AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 6 1103-R1108, Copyright © 1986 by American Physiological Society
Effect of autonomic agents on renin release in the turtle, Pseudemys scripta
M. D. Cipolle, J. E. Zehr and G. A. Reinhart
Experiments were conducted in the freshwater turtle, Pseudemys scripta, to
study the effect of autonomic agents on the control of renin in this
primitive species. The unique finding in these studies was that, unlike
mammals, isoproterenol infusion fails to increase renin activity even
though heart rate and arterial pressure patterns indicated that systemic
responses were similar to that in mammals. On the other hand, acetylcholine
(ACh) infusion resulted in a prompt threefold elevation (P less than 0.01)
of renin activity. This response was blocked by propranolol but not
atropine. Other experiments demonstrated that ACh elicited a prompt
elevation of circulating norepinephrine and epinephrine in these turtles
and led to the hypothesis that the renin response to ACh was secondary to
the release of endogenous catecholamines. This hypothesis was supported by
the fact that, in reserpinized turtles, ACh failed to elicit the usual
renin response. Further evidence stemmed from the fact that epinephrine
administration led to a prompt fourfold increase (P less than 0.01) in
renin, which could be blocked by propranolol. On the other hand,
phenoxybenzamine failed to block the response under identical conditions.
Taken as a whole, these data suggest that in this primitive species renin
activity is elevated by endogenous catecholamines even though
isoproterenol, a classical beta-adrenergic agonist, is without effect.
These data illustrate again the need for caution when assuming analogy when
comparing responses in primitive species with that of mammals.
