Acclimatization of rats to moderate heat: body water distribution and adaptability of the submaxillary salivary gland.

Changes in plasma and extracellular fluid volumes were studied in rats during exposure to 35 degree C for 28 days. In addition the adaptability of the submaxillary salivary gland to these conditions was studied by measuring its weight, plasma and extracellular volumes during the acclimatization period. Major changes in parameters studied occurred during the first 10 days of acclimatization. Total plasma volume on day 10 was less than in controls (P = 0.02), but from then on returned to normal values. Extracellular fluid volume was expanded for most of the period. An enlargement of the submaxillary salivary gland was present during the whole period, but maximal enlargement was observed on day 10 (42%). On day 28 the gland was 14% larger. No changes in plasma and extracellular volumes of the gland were observed. It appears that due to redistribution of the blood pool at the beginning of heat exposure, plasma and extracellular volumes remain constant.