Sotirios Raptis

Effects of somatostatin on the exocrine pancreas and the release of duodenal hormones

Abstract Using the artificial beta cell, previous studies have demonstrated that in insulin-dependent diabetics somatostatin reduces insulin requirements up to 70% and causes a marked flattening of the blood glucose curve after food intake. 1 Furthermore, in insulin-dependent diabetics somatostatin diminishes by 75%–100% rises in blood glucose after oral glucose, but did not influence glucose levels following intravenous glucose. 2 Since during the somatostatin infusion, a 30% reduction in splanchnic blood flow was observed, 2 the diminution of postprandial hypoglycemia following somatostatin seemed attributable primarily to a circulation-dependent delay in carbohydrate absorption. The fact that radioimmunoassayable somatostatin has been found not only in the stomach of the rat but also in the upper intestine, 3 in amounts comparable to those found in the hypothalamus, allow the assumption that somatostatin is a hormone in the gastrointestinal tract, coordinating the secretion of the other hormones. Recently, somatostatin-positive cells were shown to be present in the bottom of the intestinal crypt by immunohistochemical methods; 18 these cells were distinguished from those in other organs by the presence of a cytoplasmic process reaching the gut lumen (external environment). The assumed physiological importance of somatostatin or a somatostatin-like substance in the alimentary tract is emphasized by the fact that recently 4 a somatostatin-like immunoreactive peptide was isolated from the porcine duodenum. It has been known for many years that various gastrointestinal hormones exert an influence on the blood flow of the gastrointestinal tract. 5,6 It is unclear whether the effect of somatostatin on the splanchnic blood flow can be explained by the inhibition of various gastrointestinal hormones. The fact that in insulin-dependent diabetics somatostatin did not improve the intravenous glucose tolerance but only the peroral one suggests that the different effects of somatostatin in the gut may be partly the result of inhibition of various duodenal hormones. The present studies were undertaken to characterize the influence of somatostatin on the release and the biological activities of the two classic intestinal hormones, secretin and pancreozymin.

Immunoreactivity of the Endocrine Pancreas. Evidence for the Presence of Cholecystokinin- Pancreozymin within the A-cell *

SummaryThe pancreas of man and rat were investigated immunohistochemically on occurrence and distribution of the “classical” enterohormones gastrin, secretin and cholecystokinin-pancreozymin (CCK-PZ). Concomitantly insulin-, glucagon- and somatostatin-immunoreactive cells have been demon-strated. The unlabelled antibody-enzyme (PAP) method was the most specific and sensitive one when compared with the other immunohistochemical methods performed in this investigation (immunofluorescence, immunoperoxidase). The PAP method reveals reliable and reproducible results, running with high dilutions of antisera and showing a minimum of nonspecific background staining. Extended specificity controls are necessary in immunohistochemistry, however, to exclude nonspecific or crossreactive staining results. From the numerous specificity methods tested, we propose the use of sequential immunohistochemical staining with increasing dilutions of the antisera as an essential control. The use of specific antisera, previously “adsorbed” with related or corresponding antigens (hormones) as specificity tests should be regarded with some restrictions, at least in the PAP method. When possible a radioimmunological assay should be performed as a final proof of immunohistochemical findings. — The immunohistochemical findings of the present investigations have confirmed previous results of other authors concerning occurrence and distribution of insulin-, glucagon- and somatostatin-immunoreactive cells in the pancreas of rat and man. From the enterohormones gastrin, secretin and CCK-PZ only CCK-PZ (or a CCK-PZ-like peptide) was found to occur in the human and rat pancreas. The presence of CCK-PZ in the pancreas was also confirmed by radioimmunological estimations of CCK-PZ in the rat pancreas. The concentration of CCK-PZ-immunoreactive substance was about 1400 pg/g pancreatic tissue (wet weight) and about 1200 pg/g tissue in the small intestine of rats. Concerning the type of endocrine cells in the endocrine pancreas which contain CCK-PZ, it could be demonstrated that obviously the A-(glucagon) cells are immunoreactive to CCK-PZ. Thus A-cells may contain two polypeptide hormones of different molecular structure. These findings, in addition to other consequences of our results put the “one cell — one hormone theory” in question. — Gastrin- and secretin-immunoreactivity was also present in the A-cells. The immunohistochemical staining was only possible with the PAP method, however. These immunoreactivities in the endocrine pancreas have to be regarded as nonspecific ones, as proved by specificity controls. The secretin-immunoreactivity may be interpreted as a cross-reaction to the structurally similar glucagon. The gastrin-immunoreactivity might be a cross-reaction to the structurally similar CCK-PZ. In fact these cross-reactivities could only be observed in immunohistochemistry but not in the radioimmunoassay. — The occurrence of CCK-PZ, a classical enterohormone, in its “target organ” itself forces to reflections on the concept of endocrine and paracrine functions of entero-endocrine cells. Moreover, the functional unity of the endocrine pancreas and the gastrointestinal endocrine system on the one hand as well as the close interrelationships between the endocrine and the exocrine part of the pancreas on the other is emphasized by these findings.

Estimation of cholecystokinin-pancreozymin (CCK) in human plasma and tissue by a specific radioimmunoassay and the immunohistochemical identification of pancreozymin-producing cells in the duodenum of humans.

A reliable, sensitive, reproducible and specific radioimmunoassay for cholecystokinin-pancreozymin (CCK) has been developed, using rabbit antisera to highly purified porcine hormone. The natural occurring variant of CCK (39-CCK), in which the ordinary CCK is lengthened from its N-terminus by a hexapeptide, labelled with 125J, and repurified by column chromatography on Sephadex G-10 and on SP-Sephadex C-25, was used as tracer. Separation from antibody-bound labelled 39-CCK was carried out using a double antibody procedure. Non-specific interference with the assay system was abolished by ethanol extractions. Highly purified porcine CCK was used as standard. No significant crossreaction was found with gastrin, motilin, vasoactive polypeptide (VIP), gastric inhibitory polypeptide (GIP), natural and synthetic secretin, pancreatic glucagon or insulin. The sensitivity of the assay is approximately 40 pg/ml of test solution. The mean immunoreactive CCK concentration in 45 fasting normal subjects was 222 pg/ml increasing after food ingestion to 480 pg/ml. Somatostatin was able to abolish the stimulated CCK release. Elevated CCK concentrations were found in chronic pancreatitis. Immunohistochemical identification of pancreozymin cells was carried out either in surgical samples or in biopsy material. Approximately 1650 CCK cells per cross-section in the duodenum of humans have been found. The CCK cells usually appeared elongated, oval or pyramidal in shape and were observed to reach the lumen with their apical cell pole.

PREVENTION BY SOMATOSTATIN OF RISE IN BLOOD PRESSURE AND PLASMA RENIN MEDIATED BY BETA‐RECEPTOR STIMULATION

The interrelationships of increased plasma renin and elevated blood pressure following acute β‐stimulation by orciprenaline and its prevention by somatostatin was studied in normal man. During somatostatin infusion basal values of renin and blood pressure were unchanged. Following orciprenaline both variables increased significantly. Combination of somatostatin and orciprenaline reduced the rise in plasma renin activity by 49%, mean arterial blood pressure by 21% and heart rate by 19%, compared with β‐stimulation alone.

Inhibition of TSH-stimulated radioiodine turnover and release of T4 and T3 in vivo by somatostatin☆

Abstract With respect to the hypothalamic-pituitary-thyroid axis, it has been demonstrated that somatostatin blocks the pituitary thyrotropin (TSH) release stimulated by thyrotropin-releasing hormone (TRH).1,2 Recently, somatostatin has been shown to be present in the thyroid gland.3,4 To elucidate the role of somatostatin in the regulation of thyroid function, the effect of somatostatin on TSH-stimulated thyroidal radioiodine turnover and thyroid hormone release in vivo were studied in euthyroid volunteers.

A reliable method for generating antibodies against pancreozymin, secretin and gastrin.

High specific antibodies against the gastrointestinal hormones pancreozymin, secretin, and gastrin were generated by coupling these peptides with N,N-carbonyldiimidazole to bovine serum albumin. None of the antisera showed any cross reaction with gut and pancreatic hormones tested for cross reactivity. The dilution of antisera which were useful for the detection of 5-250 pg of hormone in human serum were 1:150 000 for secretin, 1:2000 for gastrin, and 1:2000 for pancreozymin. The N,N-carbonyldiimidazole reagent is therefore highly effective for binding labile peptides to protein carriers without destroying the immunogenic features.

Hemodynamic and renin responses to somatostatin in essential hypertension.

Abstract Recent studies indicate that somatostatin inhibits furosemide-induced hyperreninemia; 1,2 in addition, somatostatin has been reported to block increases of blood pressure induced by administration of β-adrenergic agents. 3 These findings in normal subjects prompted further investigations in patients with essential hypertension.

Antidiabetic action of somatostatin assessed by artificial β-cell

Abstract Undoubtedly, of the many effects of somatostatin on the endocrine system and on the hormones of digestion and metabolism in particular, its hypoglycemic effect in normal and diabetic man 1–4 deserves highest attention in regard to its antidiabetic implication. However, the results reported as to the hypoglycemic action of somatostatin in normal subjects, insulin-dependent, and insulin-independent diabetics have been quite variable. 1,5,6 Consequently, the present study was undertaken to examine the effect of prolonged infusion of somatostatin on carbohydrate metabolism in insulin-dependent diabetics in whom provision of sufficient amounts of insulin was secured and the release of which was not influenced by the inhibiting hormone. The ideal method for realizing this purpose was offered by the artificial endocrine pancreas or β cell permitting continuous monitoring of blood glucose and automated insulin supply on a computerized basis. 7,8 In addition, changes in growth hormone (GH), glucagon, gastrin and, if present, C-peptide levels were measured not only in juvenile-onset and some maturity-onset diabetics, but also in a selected group of patients, demonstrating special endocrine features such as complete lack of growth hormone or pancreatic glucagon following hypophysectomy or pancreatectomy.

Effects of secretin and cholecystokinin-pancreocymin on water, electrolyte and glucose absorption in human jejunum: A Comparison Between Different Hormone Preparations

SummaryThe effects of natural secretin (90%) and synthetic secretin as well as impure (10%) and pure (99%) cholecystokinin-pancreozymin (CCK) on net absorption of water, electrolytes, and glucose in human jejunum were studied in 31 normal subjects. An intestinal perfusion technique with a triple-lumen tube was used. Net absorption of water and solute was significantly inhibited by both hormones only with larger doses, pure CCK being less active than impure CCK. A dose-dependent response of water and electrolyte absorption to graded doses of pure CCK was observed, without concomitant inhibition of glucose absorption with lower doses. The findings suggest that secretin and CCK may not be of physiologic importance regarding intestinal absorption in man. The definite changes in intestinal motility and transit rate caused by these hormones seem more likely to result in a reduction of intestinal absorption and an increase in the secretion of water and electrolytes along the proximal small bowel.

Behavior of Secretin in the Hypoxia-Immobilisation Stress on the Rat

Secretin was determined radioimmunologically in portal vein blood and in duodenal mucosa biopsies in stressed male Wistar rats as compared to control animals. The stressed animals showd a significantly higher scretin content of the duodenalmucosa and no different levels of the portal vein blood. A stress ulcer-reducing cimetidine application does not demonstrate any influence of secretin content on duodenal mucosa. The obvious elevation of duodenal secrtin is not the result of an increased gastric acid production, but may be a consequence of a stress-reduced susceptibility of the pancreas to endogenous secretin.