Phenoxybenzamine discriminates between two distinct populations of histamine H1-receptors in longitudinal muscle of guinea-pig ileum.

The longitudinal muscle of guinea-pig ileum was used as a test tissue. Progressive (up to 70 min) treatment with phenoxybenzamine (10(-6) M) inhibited progressively the response to histamine and progressively decreased the density of histamine H1-receptors. However, the 90 min treatment has no further significant inhibitory effect on the contractile response and did not decrease the density of the receptors. These results suggest that phenoxybenzamine discriminates between two distinct populations of H1-receptors. Furthermore, it was found that the presence of GTP gamma-S made some populations of H1-receptors resistant to phenoxybenzamine and facilitated an interaction of mepyramine with H1-receptors.