Abstract
The effects of histamine and its analogues on the cyclic AMP levels in the submandibular glands of guinea pigs and the characteristics of the receptors which mediate such effects were investigated.
Histamine and 4-methylhistamine dose-dependently increased the cyclic AMP levels in chopped submandibular glands. The ED50 values for histamine and 4-methylhistamine were approximately 1.3×10-5 M and 2.2×10-5 M, respectively. 4-Methylhistamine had a higher efficacy than histamine. 2-(2-Pyridyl)ethylamine was far less effective than either histamine or 4-methylhistamine.
Although metiamide markedly inhibited the cyclic AMP-increasing effects of histamine and 4-methylhistamine, mepyramine was completely ineffective. A combination of aminoguanidine and quinacrine had no influence on the effect of histamine on the cyclic AMP levels.
From these results it was concluded that histamine H2-receptors which mediate the cyclic AMP increase are present in the guinea-pig submandibular gland.
