Effect of thyrotropin-releasing hormone (TRH) on the synthesis and secretion of polysaccharides by the integument of gastropods.

The hypothesis that thyrotropin-releasing hormone (TRH) affects salt and water transport in gastropod skin by means of altering the secretion of epithelial surface mucus was tested. The synthesis and secretion of 35S-labeled sulfated polysaccharides was measured as an index for the synthesis and secretion of mucus. It was found that physiological concentrations of TRH significantly inhibited the secretion of 35S-labeled sulfated polysaccharides by short-term in vitro incubated gastropod foot integument. TRH did not alter the rate of synthesis of 35S-labeled sulfated polysaccharides in short-term in vitro incubated gastropod foot skin. The synthesis and release, but not the tissue/medium ratio of 35S-labeled sulfated polysaccharides was significantly lower in animals with an elevated endogenous TRH content than in control animals. The results from these studies suggest that acute exposure of gastropod skin to TRH results in a decrease in the secretion of preformed epithelial surface mucus and that chronic exposure also results in a reduction of the synthesis of surface mucus. It thus appears that TRH indirectly modulates gastropod skin ion transport by altering the thickness of the surface mucus coat which results in a change in the ion concentration at the cell surface and a change in the activity of the ion transporting mechanisms.