AJP - Heart and Circulatory Physiology, Vol 253, Issue 5 1192-H1198, Copyright © 1987 by American Physiological Society
Adenosine and hypoxia effects on atrioventricular node of adult and neonatal rabbit hearts
M. L. Young, B. M. Ramza, R. C. Tan and R. W. Joyner
Department of Pediatrics, University of Iowa Hospital and Clinics, Iowa City.
An isolated perfused heart model was used to assess the effects of hypoxia
and adenosine on the adult and neonatal (1-5 days) rabbit atrioventricular
(AV) node. The AV nodal function was assessed by the A-H interval at a
constant atrial pacing cycle length and by the longest pacing cycle length
resulting in Wenckebach periodicity. We defined the pacing cycle length at
or below which the AV node demonstrated Wenckebach periodicity as the
Wenckebach cycle length. Adenosine produced a smaller dose-dependent
increase in A-H interval in neonates than in adults, but the increase in
Wenckebach cycle length was similar in the two age groups. When the hearts
were exposed to 5 min of hypoxia the increase of Wenckebach cycle length
was greater for adults than for neonates. The change in Wenckebach cycle
length in adults caused by hypoxia was significantly greater than that
caused by 1 mM adenosine. In addition, in adults aminophylline could
partially attenuate the increase in Wenckebach periodicity caused by
adenosine, but aminophylline could not attenuate the increase in Wenckebach
cycle length caused by hypoxia. We conclude that in the rabbit AV node 1)
the adenosine effect in neonates is similar to that in adults; 2) neonates
are relatively resistant to acute hypoxia compared with adults; and 3) the
response to acute hypoxia in adults cannot be totally explained by the
adenosine release theory.
