The Control of Salt Appetite in Wild Rabbits during Lactation*

The factors which result in high voluntary intakes of 500 meq/liter solutions of NaCl, KC1, CaCl2> and water in the wild rabbit [Oryctolagus cuniculus (L)] have been investigated. The NaCl intake of does from which the infants were removed at birth increased for 3-4 days, and during the first 5 postpartum days was indistinguishable from that occurring during the same phase of normal lactation. The intake, as in suckled animals, was dependent on the number of young born. The elevated intakes of KC1, CaCl2) and water present during late pregnancy and maintained or further increased in lactation did not continue after early little removal Commencing at the end of pseudopregnancy, treatment with a combination of physiological amounts of ACTH (4 IU/day), PRL (50 IU/day), and oxytocin (200 mU/day) produced increases in NaCl, KC1, CaCl2, and water intakes comparable to those present during lactation. Similar results were obtained when this hormone riplet was given to male or female rabbits which had been pretreated for 28 days with 12.5 ng estradiol and 1 mg progesterone/day. All increases were smaller when the hormone triplet was given to normal rabbits or when PRL was not included. The level of response established during the three-hormone regime was maintained if ACTH alone was then administered, but was not maintained when PRL and oxytocin were used The findings show that the general pattern of increased water and electrolyte intake of pregnancy and lactation may be closely replicated by the appropriate sequential administration of jointly sufficient and severally necessary physiological amounts of four or perhaps five steroid and peptide hormones which are required for maintenance of pregnancy and the establishment and continuation of normal lactation. It is proposed that the findings suggest a behavioral effect of reproductive hormones of important survival value for herbivorous animals in the large areas of the earth which are sodium deficient.