The release of prolactin (PRL) from a clonal cell‐line of anterior pituitary cells (GH 4 C 1 ) was inhibited by somatostatin (SRIH) in a dose‐dependent manner (ED 50 nM). The inhibition (20% of control levels) was detectable within 50 s and maximal within 90 s. Thyroliberin (TRH) enhancement of PRL secretion was biphasic. SRIH inhibited both phases equally. Ionomycin in combination with the phorbol ester, TPA, mimics the TRH‐elicited PRL release, and SRIH partly inhibited this effect. SRIH had no effect on TRH‐stimulated formation of inositol trisphosphate, and only small effects on TRH‐activated adenylate cyclase. Vasoactive intestinal peptide (VIP) and forskolin stimulated cAMP formation and PRL release potently. SRIH inhibited both effects of VIP and forskolin, and there was a close correlation between the inhibition of PRL secretion and cAMP accumulation. 8‐Bromo‐cAMP enhanced PRL release, an effect that was also partly reduced by SRIH. The Ca 2+ channel activator, BAY‐K‐8644 and high extracellular K + increased PRL release, and SRIH caused a partial reduction in the release response to both secretagogues. SRIH lowered [Ca 2+ ] 1 , and markedly reduced the rise in [Ca 2+ ] 1 elicited by TRH, VIP and K + . SRIH did not influence the Ca 2+ spikes recorded in Na + ‐free solution, and had no effect on the TRH‐induced membrane potential changes. Our results demonstrate that SRIH may inhibit PRL release from GH 4 C 1 cells by (1) inhibiting hormone‐sensitive adenylate cyclase, (2) blocking the effect of cAMP and (3) lowering [Ca 2+ ] 1 . None of these effects is, however, sufficient to explain all the effects of SRIH, suggesting that SRIH also exerts a major action at a step subsequent to cAMP accumulation and [Ca 2+ ] 1 elevation. Since the GH 4 C 1 cells possess one single class of binding sites, this implies that the same SRIH receptor is coupled to several cellular signalling systems.

Plasma immunoreactive somatostatin (IRS) levels were measured fasting at 09.00 h in groups of adult individuals and children of different ages, as well as in pregnant women, in patients with pernicious anaemia documented to be achlorhydric, and in children with growth hormone deficiency. There was a gradual rise in the mean level of IRS from the third decade (mean 35.8 +/- 3.8 pg/ml), which reached significance at the seventh (61.1 +/- 8.4 pg/ml), eighth (66.7 +/- 5 pg/ml) and ninth decade (82.6 +/- 13.8 pg/ml). No change was observed in the second 28.3 +/- 3.8 pg/ml) and third (31.1 +/- 3.2 pg/ml) trimester of pregnancy when compared with matched, non-pregnant controls (29.7 +/- 2.2 pg/ml); however, the children aged under 2 years (69.6 +/- 11.2 pg/ml) had significantly higher values than the eldest group (12 to 16 years old) (46.3 +/- 7.2 pg/ml) (P less than 0.05). In achlorhydric patients, basal (27.2 +/- 3.7 pg/ml; P less than 0.01) and postprandial IRS (42.8 +/- 7.7 pg/ml; P less than 0.001) was significantly lower than in a matched, normal control group (basal 59.4 +/- 7.2; postprandial 132.1 +/- 26.3 pg/ml). Growth hormone deficiency was not associated with any differences in circulating IRS, basally or after insulin hypoglycaemia, when compared with values in normal children.(ABSTRACT TRUNCATED AT 250 WORDS)

A highly specific and sensitive radioimmunoassay was developed for measuring circulating growth hormone releasing factor (GRF) in human plasma. Before measuring immunoreactive GRF plasma samples were extracted on to Vycor glass. Immunoreactive GRF concentrations in plasma samples from 37 fasting normal subjects ranged from less than 10 to 60 ng/l (mean 21 ng/l). Fasting concentrations in 76 out of 80 acromegalic subjects were within the normal range, but the remaining four patients had values of 92 to 25 000 ng/l. Of these, only the patient with the highest concentration had evidence of ectopic GRF secretion from a disseminated carcinoid tumour. Two of the others had longstanding pituitary tumours, and the fourth patient had a pituitary growth hormone (GH) secreting tumour proved by its removal and subsequent remission of acromegaly. There was no correlation between serum GH and plasma immunoreactive GRF concentrations, irrespective of whether the patients were untreated or had been given radiotherapy or dopamine agonists. The assay should help elucidate the physiological role(s) of GRF and may also prove useful in differentiating between pituitary and hypothalamic defects in patients with acromegaly.

Food and insulin hypoglycaemia raise plasma concentrations of somatostatin. Both also stimulate gastric acid secretion but it is not clear whether gastric acid itself has any effect on somatostatin secretion. We, therefore, studied the effect on plasma concentrations of somatostatin of infusion of 0.1 N HC1 into the stomach and duodenum of healthy subjects. Plasma somatostatin did not rise with a small dose of HC1 given intragastrically (15 mmol) or intraduodenally (4 mmol). After an intraduodenal infusion of 60 mmol HC1 over 30 minutes, sufficient to reduce intraluminal pH to 2, plasma somatostatin rose moderately in five subjects from a mean value (+/- SEM) of 32 +/- 3 pg/ml to a peak at 10 minutes of 54 +/- 11 pg/ml. It is concluded that: (a) intragastric acid infusions do not release circulating somatostatin in man; and (b) that intraduodenal acidification albeit at grossly supraphysiological doses is a moderate stimulus of plasma somatostatin release. Therefore, gastric acid is unlikely to be a major factor mediating postprandial plasma somatostatin release in man.

SUMMARY Insulin‐induced hypoglycaemia, which stimulates gastric acid secretion, is associated with an increase in circulating somatostatin levels in man. In order to assess the mechanisms involved in this rise, six normal volunteers connected to a Biostator for continuous glucose monitoring were studied, on three separate occasions. On each occasion after basal blood sampling, 0.15 i.u. /kg body weight of insulin was administered i.v. and further samples were obtained intermittently over 150 min. On one occasion, dextrose was infused by the Biostator to prevent hypoglycaemia, while on the other two, a constant infusion of either normal saline or the specific H 2 antagonist cimetidine was administered. Insulin plus dextrose caused no significant changes in circulating somatostatin levels, whereas insulin plus saline was associated with a marked, sustained and significant rise in all subjects; insulin plus cimetidine also produced a rise but it was delayed; the area under the curve was significantly (P<0.05) greater with insulin plus saline than with insulin plus cimetidine. These results show that in man insulin itself does not stimulate somatostatin secretion directly, but indirectly via hypoglycaemia. Further, the inhibition of gastric acid secretion with cimetidine reduces somatostatin release during insulin‐induced hypoglycaemia. This suggests that gastric acid may mediate somatostatin secretion associated with insulin‐induced hypoglycaemia.

In the present study the distribution and molecular characteristics of bombesin-like immunoreactivity (BLI) were studied in acid extracts of human gastrointestinal tract. The highest levels were found in the fundus, antrum, pylorus and pancreas with lower levels in the duodenum, jejunum, terminal ileum and colon. BLI was also detected in both the muscle and mucosal layers of the antrum and colon. Sephadex G-50 gel chromatography under acid dissociating conditions revealed two peaks of immunoreactivity, one in the position of synthetic porcine gastrin releasing peptide (GRP) and the second eluting with synthetic amphibian bombesin. Variations in the proportions of the two molecular forms were seen in different regions of the gut. In the stomach and pancreas > 70% of the BLI eluted with the GRP marker while in pylorus, jejunum and terminal ileum only 20% was present in this form. Reverse-phase ODS silica HPLC of the major antral BLI peak, utilising a methanol/trifluoroacetic acid gradient indicated that this peptide was similar to porcine GRP. We have therefore (1) demonstrated the presence and heterogeneity of bombesin-like immunoreactivity throughout the human gastrointestinal tract and (2) shown for the first time that a proportion of this BLI closely resembles porcine GRP.

Immunoreactive somatostatin (IRS) was measured in acid extracts of human gastrointestinal tissue. The highest levels were found in the duodenum, pancreas, jejunum and stomach with lower levels in the ileum and colon. In the antrum, pylorus, duodenum and pancreas the main peak of IRS (1.6K IRS) coeluted with synthetic somatostatin-14 on both gel filtration chromatography and HPLC. In the body of stomach, jejunum, ileum and colon, a large peak coeluting with synthetic somatostatin-28 (3.5K IRS) on both chromatographic systems was also identified, while minor peaks of IRS assigned molecular weights of 6000 (6K) and > 15 000 (15K) were seen in some extracts. The total IRS content and pattern of molecular forms were similar in tissues obtained from adults at surgery or rapid post mortem, and in tissue taken from human fetuses after prostaglandin termination of pregnancy.

Dynorphin-[1-13], at concentrations of 5.8 X 10(-12) to 5.8 X 10(-9) M, stimulated insulin secretion from isolated islets of Langerhans of the rat, in medium containing 6 mM glucose. Higher concentrations of dynorphin had no significant effect on secretion. Dynorphin (5.8 X 10(-9) M) was unable to initiate insulin release from islets in the presence of 2 mM glucose, or to increase insulin secretion further in the presence of 20 mM glucose or 6 and 12 mM glyceraldehyde. Dynorphin-induced insulin secretion from islets was blocked by verapamil (5 microM) or by chlorpropamide (72 microM), but not by a mu opiate receptor antagonist, naloxone (0.11 microM), or by ICI 154129, a specific antagonist for the delta receptor (0.25 microM). Dynorphin had no effect on islet somatostatin secretion, under conditions in which insulin secretion was greatly stimulated. Glucose (20 mM) and glyceraldehyde (6 and 12 mM) significantly increased both insulin and somatostatin secretion. Dynorphin (5.8 X 10(-9) M) increased 45Ca2+ uptake into islets, and also increased intracellular islet c-AMP levels. These changes persisted when higher concentrations of dynorphin were used. These results suggest that (1) dynorphin is a very potent stimulus for insulin secretion; (2) dynorphin does not affect somatostatin secretion in static incubations of islets, in the same way as does glucose and glyceraldehyde; (3) dynorphin's effects may involve increased calcium ion movement and can be blocked by verapamil; (4) dynorphin can also increase islet c-AMP, and could thereby modulate the responsiveness of other secretagogues; (5) the actions of dynorphin on insulin secretion are not mediated by delta or mu opiate receptors in islets.

Gel-filtration chromatography of an acid-extract of a phaeochromocytoma, under dissociating conditions, revealed 4 peaks of immunoreactive somatostatin (IRS) of approx. 8–10 kilodaltons (K), 6K, 3.5K and 1.6K as detected by an antiserum (R9) directed against the central region of tetradecapeptide somatostatin (S14). The 3.5K and 1.6K forms of IRS co-eluted with synthetic cyclic S28 and S14 respectively on reversed phase HPLC. Using another radioimmunoassay for the 1–14 sequence of S28 (N-peptide) a peak of immunoreactive N-peptide (IRN) with a molecular weight of approx. 4500 was observed. The antiserum (N3) used in the N-peptide assay was raised against N-Tyr N-peptide and cross-reacts less than 5% with synthetic S28. Two peaks were further characterised by partial tryptic digestion and gel-filtration chromatography. The 3.5K IRS peak was partially converted to a 1.6K IRS form together with an approximately equimolar amount of IRN with apparent molecular weight of 2500. This 2.5K IRN co-eluted both with N-Tyr N-peptide and with the IRN generated by tryptic digestion of synthetic cyclic S28. No IRN peak of this size was observed in the original extract. Tryptic digestion of the 6K IRS peak generated 3.5K and 1.6K IRS and 2.5K IRN. These results suggested that (1) this human phaeochromocytoma contains IRS very similar to the known structure of ovine and porcine S28 and S14. (2) The 6K IRS is composed of an unknown peptide sequence attached via a trypsin-susceptible bond to the N-terminus of S28. (3) In this tumour S14 is being generated directly from 6K IRS and not via S28.

Conference Abstract| September 01 1982 Hypochlorhydria Reduces Plasma Somatostatin Response to Food M R Lucey; M R Lucey 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar J A H Wass; J A H Wass 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar P D Fairclough; P D Fairclough 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar M Murphy; M Murphy 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar E Penman; E Penman 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar S Webb; S Webb 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar J Webb; J Webb 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar G M Besser; G M Besser 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar L H Rees; L H Rees 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar A M Dawson A M Dawson 1Departments of Gastroenterology, Chemical Endocrinology, Endocrinology and Haematology, St. Bartholomew's Hospital, London EC1 Search for other works by this author on: This Site PubMed Google Scholar Clin Sci (Lond) (1982) 63 (3): 29P. https://doi.org/10.1042/cs063029P Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation M R Lucey, J A H Wass, P D Fairclough, M Murphy, E Penman, S Webb, J Webb, G M Besser, L H Rees, A M Dawson; Hypochlorhydria Reduces Plasma Somatostatin Response to Food. Clin Sci (Lond) 1 September 1982; 63 (3): 29P. doi: https://doi.org/10.1042/cs063029P Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll JournalsClinical Science Search Advanced Search This content is only available as a PDF. © 1982 The Biochemical Society and the Medical Research Society1982 Article PDF first page preview Close Modal You do not currently have access to this content.

We have previously reported that in normal subjects plasma immunoreactive somatostatin levels rise after a mixed meal. The contribution of individual nutrients to this rise, and the molecular nature of the somatostatin immunoreactivity measured, have now been studied. Six normal healthy subjects received, on separate occasions, isocaloric (520 calories) and isovolumetric (260 ml) quantities of carbohydrate, protein, and fat. The mean fasting plasma somatostatin level was 29 +/- 5 pg/ml. After carbohydrate a peak of 48 +/- 7 pg/ml was reached at 30 min, and after protein and fat there were more sustained rises with peak levels of 74 +/- 8 pg/ml and 80 +/- 9 pg/ml, respectively. Sephadex G50 chromatography of extracts of fasting peripheral plasma showed two main peaks of somatostatin immunoreactivity, one coeluting with cyclic somatostatin and a larger peak of approximately 3500 molecular weight (mol wt). Levels of both 1600 and 35000 mol wt somatostatin were increased 60 min after a mixed meal. Approximately 80% of the 3500 mol wt form of somatostatin could be converted to the 1600 mol wt form by treatment with dithiothreitol (an agent which reduces disulphide bonds). It is concluded that: (a) in normal subjects fat and protein are potent stimuli for somatostatin release; (b) somatostatin in normal peripheral plasma exists in multiple forms, and that both 1600 and 35000 mol w forms of somatostatin immunoreactivity are stimulated by feeding; (c) the 3500 mol wt form could represent a dimer of somatostatin or a somatostatin molecule linked to a second peptide chain by disulphide bonds.

SUMMARYEctopic secretion of somatostatin in one patient with a thymic tumour and in two patients with lung tumours is described. All three patients also had ectopic ACTH secretion. Gel filtration chromatography under dissociating conditions showed the two lung tumour extracts to contain predominantly 1600 MW somatostatin monomer while the thymic tumour contained predominantly a 3000–3500 MW form of somatostatin, 77% of which was not converted to 1600 MW somatostatin by dithiothreitol (an agent which reduces disulphide bridges). This form may therefore represent a covalently‐bound precursor of somatostatin rather than a dimer of two somatostatin monomers. Plasma from all three tumour patients and from normal subjects contained both 1600 and 3000–3500 MW somatostatin. It is suggested that somatostatin secretion may frequently be associated with multiple hormone producing tumours.