Role of endogenous somatostatin in the secretion of parathyroid hormone and calcitonin.

Our previous in vitro and in vivo studies demonstrated that exogenous somatostatin inhibited secretion of both parathyroid hormone (PTH) and calcitonin (CT). This study evaluates the possible role of endogenous somatostatin in PTH and CT secretion. Rats receiving somatostatin antiserum i.v. had significantly greater circulating levels of serum immunoreactive PTH (iPTH) and CT (iCT) than rats receiving normal rabbit serum. In in vitro studies with bovine parathyroid tissue, the addition of somatostatin antiserum to the medium significantly increased PTH secretion from basal, low calcium-stimulated and high calcium-suppressed parathyroid tissue. These combined observations strongly suggest that endogenous somatostatin must have a suppressive effect on PTH and CT secretion. The in vitro observations with isolated parathyroid tissue suggest that somatostatin is synthesized by cells within this tissue. These data strongly suggest that somatostatin is a locally-synthesized hormone that has a role in modulation of both PTH and CT secretion.