AJP - Endocrinology and Metabolism, Vol 241, Issue 3 171-E177, Copyright © 1981 by American Physiological Society
Episodic secretion of parathyroid hormone in the dog
J. Fox, K. P. Offord and H. Heath 3rd
This study was designed to determine whether parathyroid hormone (PTH) is
secreted episodically, to characterize any such rhythms, and to see whether
the rhythms can be altered by stimulating PTH secretion using constant
hypocalcemia. We collected blood samples at 1-min intervals for 1 h from
the precava or postcava of conscious dogs during normocalcemia or induced,
constant hypocalcemia. In two anesthetized normocalcemic dogs we
catheterized a caudal thyroid vein and collected all the effluent blood in
1-min fractions. Immunoreactive PTH (IPTH) concentrations were determined
in quadruplicate, and the results were subjected to spectral analysis. In
both the precava and postcava of normocalcemic dogs, there were regular
oscillations in IPTH levels with a period of 12 min (range, 10-15 min) and
a +/- 14% variation about the overall mean. Although significant two- to
fourfold changes in IPTH levels still occurred during constant
hypocalcemia, there was no significant rhythmicity. Significant cycles in
IPTH concentration (mean 8.4-min period) were observed in thyroid venous
effluent plasma during normocalcemia, confirming that the phenomenon
represented episodic secretion that was not affected by pentobarbital
anesthesia.
