Parasympathetic control of parathyroid hormone and calcitonin secretion in rats.

Cholinergic nerve fibers can be traced to the vicinity of C- and parathyroid cells. The objective of this study was to examine the changes in circulating calcium, parathyroid hormone (PTH) and calcitonin levels after a bilateral surgical section of thyroid (TN) or inferior laryngeal nerves (ILN) in rats. Parasympathetic surgical section decreased significantly thyroid and parathyroid neuronal [3H]choline uptake. A significant fall in total serum calcium and a significant increase in serum PTH were observed 10 days after TN and ILN sections, while calcitonin levels decreased significantly after ILN sections only. When parathyroid sensitivity to a hypocalcemic challenge was assessed, a significantly larger serum PTH response to EDTA was detectable in TN- or ILN-sectioned rats. A significantly smaller hypocalcemia after EDTA was observed in TN-sectioned rats only. Following calcium chloride injection, the increase in serum calcitonin was greater, and the increase in serum calcium levels smaller, in TN-sectioned rats as compared to sham-operated controls. In ILN-sectioned rats, the secretory response of calcitonin and the hypercalcemia achieved after a calcium chloride challenge was significantly greater than in controls. The results indicate that ILN or TN sections induced hypocalcemia and increased serum PTH levels in rats, as well as bringing about a greater secretory response of PTH and calcitonin when challenged with an appropriate stimulus. An inhibitory parasympathetic influence parathyroid and C-cell secretion can be envisioned.