Regulation of plasma antidiuretic hormone in the dehydrated kangaroo rat (Dipodomys spectabilis M.)

A sensitive and specific radioimmunoassay was used to measure plasma antidiuretic hormone (plasma arginine vasopressin, PAVP) concentrations in a conscious desert-adapted mammal, the banner-tailed kangaroo rat (Dipodomys spectabilis; 131 +/- 2.3 g body mass), during normal hydration and in response to progressive dehydration. Simultaneous measurements of PAVP and plasma osmolality (POSM) in these experiments permitted determination of the hypothalamo-neurohypophyseal system-osmoreceptor set point and sensitivity to extracellular hyperosmolality during dehydration. In normally hydrated kangaroo rats, acclimated to room temperature (20-24 degrees) and fed a dry grain diet, POSM and PAVP averaged 308.6 +/- 0.7 mosmol/kg H2O and 6.0 +/- 0.7 pg/ml (2.2 +/- 0.2 microU/ml), respectively (means +/- SE). In separate groups of animals subjected to 48, 96, 144, or 192 hr of dehydration, POSM and PAVP increased in a parallel linear manner with time to maxima of 329.7 +/- 2.4 mosmol/kg H2O and 68.8 +/- 4.4 pg/ml (24.9 +/- 1.6 microU/ml), respectively, at 192 hr of dehydration. Thus, a highly correlated and significant relationship between POSM and PAVP (r2 = 0.941, P less than 0.001) exists in dehydrated kangaroo rats, quantitatively defined by the linear regression equation PAVP (pg/ml) = 2.99 (POSM - 306.4), with an apparent osmotic threshold for AVP release at a POSM of 306.4 mosmol/kg H2O.(ABSTRACT TRUNCATED AT 250 WORDS)