Acute versus chronic effects of human chorionic gonadotrophin on relaxin secretion in rhesus monkeys

Corpora lutea (CL) were removed from rhesus monkeys (N = 26) at 0 h, 9 h, 3 days, 6 days and 10 days during treatment with hCG to simulate blood concentrations of CG during normal pregnancy. Dispersed luteal cells were incubated in vitro at 37 degrees C for 8 h. Immunoreactive relaxin was measured in incubation medium and in cell extract by radioimmunoassay (RIA). Cellular content and release of relaxin into medium increased as simulated early pregnancy progressed. By 3 days, relaxin content had significantly increased (P less than 0.05) and continued to rise throughout simulated early pregnancy. Significant increases in cellular content and release were observed before the time when relaxin has been detected in the peripheral circulation during this treatment regimen. Within group, total relaxin (cells plus medium) was similar before and after incubation (P greater than 0.05). As such, production of relaxin during the 8-h incubation was not evident. In-vitro exposure of the luteal cells to hCG or dbcAMP had no acute effect on cell content or medium concentration of relaxin at any stage of simulated early pregnancy. Since acute effects of hCG and dbcAMP were not evident in vitro, a sustained gonadotrophic influence may be necessary to augment relaxin production/secretion in the primate CL.