Adaptation to sucrose loading in the rat.

Abstract

Four groups of unanesthetized rats were infused with standardized volumes of 1.46 M (50% w/v) sucrose solutions through chronically indwelling arterial catheters. The excretion of water and solutes was measured during the following 6 hours. Five days later, after the animals had returned to their pre-loading weights, each group was infused again with the same load given initially. After the second loading, a pattern of excretion of water and solutes was observed which was different from that elicited by the first loading. The adaptations manifested after a second loading were characterized principally by (a) a smaller total volume excretion of urine (milliliters per 100 g body weight), (b) the excretion of a smaller fraction of the infused load, (c) an earlier inhibition of the initial diuresis, and (d) the production of a more concentrated urine. It is suggested that the initial loading conditions generate a physiological adaptation which promotes the water conservation mechanisms of the animal. This may involve a greater sensitivity of the adapted animal to antidiuretic hormone. It was further observed that the characteristics of the adaptations generated by intra-arterial infusion are qualitatively different from those produced by intraperitoneal infusion. This suggests that the ability of hypertonic solutions to evoke adaptive responses is dependent on the route through which such solutions are given.