AJP - Heart and Circulatory Physiology, Vol 242, Issue 2 133-H141, Copyright © 1982 by American Physiological Society
Capillary density in rat myocardium during timed plasma staining
F. Vetterlein, H. dal Ri and G. Schmidt
In urethan-anesthetized thoracotomized rats the density of myocardial
capillaries that had been stained during timed infusions of a plasma label
was determined. gamma-Globulin-coupled fluorochromes [lissamine-rhodamine B
200 (RB 200) and fluoresceinisothiocyanate (FITC)] were applied to the
vascular system for different intervals of time. The circulation in the
heart was freeze stopped, and the dye-containing capillaries were counted
in histological cross sections of the organ. When the dyes had been infused
into the left atrium for 1, 2, 5, or 10 s the number of stained vessels
continuously increased (1,960 +/- 170, 2,780 +- 160, 3,310 +/- 130, and
3,340 +/- 140 cap/mm2 in the subepicardium and 1,990 +/- 210, 2,490 +/-
190, 3,090 +/- 160, and 3,210 +/- 160 cap/mm2 in the subendocardium,
respectively). However, further prolongation of dye exposure (2, 10, or 30
min) did not increase significantly the number of marked capillaries. The
induction of a general hypoxia (30-s stop of ventilation) after dye
application also did not induce higher capillary counts than were found in
the normoxic animals during long-time plasma labeling. Changes in red blood
cell-containing capillaries were not covered by these observations. The
distribution of stained capillaries in the evaluated areas was more
inhomogeneous after incomplete filling with RB 200 for 1 s than after
complete staining with FITC for 4 min. The results favor the view that in
the rat heart at rest the blood plasma passes the microcirculation in an
inhomogeneous manner; in all capillaries the slowest transit times do not
exceed 5 s, however.
