Episodic secretion of parathyroid hormone in the dog

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Abstract
Whether parathyroid hormone (PTH) is secreted episodically, characterization of any such rhythms and whether the rhythms can be altered by stimulating PTH secretion using constant hypocalcemia were determined. Blood samples were collected at 1 min intervals for 1 h from the precava or postcava of conscious dogs during normocalcemia or induced, constant hypocalcemia. In 2 anesthetized normocalcemic dogs a caudal thyroid vein was catheterized and all the effluent blood collected 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 2- to 4-fold 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.

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