Somatostatin and calcitonin release from perfused dog thyroid lobes. Studies with calcium and pentagastrin

The C-cells of the thyroid contain and secrete at least two hormones, calcitonin and SRIF. In the present study we have investigated the possible relationship and interdependence of calcitonin and SRIF secretion from perfused dog thyroid lobes. Increases in perfusate Ca++ induced pronounced secretion of both SRIF-like immunoreactivity and of calcitonin-like immunoreactivity. However, the secretory patterns were not identical. The release of calcitonin-like immunoreactivity was more sensitive to small increases in Ca++ than that of SRIF-like immunoreactivity and the shapes of the release curves of calcitonin and SRIF during a 14-min Ca++ infusion were different. Pentagastrin induced only modest increases in SRIF release. The calcitonin response to pentagastrin was characterized by an initial increase followed by a rapid return to near basal levels. This observation was very different from Ca++-induced calcitonin release. Exogenous SRIF infused during pentagastrin or Ca++ stimulation of calcitonin secretion had only a marginal inhibitory effect. The studies indicate that the dynamics of release of various C-cell substances are different when challenged by the same stimulant, and that different stimulants induce different types of variations in the release of the same substance.