AJP - Heart and Circulatory Physiology, Vol 246, Issue 2 189-H196, Copyright © 1984 by American Physiological Society
Effects of propranolol and epinephrine on density of capillaries in rat heart
F. Vetterlein and G. Schmidt
The influence of propranolol and epinephrine on the time course of
capillary plasma filling and the maximal obtainable capillary density was
studied in the hearts of anesthetized rats. The blood plasma was labeled in
vivo with macromolecule-coupled fluorochromes (lissamine-rhodamine B 200
and fluorescein isothiocyanate) for different periods of time and the
density of marked capillaries determined in frozen sections of the heart.
In the propranolol-treated (1.0 mg/kg) rats complete filling was observed
after 40 s (controls: 10 s). When epinephrine (5.0 micrograms X kg-1 X
min-1) was infused, plasma filling was completed within 5 s. Maximal
capillary densities were higher in the drug-treated groups than in the
control group (controls 3,530 capillaries/mm2; propranolol 3,890
capillaries/mm2; epinephrine 3,930 capillaries/mm2, subepicardium). This
increase was induced by a reduction in mean diameter of muscular fibers due
to a higher distension of the left ventricular wall in the drug-treated
rats. It is concluded that changes in plasma transit times and in
intercapillary distances due to fiber lengthening were induced by high
doses of propranolol or epinephrine.
