AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 2 222-R229, Copyright © 1983 by American Physiological Society
Diving responses in ducks after acute barodenervation
D. R. Jones, W. K. Milsom, F. M. Smith, N. H. West and O. S. Bamford
The contribution of systemic arterial baroreceptors to the cardiovascular
adjustments to diving has been investigated in unanesthetized ducks after
acute baroreceptor denervation. Both intact and denervated ducks exhibited
bradycardia on diving, although denervated ducks showed a lesser and more
variable fall in heart rate. Hindlimb vascular resistance rose
significantly in both intact and denervated ducks. Continuous stimulation
of one depressor nerve, through miniature electrodes implanted on the cut
central end, resulted in a diving bradycardia intermediate between that
recorded in intact and denervated animals. Intermittent stimulation of the
depressor nerve, for 20-s periods, at intensities high enough to cause a
large fall in mean arterial pressure (MAP) predive caused a smaller
reduction in MAP as a dive was prolonged, due to a large decline in the
ability of the baroreceptor reflex to affect peripheral resistance. There
was no change in the effect of stimulation on cardiac control before or
during diving. The present experiments indicate that a barostatic reflex,
which exerts its effects primarily through cardiac control and not control
of total peripheral resistance, is active through the dive but that the
majority of the diving response in ducks is independent of baroreceptor
integrity.
