EVIDENCE FOR FOLLICLE-STIMULATING-HORMONE MEDIATION IN THE HEMIORCHIDECTOMY-INDUCED COMPENSATORY INCREASE IN THE FUNCTION OF THE REMAINING TESTIS OF THE ADULT MALE BONNET MONKEY (MACACA-RADIATA)

Hemiorchidectomy (HO) in the adult male bonnet monkey results in a sel ective increase in circulating concentrations of FSH and testosterone, and this is accompanied by compensatory increase in sperm production by the remaining testis. We investigated the possible role of increase d FSH concentration that occurs after HO in the compensatory increase in the activity of the remaining testis. Of eight adult male bonnet mo nkeys that underwent HO, four received i.v. injections every other day for 30 days of a well-characterized ovine FSH antiserum (a/s) that cr oss-reacts with monkey FSH. The remaining four males received normal m onkey serum (NMS) as control treatment in a protocol similar to that e mployed for ais-treated males. Blood samples were collected between 21 00 and 2200 h before and 1/2, 1, 3, 5, 7, 14, 22, and 29 days after HO . Testicular weight, number of 3 beta-hydroxy steroid dehydrogenase-po sitive (3 beta-HSD+) cells, and DNA flow cytometric analysis of germ c ell populations were obtained for testes collected before and at the t ermination of NMS or ais treatment. In NMS-treated males, circulating serum FSH concentrations progressively increased to reach a maximal le vel by Day 7 after HO (1.95 +/- 0.3 vs. 5.6 +/- 0.7 ng/ml on Days -1 a nd 7, respectively). Within 30 min of ais injection, FSH antibodies we re detected in circulation, and the antibody level was maintained at a constant level between Day 7 and end of treatment (exhibiting 50-60% binding to I-125-hFSH). Although circulating mean nocturnal serum test osterone concentration showed an initial decrease, it rose gradually t o pre-HO concentrations by Day 7 in NMS-treated males. In contrast, no cturnal mat serum testosterone concentrations in a/s-treated males rem ained lower than in NMS-treated controls (p < 0.05) up to Day 22 and t hereafter only marginally increased. Testicular weights increased (p < 0.05) over the pre-HO weight in NMS- but not in ais-treated males. Af ter HO, the number of 3 beta-HSD+ cells (Leydig cells) was markedly in creased but was significantly (p < 0.05) higher in NMS-treated males c ompared to a/s-treated males. A significant (p < 0.05) reduction in th e primary spermatocyte population of germ cells was observed in ais-tr eated compared to NMS-treated males. These results suggest that the in creased FSH occurring after HO could be intimately involved in increas ing the compensatory functional activity of the remaining testis in th e male bonnet monkey.