AJP - Heart and Circulatory Physiology, Vol 234, Issue 4 412-H415, Copyright © 1978 by American Physiological Society
Progressive postnatal changes in sinus node response to atropine and propranolol
W. T. Woods, F. Urthaler and T. N. James
Postnatal development of autonomic control of heart rate was evaluated in
the sinus nodes of isolated, perfused right atria obtained from 21 sibling
puppies in three different litters between 3 and 11 wk postpartum.
Age-related changes in response to autonomic blockade indicated that
propranolol administered after atropine had its most profound direct
depressive effect on less mature atrial cells. In the youngest sinus nodes
the familial antimuscarinic action (increase in sinus rate) of atropine was
regularly preceded by a brief period of cholinomimetic action (a marked
slowing of sinus rate) in the youngest sinus nodes. These two opposing
effects of atropine underwent a developmental change during the 2-mo study.
The cholinomimetic action diminished, whereas the antimuscarinic action
increased as a function of age.
