AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 1 141-R150, Copyright © 1982 by American Physiological Society
Model for parathyroid hormone secretion and metabolism in calves
A. Jung, G. P. Mayer, J. G. Hurst, R. Neer and J. T. Potts Jr
A model for parathyroid gland response to differing calcium and magnesium
concentrations is proposed based on direct determinations of parathyroid
hormone (PTH) secretion rate. A proportional control seems adequate for
physiological variations of calcium and magnesium levels. At extreme
hypocalcemia, nonlinearities are observed: a model involving the depletion
of a storage compartment is proposed, the size of which is calculated. PTH
distribution was studied in another group of animals; sampling was made
from the saphenous artery and the thoracic duct. Concentrations of plasma
and lymph-intact PTH and carboxy-terminal fragments were determined by
means of two different radioimmunoassays. The analysis of the results leads
to the formulation of a five-compartment model, which shows that the
metabolism of intact PTH is only partly due to the formation of
carboxy-terminal fragments, most being directly secreted or catabolized.
Linking these models for secretion and distribution of PTH, simulation
studies were undertaken and compared with published data. This model is
then discussed in comparison with previous work concerning other
polypeptide hormones.
