The presence of a triacylglycerol lipase in human gastric juice was described in previous studies. Its source and role in intragastric lipolysis was, however, uncertain. Our study presents definitive evidence for gastric origin of a lipase and its release by secretagogues. Both carbachol and cholecystokinin-8 stimulate release of this enzyme for dispersed human gastric glands. While the two secretagogues had similar efficacies, with nearly a 3-fold stimulation over basal rates, cholecystokinin-8 was about four orders of magnitude more potent in releasing lipolytic activity than carbachol (maximum stimulation at concentrations of 1 X 10(-9) and 1 X 10(-5) M, respectively). Lipolytic activity measured against triolein (18:1), tricaprylin (8:0) and tributyrin (4:0) emulsions was 1.18 +/- 0.12, 4.48 +/- 0.64, and 12.17 +/- 0.88 units (1 unit = 1 mumol free fatty acid released/min per mg protein), respectively. Characterization of the pH optimum for each substrate showed maximum lipolysis at 4.5 for tributyrin, and at 5.5 for tricaprylin and triolein. These results indicate that a lipase which hydrolyzes long-, medium- and short-chain triacylglycerols is secreted by human gastric mucosa. At pH 6.0, the pH of the duodenum, there is appreciable lipolytic activity in the presence of bile salts. This suggests that gastric lipase, in addition to initiating lipolysis in the stomach, might also aid in the digestion of lipids in the duodenum. It remains to be determined whether gastric lipase is distinct from lingual lipase, or is the same enzyme secreted by the lingual serous glands and the gastric mucosa.