Hypothalamic areas involved in prostaglandin(pg)-induced gonadotropin release. II: Effects of PGE₂ and PGF_2α implants on follicle stimulating hormone release

The effect of unilateral intrahypotha-lamic implants of PGE₂ or PGF_2α on FSH release i n ovariectomized, estrogen-treated rats was studied. Both PGs induced an equally small increase in plasma FSH following their implantation in the body of the arcuate nucleus-median eminence region (BARH-ME). Levels were maximally elevated 120 min post-implantation. PGE₂ implanted in the caudal portion of the ARH-ME (TARH-post-ME) also induced a similar increase in plasma FSH, whereas its placement in the region of the ventromedial nucleus (VMH)-dorsomedial nucleus (DMH) did not significantly alter FSH titers. By contrast, PGE₂ placed i n the post-chiasmatic region (HARH-ME) clearly elevated plasma FSH as early as 40 min after implantation. Implants of PGF_2α in this area were ineffective. PGE₂ implants located more than 1 mm lateral from the midline or outside the hypothalamus were also ineffective. When PGE₂ was. placed in the preoptic area (POA) or anterior ventral portion of the anterior hypothalamic area (AHA), plasma FSH rose markedly showing the first significant increase between 40 and 60 min after implantation. PGE₂ implants located in the dorsal portion of the AHA-paraventricular nucleus (DAHA-PVH) were also clearly more effective than implants in BARH-ME, but less effective than implants in the POA. PGF_2α implanted in the POA evoked a smaller increase in plasma FSH than that induced by PGE₂ implants in this region. Implantation of empty cannulae in the ARH-ME region or POA failed to increase plasma FSH levels significantly. Intrapituitary implants of PGE₂ did not alter plasma FSH. The results indicate that PGE₂acts mainly on the POA-AHA region to induce FSH release and that PGF_2α, although less effective, also stimulates FSH release ni this area. The ARH-ME appears to be a less important site. The greater effectiveness in the POA-AHA region than in the ARH-ME may indicate that PGE₂ is more effective in stimulating cell bodies of LHRH neurons than their axons. Although most of the sites at which PGE₂ released FSH coincide with the distribution of LHRH, it is noteworthy that a relatively enhanced release of FSH took place from certain sites in the dorsal AHA-PVH and from sites in the post-ME, which suggests that (PGE₂ may act on neurons which secrete a specific FSH-RF as well as on neurons which release LHRH.