Thyroid hormone activated upper gastrointestinal motility without mediating gastrointestinal hormones in conscious dogs

This study was conducted to clarify the relationship between thyroid function and gastrointestinal motility. We established an experimental configuration in which the feedback of thyroid function was completely removed using conscious dogs. With hypothyroidism, time of phase I of interdigestive migrating contractions (IMC) was longer, time of phase II and phase III was significantly shortened, and both the continuous time of strong tetanic contraction at antrum and 10-h frequency of phase III counted from the first IMC after meal significantly decreased. Whereas, hyperthyroidism caused the opposite events to those with hypothyroidism. Furthermore, We found giant migrating contractions (GMC) occurred from the upper gastrointestinal tract when we administrated high dose of thyroid hormone. One GMC occurred from anal sides propagated to cardiac, and this propagation was similar to the emesis-like interdigestive motor activity, the other GMC occurred from oral sides propagated to anal sides and this was similar to the diarrhea-like interdigestive motor activity. We examined the relationship between thyroid function and gastrointestinal hormones including of ghrelin, GLP-1, and cholecystokinin (CCK). However, we could not find significant differences under different thyroid hormone status. This is the first report that thyroid hormone activated upper gastrointestinal motility without mediating gastrointestinal hormones.