title: The effects of thyroxine on metabolism and water balance in a desert-dwelling rodent, Merriam's kangaroo rat (Dipodomys merriami).
abstract: Desert-dwelling mammals such as Merriam's kangaroo rat (Dipodomys merriani) need to conserve both energy and water to survive desert conditions characterized by aridity and low productivity. The thyroid hormone thyroxine increases both basal metabolic rate and urinary water loss in mammals. Increases in basal metabolism and urinary water loss are likely to be detrimental to D. merriami, therefore the regulation of this hormone may be important. To examine the effects of thyroxine in this species, we implanted adult kangaroo rats with pellets designed to release specific doses of thyroxine at a constant rate for 90 days or a placebo pellet. We measured plasma thyroxine concentration, basal metabolic rate, food consumption, urine concentration and water loss in all implanted animals. Thyroxine implants significantly increased both plasma thyroxine and basal metabolic rate in a relatively dose-dependent manner. In response to thyroxine. kangaroo rats increased food consumption only slightly, but this small increase was sufficient to compensate for their elevated metabolic rates. Neither urine concentration nor water loss varied among treatment groups. Thyroxine increased energy expenditure but not water loss in this species.
authors.affiliation: Ecology, Evolution, and Conservation Biology Program, University of Nevada, Reno 89557, USA. lsbanta@scifac.indstate.edu
authors.forename: Marilyn R
authors.initials: MR
authors.lastname: Banta
authors.forename: Dale W
authors.initials: DW
authors.lastname: Holcombe
mesh_terms: D000818:Animals; D001481:Basal Metabolism / Q000187:drug effects* / Q000502:physiology; D003889:Desert Climate; D004173:Dipodomys / Q000502:physiology*; D004435:Eating / Q000187:drug effects / Q000502:physiology; D007671:Kidney Concentrating Ability / Q000187:drug effects / Q000502:physiology; D013974:Thyroxine / Q000097:blood / Q000494:pharmacology*; D014882:Water-Electrolyte Balance / Q000187:drug effects* / Q000502:physiology
chemical_list: D013974:Thyroxine