Gastrointestinal somatostatin in man and dog

Roles of hormones in taste signaling

Proper nutrition, avoidance of ingesting substances that are harmful to the whole organism, and maintenance of energy homeostasis are crucial for living organisms. Additionally, mammals possess a sophisticated system to control the types and content of food that we swallow. Gustation is a vital sensory skill for determining which food stuffs to ingest and which to avoid, and for maintaining metabolic homeostasis. It is becoming apparent that there is a strong link between metabolic control and flavor perception. Although the gustatory system critically influences food preference, food intake, and metabolic homeostasis, the mechanisms for modulating taste sensitivity by metabolic hormones are just now being explored. It is likely that hormones produced in the tongue influence the amounts and types of food that we eat: the hormones that we associate with appetite control, glucose homeostasis and satiety, such as glucagon-like peptide-1, cholecystokinin, and neuropeptide Y are also produced locally in taste buds. In this report, we will provide an overview of the peptidergic endocrine hormone factors that are present or are known to have effects within the gustatory system, and we will discuss their roles, where known, in taste signaling.

Somatostatin in eating disorders

Somatostatin concentrations in plasma were measured before and after a standardized fat and protein-rich fluid test meal in patients with anorexia nervosa, weight-recovered anorectic patients, obese women, and healthy controls. Somatostatin was significantly elevated in all four groups after the test meals. Hormone levels remained elevated for up to 100 min after the test meal. The area under the response curve was significantly higher (p < .01) in the anorectic patients as compared with healthy controls and weight-recovered anorectics. Obese women had blunted somatostatin responses. The findings may explain alterations in insulin secretion and in gastric emptying described earlier in patients with eating disorders.

Effect of substance P on somatostatin release from the isolated perfused rat stomach

The effect of substance P (SP) on the release of gastric somatostatinlike immunoreactivity (SLI) was studied. Substance P inhibited both basal SLI release and SLI release stimulated by gastric inhibitory polypeptide or 1-isoproterenol. This inhibitory action of SP was not blocked by atropine or hexamethonium, suggesting that a cholinergic mechanism was not involved. The SP-suppressed SLI release was also not reversed by the administration of naloxone, which indicated that enkephalinergic involvement was absent. However, the SP antagonist [D-Pro2, D-Trp7,9]-SP abolished the inhibition of SLI release by SP. It is concluded that SP might be involved in the control of gastric SLI release and that the inhibitory action of SP was probably mediated directly or indirectly on the gastric D cells through SP receptors.

Histamine is able to suppress the inhibitory effect of somatostatin on exogenous gastrin: comparison between extractive antral histamine and synthetic histamine

In view of examining inhibition by somatostatin of gastrin-induced gastric secretion, antral histamine (AH) and synthetic histamine (SH) were comparatively studied in dogs. Both AH and SH were able to antagonize somatostatin: their potencies did not differ significantly as regards acid secretion, but AH is more potent than SH on pepsin secretion. The dose-dependent activity of AH was limited for the period of infusion. The denervated pouch is more sensitive than the innervated stomach. We suggest that antral histamine might intervene in the complex regulation of gastric secretion where somatostatin and gastrin act antagonistically and where the stimulatory as well as inhibitory fibers of the vagus intervene.

Gastrointestinal/pancreatic hormone concentrations in the portal venous system of nine patients with organic hyperinsulinism

Percutaneous transhepatic sampling of blood in the portal venous system (TPVS) was used to; (1) localize hormone secreting tumors and help in differentiating tumors from diffuse disease (nesideoblastosis and hyperplasia with adenomata) in 9 patients with fasting hypoglycemia and hyperinsulinism, and (2) study the concentration an distribution of the immunoreactive peptides: insulin (IRI), gastrin (IG), glucagon (IRG), pancreatic polypeptide (hPP), and somatostatin (SRIF-LI), in the venous drainage of the uninvolved portion of the pancreas and GI tract. Localized elevations of IRI (64-920 microunits/ml) predicted tumor localization in 6 patients with single tumors that were not demonstrable angiographically. In one patient with nesideoblastosis and another with islet cell hyperplasia with adenoma, elevated IRI concentrations at multiple locations suggested a diffuse or multicentric process. Elevations of SRIF-LI in the same region as IRI elevations in one patient and of IRG in another patient suggested that these tumor produced two hormones. Some problems in the interpretation of portal venous insulin concentrations are discussed. The locations of maximum portal venous system plasma concentrations and portal-arterial gradients (mean +/- SE pg/ml) in five patients with small single insulinomas were: IG, gastrocolic trunk (126 +/- 27, 46 +/- 22); IRG, proximal splenic vein (130 +/- 30, 47 +/- 13) and gastrocolic trunk (131 +/- 23, 60 +/- 13); hPP, portal vein (164 +/- 48, 49 +/- 22); SRIF-LI, superior mesenteric vein (186 +/- 50, 57 +/- 20) and gastrocolic trunk (178 +/- 59, 55 +/- 21). It is concluded; (1) TPVS can be used successfully to localize single insulin-secreting tumors of the pancreas and to help distinguish them from diffuse disease but problems in such differentiation do occur, (2) circulating SRIF-LI and IRG are derived from both the pancreas and the gut, IG predominantly from the proximal gut and hPP from the head of the pancreas, and (3) The data provide new information for the interpretation of portal insulin concentrations in patients with organic hyperinsulinism and of hormone concentrations for localization of peptide-producing tumors of the pancreas other than insulinomas.

Actions of GIP

Two structurally similar peptides were isolated from a preparation of GIP using an HPLC system. The major peptide corresponds to GIP1-42 and the minor has the sequence GIP3-42. GIP1-42 has both insulinotropic and somatostatinotropic activities, whereas GIP3-42 has only insignificant activity. GIP was also shown to potentiate insulin release initiated by D-glyceraldehyde, L-leucine/L-glutamine and 2-keto-isocaproic acid. No potentiation was observed with 2-ketocaproate. The 4 substrates studied are all metabolized but via different mechanisms.

Somatostatin and gastrin release from canine stomach

Somatostatin and gastrin release into the veins draining the stomach was studied in 27 anaesthetized dogs. Basal somatostatin-like immunoreactivity (SLI) in corpus veins (136 +/- 36 pg/ml) was significantly higher than in antrum veins (83 +/- 20 pg/ml; p less than 0.05) and the femoral artery (58 +/- 15 pg/ml; p less than 0.02). During peptone, pH 6.5, perfusion of the stomach, SLI concentration increased significantly in the corpus veins to approximately four times basal and in the antrum veins to three times basal, whereas SLI levels in the peripheral circulation remained constant. Peptone, pH 3.5, and sodium oleate did not stimulate gastric SLI. Gastric distension increased significantly SLI release from the corpus. In gel filtration studies 50%--70% of SLI from gastric vein plasma samples but greater than 90% from femoral artery samples eluted in the void volume of Sephadex G-25 columns. Gastrin secretion was stimulated significantly only by peptone, pH 6.5.

Somatostatinoma syndrome. Biochemical, morphologic and clinical features

Diabetes mellitus, steatorrhea, cholelithiasis and a tumor distorting the duodenum prompted a work-up for somatostatinoma in a 52-year-old man. The responses of pancreatic B-cells but not of A-cells to nutrient stimuli were inhibited, and growth-hormone release was suppressed, suggesting somatostatin resistance in some target tissues. Plasma somatostatin-like immunoreactivity ranged from 9000 to 13,000 pg per milliliter (normal: 88+/-8, mean +/- S.E.M.) and was distributed in four molecular forms, including free somatostatin. The primary tumor contained 5 microgram of somatostatin-like immunoreactivity per milligram of wet tissue, distributed in three of the molecular forms noted in plasma. Plasma calcitonin was also elevated (4650 pg per milliliter; normal: less than 120). Immunocytochemical studies showed that cells of the primary tumor contained somatostatin and calcitonin but no other peptide hormones. Only somatostatin was present in the metastases. Somatostatin was localized electron microscopically in all secretory granules, irrespective of size and shape, whereas calcitonin was present only within a single subpopulation of small granules in the same cells.