AJP - Endocrinology and Metabolism, Vol 260, Issue 1 E154-E161, Copyright © 1991 by American Physiological Society
Intravenous acid infusion stimulates ACTH secretion in sheep
C. E. Wood and A. Isa
Department of Physiology, University Florida College of Medicine, Gainesville.
Both respiratory and metabolic acidemia stimulate the secretion of
adrenocorticotropic hormone (ACTH), vasopressin, and renin. The present
study was designed to test the blood pressure, heart rate, and endocrine
responses of conscious sheep to low-rate infusions of H+. We infused HCl
and lactic acid at a rate of 500 mueq/min into the inferior vena cava of
seven chronically catheterized adult sheep. Control experiments in six
sheep consisted of infusion of HCl at a rate of 100 mueq/min. Only the 500
mueq/min infusion of HCl stimulated reflex responses. This infusion
increased mean arterial blood pressure and plasma ACTH concentration but
transiently decreased blood pH only after the onset of the reflex
responses. Heart rate appeared to increase initially but then decreased.
Overall, the apparent changes in heart rate were not statistically
significant. None of the infusions significantly altered plasma renin
activity or vasopressin concentration. We speculate that heart rate, plasma
renin activity, and vasopressin may have been partially inhibited by the
increase in blood pressure. However, the lack of effect of lactic acid
suggests that the HCl stimulated reflex ACTH and blood pressure responses
via a mechanism not related to the concentration of the acid in the
infusate or to the total amount of acid infused. It is possible that HCl,
but not lactic acid, stimulated release of a humoral agent that stimulated
ACTH secretion directly or reflexly. The results do not appear consistent
with the stimulation of a venous chemoreceptor sensitive to H+.
