AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 6 1363-R1370, Copyright © 1990 by American Physiological Society
Acid-base-electrolyte balance responses to catecholamine antagonists in Ambystoma tigrinum
D. F. Stiffler, M. E. Kopecky, M. L. Thompson and R. G. Boutilier
Biological Sciences Department, California State Polytechnic University, Pomona 91768.
Neotenic larval Ambystoma tigrinum were subjected to hypercapnia (3% CO2,
22 Torr) for 24 h under different conditions: alpha-adrenergic blockade
using phentolamine, beta-adrenergic blockade using propranolol, and sham
treatments. The sham animals were able to carry out a partial extracellular
pH compensation that consisted of an increase in extracellular [HCO3-].
Animals treated with catecholamine antagonists did not compensate to the
same extent. Analysis of plasma samples by high-performance liquid
chromatography with electrochemical detection revealed a significant
increase in circulating norepinephrine, but not epinephrine, during the
high-CO2 exposure. Measurements of cutaneous ion transport showed that
beta-antagonists block the increased Na+ influx associated with
hypercapnia, whereas alpha-antagonists inhibited the decrease in cutaneous
Cl- influx that is also associated with respiratory acidosis. Additionally,
both alpha- and beta-blockers inhibited the increase in transcutaneous
potential difference that accompanied the respiratory acidosis. The results
are consistent with a role for circulating catecholamines in compensatory
ion transport responses to respiratory acidosis in this species.
