Physiological effects of water stress on two species of heteromyid rodents

Abstract

Few studies of desert rodents (Mammalia: Heteromyidae) have been designed to address the adaptive role of arginine vasopressin (AVP). The objectives of this study were to determine the effects of water stress on plasma and pituitary arginine vasopressin (AVP) and the Impact of increased hormone levels on blood and urine parameters. Adult males of two sympatric species of heteromyid rodents (Dipodomys ordii and Chaetodipus hispidus) were live-trapped on the Llano Estacado of western Texas and acclimated to laboratory conditions. Experimental groups, which were fed different diets for 15 days, included: water control (grain, carrots, and water); baseline control (grain and carrots); and water-stressed (grain only). Plasma and whole pituitary AVP concentrations, urine and plasma osmolalities, hematocrit, and weight changes were each compared among experimental groups. Kidneys were processed for AVP receptor studies. Two-way (species and treatments) analysis of variance for each variable revealed that the two species reacted differently to the treatments. Water-stressed C. hispidus had significantly greater concentrations of pituitary AVP (1.017 µg AVP/mg) compared to concentrations in D. ordii (0.088 jig AVP/mg). Dipodomys ordii had higher plasma AVP levels compared to those in C. hispidus. Urine osmolality increased significantly with dehydration in both species, but no significant difference existed between species. Values ranged from 1878 mOsm/kg In water controls to 3535 mOsm/kg In water-stressed C. hispidus, and from 1158 mOsm/kg to 3267 mOsm/kg for the same treatments in D. ordii. Compared to both control groups, values for plasma osmolality were higher in water-stressed D. ordii but lower in 0. hispidus. Hematocrit increased in both species with dehydration. Limited data indicated that receptor concentration in all treatment groups was higher for C. hispidus than for D. ordii. Together, data indicate that the aridadapted D. ordii appears to be more stressed by 15 days of dehydration than the more mesic-adapted C. hispidus