OBSERVATIONS ON THE EXCRETION OF WATER AND ELECTROLYTES IN THE DESERT RAT (DIPODOMYS SPECTABILIS SPECTABILIS M.) AND IN THE LABORATORY RAT

Abstract

SUMMARY: A comparison was made between two species of rodent, the banner-tailed kangaroo rat (Dipodomys spectabilis spectabilis M., a desert rat) and the laboratory rat. The sodium and potassium content of blood and muscle and the water content of muscle were similar and were affected in the same way by adrenalectomy. Antidiuretic activity of the blood and urine of the desert rat was higher than the published figures for the laboratory rat. Reference is made to unpublished work showing the capacity of the adrenal gland of the desert rat to synthesize cortisol and corticosterone (ratio 10:7) and aldosterone. Loads of water or saline or potassium chloride solution were given by stomach tube together with drugs and hormones (acetazoleamide, cortisone, anti-aldosterone compounds, vasopressin). The rate of excretion and the amount and composition of the urine were determined. Estimates were made of the rates of absorption from the gut and of glomerular filtration and these were of the same order in both species. The desert rat showed a characteristic delay in the excretion of water and saline, called the diuretic lag. Only potassium chloride was excreted promptly and the diuretic lag supervened when anti-aldosterone was also administered. In general, the desert rat is able to reabsorb water in situations which demand water excretion in the laboratory rat. In similar circumstances the desert rat reabsorbs proportionately more sodium and excretes more potassium than the laboratory rat. The factors which occasion the diuretic lag and its termination are discussed and the possible contribution of aldosterone considered.