Influence Of Estrous Cycle On The Sensitivity Of Cronotropic Answer To Norepinephrine In Rats Submitted To Acute Stress [influência Do Ciclo Estral Sobre A Sensibilidade Da Resposta Cronotrópica à Norepinefrina Em Ratas Submetidas A Estresse Agudo]

Stress may change the response to catecholamines in many tissues. The aim of this study was to investigate the influence of the estrous cycle on the sensitivity to norepinephrine in right atria from female rats submitted to a single swimming session. Wistar female rats were submitted to one swimming session at estrus or proestrus. Immediately after the stress session, the animal was sacrificed and its right atria set up for isometric recording of spontaneous beating. Concentration-effect curves to norepinephrine were obtained before and after inhibition of uptake1 (phenoxibenzamine) and uptake2 (estradiol). Swimming stress did not change the sensitivity to noradrenaline in right atria from rats at estrus. However, at proestrus swimming induced supersensitivity to norepinephrine (pD2 control: 7.14 ± 0.03 vs. pD2 swimming: 7.55 ± 0.04; p<0.05). 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