AJP - Regulatory, Integrative and Comparative Physiology, Vol 237, Issue 3 210-R216, Copyright © 1979 by American Physiological Society
Autonomic cardiovascular control during submergence and emergence in bullfrogs
R. S. Lillo
Unanesthetized bullfrogs were involuntarily submerged for 25 min in
air-saturated water at 21 degrees C. Significant bradycardia was observed
while systemic blood pressure was maintained or slightly elevated. Upon
emergence, heart rates immediately returned to presubmergence levels or
higher. Similar responses were observed in frogs allowed to make voluntary
dives in an experimental tank. Heart rates of vagal-blocked (atropine)
frogs did not change during submergence or emergence. beta-Adrenergic
blockade (propranolol) had little effect on the magnitude of heart rate
decrease during submergence or its increase upon emergence. After
alpha-adrenergic blockade (phentolamine), frogs developed diving
bradycardia while undergoing a fall in systemic blood pressure. It is
concluded that, in bullfrogs, 1) bradycardia during submergence is entirely
due to increased vagal activity, 2) the immediate cardiac rate increase
upon emergence apparently results from a decrease in vagal tone; and 3)
there appears to be no substantial reciprocal sympathetic influence on
heart rate during alterations in vagal tone.
