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 α -and β -adrenergic responses, sensitivity to agonists ( EC 50 ) and maximum response ( P m ) 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 ° C for 6 h). The responses to phenylephrine, noradrenaline, adrenaline, clonidine ( α -agonists), and isopropylnoradrenaline ( β -agonist) corresponded to the equation p = ( P m A n )/( EC 50 n + A n ) (1) with n = 1 and n = 2, respectively. Cold adaptation induced reciprocal changes in the response of both EC 50 and P m to α -agonists and in the response of P m 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 = P m /2 EC 50 ) of response to α -and β -agonists of adrenoceptors significantly increased.