase or adenylate cyclase was greater in pregnant rats. Moreover, ADM-induced cyclic nucleotide generation, both cGMP and cAMP, in the mesenteric artery was elevated during pregnancy and was sensitive to the receptor antagonist, ADM22-52. These findings suggest that during pregnancy the vasodilatory effects of ADM are greater and are associated with increased generation of cyclic nucleotides in resistance vessels, and these changes may be part of the cardiovascular adaptations that occur during pregnancy.

Endothelium-independent relaxation by adrenomedullin in pregnant rat mesenteric artery: role of cAMP-dependent protein kinase A and calcium-activated potassium channels

The mechanisms of relaxation of adrenomedullin were investigated in isolated mesenteric artery from pregnant rats. Adrenomedullin (1 nM-0.3 microM) produced concentration-dependent relaxation of endothelium-denuded mesenteric artery rings precontracted with norepinephrine at a concentration required to produce 70% of maximal response (ED70). The concentration-response curve of adrenomedullin was shifted to the right by adrenomedullin receptor antagonist adrenomedullin(22-52) (10 microM) or calcitonin gene-related peptide(8-37) (1 microM). Inhibition of adenylate cyclase by 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536) (10 microM) or protein kinase A [Rp-cyclic adenosine monophosphorothioate (Rp-cAMP); 10 microM] reduced the adrenomedullin-induced relaxation to the same magnitude. Adrenomedullin increased the intracellular cAMP level from 0.38 +/- 0.07 to 2.00 +/- 0.47 pmol/mg tissues, which was completely inhibited by adrenomedullin(22-52) (100 microM). Extracellular high potassium (80 mM), which inactivates the potassium channels, reduced the adrenomedullin-induced relaxation. Blockade of ATP-sensitive, voltage-gated, or inward rectifier potassium channels did not affect the adrenomedullin-induced relaxation. Blockade of calcium-activated K+ channels (KCa) by tetraethylammonium (1 mM) or iberiotoxin (100 nM) inhibited the adrenomedullin-induced relaxation, whereas there was no additional inhibition by SQ22536 or Rp-cAMP when KCa channels were already inhibited. In conclusion, this study provides evidence that cAMP-dependent protein kinase A and KCa channels seem to mediate as the cellular pathways in the adrenomedullin-induced endothelium-independent relaxation of mesenteric artery from pregnant rats.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

Relaxation effects of adrenomedullin in isolated rabbit corpus cavernosum smooth muscle

OBJECTIVES

To clarify the pharmacological effects of adrenomedullin, a potent vasodilator and hypotensive peptide isolated from human phaeochromocytoma cells, on corpus cavernosal smooth muscle in vitro, as the intracavernosal injection of adrenomedullin induces penile erection in the anaesthetized cat.

MATERIALS AND METHODS

The effects of adrenomedullin were investigated in isolated muscle strips from New Zealand rabbit corpus cavernosum smooth muscle pre-contracted with phenylephrine alone, in the presence of indomethacin (cyclooxygenase inhibitor), Nomega-nitro l-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), and K+-channel blockers.

RESULTS

Adrenomedullin caused relaxation of isolated pre-contracted rabbit corpus cavernosum strips in a concentration-dependent manner. The response of corpus cavernosum was unaffected L-NAME, indomethacin and K+-channel blockers.

CONCLUSION

The relaxation exerted by adrenomedullin in rabbit corporal tissue may arise from the effect of the drug on its specific receptors and/or calcitonin gene-related peptide-1 receptors. The relaxant effect of adrenomedullin might lead to novel clinical applications for erectile dysfunction.

Involvement of calcitonin gene-related peptide in elevation of skin temperature in castrated male rats

OBJECTIVES

To assess the involvement of calcitonin gene-related peptide (CGRP) in the occurrence of hot flashes in men after castration for treatment of prostate cancer, we investigated the effects of CGRP on skin temperature in surgically and medically castrated male rats.

METHODS

Changes in skin temperature of the hind paws after intravenous injection of 10 microg/kg of CGRP and CGRP family peptides (adrenomedullin and amylin) were measured at 5-minute intervals for 120 minutes, 3 weeks after bilateral orchiectomy or 2 weeks after subcutaneous injection of a gonadotropin-releasing hormone analogue (1.0 mg/kg Leuplin) in male rats. Antagonism with CGRP8-37 (1000 microg/kg intravenously), a CGRP1 receptor antagonist, to the CGRP-induced response was examined by injecting it 10 minutes before injection of CGRP. The effect of testosterone replacement on castration was evaluated in each castrated rat by the administration of testosterone (1.0 mg/kg subcutaneously once a day) for 14 days before the day of the temperature analysis.

RESULTS

CGRP, but not adrenomedullin and amylin, elevated the skin temperature in surgical or medical castration-induced testosterone-deficient rats more than in the sham-treated rats. The difference was statistically significant. The CGRP-induced potentiation in the castrated rats was inhibited by pretreating with CGRP8-37 or by supplying testosterone.

CONCLUSIONS

CGRP is the most potent peptide in a family that elevates the skin temperature in male rats. The elevation of the skin temperature was more affected by the testosterone deficiency resulting from castration. These results suggest that CGRP is involved in the mechanism underlying hot flashes in men.