Acute dehydration: Body water distribution in acclimated and nonacclimated Psammomys obesus

Body water distribution after 'acute dehydration' treatment (37°C) was studied in Psammomys obesus before and after acclimation at 34 ± 1°C for 16-18 days. Determinations of water compartment volumes were performed on anaesthetized (thiopental sodium) nephrectomized animals. Plasma volume (PV) and extracellular volume (ECV) were measured by T-1824 and [¹⁴C]inulin, respectively. Total body water was determined after desiccating the animals. Albumin outflux was calculated from the half-life (T1/2) of T-1824 and total plasma albumin mass. Nonacclimated animals conserved PV as long as dehydration did not exceed 10-11% loss of body wt. This conservation was at the expense of ECV and was associated with diminished albumin outflux (T1/2) T-1824 approached infinity). With increased dehydration PV retention failed and a resumption of albumin outflux occurred. Acclimation resulted in diminished albumin outflux in both control and dehydrated animals (T1/2) T-1824 approached infinity). Most of the water lost during dehydration was intracellular origin. It was concluded that reduction in permeability of the capillary bed during dehydration and acclimatization plays an important role in PV and ECV regulation.