Evidence for a function of calcium influx in the stimulation of hormone release from the parathyroid gland in the goat

The acute effects of various drugs on the release of parathyroid hormone (PTH) in goats were studied by local infusions in vivo. Infusions of Ca²+ or Sr²+ reduced the PTH secretion rate, whereas hypocalcemia induced by EDTA increased the PTH release. Blockers of voltage sensitive Ca²+ channels (verapamil, D-600 and nifedipine) lowered the PTH secretion rate, while infusion of 4-aminopyridine, which is a blocker of voltage sensitive K+ channels, increased the PTH release. These effects were not due to altered βadrenergic tonus, since the effects persisted when the drugs were administered during contineous infusion of the β-blocker propranolol. We suggest that the parathyroid cells possess voltage sensitive K+ and Ca²+ channels, and that exocytosis of stored PTH depends on the influx of extracellular Ca²+ as in other secretory cells. In order to explain the inverse relationship between the plasma Ca²+ level and the PTH release, we postulate a suppressive effect of the plasma Ca²+ on the membrane permeability to Ca²+ in parathyroid cells.