Histamine H1-receptors in the guinea-pig urinary bladder.

Histamine H1-receptors were identified in the guinea-pig urinary bladder. Histamine (10(-8)-10(-3) M) produced a dose-dependent contraction which was not altered by either scopolamine or tetrodotoxin. Specific [3H]mepyramine binding to the urinary bladder was saturable and there was a single population of high affinity binding sites with an equilibrium dissociation constant (KD) of 0.77 nM and maximum binding capacity (Bmax) of 68.5 fmol/mg protein. Histamine-induced contraction and [3H]mepyramine binding were inhibited by triploridine, promethazine, d-chlorpheniramine and mepyramine but not by cimetidine. There was a good correlation between mechanical activity and [3H]mepyramine binding as shown by the inhibition affinity constant (Ki) of H1-antagonists. These results provide evidence that the histamine H1-receptor in the guinea-pig urinary bladder is involved in the histamine-induced contraction.