Arachidonic acid metabolites and chloride secretion in rabbit distal colonic mucosa

Abstract

The relationships between arachidonic acid (AA) metabolism and chloride secretion were investigated in mucosal preparations of rabbit distal colon. Tissues displayed a significant cyclooxygenase activity already in nonstimulated conditions and incubation with exogenous AA and calcium ionophore A23187 produced a predominant prostaglandin F2 alpha (PGF2 alpha) profile [PGF2 alpha greater than PGE2 greater than thromboxane B2 (TxB2) greater than 6-keto-PGF1 alpha] as assessed by HPLC of tissue homogenates, whereas 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) was not detected in AA- or A23187-stimulated tissues. Radioimmunological assays showed that PGE2 synthesis was time dependent, plateaued at 10 min, and proceeded at rates 15-20 times over TxB2 and 6-keto-PGF1 alpha. Among the PGs produced by colonic mucosa, only PGE2 and, to a lower extent, PGF2 alpha were found to stimulate chloride secretion and cAMP synthesis. Pretreatment with 10 microM 5,8,11,14-eicosatetraynoic acid, a cyclo- and lipoxygenase inhibitor, prevented AA-induced chloride secretion and PG and cAMP synthesis with the same strength as the cyclooxygenase inhibitor indomethacin. No effects were found after preincubation with nordihydroguaiaretic acid, a lipoxygenase blocker with moderate cyclooxygenase inhibitory properties, and caffeic acid, a lipoxygenase inhibitor. 5-HETE (5 microM) had no effect on short-circuit currents (Isc) and chloride transport, but it significantly reduced the increase in Isc, chloride secretion, and PGE2 synthesis elicited by AA or A23187. Platelet-activating factor, reported to stimulate rabbit colon Isc through an indomethacin-sensitive pathway, was not detected at concentrations as low as 10(-10) M.