Crude and highly purified preparations of enteric peptide hormones were shown to stimulate trout calcitonin (tCT) secretion in vitro. Since the maximal stimulatory effects of crude pancreozymin/secretin preparations were seen to be greater than the secretory effects obtained with the individual purified enteric peptides, the current study has 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 x 10-5M) with pentagastrin (10-6M) or the carboxyl-terminal octapeptide of pancreozymin (10-6M). 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.
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