Effects of four orally administered analogues of prostaglandin E1 and E2 on glucose tolerance and on the secretion of pancreatic and gastrointestinal hormones in man

Effect of duodenectomy on gastric motility and gastric hormones in dogs

OBJECTIVE

To test the hypothesis that the duodenum is required to coordinate interdigestive insulin secretion with gastrointestinal motility and to determine whether duodenectomy alters the interdigestive cycles of plasma motilin and insulin levels and their relations to insulin secretion and motility.

METHODS

Adult mongrel dogs were chronically implanted with force transducers in the stomach, duodenum, and upper jejunum to monitor contractile activity. Eight healthy mongrel dogs were divided into control and duodenectomized dogs. Insulin secretion, gastrointestinal motility, and plasma concentrations of motilin during the interdigestive period were measured in normal and duodenectomized dogs.

RESULTS

After duodenectomy, no obvious phase III contractions were seen in the gastric antrum, but migrating phase III contractions were seen in the upper jejunum. The plasma motilin concentration did not fluctuate as it does in normal dogs, and remained low. After duodenectomy, insulin secretory cycles were not coordinated with either cycles of interdigestive motility or the plasma concentration of motilin. Exogenous motilin administration stimulated endogenous insulin release significantly compared with saline-treated controls. The contractile response of the stomach to exogenous motilin after duodenectomy was similar to that of intact dogs.

CONCLUSIONS

Duodenectomy disrupts the relation between cycles of both interdigestive gastrointestinal motility and insulin secretion. These effects of duodenectomy may be attributable to interruption of the duodenopancreatic neural connections, hormonal abnormalities, or loss of vagus-sensitive humoral factors. The duodenum, which stores motilin, seems to play an important role in the relations between gastric migrating motor complexes and the concomitant increase of insulin secretion in fasted dogs. The mechanism responsible for the effect of motilin in both duodenectomized and normal dogs may involve a cholinergic pathway.

Misoprostol therapeutics revisited

Misoprostol, a prostaglandin E1 analog, is a racemate of four stereoisomers. On administration it rapidly de-esterifies to its active form, misoprostolic acid. Misoprostolic acid is 85% albumin bound and has a half-life of approximately 30 minutes. It is excreted in urine as inactive metabolites. No significant drug interactions have been reported. Besides its gastrointestinal protective and uterotonic activities, misoprostol regulates various immunologic cascades. It inhibits platelet-activating factor and leukocyte adherence, and modulates adhesion molecule expression. It protects against gut irradiation injury, experimental gastric cancer, enteropathy, and constipation. It improves nutrient absorption in cystic fibrosis. Misoprostol has utility in acetaminophen and ethanol hepatotoxicity, hepatitis, and fibrosis. It is effective in asthmatics and aspirin-sensitive asthmatic and allergic patients. It lowers cholesterol and severity of peripheral vascular diseases, prolongs survival of cardiac and kidney transplantation, synergizes cyclosporine, and protects against cyclosporine-induced renal damage. It works against drug-induced renal damage, interstitial cystitis, lupus nephritis, and hepatorenal syndrome. It is useful in periodontal disease and dental repair. Misoprostol enhances glycosoaminoglycan synthesis in cartilage after injury. It prevents ultraviolet-induced cataracts and reduces intraocular pressure in glaucoma and ocular hypertension. It synergizes antiinflammatory and analgesic effects of diclofenac or colchicine and has been administered to treat trigeminal neuralgic pain. It reduces chemotherapy-induced hair loss and recovery time from burn injury, and is effective in treating sepsis, multiple sclerosis, and pancreatitis.

Enprostil impairs cholesterol and fat absorption

BACKGROUND

Enprostil, a synthetic dehydroprostaglandin E2 structural analogue primarily developed for treatment of gastritis, has been shown also to lower serum cholesterol.

METHODS

We studied cholesterol metabolism in seven hypercholesterolemic subjects before, during, and after a low-dose enprostil (18 micrograms/day) treatment, measuring serum lipids, cholesterol absorption by an oral double-isotope method, fecal cholesterol elimination by the balance technique, and fecal fat. In addition, an oral fat load test with vitamin A was performed.

RESULTS

The drug treatment reduced serum concentrations of total and low-density lipoprotein (LDL) cholesterol by 8.2% and 7.9% (p < 0.05), respectively, and cholesterol absorption efficiency by 18% (p < 0.05), and increased fecal output of neutral sterols by 20% (p < 0.05), bile acids by 24% (NS), and cholesterol synthesis by 30% (p < 0.05). Postabsorptive concentrations of triglycerides and vitamin A in chylomicrons were reduced 3-4 h after the intake of the test meal. Fecal fat excretion was doubled during the enprostil treatment.

CONCLUSIONS

Enprostil reduces serum cholesterol concentrations, apparently by inhibiting cholesterol absorption so that fecal cholesterol elimination is increased in association with a mild fat malabsorption. Enhanced intestinal motility may contribute to these changes, frequently causing abdominal fullness or mild pain without diarrhea.

Effect of rioprostil, a methylprostaglandin E1 analog, on basal and stimulated plasma pancreatic hormone levels in man

The effect of rioprostil, a methylprostaglandin E1 analog on circulating pancreatic hormones was evaluated in 13 healthy male subjects. Rioprostil administration, 300 micrograms twice daily resulted in a significant decrease of fasting insulin, C-peptide, glucagon, and pancreatic polypeptide. No change in fasting plasma glucose or somatostatin levels was observed. An oral glucose tolerance test induced similar increments in plasma glucose concentration before and during treatment, but a delayed rise of insulin and C-peptide levels occurred during the administration of the drug. On rioprostil, the glucose load no longer inhibited peripheral glucagon or somatostatin. Treatment with rioprostil remained without effect on mixed meal-induced changes in plasma glucose levels and concomitant increases in insulin, pancreatic polypeptide, and somatostatin levels. It is concluded that in healthy individuals rioprostil influences the basal and glucose-induced levels of glucagon, insulin, and somatostatin. In healthy men this effect did not, however, result in glucose intolerance.