AJP - Endocrinology and Metabolism, Vol 264, Issue 1 E37-E44, Copyright © 1993 by American Physiological Society
Effects of thyroparathyroidectomy, parathyroid hormone, and PTHrP on kidneys of ovine fetuses
R. J. MacIsaac, R. S. Horne, I. W. Caple, T. J. Martin and E. M. Wintour
Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria, Australia.
The fetal parathyroid glands and parathyroid hormone-related protein
(PTHrP) have been shown to be important regulators of fetal calcium
metabolism through their actions on the placenta and bone. This study
examined the effects of fetal thyroparathyroidectomy (with thyroxine
replacement) and exogenous infusion of human parathyroid hormone
[PTH-(1-34)], PTHrP-(1-34), and PTHrP-(1-141) on the urinary excretion of
calcium in chronically cannulated ovine fetuses during the last one-fifth
of gestation. Fetal plasma total and ionized calcium concentrations were
significantly lower in thyroparathyroidectomized (TxPTx) fetuses when
compared with intact fetuses, but there were no significant differences in
urinary excretion rates of total calcium. However, TxPTx produced a
significant increase in the fractional excretion rate of total calcium and
a significant decrease in the excretion of adenosine 3',5'-cyclic
monophosphate (cAMP) compared with intact fetuses. Infusions of PTH-(1-34),
PTHrP-(1-34), and PTHrP-(1-141) into the jugular vein of TxPTx fetuses (n =
5) at the rate of 1 nmol/h for 2 h, after a 1-nmol loading dose,
significantly decreased the excretion rate of total calcium and increased
the excretion rate of cAMP in fetal urine. Infusions of all three peptides
resulted in significant increases in the concentration of total calcium in
fetal plasma but had no effect on the plasma concentrations or urinary
excretion rates of phosphate. Infusion of either PTH-(1-34), PTHrP-(1-34),
or PTHrP-(1-141) also resulted in an increase in fetal urine osmolality and
pH and a decrease in free water clearance in TxPTx fetuses.(ABSTRACT
TRUNCATED AT 250 WORDS)
