Hormonal factors influencing salt appetite in lactation.

Abstract

SummaryThe appetite of wild rabbits (Oryctolagus cuniculus (L)) for 500 mEq/1 solutions of NaCl, KCl, MgCl2, and CaCl2, was studied during daily injections of ovine prolactin, ovine growth hormone or synthetic oxytocin. The animals were individually caged and external sodium balances were made. Under all experimental conditions the animals were obtaining ample sodium from the food, as evidenced by a substantial urinary sodium excretion. Injection of 50 I.U. prolactin significantly increased NaCl intake from a control value of 0·4 mEq/day to 2·3 mEq/day during the course of injections. CaCl2 intake was also significantly increased. The mean daily intake of NaCl during the oxytocin treatment was 1·34 mEq/day, 21/2; times the control value. Water intake was reduced but there were no significant changes in the intakes of KCl, MgCl2 and CaCl2,. Growth hormone had no effect on electrolyte or H2O intakes.Previously reported work shows that a significant increase in NaCl intake occurs during lactation in the wild rabbit. The metabolic studies indicate that, as in lactation, the increase in NaCl intake witb prolactin and oxytocin occurs without any preceding change in urinary sodium excretion. The results suggest that the increase in NaCl intake in lactation is hormonal in origin and not caused by the sodium requirements of lactation.