Calcitonin Secretion in Vitro. III. Synergistic Secretory Effects of Enteric Polypeptide Hormones

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Abstract
Crude and highly purified preparations of enteric peptide hormones stimulate trout [Salmo gairdneri] calcitonin (tCT) secretion in vitro. Since the maximal stimulatory effects of crude pancreozymin/secretin preparations were greater than the secretory effects obtained with the individual purified enteric peptides, the current study focused on the secretory effects of several combinations of enteric peptides. The additive and synergistic secretory effects of various specific peptide combinations are demonstrated. Marked (85-fold) stimulation of tCT secretion occurs in response to combinations of synthetic secretin (5 .times. 10-5 M) with pentagastrin (10-6 M) or the carboxyl-terminal octapeptide of pancreozymin (10-6 M). These findings have significance with regard to the potentiation of hormone action, and are preliminary evidence for the presence of separate receptors for various enteric peptide secretagogues on C-cells.