Postjunctional alpha2-adrenoceptors in the rat tail artery: effect of sex and castration

Docosahexaenoic Acid Supplemented Diet Influences the Orchidectomy-Induced Vascular Dysfunction in Rat Mesenteric Arteries

Over the past few decades, the cardiovascular benefits of a high dietary intake of long-chain polyunsaturated fatty acids (PUFAs), like docosahexaenoic acid (DHA), have been extensively studied. However, many of the molecular mechanisms and effects exerted by PUFAs have yet to be well explained. The lack of sex hormones alters vascular tone, and we have described that a DHA-supplemented diet to orchidectomized rats improve vascular function of the aorta. Based on these data and since the mesenteric artery importantly controls the systemic vascular resistance, the objective of this study was to analyze the effect of a DHA-supplemented diet on the mesenteric vascular function from orchidectomized rats. For this purpose mesenteric artery segments obtained from control, orchidectomized or orchidectomized plus DHA-supplemented diet were utilized to analyze: (1) the release of prostanoids, (2) formation of NO and ROS, (3) the vasodilator response to acetylcholine (ACh), as well as the involvement of prostanoids and NO in this response, and (4) the vasoconstrictor response to electrical field stimulation (EFS), analyzing also the effect of exogenous noradrenaline (NA), and the NO donor, sodium nitroprusside (SNP). The results demonstrate beneficial effects of DHA on the vascular function in orchidectomized rats, which include a decrease in the prostanoids release and superoxide formation that were previously augmented by orchidectomy. Additionally, there was an increase in endothelial NO formation and the response to ACh, in which NO involvement and the participation of vasodilator prostanoids were increased. DHA also reversed the decrease in EFS-induced response caused by orchidectomy. All of these findings suggest beneficial effects of DHA on vascular function by reversing the neurogenic response and the endothelial dysfunction caused by orchidectomy.

Regional differences in sexually dimorphic protein expression in the spontaneously hypertensive rat (SHR)

Hypertension is sexually dimorphic and modified by removal of endogenous sex steroids. This study tested the hypothesis that endogenous gonadal hormones exert differential effects on protein expression in the kidney and mesentery of SHR. At ~5 weeks of age male and female SHR underwent sham operation, orchidectomy, or ovariectomy (OVX). At 20-23 weeks of age, mean arterial pressure (MAP) was measured in conscious rats. The mesenteric arterial tree and kidneys were collected, processed for Western blots, and probed for Cu Zn superoxide dismutase (SOD1), soluble epoxide hydrolase (sEH), and Alpha 2A adrenergic receptor (A2AR) expression. MAP was unaffected by ovariectomy (Sham 164 ± 4: Ovariecttomy 159 ± 3 mm Hg). MAP was reduced by orchidectomy (Sham 189 ± 5:Orchidectomy 167 ± 2 mm Hg). In mesenteric artery, SOD1 expression was greater in male versus female SHR. Orchidectomy increased while ovariectomy decreased SOD1 expression. The kidney exhibited a different pattern of response. SOD1 expression was reduced in male compared to female SHR but gonadectomy had no effect. sEH expression was not significantly different among the groups in mesenteric artery. In kidney, sEH expression was greater in males compared to females. Ovariectomy but not orchidectomy increased sEH expression. A2AR expression was greater in female than male SHR in mesentery artery and kidney. Gonadectomy had no effect in either tissue. We conclude that sexually dimorphic hypertension is associated with regionally specific changes in expression of three key proteins involved in blood pressure control. These data suggest that broad spectrum inhibition or stimulation of these systems may not be the best approach for hypertension treatment. Instead regionally targeted manipulation of these systems should be investigated.

Differential contributions of alpha-1 and alpha-2 adrenoceptors to vasoconstriction in mesenteric arteries and veins of normal and hypertensive mice

Mesenteric veins are more sensitive than arteries to the constrictor effects of sympathetic nerve stimulation and alpha-adrenergic receptor agonists. In the present study, we tested the hypothesis that alpha(2)-adrenergic receptors (alpha(2)-ARs) contribute to in vitro agonist-induced constriction in veins but not arteries and that alpha(2)-AR function is down-regulated in mesenteric arteries and veins in deoxycorticosterone acetate-salt (DOCA-salt) hypertension. Norepinephrine (NE) concentration-response curves were similar in SHAM and DOCA-salt arteries and veins indicating that adrenergic reactivity of mesenteric blood vessels is not altered in murine DOCA-salt hypertension in vitro. Veins were 30-fold more sensitive to NE than arteries. The alpha(1)-AR antagonist, prazosin (0.003-0.3 microM), produced concentration-dependent rightward shifts of the NE concentration-response curves in arteries but not veins. The alpha(2)-AR agonists, clonidine and UK-14,304, did not constrict arteries or veins in the absence or presence of indomethacin (10 microM) and nitro-L-arginine (NLA; 100 microM). The alpha(2)-AR antagonists, yohimbine (0.003-0.3 microM) and rauwolscine (0.1 microM) did not affect NE responses in SHAM or DOCA-salt arteries but antagonized NE responses in veins. These data indicate that there are different alpha-AR contractile mechanisms in murine mesenteric arteries and veins. Alpha(1)-ARs, but not alpha(2)-ARs, mediate direct contractile responses in arteries and veins while alpha(2)-ARs contribute indirectly to NE-induced constrictions in veins but not arteries in vitro. There may be direct protein-protein interactions between alpha(1)- and alpha(2)-ARs or between their signaling pathways in veins. This contribution of alpha(2)-ARs may account for the greater sensitivity of veins compared to arteries to the contractile effects of NE.

Orchidectomy increases beta-adrenoceptor activation-mediated neuronal nitric oxide and noradrenaline release in rat mesenteric artery

BACKGROUND/AIMS

A previous study has demonstrated that endogenous male sex hormones do not alter neuronal nitric oxide (NO) release in rat mesenteric artery. However, the regulatory role of endogenous male sex hormones on noradrenaline (NA) release in rat mesenteric artery is not known. The present study was designed to analyze whether endogenous male sex hormones influence the NA release induced by electrical field stimulation (EFS), as well as the possible modification in NA and neuronal NO release by presynaptic beta-adrenoceptor activation.

METHODS

For this purpose, mesenteric arteries from control and orchidectomized male Sprague-Dawley rats were used. Basal and EFS-induced neuronal NO and NA release, as well as the contractile effect induced by EFS, was measured.

RESULTS

Basal and EFS-induced neuronal NO and NA release were similar in arteries from control and orchidectomized rats. The beta-adrenoceptor agonist clenbuterol did not modify EFS-induced neuronal NO and NA release in arteries from control rats. In contrast, in arteries from orchidectomized animals, clenbuterol increased both neuronal NO and NA release; this increase was prevented by incubation with the beta-adrenoceptor antagonist propranolol. However, the contractile response elicited by EFS was not modified by clenbuterol in either group of rats.

CONCLUSIONS

These results show that orchidectomy does not alter the EFS-induced NA release. What is more, activation of presynaptic beta-adrenoceptors does not modify EFS-induced NA and neuronal NO release in arteries from control rats although it increases the release of both neurotransmitters in arteries from orchidectomized rats. Despite these modifications, the EFS-induced contractile response is preserved in arteries from orchidectomized rats.

Androgen deprivation increases neuronal nitric oxide metabolism and its vasodilator effect in rat mesenteric arteries

This study examines the effects of male sex hormones on the vasoconstrictor response to electrical field stimulation (EFS), as well as neuronal NO modulation of this response. For this purpose, denuded superior mesenteric artery from orchidectomized and control male Sprague-Dawley rats was used. EFS induced similar frequency-dependent contractions in segments from both groups. The NO synthase (NOS) inhibitor N(omega)-nitro-L-arginine methyl ester strengthened EFS-elicited contractions more in arteries from orchidectomized than from control male rats. The expression of nNOS was more pronounced in segments from control than from orchidectomized animals. Basal and EFS-induced NO release was similar in segments from both groups. In noradrenaline (NA)-precontracted segments, sodium nitroprusside (SNP) induced a concentration-dependent relaxation, that was greater in segments from orchidectomized than control male rats. 8-Bromo-cGMP induced a similar concentration-dependent relaxation in NA-precontracted segments from either group, and the cGMP levels induced by SNP were also similar in the two groups. Superoxide dismutase (SOD), a superoxide anion scavenger, did not modify the relaxation in segments from control male rats. In contrast, SOD enhanced the relaxation induced by SNP in segments from orchidectomized rats, and the effect was reversed by preincubation with SOD plus catalase. The generation of superoxide anion and of peroxynitrite was greater in segments from orchidectomized than control rats. In NA-precontracted segments from control or orchidectomized rats, exogenous peroxynitrite and H(2)O(2) induced a concentration-dependent relaxation. These results suggest that EFS induces a similar nNOS-derived NO release in segments from orchidectomized and control male rats, despite the decrease in nNOS expression in orchidectomized rats. The NO metabolism is higher in segments from orchidectomized male rats due to the increases in anion superoxide generation and peroxynitrite formation. The vasodilator effects of the peroxynitrite and H(2)O(2)0 generated from the NO metabolism are what enhance the functional role of the nNOS-derived NO release in the orchidectomized rats.

The role of α1- and α2-adrenoceptors in gender differences in cutaneous LD flux response to local cooling

The present study was designed to assess the hypothesis that alpha2-adrenergic response plays a predominant role in sex differences in cutaneous microvascular response to cold. For this purpose, we studied the effect of the selective alpha1-antagonist prazosin (1 microl of 1.2 mM solution) and the alpha2-antagonist yohimbine (1 microl of 12 mM solution) microinjected into the skin area where the laser-Doppler (LD) flux response to local cooling was measured in healthy male and female subjects. Multiple regression analysis showed correlation between LD flux response at the site of local cooling (direct response) and gender (P = 0.039). The LD flux decrease was smaller in males. The application of the yohimbine significantly diminished the LD flux response at the site of local cooling in females but not in males (P < 0.05). In contrast, the injection of prazosin did not significantly affect the response. These findings strongly support the suggestion of a decisive role of alpha2-adrenoceptors in cold-induced gender difference at the level of cutaneous microvasculature at the site of local cooling. Multiple regression analysis of LD flux response to cold exposure at the site distant to cooling (indirect response) also confirmed correlation between LD flux response and gender (P = 0.022). The LD flux decrease was smaller in males. The alpha1-antagonist abolished the LD flux response to cold exposure (P = 0.000). These results corroborate the importance of alpha1-adrenoceptors in skin microcirculatory response to indirect local cooling mediated by the sympathetic vascular reflex.

Sex differences in drug- and non-drug-induced analgesia

Historically, biomedical research has been conducted almost exclusively with male subjects. A growing number of studies now demonstrate sex differences in analgesia produced both by drugs and by environmental stimuli. This review summarizes the current literature on sex differences in analgesia produced by opioids, cholinergics and other drugs, and by stress, exercise and other environmental manipulations. A brief overview of the physiological mechanisms underlying sex differences in analgesia is provided, as well as suggestions for future research. It is not yet known whether the development of sex-specific analgesia treatment guidelines is warranted.

Male-female differences in the relative contribution of endothelial vasodilators released by rat tail artery

Several different vasodilator substances can be released by vascular endothelium in response to mechanical stimuli and vasoactive agents. The purpose of this study was to determine whether there is a male-female difference in the relative contributions of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) to endothelium-dependent vasodilation. Perfusion pressure was measured in isolated tail arteries from male and female rats. Vasodilators released by mechanical shear stress were assessed by constricting the artery with methoxamine; acetylcholine was applied to induce receptor-mediated vasodilation. We used an inhibitor of NO synthase, N(G)-monomethyl-L-arginine acetate (L-NMMA), and elevated levels of K(+) (27 mM) to reveal the relative contributions of NO and EDHF, respectively. Indomethacin was present in all experiments to block prostanoid production. The results indicate that NO was the primary vasodilator released by male tail arteries in response to both mechanical stress and acetylcholine (the L-NMMA-sensitive component of the combined L-NMMA/K(+) effect was 83 +/- 8% and 101 +/- 4%, respectively). However female tail arteries appeared to utilize both NO and EDHF for vascular relaxation (e.g., L-NMMA sensitivity: 58 +/- 9%; K+-sensitivity: 42 +/- 9% in mechanical stress experiments). These findings suggest endothelial regulation differs between males and females.

Estrogen restores postischemic pial microvascular dilation

Estrogen protects the brain from experimental cerebral ischemia, likely through both vascular and neuronal cellular mechanisms. The purpose of this study was to determine whether chronic estrogen treatment in males and repletion in ovariectomized (Ovx) females reverses abnormalities in pial arteriolar reactivity during reperfusion from global forebrain ischemia (4-vessel occlusion, 15 min) and whether the site of protection is vascular endothelium. Male and Ovx female rats were implanted with either placebo or a 25-microg 17 beta-estradiol pellet 10 days before ischemia. With the use of intravital microscopy, pial vessel dilation to ACh (10 microM) and S-nitroso-N-acetyl-penicillamine (SNAP; 1 microM) and vasoconstriction to serotonin (10 microM) was examined in situ at 30--60 min of reperfusion. Postischemic changes in vessel diameter were compared with preischemic values for each agent. Postischemic response to both ACh and SNAP was lost in males and Ovx females, but not in estrogen pellet-implanted males and estrogen-implanted Ovx females, suggesting that estrogen protects both endothelial and smooth muscle-mediated vasodilation. Ischemia blunted vessel constriction to serotonin regardless of treatment. These data demonstrate that estrogen acts as a vasoprotective agent within the cerebral circulation and can improve microvascular function under conditions of an acutely evolving ischemic pathology.