Antidiuretic Hormone in the Urine and Pituitary of the Kangaroo Rat. ∗

Abstract

Summary

The kangaroo rat (Dipodomys merriami) excretes large amounts of antidiuretic hormone in the urine (up to 50 milli-units per ml). The presence of this high concentration of hormone is believed to be related to the ability of this desert rodent to excrete the most concentrated urine of any mammal and to reflect a correspondingly high rate of secretion of antidiuretic hormone by the posterior pituitary. In 2 other mammals, the dog with powerful osmotic stimulation of the cerebrum, and the laboratory rat (Long-Evans strain) deprived of water for 48-72 hours, the maximum concentration of hormone in the urine is about 6 m.u. per ml. The hormone in kangaroo-rat urine undergoes sedimentation in the ultracentrifuge and thus resembles endogenous antidiuretic hormone in canine urine. The pituitary of kangaroo rats contains more antidiuretic hormone than that of normal laboratory rats although the latter are 5 to 6 times larger. After 72 hours of thirst the laboratory rat's pituitary contains an increased amount of hormone. Each microgram of fresh posterior lobe contains about 0.9 m.u. of antidiuretic hormone in kangaroo rats and about 0.3 m.u. in normal laboratory rats.