Somatostatin and octreotide in gastroenterology

A comparison of the effects of pegvisomant and octreotide on glucose, insulin, gastrin, cholecystokinin, and pancreatic polypeptide responses to oral glucose and a standard mixed meal

Standard medical therapy for patients with acromegaly includes somatostatin analogs. Owing to the widespread expression of somatostatin receptors, these may be associated with unwanted effects, such as altered glucose tolerance and impaired gut hormone release. Pegvisomant is a novel pegylated GH analog that competes with wild-type GH for GH-receptor binding sites but contains a position 120, amino acid substitution that prevents functional GH receptor dimerization, a known prerequisite for GH signal transduction and generation of IGF-I. We have studied the short-term effects of these two therapies (pegvisomant 20 mg/d for 7 d and octreotide 50 microg thrice daily for 7 d) on glucose tolerance and stimulated gut hormone release in six healthy male volunteers in an open-label, random-order, cross-over study. Subjects were assessed at baseline (oral glucose tolerance test and standard mixed meal) and on d 6 and 7 of each therapy with a minimum washout of 2 wk between treatments. Area under the curve and peak responses were analyzed using one-way repeated-measures ANOVA (on ranks where appropriate). Pegvisomant had no effect on glucose tolerance or stimulated gut hormone response during an oral glucose tolerance test and a standard meal. In contrast, octreotide significantly increased fasting plasma glucose, lowered fasting plasma insulin, and led to deterioration in glucose tolerance; three subjects developed impaired glucose tolerance and one diabetes mellitus by World Health Organization criteria. Octreotide significantly impaired stimulated release of cholecystokinin, gastrin, insulin, and pancreatic polypeptide. In conclusion, pegvisomant, unlike octreotide, is not associated with deterioration in glucose tolerance and impairment of stimulated gut hormone release in normal males.

Improvement in the intestinal processes of hydroelectrolytic absorption and secretion in abdominal pathologies of surgical interest treated with SMS 201-995: experimental protocol

The hypothesis that octreotide can improve the intestinal absorption and secretion processes in a mixed group of intestinal pathologies, and that this effect varies according to the pathology in question, was tested. One hundred and twenty Wistar rats were randomly assigned to six pathology groups consisting of three intestinal occlusions including (1) complete, (2) partial, and (3) complete with strangulation, and three mesenteric vascular occlusions including (4) partial permanent, (5) total permanent, and (6) total temporary. Each group contained ten control and ten treated rats. The treated animals received octreotide (100 microg/kg body weight) while the controls were given the same quantity of saline solution every 8 h. After the observation period, the contents of the small intestine were extracted and its volume measured before and after centrifugation; the concentration and total content of Na, K, Cl, and bicarbonate was then analyzed. Samples of all the intestines at specific distances from the lesion zone were treated and stained, and then evaluated according to a specific score to quantify the lesions. The concentration and contents of electrolytes in the intestine and its volume (before and after centrifugation) were lower in the treated animals, but varied according to the pathology. There was a nonadditive influence between the type of pathology and treatment for the four electrolytes and intestinal volume. The effects of the drug make it directly or indirectly possible to decrease the intestinal lesions to improve the absorption-secretion processes. Octreotide acts on intestinal secretion and absorption in all the pathologies analyzed except for total permanent intestinal ischemia. Its action also varies according to the type of pathology involved.

Somatostatin and the gastrointestinal tract

Somatostatin has various significant effects on the gastrointestinal tract: it inhibits the release of several gastrointestinal hormones, blocks the exocrine function of the stomach and the pancreas, and decreases the motility of both the stomach and the gut. Its physiological effects make it potentially useful in the therapy of various gastrointestinal diseases and disorders. Somatostatin is effective in the management of active variceal bleeding and increases the effectiveness of sclerotherapy. Previous studies show controversial data about the efficacy of somatostatin in preventing complications following endoscopic retrograde cholangiopancreatography. The use of this compound may be indicated only in high-risk patients in whom endoscopic sphincterotomy may also become necessary. The perioperative use of somatostatin decreases the risk of pancreatic surgery and its application is effective in promoting the closure of pancreatic fistulae. The somatostatin analogue octreotide has a definitive role in the medical management of hormone-secreting neuroendocrine tumours of the gut.

Somatostatin: physiology and clinical applications

Somatostatin (SOM) was originally isolated as the hypothalamic inhibitor of growth hormone release but was subsequently shown to have a widespread distribution including the gastrointestinal tract. In fact the gastrointestinal tract contains about 70% of the total body SOM. SOM has inhibitory actions on gastrointestinal exocrine and endocrine secretions, motility and blood flow. Within the gut it functions as an endocrine, paracrine, autocrine and neurocrine factor. SOM is released by a meal, and a number of neurotransmitters and regulatory peptides also influence SOM release. SOM is a key component of the gastrin-acid feedback loop as luminal acid releases SOM, which in turn has inhibitory effects on both gastrin and gastric acid. Consistent with the diverse functions of SOM, a number of different although related SOM receptors with distinct distribution patterns and intracellular mediators have been cloned and sequenced. SOM is the first of the gut regulatory peptides to have a significant therapeutic use. By inhibiting both the target cell (e.g. parietal cell) and the release of the active agent (e.g. gastrin) the therapeutic potential of SOM is magnified. To date most of the clinical experience has been with the one analogue, octreotide. This analogue has a longer half-life than SOM (hours versus minutes) but has only minimal oral activity, therefore requiring subcutaneous injections several times a day. The definite gastrointestinal applications include treatment of gastroenteropancreatic tumours. It is also becoming a favoured treatment for gastrointestinal fistulae, variceal bleeding and diarrhoea. However, octreotide has no consistent effect on tumour growth. The high density of SOM receptors on tumours has allowed localization of tumours using in vivo scintography with labelled octreotide. The sequencing of a variety of SOM receptors with different distributions and differing cellular effector systems raises the likelihood of developing SOM analogues for specific clinical applications.

Resolution of pancreatic ascites with octreotide

A 7 month old infant with pancreatitis and ascites was managed successfully with subcutaneous octreotide and external drainage of a pseudocyst. An endoscopic retrograde cholangiopancreatographic examination showed no congenital abnormality and was consistent with chronic pancreatitis. Octreotide has a possible therapeutic role in pancreatic ascites.