Effect of cold adaptation of α-and β-adrenergic responses of blood pressure in hindlimb and small intestine in situ and systemic blood pressure in rabbits

Abstract

Changes in the main parameters of alpha- and beta-adrenergic responses, sensitivity to agonists (EC50) and maximum response (Pm) of hindlimb and small intestinal blood pressure in situ and systemic blood pressure were studied in rabbits adapted to cold for 1-30 days (daily exposures to -10 degrees C for 6 h). The responses to phenylephrine, noradrenaline. adrenaline, clonidine (alpha-agonists), and isopropylnoradrenaline (beta-agonist) corresponded to the equation p = (PmAn)/(EC50n + An) with n = 1 and n = 2, respectively. Cold adaptation induced reciprocal changes in the response of both EC50 and Pm to alpha-agonists and in the response of Pm alone to isopropylnoradrenaline. The significant differences of the parameters from control observed during the first 5 days of adaptation gradually decreased by day 30. After 10 days of adaptation, the efficiency (E = Pm/2EC50) of response to alpha- and beta-agonists of adrenoceptors significantly increased.