Arachidonic Acid Metabolites Modulate Rat Hypothalamic Corticotropin-Releasing Hormone Secretion in vitro

Arachidonic acid metabolites have been shown to modulate the secretion of various hormones, including luteinizing hormone, growth hormone and adrenocorticotropin. In this paper we describe the effect of a series of eicosanoids on hypothalamic secretion of corticotropin-releasing hormone (CRH) in vitro. Explanted rat hypothalami in culture were exposed to prostaglandins (PG) F2α or E₂, thromboxane (TX) B₂, the TXA₂ receptor agonist U-49,619 and leukotrienes (LI) B₄, C₄ and D₄ at concentrations ranging from 10–15 to 10–5M. PGE₂, LTD₄ and TXB₂ did not alter hypothalamic CRH secretion. On the other hand, the remaining eicosanoids tested induced a significant increase of hypothalamic CRH secretion (p < 0.05). The concentration of 10-nM dexa-methasone inhibited the effect of stimulatory eicosanoids on CRH secretion. The CRH response to U-49,619 was completely prevented by the TXA₂ receptor antagonist SQ-29,548. The latter also inhibited serotonin (5-HT)-, acetylcholine (ACh)- and PGF2α-induced CRH release. Indomethacin was capable of blocking the secretion of CRH induced by 5-HT and ACh. In addition, PGE₂ inhibited the increase of CRH secretion induced by PGF2α, 5-HT and ACh. These findings suggest that eicosanoids may be involved in the regulation of hypothalamic CRH secretion, either as autocrine/paracrine or as endocrine factors.