AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 1 1-R4, Copyright © 1986 by American Physiological Society
Effects of alpha-adrenergic blockade on cardiovascular responses to static exercise in cats
T. G. Waldrop, M. Bielecki, W. J. Gonyea and J. H. Mitchell
Static exercise performed by conscious cats elicits increases in heart rate
(HR), left ventricular systolic pressure (LVSP), and the maximal rate of
left ventricular pressure development [LV(dP/dt)max]. The increased HR is
mediated primarily by withdrawal of parasympathetic tone, whereas a
beta-adrenergic mechanism is responsible for the LV(dP/dt)max increase. In
the present study the cardiovascular responses to static exercise in awake
cats was recorded before and after alpha-adrenergic blockade. Pressure
transducers were implanted into the left ventricle of cats who had been
trained operantly to perform static exercise. Significant increases in
LVSP, LV(dP/dt)max and HR occurred in all cats during static exercise
before blockade. In contrast, alpha-adrenergic blockade (phentolamine, 2.5
mg/kg iv) abolished the exercise-induced increase in LVSP but did not
prevent increases in HR and LV(dP/dt)max. The cats performed fewer exercise
bouts per day during alpha-blockade than when unblocked. We conclude that
an alpha-adrenergic mechanism mediates the increase in LVSP in response to
static exercise in conscious cats.
