Effects of Hypophysectomy and Cell Isolation on the Transport of L-Arabinose by Adipocytes*

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Abstract
Hypophysectomy decreased the basal rate of glucose metabolism in segments of epididymal fat studied in vitro and lowered their maximum capacity to use glucose. Hypophysectomy changed neither the sensitivity to insulin nor the magnitude of the response when the results were expressed relative to the basal rate of glucose metabolism. Adipocytes isolated from both hypophysectomized and normal rats exhibited a higher basal rate of glucose metabolism than cells remaining in situ in the contralateral tissues, but this consequence of cell isolation was more pronounced for adipocytes of hypophysectomized than normal rats. Glucose metabolism could not be further increased by exposure of the adipocytes of hypophysectomized rats to insulin, whereas insulin produced a 3- to 5-fold stimulation of glucose oxidation in normal adipocytes. The effects of insulin and hypophysectomy on the transport of the nonmetabolizable sugar L-[1-14C]arabinose in tissue segments and isolated adipocytes were also studied. Uptake of L-arabinose was usually more rapid in segments of epididymal fat of normal rats than in segments of tissue obtained from hypophysectomized rats and was significantly accelerated by insulin in both groups. Uptake of L-arabinose was more rapid than normal in adipocytes isolated from hypophysectomized rats and, like glucose metabolism, could not be accelerated by insulin. The same concentration of insulin markedly promoted arabinose uptake in normal adipocytes. Efflux of L-arabinose from segments of tissue from hypophysectomized rats was twice as rapid as that from normal tissue and, in contrast with the rate of efflux from normal tissues, was not accelerated by insulin. Apparently, in the absence of pituitary secretion, sugar transport in the adipocyte membrane may be asymmetrical. Evidently hypophysectomy renders adipocytes more susceptible than normal to the cell isolation procedure which maximally accelerates glucose utilization and inward transport of arabinose in these cells.