Journal of Applied Physiology, Vol 42, Issue 3 438-443, Copyright © 1977 by American Physiological Society
Mechanical response of pulmonary artery under aerobic and hypoxic conditions
J. F. Souhrada and D. W. Dickey
The present study demonstrates the reactivity of isolated main pulmonary
artery (MPA) from guinea pigs and rats to two vasoactive drugs,
norepinephrine (NE) and histamine (H), in substrate-rich and substrate-free
medium, under both aerobic (PO2 = 95 +/- 0.5 Torr) and hypoxic conditions
(PO2 = 30 +/- 1 Torr). The sensitivity of MPA from guinea pigs to NE and H
during aerobic conditions is not significantly affected by the absence of
substrate in the experimental medium. Furthermore, it is demonstrated that
in the substrate-rich experimental medium (5.5 mM glucose), the reactivity
of MPA from guinea pigs to NE and H is not significantly affected by acute
hypoxia as compared with the response of MPA during aerobic conditions.
These experiments contrast with data obtained when substrate is absent from
the experimental medium. The dose-response curves of MPA from guinea pigs
to NE and H under this condition were significantly blunted during hypoxia.
Following the completion of the dose-response curves during aerobic
conditions, with both NE and H, spontaneous mechanical activities were seen
in the guinea pig MPA. On the other hand, it was demonstrated that during
aerobic and hypoxic conditions MPA's isolated from rats exhibit no
physiological response to histamine even when administered in the dose
required to produce the maximal response in MPA isolated from guinea pigs.
The sensitivity of MPA from rats to NE during aerobic conditions is not
significantly affected by the absence of substrate in the experimental
medium. However, when the preparation was exposed to hypoxia, the presence
of substrate failed to maintain the reactivity of MPA to norepinephrine. In
addition, MPA isolated from rats demonstrated a smaller contractile
response to NE than those from guinea pigs. Furthermore, no spontaneous
mechanical activities were observed after norepinephrine or histamine
administration. The present study, in addition to pointing out species
differences, shows the important role of exogenous substrate in maintaining
the reactivity of pulmonary vascular smooth muscle during hypoxia.
