AJP - Heart and Circulatory Physiology, Vol 250, Issue 2 208-H212, Copyright © 1986 by American Physiological Society
Improvement in relaxation by nifedipine in hypoxic isometric cat papillary muscle
J. E. Carter, I. Palacios, W. H. Frist, S. Rosenthal, J. B. Newell and W. J. Powell Jr
Hypoxia has been demonstrated to cause impairment of myocardial relaxation.
This impairment of relaxation is particularly pronounced during early
reoxygenation. This study was undertaken in 24 isometric cat papillary
muscles at 38 degrees C to determine if nifedipine can influence the
impairment of relaxation produced during reoxygenation following hypoxia. A
dose of nifedipine was chosen that produced only a minimal depression of
peak systolic tension and no change in the half time to relaxation (RT 1/2)
under well-oxygenated conditions. Thirty minutes of hypoxia were produced
in 12 muscles, and systolic tension decreased by the same amount in muscles
treated or not treated with nifedipine. During early hypoxia in the absence
of nifedipine, RT1/2 was significantly prolonged (P less than 0.01) from
104 +/- 7 to 126 +/- 9 ms. After pretreatment with nifedipine, the change
in RT1/2 with hypoxia was not significant. More striking was the near
abolition of the marked impairment of relaxation seen during early
reoxygenation (238 +/- 33 ms without nifedipine and 128 +/- 8 ms with
nifedipine, P less than 0.01). These data establish that, although
nifedipine only minimally attenuates the relaxation impairment early during
hypoxia, this agent can substantially reduce the impairment of relaxation
produced by early reoxygenation.
