Castration of male rats reduces the capacity of granules isolated from the median eminence to secrete luteinizing hormone-releasing hormone in response to copper.

The effect of castration of male rats on the secretory function of median eminence area (MEA) granules containing luteinizing hormone-releasing hormone (LHRH) was examined, using copper as a test substance. LHRH granules, isolated from MEA of sham or castrated rats 1, 2, or 12 weeks postoperatively, were incubated with various concentrations of copper complexed to histidine (CuHis) and the kinetic constants of LHRH release estimated. CuHis-stimulated release of LHRH was found to be a saturable function of the concentration of CuHis. Castration did not alter the apparent Km for CuHis-stimulated release of LHRH; the Km being 3 and 16.9 microM copper for granules obtained from 1-2 weeks and 12 weeks sham-operated rats, respectively, and 3.7-5.6 and 10.2 microM copper for the granules of castrated rats, respectively. Moreover, castration did not alter the fractional amount of LHRH released in response to CuHis. In contrast, castration markedly reduced the actual amount of LHRH released in response to CuHis; the Vmax being 1,933 and 2,942 pg LHRH released/6 min/MEA for 1-2 weeks and 12 weeks sham-operated rats, respectively, and 782 and 757 pg for the castrated rats, respectively. Similarly, the LHRH content of the MEA of castrated rats was lower than that of the shams. These results are suggestive that castration reduces the capacity of the MEA granules to release LHRH in response to a secretion stimulus such as copper and that this is due not to alterations in the biochemical parameters underlying the release process itself but to a reduced level of MEA LHRH available for release.