EVIDENCE FOR THE DIFFERENTIAL REGULATION OF OVARIAN FOLLICLE RESPONSIVENESS TO HUMAN CHORIONIC-GONADOTROPIN IN-VITRO IN A SERRANID TELEOST,CENTROPRISTIS-STRIATA

Pre-maturational or full-grown ovarian follicles were isolated from ca ptive, spawning black sea bass, Centropristis striata, at different ti mes during the spawning season and tested for their ability to undergo oocyte maturation in vitro in response to human chorionic gonadotropi n (hCG). The gonadosomatic index (GSI) was greatest in females collect ed during the mid-spawning period and the number of abnormal (atretic) follicles in the ovary progressively increased throughout the spawnin g season. The maturational response of follicles induced by hCG genera lly declined as the spawning interval progressed; an increased inhibit ion of oocyte maturation by doses greater than or equal to 50 IU ml(-1 ) hCG was also observed. Linear regression analyses indicated that the percentage of inhibition of oocyte maturation by 50, 100 and 500 IU m l(-1) hCG was positively correlated with increasing levels of atresia within the ovaries from which the follicles were isolated. Ln females with low incidence of ovarian atresia (0-5%), follicular maturation ac hieved with 1-10 IU ml(-1) hCG positively correlated with the GSI. How ever, when follicles isolated from females with a GSI greater than or equal to 8 were treated with 50-500 IU ml(-1) hCG the maturational res ponse of follicles was reduced in comparison with the maturation of fo llicles from females with lower GSI that were treated with the same do ses of hCG. In addition, doses of 100 and 500 IU ml(-1) hCG appeared t o be inhibitory on oocyte maturation once the GSI greater than or equa l to 8. These results suggest that the sensitivity of C. striata pre-m aturational follicles to gonadotropin (GtH) may be regulated different ly depending on both the overall state of follicular development and t he levels of atresia within the ovary: the desensitization of GtH rece ptors may be one of the mechanisms possibly involved. It is recommende d that the specific physiological condition of the ovary must be consi dered in selecting the timing and the dose of hCG to induce ovulation in this species. (C) 1997 Elsevier Science B.V.