Effect of a Calcium Antagonist (ICI 109,081) upon Follicular Steroidogenesis and Oocyte Maturation in the Golden Hamster

The effect of a calcium antagonist (a derivative of dihydropyridazinone: ICI 109,081), upon oocyte maturation, and steroid production by pre-ovulatory hamster follicles was determined. Sexually immature golden hamsters were injected with 40 iu PMSG, and pre-ovulatory follicles (591–740 μm) were isolated after 72–78h. The culture of intact follicles in medium containing 1 μg/ml ICI 109,081 showed an increased output of progesterone (p<0.05). However, in the presence of LH, ICI 109,081 was seen to cause significant decreases in the output of progesterone, 17α-hydroxyprogesterone and androstenedione (all p<0.05) with a significant increase in the production of oes-tradiol (p<0.05). The culture of oocytes isolated 72h after PMSG showed significant reductions in the number of oocytes resuming meiosis when compared with controls (94%) for ICI 109,081 concentrations of 0.1 μg/ml (58%, p<0.05) and 1 μg/ml (32%, p<0.05). Smilarly, the pre-treatment of animals with 3 mg ICI 190,081 lh before injection of 25 iu hCG, caused the ovulation of 96/98 ova with an intact germinal vesicle. The results suggest a role of calcium in the regulation of oocyte maturation, and as a mediator in the action of LH upon steroidogenesis by pre-ovulatory follicles.