In utero extracellular dehydration modifies thirst in neonatal rats

The main aim of this study was to investigate the effect of maternal extracellular dehydration during pregnancy in rats on the development of thirst mechanisms in the offspring. Pregnant rats underwent three episodes of extracellular dehydration induced by injecting s.c. 15 ml/kg b.w. of a 20% wt/vol solution of polyethylene glycol (PEG) in saline. The treatment given on days 14, 17 and 20 postconception is thought to induce endocrine and natriophilic responses similar to those elicited by vomiting. The offspring were tested for their responses to three different thirst stimuli at 2, 4 and 6 days of age. Like the controls, the offspring from PEG-treated mothers responded to beta stimulation by isoproterenol at 6 days of age. However, they failed to respond to cellular dehydration (NaCl hypertonic injection) at 2 days of age or to extracellular dehydration by PEG on day 4. In conclusion, offspring exposed to in utero extracellular dehydration do not respond to cellular dehydration at 2 days of age or to extracellular dehydration at 4 days of age, whereas control pups had already developed an appropriate response to these stimuli. According to these results, it therefore seems that in utero conditions determine the development of adaptive thirst responses in offspring.