Type of dietary fat alters rat liver cell responsiveness to vasopressin

Abstract

The objective of this work was to determine if rat liver cell responsiveness to the phosphoinositide cascade agonist vasopressin was influenced by the source of dietary fat. Male Sprague-Dawley rats (185–200 g) were maintained for 21 days on a diet containing 20% metabolizable energy as safflower oil, tripalmitin, or menhaden fish oil. Freshly isolated rat hepatocytes were maintained for 20 minutes in a suspension media that contained 0, 0.1, 0.25, 0.5, 1.0, or 10 nmol/L arginine-vasopressin. Hepatocyte responsiveness to vasopressin was assessed by the activation of glycogen phosphorylase a activity and glucose output. Dietary fat significantly ( P < 0.05) altered hepatocyte vasopressin responsiveness. Relative to hepatocytes isolated from rats adapted to the safflower oil diet, hepatocytes from rats fed the menhaden oil or tripalmitin diets displayed a significant ( P < 0.05) reduction in vasopressin-mediated glycogen phosphorylase activation and a reduction ( P < 0.05) in hepatocyte glucose production. Stimulation of glycogen phosphorylase a activity and the glucose output by vasopressin did not differ between the tripalmitin and menhaden oil dietary groups. The level of glycogen phosphorylase a activity in non-vasopressin treated cells was unaffected by type of dietary fat. Our data indicate that depletion of ( n-6) fatty acids from membrane phospholipids is associated with reduced hepatic responsiveness to vasopressin.