Analysis of the nature of antagonism of the reserpine-induced hypothermia by imipramine.

Antagonism of reserpine-induced hypothermia is an animal model used in the screening of antidepressants. The activity of imipramine on this test is partly impaired by propranolol. This effect of imipramine was analyzed using specific adrenoceptor and 5-HT receptor blocking drugs in order to determine the nature of this effect of propranolol. The non-selective beta 1-beta 2 adrenoceptor antagonist, propranolol as the specific beta 1 adrenoceptor antagonist betaxolol, but not the specific beta 2 blocking drug DL-erythro-3-isopropylamino-1-(7-methyl-4-indanyloxy)-2-butanol hydrochloride 313.9 (ICI 118,551), partly antagonized the effect of imipramine at 30 min. None of the serotonin (5-HT) receptor antagonists, methysergide, metergoline, ritanserin and buspirone, impaired the effect of imipramine. On the contrary, methysergide alone antagonized reserpine-induced hypothermia and methysergide or metergoline increased the action of imipramine. Propranolol impaired neither the hypothermia induced by an agonist at the 5-HT 1A receptors: 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) nor the increase in spontaneous motor activity induced by an agonist at the 5-HT 1B receptors: 5-methoxy-3(1,2,3,6-tetrahydropyridin-4-yl)1-H indole (Ru 24,969). It is concluded that the effect of propranolol is not the result of a blockade of 5-HT 1A, 5-HT 1B or 5-HT 2, but is in part due to blockade of beta 1 adrenoceptors.