title: Evidence for a function of calcium influx in the stimulation of hormone release fron the parathyroid gland in the goat.
abstract: 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 beta-adrenergic tonus, since the effects persisted when the drugs were administered during continuous infusion of the beta-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.
mesh_terms: D015761:4-Aminopyridine; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D006041:Goats / Q000502:physiology*; D010280:Parathyroid Glands / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*; D013268:Stimulation, Chemical; D013324:Strontium / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000631:Aminopyridines; D002121:Calcium Channel Blockers; D010281:Parathyroid Hormone; D015761:4-Aminopyridine; D014700:Verapamil; D002118:Calcium; D013324:Strontium