Vasopressin Responses to Corticotropin Releasing Factor and Hyperosmolality in Conscious Dogs

We recently reported that ovine corticotropin releasing factor (CRF) infusion in conscious dogs elevated plasma vasopressin. The present study examines the vasopressin, adrenocorticotropic hormone (ACTH), and cortisol responses to CRF infusion (20 ng X kg-1 X min-1), to hypertonic saline infusion (NaCl 0.054 meq X kg-1 X min-1), and to simultaneous coinfusion of CRF and NaCl (CRF + NaCl) without (no-dex) or with (dex-treated) dexamethasone pretreatment in six conscious dogs (6-8 experiments/dog). CRF had no significant effect on plasma sodium or osmolality, blood pressure, or heart rate. NaCl increased plasma sodium from 146 +/- 1 to 151 +/- 1 meq/l and plasma osmolality from 298 +/- 3 to 305 +/- 3 mosmol/kg. Vasopressin increased significantly during CRF (2.1 +/- 0.5 to 4.8 +/- 1.1 pg/ml) and NaCl (1.9 +/- 0.3 to 5.0 +/- 0.8 pg/ml). Coinfusion of CRF and NaCl resulted in a response larger than the sum of the two infusions alone (3.0 +/- 1.6 to 31.4 +/- 18.5 pg/ml). The ACTH response to CRF (45 +/- 8 to 288 +/- 88 pg/ml) was not augmented by coinfusion with NaCl. DEX attenuated the vasopressin and ACTH responses to each infusion. We conclude that CRF-induced increases in vasopressin are augmented by a simultaneous osmotic stimulus. In addition, the plasma vasopressin responses to CRF and/or hypertonic saline infusion are inhibited by glucocorticoid pretreatment.