Journal of Applied Physiology, Vol 68, Issue 1 271-274, Copyright © 1990 by American Physiological Society
Rate of disappearance of glycerol from plasma of fetal and newborn sheep
G. G. Power, K. T. Ball, H. Asakura and P. D. Gluckman
Developmental Physiology Laboratory, University of Auckland, New Zealand.
The disappearance of glycerol from plasma was studied after a single
intravenous injection to estimate its volume of distribution (Vdist),
plasma clearance rate, and rate constant for irreversible loss (kd).
Studies were repeated before and after birth of the lamb to test whether
loss of the placenta could account for rapidly increasing plasma
concentrations in the newborn. The disappearance of glycerol was closely
described by a double-exponential model in each instance. In fetal sheep
Vdist averaged 0.41 +/- 0.15 (SD) 1/kg fetal wt (n = 15). This volume
decreased to 0.33 +/- 0.11 l/kg (n = 8) soon after functionally removing
the placenta (by snaring the umbilical cord and maintaining the fetus with
intrauterine ventilation), but the change was not significant. In newborn
lambs 1-3 days of age, Vdist averaged 0.45 +/- 0.11 l/kg (n = 5, NS).
Plasma clearance rate also did not change significantly, averaging 7.9 +/-
2.9, 7.9 +/- 3.8, and 9.0 +/- 5.9 ml.min-1.kg-1 in the fetus, after
simulated birth, and in the newborn lamb, respectively, kd also was not
altered measurably and averaged 0.020 +/- 0.006, 0.024 +/- 0.007, and 0.019
+/- 0.007 min-1 during the same time periods. Similar results were obtained
by using three widely different amounts of infused glycerol. The results
indicate that removal of glycerol does not depend on placental function to
an appreciable extent. It is concluded that plasma glycerol concentration
reflects principally glycerol turnover and, hence, lipolysis before and
after birth.
