Biology of Reproduction, Vol 31, 759-770, Copyright © 1984 by Society for the Study of Reproduction

ARTICLES

Gossypol modulation of nucleotide metabolizing enzymes in the reproductive tract of male rats

KL Olgiati, AP Hoffer and WA Toscano Jr

The activities of several pivotal nucleotide metabolizing enzymes from the testis and vasal sperm of rats treated for 7 wk with 0, 20 or 30 mg X kg X day gossypol acetic acid were examined. Total testicular lactate dehydrogenase (LDH) activity increased 40% above control in the highest treatment group examined. However, the specific activity of the testis- specific isozyme of LDH, LDH-C4, decreased to 50 and 20% of control in the 20 and 30 mg X kg X day treatment groups, respectively. Basal soluble adenylate cyclase from a 100,000 X g supernatant of testis homogenate exhibited a 25% decrease in activity only in the 30-mg treatment group. Basal adenylate cyclase activity in the testicular membrane fraction increased 20 to 30% above control in response to gossypol administration. Testis membranes from the 20- and 30-mg treatment group exhibited a 2- and 4-fold greater activation of adenylate cyclase by guanine nucleotides. In vitro dose-response curves showed a half-maximal inhibitory concentration (IC50) for inhibition of soluble testicular adenylate cyclase by gossypol of 400 microM in each treatment group. Caudal epididymal sperm adenylate cyclase activity decreased to 25% of control levels in gossypol-treated animals, and the in vitro sensitivity of the enzyme to the inhibitory effects of gossypol increased 4-fold. IC50 values for gossypol inhibition of sperm adenylate cyclase decreased from 200 microM in control animals to 75 and 50 microM in the 20 and 30 mg X kg X day treatment groups, respectively. Cyclic adenosine 3':5' monophosphate phosphodiesterase activity in caudal sperm increased 6-fold in the 20- and 30-mg treatment groups. These results demonstrate that nucleotide metabolizing enzymes in sperm are major targets for the actions of gossypol and provide a possible mechanism for the inhibition of normal sperm function by this compound.