Ma. Dijkman et al., PERFUSION-INDUCED CHANGES IN CARDIAC CONTRACTILITY DEPEND ON CAPILLARY PERFUSION, American journal of physiology. Heart and circulatory physiology, 43(2), 1998, pp. 405-410
The perfusion-induced increase in cardiac contractility (Gregg phenome
non) is especially found in heart preparations that lack adequate coro
nary autoregulation and thus protection of changes in capillary pressu
re. We determined in the isolated perfused papillary muscle of the rat
whether cardiac muscle contractility is related to capillary perfusio
n. Oxygen availability of this muscle is independent of internal perfu
sion, and perfusion may be varied or even stopped without loss of func
tion. Muscles contracted isometrically at 27 degrees C (n = 7). During
the control state stepwise increases in perfusion pressure resulted i
n all muscles in a significant increase in active tension. Muscle diam
eter always increased with increased perfusion pressure, but muscle se
gment length was unaffected. Capillary perfusion was then obstructed b
y plastic microspheres (15 mu m). Flow, at a perfusion pressure of 66.
6 +/- 26.2 cmH(2)O, reduced from 17.6 +/- 5.4 mu l/min in the control
state to 3.2 +/- 1.3 mu l/min after microspheres. Active tension devel
oped by the muscle in the unperfused condition before microspheres and
after microspheres did not differ significantly (-12.8 +/- 29.4% chan
ge). After microspheres similar perfusion pressure steps as in control
never resulted in an increase in active tension. Even at the two high
est perfusion pressures (89.1 +/- 28.4 and 106.5 +/- 31.7 cmH(2)O) tha
t were applied a significant decrease in active tension was found. We
conclude that the Gregg phenomenon is related to capillary perfusion.