AJP - Endocrinology and Metabolism, Vol 249, Issue 6 634-E638, Copyright © 1985 by American Physiological Society
Pituitary and adrenal hormone responses to naloxone in euhydrated and dehydrated dogs
C. E. Wade
To assess the role of endogenous opioids in the secretion of pituitary and
adrenal hormones, we injected intravenously the antagonist naloxone (1
mg/kg) into six dogs, euhydrated or dehydrated. Plasma renin activity
(PRA), osmolality, and concentrations of adrenocorticotropic hormone
(ACTH), cortisol, aldosterone, vasopressin, Na+, and K+ were measured.
Dehydration elevated (P less than 0.05) PRA, vasopressin, osmolality, and
Na+. Thirty minutes after injection of naloxone, osmolality, Na+, K+,
hematocrit, and plasma protein were not altered. Naloxone-induced
elevations of ACTH (25 +/- 10 and 22 +/- 4 pg/ml) and cortisol (4.8 +/- 1.0
and 5.1 +/- 1.0 micrograms/dl) were similar during euhydration and
dehydration, respectively. The increase in aldosterone due to naloxone was
greater after euhydration (7.7 +/- 3 ng/dl) than during dehydration (2.3
+/- 0.8 ng/dl). Naloxone increased vasopressin by (5.3 +/- 2.8 microU/ml)
during dehydration but not during euhydration. Intravenous hypertonic
saline infusions showed that naloxone potentiates the osmotic release of
vasopressin. Our results indicated that dehydration did not alter the
inhibitory role of opioids in regulation of ACTH and cortisol but
suppressed the inhibition of aldosterone secretion. Our findings also
showed that opioids inhibit secretion of vasopressin during dehydration by
decreased responsiveness to osmotic stimulation.
