The effect of glucagon on enterokinase secretion from Brunner's gland pouches in dogs

Physiological factors controlling release of enterokinase from rat enterocytes

The quantitative release of enterokinase from isolated rat enterocytes following treatment with taurocholate-taurodeoxycholate, papain, chymotrypsin, elastase, carbamylcholine, and cholecystokinin-octapeptide was examined. Alkaline phosphatase and lactate dehydrogenase activities were evaluated simultaneously to check for specificity. Bile salts promoted a concentration-dependent release of all enzymes. Concomitantly, bile salts also led to cell destruction in proportion to the amount of enzymes released. Proteases caused the release of enterokinase and alkaline phosphatase with no concomitant increase of lactate dehydrogenase or cell lysis. At equal concentrations, papain released more enzymes than chymotrypsin and elastase. Chymotrypsin and elastase, however, led to higher ratios of enterokinase to alkaline phosphatase found in the media and suggested a selective release of enterokinase (EK) over that of alkaline phosphatase. Bile salts and pancreatic proteases together seem to have an additive effect of the release of EK. Carbamylcholine and cholecystokinin-octapeptide had no effect on enzyme release. These results suggested that pancreatic proteases are involved in the release of enterokinase by a selective action. Bile salts may also play a role through a nonselective detergent effect.

Studies on intestinal enzyme secretion; the action of cholecystokinin-pancreozymin, pentagastrin and bile

Intravenous administration of 1 U cholecystokinin-pancreozymin (CCK-PZ) to rats caused the release of enteropeptidase, alkaline phosphatase (AP), and sucrase to the intestinal lumen in the absence of a concomitant increase in luminal DNA. Thus, the hormone elicited hydrolase secretion was not due to cell desquamation. Pentagastrin also stimulated hydrolase release. Following CCK-PZ administration enteropeptidase was released preferentially over sucrase and AP and showed a linear correlation with total protein output. The specific enteropeptidase activity was higher in the perfusate following secretion than in the mocosa. Enteropeptidase was found mainly in soluble form in both mucosa and perfusate; addition of bile following enteropeptidase release further increased its activity. In contrast, sucrase and AP were found mainly in insoluble form in both mucosa and perfusate and their specific activities were higher in the mucosa. The presence of bile rendered both sucrase and AP more soluble in the perfusate. The data indicate that enteropeptidase is released by a specific secretory process and that its subcellular site of origin is different from that of sucrase and AP. By eliciting the coordinated release of trypsinogen, enteropeptidase and bile, CCK-PZ plays a central role in the initiation of protein digestion.

Enteropeptidase levels in duodenal juice of normal subjects and patients with gastrointestinal disease

Enteropeptidase, trypsin, and chymotrypsin activity in basal and secretin-stimulated duodenal juice of 20 normal adult volunteers and 15 patients with gastrotestinal disease were determined. All enzyme concentrations showed skew distributions, but fluctuations in the secretin-stimulated juices were less pronouced than in the basal secretions. Secretin administration had no influence on the release of enteropeptidase from human duodenal mucosa, but resulted in a very small increase in secretion of pancreatic enzymes. Six out of seven patients with chronic alcoholic pancreatitis or cancer of the pancreas exhibited highly significant elevations of enteropeptidase in their basal as well as secretin-stimulated duodenal juice. It is suggested that raised luminal enteropeptidase activity may be the result of pancreatic insufficiency or elevated blood glucagon concentrations.

Hormonal stimulation of intestinal brush border enzymes release

The rat small bowel was perfused in vivo and ex vivo in the absence of biliary and pancreatic secretion. Intraluminal release of sucrase, alkaline phosphatase, aminopeptidases and enterokinase was significantly increased after administration of pentagastrin, caerulein and glucagon at doses ranging between 1 pg and 10 microgram. This suggests that there is a direct hormonal stimulation of the intestinal mucosa. This effect might at least partly be mediated through cyclic AMP since dibutyryl derivates of this cyclic nucleotide exerted a significant stimulatory effect on intraluminal release of proteins, sucrase and enterokinase, although the pattern of enzyme was quite different from the effect produced by the three peptides.

Hormone-elicited enzyme release by the small intestinal wall

Three enzymes of intestinal origin-enterokinase, alkaline phosphatase, and sucrase-were released into the perfused small intestinal lumen of the rat upon intravenous injection of the gastrointestinal hormone cholecystokinin-pancreozymin (CCK-PZ). The presence of bile in the perfusion fluid greatly augmented this release. The results suggest that a combined mechanism of enzyme liberation due to direct hormonal stimulation of the gut wall and further solubilization of released intestinal enzymes by bile may be responsible for the appearance of these enzymes in the gut lumen.