VASOPRESSIN, CORTICOTROPIN-RELEASING FACTOR, AND PITUITARY-ADRENAL RESPONSES TO ACUTE COLD STRESS IN NORMAL HUMANS

Acute cold stress is a consistent stimulus to ACTH secretion in rats yet inhibits arginine vasopressin (AVP) in both rats and humans. We have studied the interrelationships of AVP, corticotrophin-releasing factor, and atrial natriuretic factor (ANF) in the hypothalamo-pituitary-adrenal response to acute cold stress in normal humans. Six healthy male volunteers deprived of food and fluid for 6 h, and minimally clothed, were studied in the early afternoon. After a 30-min period at 22 C, subjects were exposed to cold stress (4 C for 30 min), followed by a 30-min equilibration period at 22 C. By the end of the period of cold exposure there was a fall in plasma volume of 7.8 +/- 1.4% (mean +/- SEM), a significant increase in both systolic blood pressure (P = 0.0001) and in plasma norepinephrine level (P = 0.0001), but no change in plasma epinephrine or in plasma ANF. Plasma AVP levels fell significantly (P < 0.01) to reach a nadir at 5-10 min after cold exposure before returning to baseline levels. A significant fall in plasma cortisol levels occurred during the first 15 min of the baseline period and remained stable thereafter. No significant changes in plasma corticotrophin-releasing factor or ACTH occurred. These results suggest that cold inhibition of AVP release, presumably via afferent baroreceptor pathways, may act to reduce the response of the corticotrophs to a potentially noxious stimulus. Inhibition of AVP and/or ACTH during acute cold exposure are not dependent upon an increase in plasma ANF.