AJP - Endocrinology and Metabolism, Vol 254, Issue 3 E318-E322, Copyright © 1988 by American Physiological Society

ARTICLES

Disappearance of growth hormone from plasma of fetal and newborn sheep

G. G. Power, K. T. Ball and P. D. Gluckman
Department of Paediatrics, School of Medicine, University of Auckland, New Zealand.

The disappearance of growth hormone (GH) from plasma was measured after a single intravenous injection in fetal and newborn sheep and fetal sheep after simulated birth in utero. The process was adequately described when separated into two exponential components, consistent with an inner (plasma) and outer (composite tissue) pool. Plasma clearance rate increased from 3.4 +/- 0.2 (SE, n = 6) in fetuses to 3.9 +/- 0.1 (n = 5) ml.min-1.kg-1 in newborns (P less than 0.05), but was not altered significantly after simulated delivery in utero. The volume of distribution decreased from 74 +/- 4 ml/kg before birth to 47 +/- 2 ml after natural birth (P less than 0.001). The basal secretory rate decreased from 2.4 +/- 0.2 before birth to 0.27 +/- 0.02 microgram/min after birth (P less than 0.001) and to a lesser extent after simulated delivery. The rate constant for irreversible loss, Kd, increased from 0.052 +/- 0.004 min-1 before birth to 0.093 +/- 0.002 min-1 after birth (P less than 0.001). Because plasma GH concentration in steady state equals secretory rate/(volume of distribution X Kd), one may calculate that 83% of the total decrease in GH, which occurs after birth, can be explained by diminished secretory rate, whereas 17% can be explained by more rapid loss from the plasma.

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