INFLUENCE OF THYROID STATUS ON WATER METABOLISM AND SURVIVAL OF NORMAL AND DEHYDRATED DESERT RODENTS MERIONES LIBYCUS

The relationship between thyroid status and resistance to water depriv ation in a desert rodent, Meriones libycus, has been studied in normal , radiothyroidectomized (Tx), and thyroidectomized T4-supplemented (1. 5 mu g T4/day) (Tx + T4) animals. In animals given free access to wate r, 1 month after thyroidectomy water influx and efflux decreased 3-fol d. This decrease was partially corrected after 5 days of T4 administra tion. Thyroidectomy did not modify urinary osmolality nor affect survi val. In dehydrated animals, the body weight decreased (about 15%) over 2 weeks in all groups and then stabilized. Water flux decreased sharp ly in normal or Tx + T4 animals during the 1st week and then stabilize d. A further decrease of water flux occurred in hypothyroid animals, w hich continued over 4 weeks, when fluxes were half those of normal or Tx + T4 animals. The urinary osmolality increased equally sharply in t he three groups, at least during the first 5 days of dehydration when sampling was possible. Whereas dehydrated normal and Tx + T4 animals s urvived at least 7 weeks, 70% of Tx animals had died after 4 weeks and none survived more than 7 weeks. The daily metabolic energy intake wa s estimated from water flux and metabolic water of the dietary barley. After 4 weeks, when water influx represented only metabolic water fro m food, metabolic energy intake decreased 2.5-fold in hypothyroid comp ared with normal or Tx + T4 animals. This low metabolic energy intake led to a trend of body dehydration, hypothermia, and death. Thus, alth ough an effect of thyroidectomy on survival of hydrated animals beyond 4 weeks cannot be excluded, we infer that thyroid hormones play a sig nificant role in the survival of desert rodents under conditions of hy dric stress. (C) 1997 Academic Press