INHIBITION OF MATURATION OF ISOLATED RAT OOCYTES BY PORCINE FOLLICULAR FLUID

Abstract The inhibitory action of porcine follicular fluid (FF1) on the spontaneous maturation of isolated rat oocytes was studied. Both FF1 and a low-molecular-weight fraction thereof (PFF1) inhibited the maturation of oocytes in culture. When the oocytes were scrutinized for maturation after culturing for 6 h in a medium containing 50% (v/v) FF1, the incidence of germinal vesicle breakdown (GVB) was reduced from 75 to 53% (P < 0·001) in oocytes collected 20 h after administration of pregnant mare serum gonadotrophin (PMSG), and from 94 to 53% (P < 0·01) in oocytes collected from preovulatory follicles 44 h after treatment with PMSG. Prolongation of the culture period to 20 h resulted in an increase in the number of oocytes undergoing GVB to 58% (harvested 20 h after PMSG treatment; P < 0·001) or 71% (44 h after treatment with PMSG; P > 0·05). Inhibition of GVB by PFF1 occurred at concentrations ≥ 0·085 mg protein/ml; the extent of inhibition was related directly to the concentration of inhibitor and inversely to the duration of culture and the developmental stage of the follicles from which the oocytes were derived. The inhibition of the resumption of meiosis by FF1 or PFF1 was overcome by ovine LH (5 μg/ml). However, GVB was delayed even in the presence of LH, compared with controls cultured in the absence of the inhibitor. These results demonstrate that the maturation-inhibiting action of porcine follicular fluid is not species specific and that the sensitivity of the rat oocyte to the inhibitor changes during the course of follicular development.