Stress alone or associated with ethanol induces prostanoid release in rat aorta via alpha2-Adrenoceptor

Abstract

Background: Stress and ethanol are both, independently, important cardiovascular risk factors.

Objective: To evaluate the cardiovascular risk of ethanol consumption and stress exposure, isolated and in association, in male adult rats.

Methods: Rats were separated into 4 groups: Control, ethanol (20% in drinking water for 6 weeks), stress (immobilization 1h day/5 days a week for 6 weeks) and stress/ethanol. Concentration-responses curves to noradrenaline - in the absence and presence of yohimbine, L-NAME or indomethacin - or to phenylephrine were determined in thoracic aortas with and without endothelium. EC50 and maximum response (n=8-12) were compared using two-way ANOVA/Bonferroni method.

Results: Either stress or stress in association with ethanol consumption increased the noradrenaline maximum responses in intact aortas. This hyper-reactivity was eliminated by endothelium removal or by the presence of either indomethacin or yohimbine, but was not altered by the presence of L-NAME. Meanwhile, ethanol consumption did not alter the reactivity to noradrenaline. The phenylephrine responses in aortas both with and without endothelium also remained unaffected regardless of protocol.

Conclusion: Chronic stress increased rat aortic responses to noradrenaline. This effect is dependent upon the vascular endothelium and involves the release of vasoconstrictor prostanoids via stimulation of endothelial alpha-2 adrenoceptors. Moreover, chronic ethanol consumption appeared to neither influence noradrenaline responses in rat thoracic aorta, nor did it modify the increase of such responses observed as a consequence of stress exposure.

Figure 1

Concentration-response curves to noradrenaline obtained from intact thoracic aorta rings taken from animals exposed to ethanol consumption and/or stress, in the absence or presence of L-NAME (10^-4 M), indomethacin (10^-5 M) or yohimbine (10^-6 M). Values are expressed as means ± SEM. The number of independent determinations was 8-10. *Indicates a significant difference (p < 0.05) in relation to the control animals.

Figure 2

Concentration-response curves to noradrenaline obtained from denuded thoracic aorta rings taken from animals exposed to ethanol consumption and/or stress, in the absence or presence of L-NAME (10^-4 M), indomethacin (10^-5 M) or yohimbine (10^-6 M). Values are expressed as means ± SEM. The number of independent determinations was 8-10.

Figure 3

Concentration-response curves to phenylephrine obtained from rings of thoracic aorta with and without endothelium taken from animals exposed to ethanol consumption and/or stress. Values are expressed as means ± SEM. The number of independent determinations was 8-10.

Figure 4

Plasma concentration of nitrite/nitrate determined by the Griess Reaction taken from animals exposed to ethanol consumption and/or stress. Values are expressed as means ± SEM. The number of independent determinations was 10-12.