Changes in LH-releasing hormone content of the hypothalamus and electron microscopy of the anterior pituitary after prostaglandin E2 injection in rats.

The purpose of this study is to present evidence that prostaglandin (PG) E2 stimulates a release of luteinizing hormone-releasing hormone (LH-RH) from the hypothalmus. In experiment 1, 72 hours after estrogen and progesterone treatment, a solution of 700 mug of PGE2 was injected into the jugular vein. Blood samples for plasma LH and the hypothalamus for LH-RH assay were collected before and 5, 10, and 30 minutes after PGE2 injection and subjected to radioimmunoassay. The total LH-RH content of the hypothalamus decreased from 20.4 to 15.3 ng. at 5 minutes after PGE2 and had returned to the pretreatment level by 30 minutes after PGE2 administration. On the other hand, plasma LH levels increased at 5 minutes, reached a peak at 10 minutes, followed by a decline at 30 minutes after PGE2 injection. In Experiment 2, 10 and 30 minutes after a single injection of PGE2 or synthetic LH-RH, the anterior pituitary were excised for an electromicroscopic study. Ten minute after PGE2, an enlarged Golgi apparatus, well-developed rough endoplasmic reticulum, and decreased secretory granules were observed in pituitary gonadotropins as compared with the control group. These changes were more conspicuous in the pituitaries obtained 30 minutes after PGE2. In Experiment 3, plasma LH levels were determined serially before and 10, 30, 60, and 90 minutes after a single injection of PGE2, LH-RH, or saline. There is a striking resemblance between the PGE2- and LH-RH-treated groups. Plasma LH levels in both these groups reached a peak at 10 minutes and started to decline 30 minutes after PGE2 or LH-RH administration. Our findings would indicate that PGE2 stimulates LH-RH secretion from the hypothalamus.