p-Hydroxymercuribenzoic acid inhibits arachidonic acid esterification into two distinct pools and stimulates insulin release in intact rat islets

SA Metz

Activation of an islet phospholipase A2 may contribute to glucose- induced insulin release. In order to simulate the accumulation of the resultant hydrolytic products (arachidonic acid, AA; its lipoxygenase- derived oxygenation product 12-hydroxyeicosatetraenoic acid; and lysophospholipids) without many of the other concomitants of beta cell activation, we studied the effects on intact rat islets of p- hydroxymercuribenzoic acid (PHMB), which inhibits the reacylation of lysophospholipids with AA in other cell types. PHMB inhibited in a dose- responsive fashion (-90% at 500 microM) the incorporation of [3H]AA into a "basal" pool or pools whose release and reuptake mechanisms appeared to be largely energy- and Ca++-independent (resistant to inhibition by mannoheptulose, antimycin A or CoCl2); reciprocally, islets prelabeled with [3H]AA accumulated an increased amount of [3H]- 12-hydroxyeicosatetraenoic acid (twice basal at 200 microM PHMB and three times basal at 500 microM) when reacylation of any [3H]AA released basally at 1.7 mM glucose was inhibited. PHMB also blocked (by up to 99% at 500 microM) the incorporation of [3H]AA into a functionally defined, glucose-stimulated compartment of fatty acid (tightly coupled to the islet 12-lipoxygenase) whose release and reuptake required metabolic energy and Ca++. It was also demonstrated that PHMB inhibited the esterification of [3H]AA (at low or high glucose concentrations) into specific phospholipids in islet membranes. In parallel with these alterations in lipid metabolism, PHMB caused rapid, potent and reversible increments in insulin release with a threshold concentration (about 25 microM) identical to that inhibiting AA fluxes. PHMB both initiated release (at 1.7 mM glucose) and potentiated the effects of islet fuels (16.7 mM glucose or 15 mM alpha- ketoisocaproic acid). Thus, pharmacologic manipulation of the AA reuptake mechanism is a new approach to unmask potential roles in insulin release of phospholipid hydrolysis products from different lipid pools and in the absence or presence of phospholipase A2 activation.

Volume 238, Issue 3, pp. 809-818, 09/01/1986
Copyright © 1986 by American Society for Pharmacology and Experimental Therapeutics