THE INFLUENCE OF CASTRATION ON PHARMACOLOGICALLY INDUCED PENILE ERECTION IN THE CAT

The purpose of this study was to investigate the in vivo effects of in tracavernosal injections of adrenomedullin (ADM), calcitonin gene-rela ted peptide (CGRP), nociceptin, vasoactive intestinal polypeptide (VIP ), sodium nitroprusside (SNP), and prostaglandin E, (PGE(1)) on penile erection in castrated and intact (control) anesthetized cats. Erectil e responses to ADM, CGRP, nociceptin, VIP, SNP, and PGE(1) were compar ed with responses to a standard triple-drug combination (1.65 mg of pa paverine, 25 mu g of phentolamine, and 0.5 mu g of PGE(1)) in both cas trated and control cats. In control animals, ADM, CGRP, nociceptin, VI P, SNP, and PGE(1) induced penile erections similar to those elicited by the triple-drug combination. However, in castrated animals, there w as a significant decrease in erectile response; the response to intrac avernosal injection of the standard triple-drug combination in castrat ed cats was 28% of that of the control group of animals. Serum testost erone levels demonstrated a significant (P < 0.0001) positive correlat ion (r = 0.52) with intracavernosal pressure in response to the standa rd combination. A marked reduction in serum testosterone levels was ob served in castrated cats when measured by radioimmunoassay (0.34 = 0.1 ng/dl in castrated cats, compared with 31.15 +/- 6 ng/dl in control c ats). These data suggest that the presence of testosterone is a necess ary prerequisite to sustain a pharmacologically induced penile erectio n in the cat.