Journal of Applied Physiology, Vol 55, Issue 2 383-391, Copyright © 1983 by American Physiological Society
Pulmonary metabolic function in the awake lamb: effect of development and hypoxia
B. R. Pitt and G. Lister
The effect of postnatal development and acute alveolar hypoxia on pulmonary
metabolic function was studied in conscious newborn lambs. Measurements of
the ability of the lungs of these animals to metabolize
[3H]benzoyl-L-phenyl-alanyl-L-alanyl-L-proline ([3H]BPAP; a synthetic
substrate for angiotensin-converting enzyme, ACE) and to remove
5-hydroxy-[14C]tryptamine (5-[14C]HT) were made by modified
indicator-dilution techniques during normoxic and hypoxic (fraction of
inspired O2 = 0.10) conditions at 1 day, 1 wk, and 1 mo of age. Six
additional sheep (8-23 wk old) were studied acutely as "adult" controls.
BPAP metabolism in the 1-day-old group was 48 +/- 3% and increased slowly
to 57 +/- 1% (P less than 0.05) at 1 mo of age and to 79 +/- 3% (P less
than 0.01) by 23 wk of age. Pulmonary 5-[14C]HT removal was adultlike at
birth (69 +/- 2%). Alveolar hypoxia significantly decreased BPAP only in
the 1-day-old group (41 +/- 3%; P less than 0.05) and had no significant
effect on 5-[14C]HT removal over the range of ages studied. These data
demonstrate a selective and gradual postnatal development of pulmonary ACE
which could be due to alterations in either the affinity or maximal
capacity of pulmonary ACE, or increased endothelial cell surface area
secondary to rapid growth of small blood vessels in this period. Alveolar
hypoxia does not appear to closely regulate either ACE activity or 5-HT
removal in conscious lambs greater than 1 day old when trace amounts of
substrate are used.
