Role of Arachidonic Acid Metabolites in the Hypothalamic Control of Ovulation in the Rat

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Abstract
The action of several synthesis inhibitors of arachidonic acid metabolites on ovulation in the rat was investigated and the effectiveness of intraventricular microinjections vs. intracerebral injections has been compared. Indomethacin, aspirin and paracetamol, 3 prostaglandin (PG) synthesis inhibitors, were completely ineffective at the doses given in blocking ovulation when injected into the 3rd ventricle on the morning of proestrus. Similar results were obtained with intraventricular injections of 15-hydroxyperoxyarachidonic acid (15-HPAA), which selectively inhibits the formation of prostacyclin from the endoperoxide intermediates, and with imidazole, an inhibitor of thromboxane biosynthesis. Intracerebral administration of indomethacin or aspirin blocked ovulation in a significant proportion of rats when infused directly into the preoptic area or the anterior hypothalamic area of the brain. Intracerebral injections of paracetamol or 15-HPAA produced no ovulatory blockade. Although imidazole showed no apparent effect when injected in the anterior hypothalamus, infusion into the preoptic area blocked ovulation in a small proportion of animals. Further evidence is provided for the role of PG in the hypothalamic control of ovulation. PG of the E and F series are most likely to be the PG type involved and not thromboxanes or prostacyclin.