AJP - Endocrinology and Metabolism, Vol 255, Issue 3 E299-E305, Copyright © 1988 by American Physiological Society
Effects of calcium on synthesis and secretion of parathyroid hormone and secretory protein I
R. R. MacGregor, D. A. Hinton and R. D. Ridgeway
Department of Anatomy, University of Kansas Medical Center, Kansas City 66103.
Bovine parathyroid organoids were cultured for up to 3 wk in medium
containing 1.4 or 1.8 mM calcium. Steady-state secretion of parathyroid
hormone and secretory protein I was two- to fourfold greater at 1.4 mM. At
the end of culture, organoids were incubated 3.5 h in 1 or 2 mM calcium to
examine maximum and minimum acute secretory rates. Relative to organoids
cultured at 1.8 mM calcium, culture at 1.4 mM induced a hypersecretory
state, i.e., both the maximum and minimum acute secretory rates of
organoids previously cultured at 1.4 mM calcium were up to threefold
greater than those of organoids previously at 1.8 mM calcium.
Proparathyroid hormone synthesis was up to 50% greater in organoids
cultured at 1.4 mM calcium, whereas secretory protein I and total protein
synthesis were unaltered. The results showed that parathyroid
hypersecretion can be induced by chronic hypocalcemic conditions in vitro.
We conclude that the secretory adaptation to chronic hypocalcemia in vitro
involves alterations in both synthesis and degradation of parathyroid
hormone.
