Hypertonic saline solution treatment of uncontrolled hemorrhagic shock (UCHS) leads to increased bleeding from injured vessels, fall in arterial blood pressure, and increased mortality. The effect of dehydration induced by either water deprivation or heating on this response was studied in rats. The animals were divided into four groups: group 1 (n = 32), normal rats; group 2 (n = 30), water deprivation for 12 hours; group 3 (n = 30), heating at 37 degrees C for 5 hours; and group 4 (n = 30), heating as in group 3 and water deprivation as in group 2. UCHS was induced in all rats by 20% resection of the animals' tail. The rats were then divided into four treatment subgroups: group a was untreated, group b was treated after 15 minutes with 5 mL/kg NaCl 7.5% hypertonic saline (HTS), group c was treated after 15 minutes with 41.5 mL/kg NaCl 0.9% large volume normal saline (LNS) and group d was treated after 15 minutes with HTS + LNS. Tail resection in group 1a resulted in bleeding of 4.9 +/- 0.3 mL, and fall in mean arterial pressure (MAP) to 50 +/- 3 mm Hg (p < 0.001). Blood loss and fall in hematocrit in groups 2, 3, and 4 was significantly lower than in group 1. The fall in MAP and pulse rate was similar in all four groups.(ABSTRACT TRUNCATED AT 250 WORDS)