Influence of castration upon the seminal vesicle response to parasympathomimetic drugs.

The influence of castration upon rat seminal vesicle responses to acetylcholine, carbachol and betanechol has been investigated through the determination of the parameters pD2 (the apparent affinity constant), alpha (the intrinsic activity) and rho (the relative responsiveness) of such drugs on vesicles excised from normal and castrated rats. The pD2 and alpha values for carbachol and betanechol and the pD2 value for acetylcholine increased after orchiectomy; the pD2 increase was greater for the first two drugs than for acetylcholine. No significant difference in the values of rho of the acetylcholine receptor system was obtained after castration. Since carbachol and betanechol are not metabolized by cholinesterase, these results may indicate that the reported change in cholinesterase activity following castration is not the only factor to be considered as responsible for the variation in the seminal vesicle pharmacological reactivity. These results suggest that additional experimentation may be necessary to clarify the mode of action of these drugs in this system.