Rabbit mesenteric artery receptors formed by cold exposure mediating increased histamine-induced relaxation

On helically-cut strips of rabbit mesenteric artery contracted with phenylephrine, histamine in the presence of mepyramine caused a partial relaxation at 42 degrees C which was potentiated by reducing the temperature to 25 degrees C. However, under the same conditions, the selective H2 agonist, dimaprit, caused a smaller partial relaxation not enhanced by cooling the strips. Neither changing the temperature range (to 38 degrees and 22 degrees C), deleting the H1 blocker, nor substitution of another H1 blocker (pyribenzamine) resulted in an enhanced relation to dimaprit in the cold. Prior reserpinization of the rabbit did not abolish the cooling-enhanced relaxation to histamine, but did abolish the reversal of relaxation observed at high (10(-3) M) histamine concentrations. Metiamide (3 X 10(-4) M) blocked both histamine (H2)- and dimaprit-induced relaxations more effectively in cooled strips. Thus the H2 receptor activity observed in cooled strips differs in selectivity for the two agonists and antagonist from that observed at normal temperature.