Effect of parathyroid hormone and calcitonin on cholinergic markers in rat parathyroid gland.

The effect of parathyroid hormone (PTH) and calcitonin on 3H-choline uptake and on 3H-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 3H-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 3H-choline conversion to 3H-acetylcholine, with significant effects at 10(-8) M concentration or higher. This inhibitory effect of PTH on 3H-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 3H-acetylcholine by parathyroid fragments. The results indicate that, in vitro, PTH, and to a less extent, calcitonin, inhibit cholinergic activity in rat parathyroid glands.