The dynamics of in vitro 17 beta-estradiol secretion by isolated ovarian follicles of the rainbow trout (Oncorhynchus mykiss)

This study investigated the effects of human chorionic gonadotropin (hCG), 17-hydroxyprogesterone (17P) and testosterone (T) on the in vitro production of 17β-estradiol (E2) by isolated ovarian follicles of the rainbow trout (Oncorhynchus mykiss). T and 17P at 100 ng ml-1, and hCG at 100 IU ml-1 stimulated E2 production relative to controls, whereas lower doses were ineffective. T was the most effective in stimulating E2 production, followed by 17P and hCG respectively. The timecourse of E2 production was investigated for both static culture, and incubations with media replacement, with follicles being exposed to hormone treatment for 30 min, 1 or 3 h, or constantly. E2 production was observed after 30 min, 3 and 3-6 h in response to T, 17P and hCG respectively. Under static culture, E2 levels reached maximal levels in 6 h. Longer incubations resulted in further metabolism of E2 to E2-glucuronide, which resulted in the blurring of treatment effects after 18 h. Incubations with media replacement resulted in higher E2 production than in static culture. The results indicate that a 6 h incubation period is sufficient to produce significant increases in E2 production in response to hCG, 17P and T, and that incubations longer than 12 h result in losses of E2 from the incubation media. These findings have implications for the validity of using static cultures to examine the effects of hormone treatment on the activity of steroid converting enzymes in vitro.