AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 2 382-R388, Copyright © 1992 by American Physiological Society
Effect of hypotension and hyperosmolality on vasopressin and ACTH responses to hypoglycemia in conscious dogs
H. Raff, P. E. Papanek and A. W. Cowley Jr
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226.
The purpose of these studies was, first, to determine whether hypertonic
saline (HS) infusion or nitroprusside (NiPr)-induced hypotension augments
the vasopressin (AVP) and adrenocorticotropic hormone (ACTH) responses to
insulin (Ins)-induced hypoglycemia and, second, to determine whether
neurohypophysectomy could attenuate the augmentation. Conscious, male dogs
(n = 8) underwent two different types of experiments. In the first, Ins was
preceded by either a 30-min infusion of normal saline (control) or HS to
raise plasma osmolality and AVP. HS augmented the AVP response but
diminished the ACTH response to Ins. In the second group of experiments,
Ins was preceded by a controlled decrease in mean arterial pressure using
NiPr, which led to an increase in AVP and ACTH. The initial ACTH and AVP
response to Ins was augmented by NiPr, but this early augmentation was not
sustained. Neurohypophysectomy attenuated the early augmentation of the
ACTH response to Ins by NiPr, but did not alter the final ACTH level
achieved. We conclude that HS augmented the AVP but inhibited the ACTH
response to Ins probably because of expansion of plasma volume. Concomitant
hypotension led to an augmentation of the early but not sustained AVP and
ACTH response to Ins. Neurohypophysectomy eliminated this augmentation,
suggesting a role for AVP from the neural lobe in the early ACTH response
to combined hypotension and Ins-induced hypoglycemia.
