Blockade of ovulation in the rat by a prostaglandin antogonist (N-0164

There is evidence accumulating to suggest that prostaglandins (PG) have a hypothalamic action in mediating the preovulatory surge of luteinizing hormone from the pituitary gland. Intraventricular injection of inhibitors of PG synthesis has been shown to block ovulation(Behrman, Orczyk & Greep, 1972; Orczyk & Behrman, 1972) and this effect can be overcome by subsequent administration of PG or luteinizing hormone releasing hormone. Similarly, PGE2, administered intraventricularly, can overcome the ovulatory blockade induced by the \g=a\-adrenoceptor antagonist phentolamine (Linton, Perkins & Whitehead, 1977). In this study, we have investigated the action of the prostaglandin antagonist N-0164 (Eakins, Rajadhyaksha & Schroer, 1976) on ovulation in the rat. Female Wistar rats weighing between 230 and 280 g were maintained under a controlled lighting schedule (12h light centred on midday) at a constant temperature of 21°C. Daily vaginal smears were taken and only rats which displayed at least three consecutive 4 day cycles were used for these experiments. On the day of pro-oestrus, between 11.00 and 13.45 h, an aqueous solution of N-0164 (pH 6-6-7-0) was injected stereotaxically into the third ventricle under light ether anaesthesia. Doses of N-0164 ranged from 10 to 40 µg and were administered through a Hamilton 10µ1 syringe in a 2µ1 volume over a period of 1 min. Control animals received a