Identification and specific blockade of histaminergic receptors in guinea pig vasa deferentia

Abstract

Histamine produces contractions of the guinea pig vas deferens. The present investigation was undertaken to characterize the nature of histaminergic receptors in this tissue. Histamine (1.6 × 10−6 M to 3.2 × 10−5 M) produced dose-related contractions of guinea pig vas deferans (GPVD). Mepyramine (5.3 × 10−8 M and 1 × 10−9 M) blocked the responses to histamine competitively. Metiamide (1.23 × 10−5 M) did not block the responses to histamine significantly. Specific H1 and H2 receptor agonists, namely 2-(2′-pyridyl)ethylamine (PEA) (2.55 × 10−6 M to 3.0 × 10−5 M) and 4-methylhistamine (4-MH) (2.52 × 10−5 M to 3.0 × 10−4 M), respectively, produced dose-related contractions of GPVD. The responses to PEA were blocked competitively by mepyramine, whereas the responses to 4-MH were blocked by metiamide. Reserpine pre-treatment (5 mg/kg, i.p., 24 h) did not alter the responses to histamine and PEA. Our data suggest the presence of both H1 and H2 receptors in the GPVD which are excitatory in nature.