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 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.
Chaouacha-Chekir
R B
RB
Laboratoire de Physiologie, Faculté de Médecine Dentaire 5000 Monastir, Tunisie.
Leloup
J
J
Lachiver
F
F
D000818:Animals; D001835:Body Weight / Q000502:physiology; D015331:Cohort Studies; D005260:Female; D005849:Gerbillinae / Q000502:physiology*; D007274:Injections, Intraperitoneal / Q000662:veterinary; D008297:Male; D009994:Osmolar Concentration; D013961:Thyroid Gland / Q000502:physiology*; D013965:Thyroidectomy / Q000662:veterinary; D013974:Thyroxine / Q000008:administration & dosage / Q000494:pharmacology*; D013997:Time Factors; D014556:Urine / Q000737:chemistry / Q000502:physiology; D014867:Water / Q000378:metabolism*; D014868:Water Deprivation / Q000502:physiology*
D014867:Water; D013974:Thyroxine