Effects of isoproterenol and cycloheximide on parathyroid secretion.

Tissue slices or dispersed cells of bovine parathyroid gland were incubated with [3H]leucine to label the intracellular proteins and then tested for their secretory response to isoproterenol and cycloheximide at different calcium concentrations. Secretion of the newly synthesized as well as the older PTH and SP-I was stimulated by isoproterenol at all calcium levels tested, even when it was maximally enhanced by low calcium. Cycloheximide interfered with neither the secretory process nor the secretory response to different stimuli, but decreased the amount of PTH and SP-I secreted. We conclude that the inhibitor decreased the secretion by reducing the supply of PTH and SP-I. Calculations derived from the data reveal that, under most secretory conditions, newly synthesized PTH contributed a major portion of the total hormone secretion in bovine parathyroid cells.