Dehydration attenuates the acute natriuretic response to rat atriopeptin III (rAPIII)

The acute natriuretic response to atrial peptides (AP) is highly variable in anesthetized rats, and some rats are unresponsive. To determine if this response to AP was affected by dehydration, we measured hematocrit, plasma volume, and natriuresis (delta UNaV) after intravenous injection of 3 micrograms/kg of rat atriopeptin III (rAPIII) in anesthetized rats deprived of water for 0, 12, 20, 29, 44, and 68 hours. Data were compared with those from rats receiving 1.5 mg/kg furosemide (FU) after 0 and 68 hours without water. There were 10- and 3-fold decreases in delta UNaV following rAPIII and FU injection after 20 and 68 hours without water, respectively. Hematocrit increased and plasma and total blood volumes decreased after 12 hours of dehydration. Plasma volumes and delta UNaV were correlated (r = 0.64, p less than 0.05; r = 0.75, p less than 0.001) in the combined groups receiving rAPIII (n = 30) and FU (n = 10), respectively. These results demonstrate that a relatively short period of water deprivation (WD) and the resulting hemoconcentration in rats decreased their acute natriuretic response to diuretics. Thus, differences in water intake may account for some of the large variation in delta UNaV after exogenous administration of rAPIII.