Characterization of an in vitro perfused rat ovary model: ovulation rate, oocyte maturation, steroidogenesis and influence of PMSG priming.

An in vitro perfused rat ovary model was characterized with respect to ovulation rate, oocyte maturation and steroidogenesis after priming with various doses of pregnant mare's serum gonadotrophin (PMSG) (10, 20 or 30 IU PMSG s.c. in the morning of day 28). In ovaries stimulated with LH 0.1 microgram ml-1 after 1 h of perfusion the number of ovulations was significantly higher in the 20 IU PMSG group than in the to IU PMSG group (6.8 +/- 1.0 ovulations per treated ovary versus 2.4 +/- 1.2, P less than 0.01). Priming with 30 IU PMSG did not result in significantly more or fewer ovulations than did 10 or 20 IU PMSG. No ovaries in the non-stimulated control groups ovulated. Oocytes retrieved directly at ovulation were mature (GVB or PB stage). Among oocytes retrieved from pre-ovulatory follicles punctured at 0, 2, 4, 6 and 8 h after stimulation with LH 0.1 microgram ml-1 there was an increasing number of oocytes with GVB (0/10 at 0 h and 10/10 at 8 h). Stimulation with LH resulted in a rapid release of progesterone, testosterone and oestradiol into the medium, whereas non-stimulated control ovaries exhibited a slow rise of all steroids throughout the perfusion period. It is concluded that priming with 20 IU PMSG in this model results in an optimal number of ovulations and that this model provides a useful tool in studies of various kinds of modifying influences on the ovulatory process.