The inhibitory effects of D-600 and cobalt on theophylline-mediated calcitonin secretion and calcium distribution in porcine thyroid slices.

Theophylline (5mM) produced a two-fold rise in calcitonin release from porcine thyroid slices; however, tissue uptake of 45Ca was not affected by theophylline. The calcium antagonists D-600 (5mM) and cobalt (5mM) which reduced the total tissue and cell associated 45Ca spaces in this incubation system were found to reduce theophylline-stimulated calcitonin release. Cobalt produced a greater reduction in tissue uptake of 45Ca and also reduced basal calcitonin secretion. The results suggest that calcium is necessary for theophylline-mediated calcitonin secretion.