Mechanisms of impaired vascular response to ANG II in perivascular injured carotid arteries of ovariectomized rat

Aging and total stenosis triggers differential responses of carotid and basilar arteries to endothelin-1 and phenylephrine

Our aim was to investigate the effects of ageing on the vascular contractility of carotid and basilar arteries from guinea-pigs, in a model of total stenosis. Moreover, we attempted to identify whether total stenosis of the left common carotid (stenosed) in adult guinea-pigs, would affect the contractions of contralateral carotid (intact) and basilar arteries to different vasoconstrictors. With this purpose, the left carotid was occluded with a silk thread at a position close to its origin. Vascular reactivity experiments using standard muscle bath were performed 7, 15, 30, and 90 days after carotid occlusion. Reactivity of carotid and basilar arteries to endothelin-1, phenylephrine and KCl was reduced with ageing in naive guinea-pigs. The endothelin-1 and KCl-induced contractions were unaltered in arteries from SHAM-operated animals. Moreover, phenylephrine-induced contractions were reduced in both carotids from 7 days SHAM-operated guinea-pigs, when compared to naive group. Stenosis induced progressive reduction in the contraction induced by endothelin-1, phenylephrine and KCl in the stenosed carotid, when compared to their respective age-matched naive and SHAM groups. Interestingly, an increased contractile-response to vasoconstrictor agents in all the contralateral carotids was observed. Stenosis (30 and 90 days) also induced an increase in the contractions induced by endothelin-1 in the basilar artery. Conversely, phenylephrine and KCl-induced contractions were reduced in basilar arteries 7, 15, 30 and 90 days after stenosis. These results showed that stenosis in adult guinea-pigs induce alterations of vascular reactivity in arteries distant from the site of injury. Thus, in spite of the common use of contralateral carotid as control, it must be aware of the potential alteration induced by stenosis in the vascular motility of such vessels. Additionally, it was verified a relationship between the period of stenosis and the alterations in the vascular reactivity to these vasoconstrictors.

Gender-specific vascular effects elicited by chronic ethanol consumption in rats: a role for inducible nitric oxide synthase

BACKGROUND AND PURPOSE

Epidemiological data suggest that the risk of ethanol-associated cardiovascular disease is greater in men than in women. This study investigates the mechanisms underlying gender-specific vascular effects elicited by chronic ethanol consumption in rats.

EXPERIMENTAL APPROACH

Vascular reactivity experiments using standard muscle bath procedures were performed on isolated thoracic aortae from rats. mRNA and protein for inducible NO synthase (iNOS) and for endothelial NOS (eNOS) was assessed by RT-PCR or western blotting, respectively.

KEY RESULTS

In male rats, chronic ethanol consumption enhanced phenylephrine-induced contraction in both endothelium-intact and denuded aortic rings. However, in female rats, chronic ethanol consumption enhanced phenylephrine-induced contraction only in endothelium denuded aortic rings. After pre-incubation of endothelium-intact rings with L-NAME, both male and female ethanol-treated rats showed larger phenylephrine-induced contractions in aortic rings, compared to the control group. Acetylcholine-induced relaxation was not affected by ethanol consumption. The effects of ethanol on responses to phenylephrine were similar in ovariectomized (OVX) and intact (non-OVX) female rats. In the presence of aminoguanidine, but not 7-nitroindazole, the contractions to phenylephrine in rings from ethanol-treated female rats were greater than that found in control tissues in the presence of the inhibitors. mRNA levels for eNOS and iNOS were not altered by ethanol consumption. Ethanol intake reduced eNOS protein levels and increased iNOS protein levels in aorta from female rats.

CONCLUSIONS AND IMPLICATIONS

Gender differences in the vascular effects elicited by chronic ethanol consumption were not related to ovarian hormones but seemed to involve the upregulation of iNOS.

Analysis of the mechanisms underlying the vasorelaxant action of angiotensin II in the isolated rat carotid

It has been suggested that low concentrations of angiotensin II cause vasoconstriction whereas high concentrations evoke vasodilation. Thus, this work aimed to functionally characterize the mechanisms underlying the relaxation induced by angiotensin II at high concentrations in isolated rat carotid rings. Experiments using standard muscle bath procedures showed that angiotensin II (0.01-3 microM) concentration dependently induces relaxation of phenylephrine-pre-contracted rings. No differences between intact or denuded endothelium were found. The angiotensin II-induced relaxation was strongly inhibited by saralasin, the non-selective antagonist of angiotensin II receptors but not by the selective antagonists of AT1 and AT2 receptors, losartan and PD123319, respectively. However, A-779, a selective angiotensin-(1-7) receptor antagonist, reduced the relaxation induced by angiotensin II. Administration of exogenous angiotensin-(1-7) on pre-contracted tissues produced concentration-dependent relaxation, which was also inhibited by A-779. HOE-140, the selective antagonist of the bradykinin in B2 receptor did not produce any significant effect on angiotensin II-induced relaxation. Pre-incubation of denuded-rings with N G-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4] Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reduced angiotensin II-induced relaxation. On the other hand, neither indomethacin nor tetraethylammonium (TEA) produced any significant effect. The major new finding of this work is that high concentrations of angiotensin II induce relaxation of the rat carotid via activation of the NO-cGMP pathway through a mechanism that seems to be partially dependent on activation of angiotensin-(1-7) receptors.