INFLUENCE OF THE ESTROUS-CYCLE ON THE SENSITIVITY TO CATECHOLAMINES IN RIGHT ATRIA FROM RATS SUBMITTED TO FOOT-SHOCK STRESS

We investigated the mechanisms of the alterations in sensitivity to ca techolamines in right atria from female rats exhibiting regular 4-day estrous cycles after three foot-shock sessions at estrus, metestrus, a nd diestrus or at diestrus, proestrus, and estrus. Right atria from st ressed rats sacrificed at diestrus showed subsensitivity to noradrenal ine and adrenaline. After in vitro sympathetic denervation (38 mu M 6- hydroxydopamine) plus inhibition of neuronal reuptake (0.1 mu M desipr amine) subsensitivity to noradrenaline was abolished, but it was again evident when extraneuronal uptake was also inhibited (10 mu M phenoxy benzamine and 30 mu M corticosterone). The same pretreatment abolished the subsensitivity to adrenaline. After addition of 1 mu M butoxamine , a beta(2)-adrenoceptor antagonist, the tissues from stressed rats we re subsensitive to adrenaline. Right atria from stressed rats sacrific ed at estrus did not show any alteration in sensitivity to catecholami nes. We conclude that after foot-shock stress, right atria from female rats sacrificed at diestrus showed subsensitivity of the chronotropic response to catecholamines as a result of a conformational alteration of beta(1)-adrenoceptors, simultaneously with an increase in beta(2)- adrenoceptor-mediated response. The mechanisms seem to be similar to t hose which underlie stress-induced alterations in catecholamine sensit ivity in right atria from male rats. However, during estrus there are some protective factors that prevent the effects of stress on right at ria.