Journal of Applied Physiology, Vol 62, Issue 2 451-458, Copyright © 1987 by American Physiological Society
Nonuniform effects of histamine on small pulmonary vessels in cats
M. Shirai, K. Sada and I. Ninomiya
In in vivo cat lung, using an X-ray TV system, we analyzed responses in
internal diameter (ID), flow velocity, and volume flow of arteries and
veins (100-500 microns ID) to histamine (8-15 micrograms/kg iv) under three
conditions. With histamine alone, three types of ID response (constriction,
dilatation, and no change) occurred in parallel-arranged arteries. Relative
frequency and magnitude of constriction were maximum in arteries of 300-400
micron ID, whereas those of dilatation were maximum in arteries of 100-200
micron ID. In veins, relatively uniform constriction occurred. Under
H2-blockade, histamine caused greater constriction than that with histamine
alone in arteries and veins of 300-500 micron ID. Under beta-blockade, with
histamine, ID of all vessels decreased significantly below the ID sizes
under the above two conditions, and no dilatation occurred. In two parallel
arteries that showed opposite ID changes to histamine, flow velocity
increased, but volume flow decreased in a constricted artery while it
increased in a dilated one. Those data indicated that, with histamine,
qualitatively and quantitatively nonuniform ID response was induced in both
parallel- and series-arranged small pulmonary arteries and, in turn,
produced heterogeneous flow distribution. Factors to cause the
nonuniformity may be partly explained by difference in density of H2- and
beta-receptors in vascular walls.
