Modification of Sucrose Adaptation in the Rat

Rats injected intraperitoneally (IP) with hypertonic sucrose solutions adapt to subsequent reexposures to the disaccharide by increasing 1) volume output of urine, 2) sucrose concentration of urine and 3) fraction of the injected load excreted within a 6-hour test period(1). Similar experiments employing intraarterial (IA) loading of the sugar demonstrated that the adaptation generated under these circumstances is qualitatively different from that induced by IP administration. Under conditions of IA infusion, re-exposure to sucrose causes a reduction in both total urine volume and the fraction of the load excreted in 6 hours, with no demonstrable difference in sucrose concentrations of urine(2). To determine whether the reductions in urine volume and sucrose excretion after a second IA infusion persist beyond the 6-hour period, experiments were conducted to examine the completeness of sucrose excretion over 24 hours. In addition a series of repeated IA loadings was performed to determine if the adaptive response, once established, was further modified.

Methods. Three groups of male albino rats (Holtzman, 188–239 g) were infused with 2.0 ml/100 g body weight (b.w.) of a 1.46 M solution of sucrose through a chronically indwelling catheter. The tip of the catheter rested in the aortic arch. Prior experiments demonstrated that this load given IA produced a maximum adaptive response with respect to total urine and sucrose excreted. At the time of loading animals were un-anesthetized and under moderate restraint(3). All urine voided within the 24-hour period following infusion was collected and analyzed for sucrose (4). Infusions of the same relative load were repeated in each group at 6-day intervals and totaled 4 exposures per group. Urine volumes excreted and urinary sucrose concentrations were measured following each exposure. Data were treated by analysis of variances of independent group means.

Results. A comparison of the sucrose excretion after 6 and 24 hours in unadapted and adapted rats is given in Table I. Unadapted rats (first exposure) excreted most of the load (92.8%) within the 6-hour period following the infusion and increased the fraction of the total load excreted in 24 hours by merely 0.7%. In contrast, adapted animals (second exposure) excreted only 78.5 ± 4.1% (S.D.) of the infused load within 6 hours and 85.9 ± 4.2% within 24 hours of infusion. Twice exposed animals therefore excrete a standard load more slowly and less completely than do unadapted rats.