Decreased prostatic secretory function in canine benign prostatic hyperplasia is not due to decreased levels of muscarinic cholinergic receptors.

The ejaculatory volume and the prostatic secretory capacity (ml. ejaculate per gm. prostate wet weight) were determined for a group of dogs with normal and hyperplastic prostates. The ejaculatory volume and prostatic secretory capacity in dogs with BPH were decreased by 70 per cent and 80 per cent respectively, compared to dogs with normal prostates. Radioligand receptor binding using [3H]N-methylscopolamine, a muscarinic cholinergic antagonist, was performed on a similar group of dogs with normal and hyperplastic prostates. The mean equilibrium dissociation constant for the binding of [3H]N-methylscopolamine to homogenates obtained from normal and hyperplastic prostates was 0.21 nM. and 0.19 nM. respectively, demonstrating that the affinity of the receptor binding sites was not altered by the development of BPH. The tissue density of the muscarinic cholinergic receptors (fmol. per mg. prostate wet weight) and the cellular density of these receptors (fmol. per mg. DNA) were not significantly different in normal and hyperplastic prostates. These data indicate that the dramatic reduction in prostatic secretory capacity associated with canine BPH is not related to changes in the muscarinic cholinergic receptor binding capacity.