INHIBITION OF FUNDULUS-HETEROCLITUS OOCYTE MATURATION IN-VITRO BY SEROTONIN (5-HYDROXYTRYPTAMINE)

The effects of serotonin (5-hydroxytryptamine [5-HT]) on oocyte matura tion in vitro were tested on Fundulus heteroclitus full-grown prematur ational ovarian follicles. F. heteroclitus pituitary extract (FPE)- an d steroid (17 alpha,20 beta-dihydroxy-4-pregnen-3-one [DHP])-induced o ocyte maturation were both inhibited by 5-HT in a dose-dependent and r eversible manner. Maximum inhibition was observed at concentrations of 0.5 and 5 mu M 5-HT, respectively. The inhibitory action was also les s effective when 5-HT was combined with human chorionic gonadotropin t han with FPE, which may indicate the presence of 5-HT and/or other inh ibitory substances in the pituitary extract. Inhibition by 5-HT was in dependent of FPE-induced steroid production by the follicle, since the levels of 17 beta-estradiol and DHP released into the culture medium were not modified by the presence of 5-HT. When follicles were preincu bated with DHP for increasing times, subsequently washed, and transfer red to steroid-free, Ei-HT-containing medium, inhibition by 5-HT was a lso observed in follicles preincubated for up to 4 h; however, inhibit ion by 5-HT was reduced or eliminated after 8 h or 16 h preincubation with DHP, respectively. These results suggest the presence of a putati ve 5-HT receptor(s) that does not affect steroidogenic pathways in the ovarian follicle yet inhibits steroid-induced oocyte maturation at so me point downstream in the steroid transduction pathway of the oocyte. (C) 1995 Wiley-Liss, Inc.