Effects of Dehydration on Metabolic Rate and Fluid Distribution in the Jackrabbit, Lepus californicus

Abstract

Chronic water restriction resulted in a 30% decrease in metabolic rate and an over 50% decrease in evaporative loss in jackrabbits with no change in body temperature. Thus, evaporative cooling as a means of maintaining body temperature was minimized. Accommodation to measuring technique may account for part of the decrease in O2 consumption. Fractional water content increased, and solids decreased associated with a 10.6% weight loss due to chronic restriction, whereas plasma and extracellular volume decreased in proportion to weight loss. The biological half-life of water, T½, was increased from 5.8 to 11.6 days while water exchange decreased from 13.0% to 5.9% of the body water per day. In acutely dehydrated jackrabbits (3–5 days without water at 25 C), all body fluid compartments lost equal proportions (10.7%) with no change in metabolic rate. Similarly, oxygen consumption was unaffected, and plasma volume decreased in proportion to weight loss (5.5%) in jackrabbits acutely dehydrated in hyperthermic conditions (12–14 h at 35–40 C). The jackrabbit is similar to several other desert species in that it minimizes the loss of plasma volume when exposed to dehydration. Evans Blue space of 8.6% of body weight was shown to be a 36% overestimation of plasma volume as measured with iodinated (125I) albumin (6.3% of body weight).