PROTEIN STIMULATION OF TRYPSIN SECRETION FROM THE OPAQUE ZONE MIDGUT CELLS OF STOMOXYS-CALCITRANS

The epithelial layer of the opaque zone of the midgut of Stomoxys calcitrans contains putative endocrine cells as well as cells synthesizing and secreting digestive enzymes. Soluble protein stimulates secretion of trypsin from in vitro preparations of the opaque zone in a time and dose-dependent manner. The half-maximal biological response (ED(50)) values for the proteins tested lie between 1 x 10(-6) and 1 x 10(-7) M. Trypsin secretion is not stimulated by amino acids or poly-L amino acids and the response to albumin is diminished by 50% following boiling. There is no apparent relationship between the type of protein, molecular weight or pi point and the ability to promote trypsin secretion-all proteins tested here promoting secretion to similar degrees. There is no stimulation of secretion by brain tissue homogenate beyond that which would be expected because of its protein content.