Type II diabetic patients with no clinical evidence of neuronal dysfunction have a significantly more rapid rate of gastric emptying of a solid high-carbohydrate meal when compared with nondiabetic control subjects.

Cholecystokinin (CCK) secretion in rats and humans is inhibited by pancreatic proteases and bile acids in the intestine. It has been hypothesized that the inhibition of CCK release caused by pancreatic proteases is due to proteolytic inactivation of a CCK-releasing peptide present in intestinal secretion. To purify the putative luminal CCK-releasing factor (LCRF), intestinal secretions were collected by perfusing a modified Thiry-Vella fistula of jejunum in conscious rats. From these secretions, the peptide was concentrated by ultrafiltration followed by low-pressure reverse-phase chromatography and purified by reverse-phase high-pressure liquid chromatography. Purity was confirmed by high-performance capillary electrophoresis. Fractions were assayed for CCK-releasing activity by their ability to stimulate pancreatic protein secretion when infused into the proximal small intestine of conscious rats. Partially purified fractions strongly stimulated both pancreatic secretion and CCK release while CCK receptor blockade abolished the pancreatic response. Amino acid analysis and mass spectral analysis showed that the purified peptide is composed of 70-75 amino acid residues and has a mass of 8136 Da. Microsequence analysis of LCRF yielded an amino acid sequence for 41 residues as follows: STFWAYQPDGDNDPTDYQKYEHTSSPSQLLAPGDYPCVIEV. When infused intraduodenally, the purified peptide stimulated pancreatic protein and fluid secretion in a dose-related manner in conscious rats and significantly elevated plasma CCK levels. Immunoaffinity chromatography using antisera raised to synthetic LCRF-(1-6) abolished the CCK releasing activity of intestinal secretions. These studies demonstrate, to our knowledge, the first chemical characterization of a luminally secreted enteric peptide functioning as an intraluminal regulator of intestinal hormone release.

A trypsin/chymotrypsin inhibitor, POT II, can delay the rate of gastric emptying, and decrease postprandial plasma glucose levels, GIP levels, and serum insulin levels in type II diabetic patients diagnosed recently. Delay of gastric emptying in diabetic patients may provide a unique or adjunctive approach to the treatment of type II diabetes.

The mechanism by which intraluminal proteases inhibit pancreatic secretion and CCK release was investigated in conscious rats. We hypothesized that the stimulation of pancreatic secretion and CCK release that occurs in the absence of luminal trypsin is caused by a trypsin-sensitive, cholecystokinin (CCK)-releasing peptide that is tonically secreted intraluminally by the small intestine. We tested whether rapid saline perfusion of the lumen of the proximal intestine in rats with jejunostomies would wash out the putative peptide, thereby inhibiting the spontaneous pancreatic secretion caused by diverting bile and pancreatic juice from the intestine. Rats were prepared with cannulas draining bile and pancreatic juice, a duodenal cannula and a jejunostomy 10-12 cm from the ligament of Treitz. During diversion of bile and pancreatic juice to the exterior, the proximal intestine was perfused with phosphate-buffered saline at 3 ml/min via the duodenal cannula and the intestinal washes collected from the jejunostomy outlet. Rapid intestinal perfusion significantly inhibited pancreatic protein and fluid secretion stimulated by diversion of bile and pancreatic juice to the exterior. Reinfusion of the concentrated intestinal washes prevented the "washout" inhibition. The active factor in the intestinal washes was heat stable and trypsin sensitive. Rapid washout perfusion of isolated jejunal loops in Thiry-Vella fistula rats reduced plasma CCK from 20.4 +/- 3.6 to 10.4 +/- 1.8 pM, and reinfusion of the washes into the loop returned plasma CCK to 17.1 +/- 3.8 pM. The results support the hypothesis that a trypsin-sensitive, CCK-releasing peptide in intestinal secretions mediates feedback regulation of pancreatic secretion in rats.

Phillips et al. [1] demonstrated abnormally rapid gastric emptying of glucose solutions in patients with recently diagnosed non-insulin-dependent diabetes mellitus (NIDDM), which contrasts with delayed gastric emptying (gastroparesis), a well-documented late manifestation of diabetes attributed to autonomic neuropathy [2]. Intravenous administration of cholecystokinin (CCK), a physiological inhibitor of gastric emptying in healthy humans [3], normalized gastric emptying of a glucose test meal in NIDDM diabetic patients and reduced the postprandial hyperglycaemia [4]. This outcome was predicted from studies in healthy human subjects which showed that CCK regulated postprandial blood glucose levels by slowing gastric emptying [5]. These studies support the hypothesis [1] that accelerated gastric emptying in early NIDDM in humans may contribute to poor glucose control by increasing the rate of glucose entry into the small intestine, thereby increasing absorption rate and exacerbating postprandial hyperglycaemia.To further examine this phenomenon, the gastric emptying of glucose was investigated in a newly Diabetologia (1997) Summary Patients with early non-insulin-dependent diabetes mellitus (NIDDM) empty glucose solutions from their stomachs more rapidly than non-diabetic control subjects, and this exacerbates postprandial hyperglycaemia.To determine if accelerated gastric emptying occurred in a rat model of NIDDM and influenced postprandial hyperglycaemia, gastric emptying of glucose was measured, and the effect of slowing the gastric emptying rate on postprandial hyperglycaemia was observed. We tested eight male obese Zucker diabetic rats and eight age-matched lean Zucker controls at 10-13 weeks of age to measure gastric emptying of glucose (by gamma scintigraphy). Rats fasted overnight were gavaged with 30 % glucose at 1 ml/100 g body weight. Separately, six Zucker diabetic rats and six lean controls were tested for sensitivity to the inhibitory effects of cholecystokinin and secretin on gastric emptying. The diabetic rats emptied glucose significantly faster than controls (t 1/2 = 37.3 ± 1.5 vs 58.8 ± 2.3 min in controls), and aging exaggerated this differential. Camostat, a stimulant of cholecystokinin and secretin release, added to the glucose meal significantly slowed gastric emptying (t 1/2 = 123 ± 23 and 166 ± 19 min, diabetic vs lean, respectively), and significantly reduced postprandial hyperglycaemia in diabetic rats. Compared to Zucker lean controls, Zucker diabetic rats were as sensitive (cholecystokinin) or more sensitive (secretin) to gastrointestinal hormones that inhibit gastric emptying. The results demonstrate accelerated gastric emptying in a rat model of NIDDM, consistant with similar observations in humans with early NIDDM. These results also support the proposal that interventions to slow gastric emptying may improve glucose control in this disease. [Diabetologia (1997) 40: 136-142]