Physiological increases in cortisol inhibit basal vasopressin release in conscious dogs

Glucocorticoid deficiency leads to elevated plasma vasopressin (AVP), while chronic endogenous hypercortisolism may inhibit osmotically stimulated AVP, suggesting that glucocorticoids may be feedback inhibitors of AVP secretion. We evaluated the effect of physiological increases in cortisol (65 mg/day iv) for 7 days on basal AVP and oxytocin (OT) in five conscious, male dogs. Cortisol increased from 1.3 +/- 0.1 to 5.0 +/- 0.8 micrograms/dl during infusion. Basal plasma AVP significantly decreased from 3.5 +/- 0.2 to 2.6 +/- 0.3 pg/ml during cortisol infusion. Plasma OT, osmolality, and sodium did not change while arterial pressure decreased (from 107 +/- 3 to 102 +/- 2 mmHg) on days 4 and 6. Increases in cortisol led to a physiologically significant, nonosmotic decrease in AVP. The effect was specific to AVP and independent of changes in arterial pressure. Glucocorticoid administration significantly decreased basal AVP within 24 h, which is comparable to the negative feedback control of adrenocorticotropic hormone. The inverse relationship between cortisol and AVP may account for the nonosmotic change in AVP in patients with disorders of glucocorticoid secretion.