EFFECT OF PARATHYROID-HORMONE AND CALCITONIN ON CHOLINERGIC MARKERS IN RAT PARATHYROID-GLAND

The effect of parathyroid hormone (PTH) and calcitonin on H-3-choline uptake and on H-3-acetylcholine synthesis by rat parathyroid glands were examined. Incubation of tissue for 120 min with PTH or calcitonin resulted in an inverted bell-shaped, dose-dependent inhibition of H-3-choline uptake, with a maximal effect at 10(-9)M concentration. The effect of PTH on parathyroid choline uptake was blunted by preincubation with the PTH antagonist NLe(8-18)-PTH(3-34) amide. PTH brought about a dose-dependent inhibition of H-3-choline conversion to H-3-acetylcholine, with significant effects at 10(-8) M concentration or higher. This inhibitory effect of PTH on H-3-acetylcholine synthesis was blocked by co-incubation with the PTH antagonist NLe(8-18)-PTH(3-34) amide. Only at a 10(-7) M concentration calcitonin was effective to impair the in vitro conversion of radioactive choline into H-3-acetylcholine by parathyroid fragments. The results indicate that, in vitro, PTH, and to a less extent, calcitonin, inhibit cholinergic activity in rat parathyroid glands.