Effects of Prolactin in Vitro on Fatty Acid Synthesis in Rat Adipose Tissue

Abstract

In preliminary experiments we have shown that ovine prolactin in t&o stimulates the oxidation of glucose carbon to CO% by adipose tissue from normal rats fed ad Z&turn (1).This increased glucose utilization is accompanied by an increased incorporation of glucose carbon into long chain fatty acid (1).These effects in vitro of prolactin are qualitatively similar to those of insulin in thii same tissue (2).Further experiments which form the basis of this report indicate that the effects in vitro of prolactin on fatty acid synthesis in adipose tissue are dependent upon its primary effect8 on glucose metabolism.EXPERIMENTAL Male albino rata of the Wistar strain weighing between 125 and 150 g and fed Purina rat pellets (Ralston Purina Company) ad libitum were used throughout these studies.Alloxan diabetic rats were prepared by the rapid intravenous injection of 45 mg per kilogram of alloxan monohydrate after a 24hour fast; the animals were not used until at least 2 weeks after the administration of alloxan, and unless random blood glucose values exceeded 306 mg per 106 ml.Uniformly labeled glucose-CY4, glu-co%!-l-04, glucose-6-t", acetate-l-C14, and pyruvat&Wl4 were obtained from the Volk Radio-Chemical Company.These materials were chromatographically pure.Glucagon-free insulin was provided through the courtesy of Dr. W. R. Kirtley of the Lilly Research Laboratories.Ovine prolactin prepared by the Armour Laboratories was a gift of the Endocrinology Study Section of the National Institutes of Health.The animals were killed by decapitation and the epididymal fat pads removed as previously described (2) with the exception that the pads were placed directly into the incubation vessels without prior weighing.At no time were the pads exposed to chilled buffer.In each instance one of each pair of epididymal fat pads was used as a control in order to minimize effects due to the variability in baseline metabolic activity of adipose tissue from one animal to another.Incubation was carried out in Stanley-Tracewell vessels as previously described (1).The ves- sels containing the appropriate substrate in 3.0 ml of Krebs bicarbonate or Krebs phosphate buffer were placed in a Dubnoff metabolic shaker set at 37", 80 cycles per minute, and exposed to the proper gas phase before the animals were killed.