The renin-angiotensin-aldosterone system and the prostaglandins (PG's) play important roles in the maintenance of blood pressure and salt and water balance. The proposed studies will investigate the interactions between angiotensin II (AII) and metabolites of arachidonic acid in the regulation of aldosterone secretion by adrenal zona glomerulosa cells. Specifically, the hypothesis will be tested that AII stimulates the synthesis of metabolite(s) of arachidonic acid in the adrenal cortex and the metabolite(s) modifies the steroidogenic action of the peptide. Initial studies suggested that PG's were involved in the stimulation of aldosterone synthesis since PG synthesis inhibitors reduced AII-induced steroidogenesis. However, subsequent findings have eliminated the PG's as possible mediators and implicated other metabolites of arachidonic acid. The adrenal cortex metabolizes arachidonic acid to PG's, hydroxyeicosatetraenoic acids (HETE's), epoxides (EET's) and several unknown compounds. These metabolites will be isolated by HPLC and identified by chemical modification and mass spectrometry. They will be tested for their ability to alter basal and stimulated steroidogenesis. In this regard, we have found that the adrenal synthesizes 12-HETE, 15-HETE, 11-HETE and 5-HETE. 12-HPETE and 5-HPETE, the precursors of the HETE's, stimulate aldosterone release in nM concentrations. Assays will be developed for metabolites that are biologically active in physiologically relevant concentrations. The relationship between aldosterone and metabolite release will be determined under several conditions in cells stimulated by AII to determine if the peptide stimulates the synthesis of the metabolite and if the concentrations of the metabolite are adequate to alter steroidogenesis. Comparisons will be made to ACTH and potassium which also stimulate aldosterone release. These studies will be repeated in the presence of inhibitors of arachidonic acid metabolizing pathways. Further studies into the biosynthesis, metabolism, site of action and mechanism of action of the metabolite will be performed.
