RESUMO
The relationship between thyroid status and resistance to water deprivation in a desert rodent, Meriones libycus, has been studied in normal, radiothyroidectomized (Tx), and thyroidectomized T4-supplemented (1.5 microg T4/day) (Tx + T4) animals. In animals given free access to water, 1 month after thyroidectomy water influx and efflux decreased 3-fold. This decrease was partially corrected after 5 days of T4 administration. Thyroidectomy did not modify urinary osmolality nor affect survival. In dehydrated animals, the body weight decreased (about 15%) over 2 weeks in all groups and then stabilized. Water flux decreased sharply in normal or Tx + T4 animals during the 1st week and then stabilized. A further decrease of water flux occurred in hypothyroid animals, which continued over 4 weeks, when fluxes were half those of normal or Tx + T4 animals. The urinary osmolality increased equally sharply in the three groups, at least during the first 5 days of dehydration when sampling was possible. Whereas dehydrated normal and Tx + T4 animals survived 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 was estimated from water flux and metabolic water of the dietary barley. After 4 weeks, when water influx represented only metabolic water from food, metabolic energy intake decreased 2.5-fold in hypothyroid compared with normal or Tx + T4 animals. This low metabolic energy intake led to a trend of body dehydration, hypothermia, and death. Thus, although an effect of thyroidectomy on survival of hydrated animals beyond 4 weeks cannot be excluded, we infer that thyroid hormones play a significant role in the survival of desert rodents under conditions of hydric stress.
