The GLP1R Agonist Liraglutide Reduces Hyperglucagonemia Induced by the SGLT2 Inhibitor Dapagliflozin via Somatostatin Release

The newest classes of anti-diabetic agents include sodium-glucose cotransporter 2 (SGLT2) inhibitors and glucagon-like peptide 1 receptor (GLP1R) agonists. The SGLT2 inhibitor dapagliflozin reduces glucotoxicity by glycosuria but elevates glucagon secretion. The GLP1R agonist liraglutide inhibits glucagon; therefore, we hypothesize that the cotreatment of dapagliflozin with liraglutide could reduce hyperglucagonemia and hyperglycemia. Here we use five complementary models: human islet cultures, healthy mice, db/db mice, diet-induced obese (DIO) mice, and somatostatin receptor-2 (SSTR2) KO mice. A single administration of liraglutide and dapagliflozin in combination improves glycemia and reduces dapagliflozin-induced glucagon secretion in diabetic mice. Chronic treatment with liraglutide and dapagliflozin produces a sustainable reduction of glycemia compared with each drug alone. Moreover, liraglutide reduces dapagliflozin-induced glucagon secretion by enhancing somatostatin release, as demonstrated by SSTR2 inhibition in human islets and in mice. Collectively, these data provide mechanistic insights into how intra-islet GLP1R activation is critical for the regulation of glucose homeostasis.

Proposed mechanisms for oligonucleotide IMT504 induced diabetes reversion in a mouse model of immunodependent diabetes

Type 1 diabetes (T1D) originates from autoimmune β-cell destruction. IMT504 is an immunomodulatory oligonucleotide that increases mesenchymal stem cell cloning capacity and reverts toxic diabetes in rats. Here, we evaluated long-term (20 doses) and short-term (2-6 doses) effects of IMT504 (20 mg·kg(-1)·day(-1) sc) in an immunodependent diabetes model: multiple low-dose streptozotocin-injected BALB/c mice (40 mg·kg(-1)·day(-1) ip for 5 consecutive days). We determined blood glucose, glucose tolerance, serum insulin, islet morphology, islet infiltration, serum cytokines, progenitor cell markers, immunomodulatory proteins, proliferation, apoptosis, and islet gene expression. IMT504 reduced glycemia, induced β-cell recovery, and impaired islet infiltration. IMT504 induced early blood glucose decrease and infiltration inhibition, increased β-cell proliferation and decreased apoptosis, increased islet indoleamine 2,3-dioxygenase (IDO) expression, and increased serum tumor necrosis factor and interleukin-6 (IL-6). IMT504 affected islet gene expression; preproinsulin-2, proglucagon, somatostatin, nestin, regenerating gene-1, and C-X-C motif ligand-1 cytokine (Cxcl1) increased in islets from diabetic mice and were decreased by IMT504. IMT504 downregulated platelet endothelial cell adhesion molecule-1 (Pecam1) in islets from control and diabetic mice, whereas it increased regenerating gene-2 (Reg2) in islets of diabetic mice. The IMT504-induced increase in IL-6 and islet IDO expression and decreased islet Pecam1 and Cxcl1 mRNA expression could participate in keeping leukocyte infiltration at bay, whereas upregulation of Reg2 may mediate β-cell regeneration. We conclude that IMT504 effectively reversed immunodependent diabetes in mice. Corroboration of these effects in a model of autoimmune diabetes more similar to human T1D could provide promising results for the treatment of this disease.

VEGF secretion by neuroendocrine tumor cells is inhibited by octreotide and by inhibitors of the PI3K/AKT/mTOR pathway

Gastroenteropancreatic (GEP) endocrine tumors are hypervascular tumors able to synthesize and secrete high amounts of VEGF. We aimed to study the regulation of VEGF production in GEP endocrine tumors and to test whether some of the drugs currently used in their treatment, such as somatostatin analogues and mTOR inhibitors, may interfere with VEGF secretion. We therefore analyzed the effects of the somatostatin analogue octreotide, the mTOR inhibitor rapamycin, the PI3K inhibitor LY294002, the MEK1 inhibitor PD98059 and the p38 inhibitor SB203850 on VEGF secretion, assessed by ELISA and Western blotting, in three murine endocrine cell lines, STC-1, INS-r3 and INS-r9. Octreotide and rapamycin induced a significant decrease in VEGF production by all three cell lines; LY294002 significantly inhibited VEGF production by STC-1 and INS-r3 only. We detected no effect of PD98059 whereas SB203850 significantly inhibited VEGF secretion in INS-r3 and INS-r9 cells only. By Western blotting analysis, we observed decreased intracellular levels of VEGF and HIF-1alpha under octreotide, rapamycin and LY294002. For rapamycin and LY294002, this effect was likely mediated by the inhibition of the mTOR/HIF-1/VEGF pathway. In addition to its well-known anti-secretory effects, octreotide may also act through the inhibition of the PI3K/Akt pathway, as suggested by the decrease in Akt phosphorylation detected in all three cell lines. In conclusion, our study points out to the complex regulation of VEGF synthesis and secretion in neoplastic GEP endocrine cells and suggests that the inhibition of VEGF production by octreotide and rapamycin may contribute to their therapeutic effects.

A short acute octreotide test for response prediction of long-term treatment with somatostatin analogues in acromegalic patients

The usefulness of the acute octreotide test in the selection of acromegalic patients for chronic somatostatin depot analogues treatment is controversial. The aim of the present study was to determine its accuracy for chronic response prediction, and the reliability of a short version of the classic 6-hour test. The data from 26 acromegalics (19 women, 7 men, mean age 52.6+/-13.1 years) studied with an acute octreotide test (6 hours sampling for GH measurement after octreotide 100 microg s. c.) were retrospectively analyzed. Eighteen of them followed chronic somatostatin depot analogues treatment for 12 months. GH nadir was always detected at 2 hours (mean decrease 75.9+/-24%). GH levels at 2 hours positively correlated with the other time-points (r(s) 0.97, 0.98, 0.97, 0.96 at 3, 4, 5 and 6 h, respectively; p<0.0001). During chronic treatment with maximal effective dose for 12 months, 61% of the patients achieved IGF1 <3 SD and 22% reached IGF1 <2 SD. GH nadir correlated with IGF1 decrease at 12 months (r(s) 0.76, p<0001). GH nadir of 9.2 ng/ml predicts IGF1 <3 SD with 82% sensitivity and 58% specificity (75% PPV, 67% NPV); for IGF1<2 SD, 75% sensitivity and 58% specificity are obtained for GH nadir 3.6 ng/ml, with 33% PPV and 89% NPV. Acute octreotide test reliably predicts response to long-term treatment; the short, 2-hour version is fully informative for therapeutic decisions in acromegalic patients.

Minocycline provides protection against beta-amyloid(25-35)-induced alterations of the somatostatin signaling pathway in the rat temporal cortex

Minocycline is a semi-synthetic second-generation tetracycline known to improve cognition in amyloid precursor protein transgenic mice. Whether it can protect the somatostatin (SRIF) receptor-effector system, also involved in learning and memory, from alterations induced by chronic i.c.v. infusion of beta-amyloid peptide (Abeta)(25-35) is presently unknown. Hence, in the present study, we tested the effects of minocycline on the SRIF signaling pathway in the rat temporal cortex. To this end, male Wistar rats were injected with minocycline (45 mg/kg body weight) i.p. twice on the first day of treatment. On the following day and during 14 days, Abeta(25-35) was administered i.c.v. via an osmotic minipump connected to a cannula implanted in the left lateral ventricle (300 pmol/day). Minocycline (22.5 mg/kg, i.p.) was injected once again the last 2 days of the Abeta(25-35) infusion. The animals were killed by decapitation 24 h after the last drug injection. Our results show that minocycline prevents the decrease in SRIF receptor density and somatostatin receptor (sst) 2 expression and the attenuated capacity of SRIF to inhibit adenylyl cyclase (AC) activity, alterations present in the temporal cortex of Abeta(25-35)-treated rats. Furthermore, minocycline blocks the Abeta(25-35)-induced decrease in phosphorylated cyclic AMP (cAMP) response element binding protein (p-CREB) content and G-protein-coupled receptor kinase 2 (GRK) protein expression in this brain area. Altogether, the present data demonstrate that minocycline in vivo provides protection against Abeta-induced impairment of the SRIF signal transduction pathway in the rat temporal cortex and suggest that it may have a potential as a therapeutic agent in human Alzheimer's disease, although further studies are warranted.

Chronic but not acute intracerebroventricular administration of amyloid beta-peptide(25-35) decreases somatostatin content, adenylate cyclase activity, somatostatin-induced inhibition of adenylate cyclase activity, and adenylate cyclase I levels in the rat hippocampus

Although alterations in adenylate cyclase (AC) activity and somatostatin (SRIF) receptor density have been reported in Alzheimer's disease, the effects of amyloid beta-peptide (Abeta) on these parameters in the hippocampus are unknown. Our aim was to investigate whether the peptide fragment Abeta(25-35) can affect the somatostatinergic system in the rat hippocampus. Hence, Abeta(25-35) was injected intracerebroventricularly (i.c.v.) to Wistar rats in a single dose or infused via an osmotic minipump connected to a cannula implanted in the right lateral ventricle during 14 days. The animals were decapitated 7 or 14 days after the single injection and 14 days after chronic infusion of the peptide. Chronic i.c.v. infusion of Abeta(25-35) decreased SRIF-like immunoreactive content without modifying the SRIF receptor density, SRIF receptor expression, or the Gialpha(1), Gialpha(2), and Gialpha(3) protein levels in the hippocampus. This treatment, however, caused a decrease in basal and forskolin-stimulated AC activity as well as in the capacity of SRIF to inhibit AC activity. Furthermore, the protein levels of the neural-specific AC type I were significantly decreased in the hippocampus of the treated rats, whereas an increase in the levels of AC V/VI was found, with no alterations in type VIII AC. A single i.c.v. dose of Abeta(25-35) exerted no effect on SRIF content or SRIF receptors but induced a slight decrease in forskolin-stimulated AC activity and its inhibition by SRIF. Because chronic Abeta(25-35) infusion impairs learning and memory whereas SRIF facilitates these functions, the alterations described here might be physiologically important given the decreased cognitive behavior previously reported in Abeta-treated rats.

Sulfonylurea compounds uncouple the glucose dependence of the insulinotropic effect of glucagon-like peptide 1

Glucagon-like peptide (GLP)-1 mimetics have been reported to cause hypoglycemia when combined with sulfonylureas. This study investigated the impact of tolbutamide on the glucose dependence of the GLP-1-mediated effects on insulin, glucagon, and somatostatin secretion in the in situ perfused rat pancreas. At 3 mmol/l glucose, GLP-1 alone did not augment insulin secretion, whereas tolbutamide alone caused a rapid increase in insulin secretion. However, when GLP-1 and tolbutamide were administered simultaneously, insulin secretion increased significantly to 43.7 +/- 6.2 pmol/min (means +/- SE), exceeding the sum of the responses to GLP-1 (2.0 +/- 0.6 pmol/min; P = 0.019) and tolbutamide (11.3 +/- 3.8; P = 0.005) alone by a factor of 3.3. At 11 mmol/l glucose, co-infusion of GLP-1 and tolbutamide augmented insulin secretion to 141.7 +/- 10.3 vs. 115.36 +/- 14.1 (GLP-1) and 42.5 +/- 7.3 pmol/min (tolbutamide). Interestingly, increases in somatostatin secretion, both by glucose and GLP-1, were consistently paralleled by suppression of glucagon release. In conclusion, we demonstrate uncoupling of GLP-1 from its glucose dependence by tolbutamide. This uncoupling probably explains the tendency of GLP-1 to provoke hypoglycemia in combination with sulfonylureas. The results suggest that closure of ATP-sensitive K(+) channels by glucose might be involved in the glucose dependence of GLP-1's insulinotropic effect and that somatostatin acts as a paracrine regulator of glucagon release.

The influence of growth hormone status on physical impairments, functional limitations, and health-related quality of life in adults

The availability of recombinant human GH and somatostatin analogs has resulted in widespread treatment for adults with GH deficiency (GHD) and those with GH excess (acromegaly). Despite being at opposite ends of the spectrum in terms of their GH/IGF-I axis, both of these populations experience overlapping somatic impairments. Adults with untreated GHD have low circulating levels of IGF-I that manifest as altered body composition with increased fat and reduced lean body and skeletal muscle mass. At the other end of the spectrum, adults with GH excess, who have elevated levels of IGF-I, also have altered body composition. Impairments that result from disorders of either GHD or GH excess are both associated with increased functional limitations, such as reduced ability to walk quickly for prolonged periods, and poorer health-related quality of life (HR-QoL). Adults with untreated GHD and GH excess both commonly complain of excessive fatigue that seems to be associated more with impaired aerobic than muscular performance. Several studies have documented that administration of GH or somatostatin analogs to adults with GHD or GH excess, respectively, ameliorates abnormal biochemical profile and the associated somatic impairments. However, whether these improvements translate into improved physical function in adults with GHD or GH excess remains largely unknown, and their impact on HR-QoL controversial. Review of placebo-controlled trials to date suggests that GH and somatostatin analogs have greater effects on gas exchange and aerobic performance than as anabolic agents on skeletal muscle mass and function. Future investigations should include dose-response studies to establish the optimal combination of pharmacological agents plus exercise required to improve not only biochemical markers but also physical function and HR-QoL in adults with GHD or GH excess.

Effect of probiotics and triple eradication therapy on the cyclooxygenase (COX)-2 expression, apoptosis, and functional gastric mucosal impairment in Helicobacter pylori-infected Mongolian gerbils

BACKGROUND

Helicobacter pylori infection in Mongolian gerbils is an established experimental model of gastric carcinogenesis that mimics H. pylori-positive patients developing gastric ulcer and gastric cancer, but the effect of probiotic therapy on functional aspects of this infection remains unknown.

METHODS

We compared the effects of intragastric inoculation of gerbils with H. pylori strain (cagA+ vacA+, 5 x 10(6) colony forming units/ml) with or without triple therapy including omeprazole, amoxicillin, and tinidazol or probiotic bacteria Lacidofil. Histology of glandular mucosa, the viable H. pylori, and density of H. pylori colonization were evaluated. The gastric blood flow was measured by H2-gas clearance method; the plasma gastrin and gastric luminal somatostatin were determined by RIA and expression of cyclooxygenase (COX)-2 and apoptotic Bax and Bcl-2 proteins were evaluated by Western blot.

RESULTS

The gastric H. pylori infection was detected in all animals by histology and H. pylori culture. Basal gastric acid was significantly reduced in H. pylori-infected animals but not in those with triple therapy or Lacidofil. Early lesions were seen already 4 weeks upon H. pylori inoculation and consisted of chronic gastritis and glandular atypia associated with typical regenerative hyperplasia and increased mitotic activity and formation of apoptotic bodies. The H. pylori infection was accompanied by the fall in gastric blood flow, the marked increase in plasma gastrin, the significant fall in gastric somatostatin levels and Bcl-2 protein expression, and the rise in expression of COX-2 and Bax proteins. These mucosal changes were counteracted by the triple therapy and Lacidofil.

CONCLUSIONS

H. pylori infection in gerbils, associated with regenerative hyperplasia of glandular structure, results in the suppression of gastric secretion, overexpression of COX-2, and enhancement in apoptosis and impairment of both, gastric blood flow and gastrin-somatostatin link that were reversed by anti-H. pylori triple therapy and attenuated by probiotics.

Gly-Pro-Glu protects beta-amyloid-induced somatostatin depletion in the rat cortex

The effect of Gly-Pro-Glu (GPE) on the somatostatinergic system of the temporal cortex in amyloid beta-peptide (Abeta) treated rats was investigated. Intracerebroventricular Abeta25-35 administration for 14 days (300 pmol/day) to ovariectomized rats produced a marked reduction in somatostatin (SRIF) content, SRIF receptor density and reduced the inhibitory effect of SRIF on adenylyl cyclase activity. I.p. injection of three doses (300 microg) of GPE on days 0, 6 and 12 resulted in a partial recovery of the parameters affected by Abeta25-35 administration. These results indicate that GPE may have an in vivo effect protecting the temporal cortical somatostatinergic system from Abeta insult.

Intermittent hypoxia causes a suppressed pituitary growth hormone through somatostatin

OBJECTIVES

The aim of this study was to investigate the response of the growth hormone (GH) in rat anterior pituitary to intermittent hypoxia (IH) and its modulation by hypothalamic somatostatin (SS).

SETTING AND DESIGN

To observe the hypoxic response, rats were exposed to simulated altitude hypoxia (2 km or 5 km) in a hypobaric chamber for various days (4 h/d); to clarify SS-involvement, rats were pretreated with SS antagonist (cysteamine, CSH, 200 mg/kg/d, s.c.) then exposed to IH (5 km) for 2d. The GH mRNA and immunostaining GH in pituitary as well as immunostaining SS in median eminence (ME) of hypothalamus were assayed by RT-PCR and immuno-histochemistry, respectively.

RESULTS

IH of 5 km altitude (IH5) markedly suppressed the body weight gain (BWG) of rats from 1d to 10d, and it was returned to control level henceforth, while no significant influence was showed in the group of IH of 2 km altitude (IH2). IH5 for 2 and 5d significantly decreased GH mRNA expression in the pituitary. The pituitary immunostaining GH was remarkably increased in groups of IH2 for 5, 10, and 15 d, and in groups of IH5 for 2, 5, and 10d. Immunostaining SS in ME was significantly reduced in group of IH2 for 5d, and in groups of IH5 for 2d and 5d. Pretreatments (s.c.) with SS antagonist (CSH) significantly reversed IH5-caused increase of immunostaining GH and reduction of mRNA levels in pituitary.

CONCLUSIONS

IH may cause a short-term and recoverable suppression of GH release, and reduce GH mRNA expression in anterior pituitary, which may depend on the intensity and duration of the hypoxia. This suppression may be due to a modulation of hypoxia-activated SS.

Pepsinogen secretion in cholecystokinin-1 receptor-deficient rats

We examined the roles of cholecystokinin (CCK)-2 receptors in the regulation of pepsinogen secretion in the CCK-1 receptor deficient Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Pepsinogen secretion was determined in fasted acute fistula OLETF and control Long-Evans Tokusima Otsuka (LETO) rats. Pepsinogen secretion in OLETF rats under basal conditions as well as in response to CCK-8 stimulation was significantly higher than that in LETO rats. CCK-1 receptor specific agonist ARL 15849 was unable to stimulate pepsinogen secretion in OLETF rats, whereas it elicited pepsinogen secretion in LETO rats to levels similar to those obtained with equimolar CCK-8 stimulation. CCK-2 receptor antagonist reduced basal pepsinogen secretion and completely abolished CCK-8-stimulated pepsinogen output in OLETF rats, whereas in LETO rats, it reduced basal pepsinogen secretion but augmented CCK-8-stimulated pepsinogen output. CCK-1 receptor antagonist loxiglumide also greatly decreased CCK-8-stimulated pepsinogen secretion in OLETF rat, which indicates that loxiglumide is not a specific CCK-1 receptor antagonist. Intravenous infusion of somatostatin antagonist significantly increased CCK-8-stimulated pepsinogen secretion in LETO rats, whereas it had no significant influence on CCK-8-stimulated pepsinogen secretion in OLETF rats. These results indicate that CCK-8 stimulates pepsinogen secretion via CCK-2 receptors in CCK-1 receptor deficient OLETF rats and that the higher CCK-8-stimulated as well as basal pepsinogen secretion in OLETF rats might result from an elimination of tonic inhibition by somatostatin that is released from D cells through mainly CCK-1 receptors.

Modulation of Brain Insulin-Like Growth Factor I (IGF-I) Binding Sites and Hypothalamic GHRH and Somatostatin Levels by Exogenous Growth Hormone and IGF-I in Juvenile Rats

The effect of exogenous growth hormone (GH) and insulin-like growth factor I (IGF-I) on brain IGF-I binding sites (IGF-IR), and on the levels of growth hormone-releasing hormone (GHRH) and somatostatin was studied in hypophysectomized and intact juvenile male rats. Animals were injected subcutaneously twice daily (n = 5 each) with recombinant GH (rGH) (2.5 U/kg per day) or rIGF-I (500 microg/kg per day). In the hypophysectomized rats, serum GH and IGF-I levels were markedly suppressed and IGF-I levels were partially restored by GH treatment. There was a significant increase in IGF-IR binding capacity in the IGF-I-treated hypophysectomized rats compared to the saline-treated hypophysectomized animals (150.61 +/- 45.66 vs 41.32 +/- 12.42 fmol/mg, p < 0.05) but no significant difference in IGF-IR mRNA levels. GHRH levels in the saline-treated hypophysectomized group were significantly lower than in the saline-treated intact rats (31.2 +/- 11.2 vs 140.6 +/- 48.1 pg/mg tissue, respectively, p < 0.01); no effect was induced by GH or IGF-I (37.5 +/- 26.8 and 53.8 +/- 22.5 pg/mg tissue, respectively). However, in the intact rats, GH and IGF-I injection led to a decrease in GHRH content, which was significant in the GH-treated compared to the saline-treated animals (33.1 +/- 16.2 vs 140.6 +/- 48.1 pg/mg tissue, p < 0.01). No difference was found in somatostatin levels between intact and hypophysectomized rats (631.2 +/- 81.2 and 625.0 +/- 62.5 pg/mg tissue, respectively). However, in the hypophysectomized animals, GH and IGF-I treatment induced a significant increase in somatostatin levels (1300 +/- 193.7 pg/mg tissue, p < 0.01, and 912.5 +/- 81.2 pg/mg tissue, p < 0.05, respectively). Our findings suggest that the bioavailability of exogenous IGF-I is greater than that of GH-stimulated endogenous IGF-I. Because IGF-I is a potent neurotrophic agent, this effect may have important implications for states of neurodegenerative diseases.

Leptin stimulates growth hormone secretion via a direct pituitary effect combined with a decreased somatostatin tone in a median eminence-pituitary perifusion study

The aim of this study was to examine the effect of recombinant human leptin on growth hormone (GH) secretion in perifused anterior pituitary slices from adult pigs. Anterior pituitary slices from sows were perifused and treated with recombinant human leptin (10 nM) and GH-releasing hormone (GHRH; 1 nM). In some experiments, pituitary slices were coincubated with stalk median eminence (SME). In a subset of the coincubation experiments, immunoneutralization of endogenous GHRH and somatostatin (SRIH) release was performed with antisera to GHRH and SRIH. Leptin increased GH secretion in pituitary slices alone (up to 100% vs. control at 40 min) as well as in pituitary slices coincubated with SME (up to 122% vs. control at 40 min). A significant difference was observed in GH secretion from pituitary slices when the tissue was coincubated with leptin and GHRH at a low concentration (0.1 nM), but not when GHRH was used at 1 and 10 nM. Furthermore, anti-SRIH antiserum increased GH release from pituitary slices in coincubation experiments with SME. Finally, SRIH secretion was significantly reduced by leptin (down by 35% vs. control from 0 to 30 min of treatment) in cultured SME. These data show that leptin is effective in stimulating GH secretion by acting at two different levels: (1) it stimulates GH secretion directly from pituitary slices, and (2) it reduces SRIH tone from the median eminence and, indirectly, increases GH secretion from the pituitary. These results support the hypothesis that leptin may be an interesting hormonal mediator of growth and related metabolic effects by acting directly on the hypothalamic-pituitary axis.

Somatostatin-14 neurons in the ovine hypothalamus: colocalization with estrogen receptor alpha and somatostatin-28(1-12) immunoreactivity, and activation in response to estradiol

Pituitary gland growth hormone (GH) secretion is influenced by two hypothalamic neuropeptides: growth hormone-releasing hormone (GHRH) and somatostatin. Recent data also suggest that estrogen modulates GH release, particularly at the time of the preovulatory luteinizing hormone surge, when a coincident surge of GH is observed in sheep. The GHRH neurons do not possess estrogen receptor alpha (ERalpha), suggesting that estrogen does not act directly on GHRH neurons. Similarly, few somatotropes express ERalpha, suggesting a weak pituitary effect of estradiol on GH. It was hypothesized, therefore, that estradiol may affect somatostatin neurons to modulate GH release from the pituitary. Using immunocytochemical approaches, the present study revealed that although somatostatin neurons were located in several hypothalamic sites, only those in the arcuate nucleus (13% +/- 2%) and ventromedial nucleus (VMN; 29% +/- 1%) expressed ERalpha. In addition, we found that all neurons immunoreactive for somatostatin-14 were also immunoreactive for somatostatin-28(1-12). To determine whether increased GH secretion in response to estradiol is through modulation of GHRH and/or somatostatin neuronal activity, a final study investigated whether c-fos expression increased in somatostatin- and GHRH-immunoreactive cells at the time of the estradiol-induced LH surge in intact anestrous ewes. Estradiol significantly (P < 0.05) increased the percentage of GHRH (estradiol, 75% +/- 3%; no estradiol, 19% +/- 2%) neurons expressing c-fos in the hypothalamus. The percentage of somatostatin-immunoreactive neurons coexpressing c-fos in the estradiol-treated animals was significantly (P < 0.05) higher (periventricular, 44% +/- 3%; arcuate, 72% +/- 5%; VMN, 81% +/- 5%) than in the control animals (periventricular, 22% +/- 1%; arcuate, 29% +/- 3%; VMN, 31% +/- 3%). The present study suggests that estradiol modulates the activity of GHRH and somatostatin neurons but that this effect is most likely mediated through an indirect interneuronal pathway.

The protective effect of catechin on gastric mucosal lesions in rats, and its hormonal mechanisms

BACKGROUND

Catechin, a polyphenol contained in tea (a cup of tea contains approximately 0.1% [w/v] catechin), has various physiological effects. The aim of this study was to investigate the mechanism of the inhibitory effect of catechin on gastric mucosal lesions.

METHODS

We studied the effect of catechin on gastric mucosal lesions in rats, using a water immersion restraint (WIR) stress-induced gastric mucosal lesion model. We used crude catechin that contained 52.6% (w/w) (-)-epigallocatechin gallate and 16.7% (w/w) (-)-epicatechin gallate. The rats were randomly divided into three groups; control rats freely drank distilled water, and the remaining rats drank 0.1% (w/v) or 1% (w/v) crude catechin-containing water for 2 weeks. We measured fractional areas of hemorrhagic erosion in the gastric mucosa induced by WIR stress for 4h, compared with findings in the controls. We also employed an isolated rat stomach infusion model and measured gastrin, somatostatin, and histamine in the perfusate to endocrinologically investigate the mechanism underlying the putative protective effect of catechin.

RESULTS

Catechin had a significant protective effect against the gastric mucosal lesions induced by WIR stress. Catechin also significantly inhibited the release of gastrin, somatostatin, and histamine.

CONCLUSIONS

Catechin confers a protective effect against gastric mucosal lesions, and anti-gastric and anti-histaminergic effects may be involved in the mechanism of this effect.

Eradication of Helicobacter pylori restores the inhibitory effect of cholecystokinin on gastric motility in duodenal ulcer patients

BACKGROUND

Increased gastric emptying and defective action of endogenous cholecystokinin (CCK), that is known to inhibit this emptying, have been implicated in the pathogenesis of duodenal ulcer (DU). The aim of this double blind study was to assess whether CCK and somatostatin participate in the impairment of gastric motility in active DU patients before and after Helicobacter pylori eradication.

METHODS

Tests were undertaken in 10 DU patients without or with elimination of the action of endogenous CCK using loxiglumide, a selective CCK-A receptor antagonist, before and 4 weeks after eradication of H. pylori with 1 week triple therapy that resulted in healing of all DUs tested. The gastric emptying rate after feeding was determined using the 13C-acetate breath test. Before each test, samples of gastric juice were obtained by aspiration using a nasogastric tube for determination of somatostatin using specific radioimmunoassay.

RESULTS

Prior to H. pylori eradication gastric emptying half-time was 31 +/- 6 min in placebo-treated DU patients and this emptying rate was not significantly affected in tests after pretreatment with loxiglumide (10 mg/kg i.v.). Following eradication of H. pylori, in tests with placebo gastric emptying half-time was significantly longer (48 +/- 9 min) compared to that prior to H. pylori eradication. Pretreatment with loxiglumide in H. pylori eradicated DU patients significantly enhanced the gastric emptying rate with an emptying half-time of only 33 +/- 4 min. Eradication of H. pylori resulted in a significant increase in somatostatin concentration in gastric juice and loxiglumide significantly reduced this luminal somatostatin in H. pylori-eradicated subjects compared to values before anti-H. pylori therapy.

CONCLUSIONS

1) H. pylori infection in DU patients is accompanied by enhanced gastric emptying and reduction in luminal release of somatostatin; 2) the failure of loxiglumide to affect gastric emptying in H. pylori-infected DU patients might be attributed, at least in part, to the failure of endogenous CCK to control gastric motility due to deficient release of somatostatin; and 3) H. pylori-infected patients appear to exhibit a deficient somatostatin release by endogenous CCK that can be reversed by the eradication of H. pylori indicating that both CCK and somatostatin may contribute to normalization of gastric emptying following H. pylori eradication in DU patients.

The use of nimodipine in the treatment of mood disorders

Nimodipine, a dihydropyridine calcium entry blocker, has been shown to protect from neuronal damage due to ischemia by providing for increased postischemic perfusion. Further, it has also been demonstrated to have antiepileptic properties. These two properties--calcium channel blockade and anticonvulsant benefits have been applied with success to mood disorder treatment. Although found helpful nearly a decade ago for uncomplicated mania, nimodipine may have particular benefits for those diagnostic subclasses of bipolar disorder most resistant to therapy, e.g., ultra-rapid-cycling bipolars and brief recurrent depressions.

Selective block of rat and human neocortex GABA(B) receptors regulating somatostatin release by a GABA(B) antagonist endowed with cognition enhancing activity

Previously, we have shown that presynaptic GABA(B) receptors regulating the release of various transmitters from CNS terminals can be differentially blocked by GABA(B) antagonists suggesting the existence of pharmacologically distinct GABA(B) receptor subtypes. We here examined the ability of CGP 36742 [(3-aminopropyl)n-butylphosphinic acid], a selective GABA(B) antagonist endowed with cognition enhancing activity, to block release-regulating GABA(B) receptors. In particular, CGP 36742 was tested against the inhibition of the depolarization-evoked release of GABA, glutamate, cholecystokinin and somatostatin produced by (-)baclofen in rat and human neocortex axon terminals. CGP 36742 potently antagonized (IC50 = 0.14 microM) the inhibition by (-)baclofen of somatostatin release from superfused rat neocortex synaptosomes. In contrast, the effects of (-)baclofen on GABA, glutamate and cholecystokinin release were insensitive to CGP 36742, at concentrations of up to 100 microM. In human neocortex synaptosomes CGP 36742 exhibited a pattern of selectivity identical to that in rat synaptosomes, although the antagonist was at least 10-fold less potent in human than in rat brain. CGP 36742 is the first compound displaying great selectivity for the GABA(B) presynaptic receptors regulating somatostatin release. Considering the proposed implication of the neuropeptide in cognitive processes, disinhibition of somatostatin release merits consideration as one of the mechanisms possibly involved in the behavioral activity of CGP 36742.

Acceleration of ulcer healing by cholecystokinin (CCK): role of CCK-A receptors, somatostatin, nitric oxide and sensory nerves

CCK exhibits a potent cytoprotective activity against acute gastric lesions, but its role in ulcer healing has been little examined. In this study we determined whether exogenous CCK or endogenously released CCK by camostate, an inhibitor of luminal proteases, or by the diversion of pancreatico-biliary secretion from the duodenum, could affect ulcer healing. In addition, the effects of antagonism of CCK-A receptors (by loxiglumide, LOX) or CCK-B receptors (by L-365,260), an inhibition of NO-synthase by N(G)-nitro-L-arginine (L-NNA), or sensory denervation by large neurotoxic dose of capsaicin on CCK-induced ulcer healing were examined. Gastric ulcers were produced by serosal application of acetic acid and animals were sacrificed 9 days after ulcer induction. The area of ulcers and blood flow at the ulcer area were determined. Plasma levels of gastrin and CCK and luminal somatostatin were measured by RIA and mucosal biopsy samples were taken for histological evaluation and measurement of DNA synthesis. CCK given s.c. reduced dose dependently the ulcer area; the threshold dose of CCK being 1 nmol/kg and the dose inhibiting this area by 50% being 5 nmol/kg. This healing effect of CCK was accompanied by a significant increase in the GBF at ulcer margin and the rise in luminal NO production, plasma gastrin level and DNA synthesis. Concurrent treatment with LOX, completely abolished the CCK-8-induced acceleration of the ulcer healing and the rise in the GBF at the ulcer margin, whereas L-365,260 remained without any influence. Treatment with camostate or diversion of pancreatic juice that raised plasma CCK level to that observed with administration of CCK-8, also accelerated ulcer healing and this effect was also attenuated by LOX but not by L-365,260. Inhibition of NO-synthase by L-NNA significantly delayed ulcer healing and reversed the CCK-8 induced acceleration of ulcer healing, hyperemia at the ulcer margin and luminal NO release, and these effects were restored by the addition to L-NNA of L-arginine but not D-arginine. Capsaicin denervation attenuated CCK-induced ulcer healing, and the accompanying rise in the GBF at the ulcer margin and decreased plasma gastrin and luminal release of somatostatin when compared to those in rats with intact sensory nerves. Detectable signals for CCK-A and B receptor mRNAs as well as for cNOS mRNA expression were recorded by RT-PCR in the vehicle control gastric mucosa. The expression of CCK-A receptor mRNA and cNOS mRNA was significantly increased in rats treated with CCK-8 and camostate, whereas CCK-B receptor mRNA remained unaffected. We conclude that CCK accelerates ulcer healing by the mechanism involving upregulation of specific CCK-A receptors, enhancement of somatostatin release, stimulation of sensory nerves and hyperemia in the ulcer area, possibly mediated by NO.

Somatostatin- and factor XIIIa-immunoreactive cells in psoriasis during clobetasol propionate and calciprotriol treatment

This study describes the changes in number and distribution of somatostatin- and factor XIIIa-immunoreactive dendritic cells in the epidermis and dermis of psoriatic lesional skin during topical treatment with clobetasol propionate or calcipotriol. Immunohistochemical analysis showed that the number of each cell type was increased in lesional skin as compared to normal skin. Investigation of serial biopsies from psoriasis lesions revealed a significant reduction in the number of somatostatin- and factor XIIIa-positive dendritic cells during the treatments. The reduction rate of the somatostatin-positive cells differed between the two groups and closely paralleled the healing process induced by the two treatments. These findings and the fact that somatostatin has been used in several studies as treatment for psoriasis may indicate that the somatostatin-positive cells are specifically involved in the healing process of psoriasis. The reduction of the factor XIIIa-positive cells was associated with the healing process as a whole, but showed no relation to either treatment.

[Hormonal changes and secretion and stomach mucosal microstructure in the course of H. pylori in patients with duodenal ulcer]

We designed this study to follow exocrine, endocrine and microstructural changes in duodenal ulcer patients with H. pylori infection in the course and after quadruple eradication regimen. Quadruple therapy appeared to be highly effective method of both ulcer healing and H. pylori eradication. We observed enhanced regeneration of gastric mucosa in the course of treatment. Almost immediate decrease of plasma gastrin and increase of plasma somatostatin and EGF concentration in gastric juice were noticed.

[Endocrine and exocrine gastric mucosal secretion in the course of H. pylori eradication in patients with non-ulcer dyspepsia]

Microstructural, endo- and exocrine changes in gastric mucosa of Non-Ulcer Dyspepsia patients with H. pylori infection in the course of eradication has been studied. Before, during and after anti H. pylori therapy plasma gastrin and somatostatin levels, EGF and somatostatin concentration in gastric juice and basal and pentagastrin stimulated gastric acid secretion were measured. Moreover microstructure of gastric mucosa specimens has been studied. Maximal Acid Output initially higher in NUD patients than in healthy volunteers increased slightly in the course of eradication. Plasma gastrin decreased while EGF and somatostatin concentration in gastric juice increased. After treatment the ratio of patients with pronounced features (activity) of gastritis was significantly reduced.

Growth hormone secretagogues: focus on the growth hormone-releasing peptides

This review systematically analyses recent knowledge of the biology of the growth hormone-releasing peptides. Many years before native GHRH had been isolated and sequenced, the synthesis of an enkephalin analog, devoid of any opioid activity but capable of specifically releasing GH from in vitro pituitaries, prompted the design of a number of structurally interrelated GHRPs with improved GH-releasing activity. Nowadays, GHRPs are the most effective GH-secretagogues known and could be used profitably in humans with GH hyposecretory disturbances to promote a pattern of GH secretion that mimics physiology in a better way than the exogenously administered GH.

Methods for the investigation of neuropeptide catabolism and stability in vitro

The protocol describes (i) methods for the investigation of neuropeptide catabolism in the central nervous system (CNS), (ii) the identification of the neuropeptidases involved, and (iii) methods for the determination of neuropeptide stability in vitro. These methods are applicable also to study the degradation of peptide hormones by peripheral cells or tissues. To identify peptide degradation products, nanomolar amounts (micromolar concentrations) of peptides are incubated in synthetic media with cell or tissue cultures. Aliquots of the supernatants are withdrawn after different times, peptide fragments separated and fractionated by reversed-phase HPLC, and identified by peptide chemical methods. The peptidases responsible for this degradation can be identified by the use of specific inhibitors listed in the protocol. For receptor binding assays or the study of peptide effects in physiological, nanomolar concentrations the stability of the peptides in an in vitro system should be checked by addition of radiolabeled peptides (femtomolar or nanomolar concentrations) and monitoring the peptide degradation by a procedure analogous to that established for unlabeled peptides. The addition of more or less specific peptidase inhibitors enhances peptide stability in vitro, and thus it can be assured that a given peptide concentration is maintained during biological assays.

The effect of gastrin-releasing peptide on gastrin and somatostatin messenger RNAs in humans infected with Helicobacter pylori

BACKGROUND & AIMS

Gastrin-releasing peptide stimulates gastrin secretion but also inhibits its release via somatostatin. Exogenous gastrin-releasing peptide stimulates a greater increase in plasma gastrin concentrations in patients infected with Helicobacter pylori than in uninfected controls. Because this infection suppressed gastric mucosal somatostatin, we studied whether the increased gastrin response was a result of an abnormal response of the somatostatin cell.

METHODS

Patients without dyspeptic ulcers received an infusion of either gastrin-releasing peptide or saline on separate occasions. Acid secretion was measured, and gastric biopsy specimens were taken for gastrin and somatostatin messenger RNA (mRNA) analysis and H. pylori diagnosis.

RESULTS

In response to gastrin-releasing peptide, the increase in plasma gastrin concentrations in the infected patients was significantly higher than in the uninfected. Antral gastrin mRNA also increased significantly in the infected group but decreased significantly in the uninfected group. Basal somatostatin was lower in the infected group; gastrin-releasing peptide produced a significant increase in antral somatostatin mRNA concentration in infected, but not uninfected, patients.

CONCLUSIONS

The somatostatin cell responds to gastrin-releasing peptide in H. pylori infection. Gastrin-releasing peptide normally inhibits gastrin mRNA expression, but inhibition is deficient in H. pylori infection, possibly because of low stimulated somatostatin levels.

Leptin suppression of insulin secretion by the activation of ATP-sensitive K+ channels in pancreatic beta-cells

In the genetic mutant mouse models ob/ob or db/db, leptin deficiency or resistance, respectively, results in severe obesity and the development of a syndrome resembling NIDDM. One of the earliest manifestations in these mutant mice is hyperinsulinemia, suggesting that leptin may normally directly suppress the secretion of insulin. Here, we show that pancreatic islets express a long (signal-transducing) form of leptin-receptor mRNA and that beta-cells bind a fluorescent derivative of leptin (Cy3-leptin). The expression of leptin receptors on insulin-secreting beta-cells was also visualized utilizing antisera generated against an extracellular epitope of the receptor. A functional role for the beta-cell leptin receptor is indicated by our observation that leptin (100 ng/ml) suppressed the secretion of insulin from islets isolated from ob/ob mice. Furthermore, leptin produced a marked lowering of [Ca2+]i in ob/ob beta-cells, which was accompanied by cellular hyperpolarization and increased membrane conductance. Cell-attached patch measurements of ob/ob beta-cells demonstrated that leptin activated ATP-sensitive potassium channels (K(ATP)) by increasing the open channel probability, while exerting no effect on mean open time. These effects were reversed by the sulfonylurea tolbutamide, a specific inhibitor of K(ATP). Taken together, these observations indicate an important physiological role for leptin as an inhibitor of insulin secretion and lead us to propose that the failure of leptin to inhibit insulin secretion from the beta-cells of ob/ob and db/db mice may explain, in part, the development of hyperinsulinemia, insulin resistance, and the progression to NIDDM.

Influence of type of dietary fat (olive and sunflower oil) upon gastric acid secretion and release of gastrin, somatostatin, and peptide YY in man

The effects of adaptation to two diets differing in the type of dietary fat on the gastric acid secretory response to food and on the circulating levels of gastrin, somatostatin and peptide YY (PYY) were examined in humans. The study involved 18 cholecystectomized subjects previously submitted to a 30-day adaptation period to diets containing olive (group O) or sunflower oil (group S) as the fat source. During the experiments, physiological stimulation was achieved by ingestion of 200 ml of oleic acid- (group O) or linoleic acid-enriched (group S) liquid mixed meals. These resulted in an immediate rise in gastric pH. In group S, the return to the premeal value was completed within 60 min, and a further decline to values significantly lower than the basal ones was observed at the end of the study period. In contrast, ingestion of the meal containing olive oil attenuated and prolonged the pH decrease after the meal, this being associated with the suppression of postprandial gastrin response. Food ingestion induced no significant changes in plasma somatostatin concentration in either group, and no significant differences were revealed between them during the basal or postprandial situations. Plasma PYY levels were consistently higher in group O throughout the entire study period, although significance was reached only at resting. In conclusion, our results show that a 30-day adaptation period to diets containing olive oil as the main source of dietary fat results, compared with those containing sunflower oil, in an attenuated gastric secretory function in response to a liquid meal in humans. The effects of olive oil were associated with a suppression of serum gastrin and higher levels of PYY.

Effects of GH and IGF-I administration on GHRH and somatostatin mRNA levels: II. A study in the infant rat

It is generally accepted that growth hormone influences its own secretion by modulating the activity of GHRH and SRIF neurons. To investigate if GH feedback mechanisms are already operating in the early postnatal life of the rat, we have studied in 10-day-old pups the effects of rhGH and rhIGF-I administration on GHRH and somatostatin mRNA levels. The same experiment was also performed in pups passively immunized with an anti-GHRH antiserum from the day of birth. The latter animal model had been previously characterized for presenting reduced levels of circulating GH and IGF-I. In control pups, neither rhGH (250 micrograms/kg, b.i.d., sc) nor rhIGF-I (150 micrograms/kg, b.i.d., sc) administration induced significant changes of GHRH and SRIF gene expression. The passive immunization against GHRH induced per se a trend toward an increase and a reduction of GHRH and SRIF mRNA levels, respectively. Also in these rats the treatment for 3 days with rhGH and rhIGF-I did not further modify the GHRH and SRIF mRNA levels. Based on these results, we conclude that in the 10-day-old rat GH feedback mechanisms are poorly operative, though a direct ultra-short loop mechanism involving the GHRH and SRIF systems seems already operating.

Effects of GH and IGF-I administration on GHRH and somatostatin mRNA levels: I. A study on ad libitum fed and starved adult male rats

The individual role played by GH and IGF-I in the regulation of hypothalamic GHRH and SRIF gene expression is still object of debate. We have investigated the effect of exogenously administered recombinant hGH (rhGH) and recombinant hIGF-I (rhIGF-I) in ad libitum fed control and starved rats, the latter an animal model which is characterized by low circulating levels of endogenous GH and IGF-I. Adult male rats were fed ad libitum (C) or food-deprived (S) for 72 hours; rats in either C or S groups were treated with systemic administration of rhGH and rhIGF-I for 3 days. GHRH, SRIF and GH mRNA levels were evaluated by Northern and slot blot hybridization. Administration of rhGH (250 micrograms/kg/twice daily, sc) induced a significant inhibition of GHRH and a significant stimulation of SRIF mRNA levels in C rats; GH treatment was, however, ineffective on both neuropeptide mRNA levels in the S group. Continuous infusion of rhIGF-I (300 micrograms/kg/day, sc) induced a significant increase of SRIF levels in both C and S rats but did not modify GHRH mRNA levels in either group. In the pituitary, GH mRNA levels followed a pattern very similar to that of GHRH. These results provide evidence for a direct role of GH in the inhibition of GHRH mRNA levels; IGF-I appears more involved in the direct stimulation of SRIF mRNA levels.

Inhibition of GH releasing factor (GRF)-induced GH secretion by intraruminal infusion of volatile fatty acids (VFA) in sheep

A VFA mixture solution containing acetate, propionate and butyrate (the molar ratio of acetate, propionate and n-butyrate = 61.7:24.3:14.0) was infused into the rumen at various rates (53.5, 107 and 214 mumol kg-1 min-1) over 6 h to examine the effects on basal and growth hormone-releasing factor (GRF, 0.25 micrograms kg-1)-induced increase in secretion of GH, insulin, glucagon and somatostatin (SRIF) in five castrated male sheep. Intraruminal infusion of the VFA mixture into the 18-h-fasted animals at the rates of 53.5, 107 and 214 mumol kg-1 min-1 finally raised the total intraruminal VFA concentration from 91.4 to 100.2 (P > 0.05), 175.9 (P < 0.05) and 234.5 (P < 0.05) mmol l-1, respectively. A preliminary experiment showed that an infusion rate of 107 mumol kg-1 min-1 mimics the postprandial increase in ruminal VFA. The basal plasma GH concentrations (2 to 4 h after the start of VFA infusion) and the area under the profiles for GH release in response to the intravenous GRF injection, which was done 4 h after the start of VFA infusion, were significantly decreased by the VFA infusion rates of 107 and 214 mumol kg-1 min-1. Furthermore, the VFA infusion noticeably increased basal plasma concentrations of insulin, but it scarcely changed the basal levels of glucagon, SRIF and glucose. From these results we conclude that an increase in the ruminal VFA concentration, even within the physiological range, would suppress GH secretion from the ovine anterior pituitary, and that the postprandial rise in the ruminal VFA concentration may be one of the factors normally suppressing GH secretion in sheep.

Suppression of histidine decarboxylase activity in rat oxyntic mucosa by beraprost sodium, a prostacyclin analogue

Prostaglandins (PGs) affect various aspects of gastric functions. In the present study the orally administered PGI2 derivative beraprost sodium (TRK-100.1 micrograms per kg body weight) decreased oxyntic histidine decarboxylase activity without changing serum gastrin levels. Antral pH increased 4 hr after treatment. Beraprost also decreased the pentagastrin-induced histidine decarboxylase activity at the same dose. Serum levels of secretin, somatostatin and glucose, and oxyntic mucosal levels of histamine and somatostatin, showed no significant change after treatment with beraprost. These results suggest that the response of oxyntic histidine decarboxylase to gastrin is modified by one or more prostanoids including PGI2. This mechanism might play a role in gastric mucosal protection.

Bowel resection and neurotensin treatment. Histochemical study of neurotensin-like and somatostatin-like immunoreactivities and receptors

The influence of a bowel-trophic neurotensin (NT) treatment (13 days, 300 micrograms/kg/every 12 hrs.) on neurotensin-like immunopositive structures (neurons, fibres and epithelial-N-cells) and the neurotensin receptors (NTr) in the residual bowel after resection (90% small bowel or 75% colon) in the rat was studied using histochemical methods. Somatostatin-like (ST) immunopositive structures (neurons, fibres and epithelial-D-cells) and somatostatin receptors (STr) were also studied, comparatively. The results displayed a general increase of N-cells (11-17%) but not of D-cells, and a higher degree of variability section-to-section in the NT and ST immunopositive nervous structures (without increased density) after both resections, both with or without NT treatment. Receptors did not change after the small bowel resection but the colon resection and/or the NT treatment produced variations in the NT binding (from -24.3 to +16.85) in different intestinal regions. In a general sense, the variations among 1) the controls, 2) the resected animals, and 3) the resected and NT-treated animals, were of less extent (< or = 24%) than previously supposed for explaining the trophic effect of NT. Our results: a) confirm the autonomy, injury-resistance and tendency to maintain the physiological features of the bowel in very diverse situations; b) open new questions on both, the neurotensinergic changes after bowel resection and the mechanisms of the trophic effect of NT treatment, and c) suggest that, when neurotensin was applied as a trophic treatment in the cases of the need of a bowel resection, no important neurotensinergic or somatostatinergic side effects should be expected in the remaining bowel. However, the higher degree of variability section-to-section after surgery in the nervous structures was not modified by the NT treatment. This fact, and the different response of various intestinal regions to the NT treatment, suggest that functional problems in the remaining bowel could be maintained despite the growth of the mucosa induced by the NT treatment.

Islet amyloid polypeptide (amylin) and insulin are differentially expressed in chronic diabetes induced by streptozotocin in rats

Islet amyloid polypeptide (IAPP) is overexpressed relative to insulin under several experimental conditions relevant to diabetes mellitus, including the immediate phase (7 days) following induction of streptozotocin diabetes. In the present study, IAPP and insulin gene expression were examined in chronic streptozotocin diabetes (3 weeks) in rats. Quantitative in situ hybridization, determining grain areas and optical densities of mRNA labelling, revealed that IAPP and insulin expression were reduced at the islet level at both low and high streptozotocin doses, partly due to reduced beta-cell mass. In contrast, the cellular levels of IAPP mRNA were either increased or unaffected at the low and high streptozotocin doses, respectively, whereas those of insulin mRNA were unaffected or reduced. When dexamethasone was administered to rats given the low streptozotocin dose, IAPP expression was increased, whereas that of insulin was markedly reduced. Immunocytochemistry revealed that IAPP predominantly occurred in insulin cells and to a lesser extent in somatostatin cells at all treatments examined. Our findings demonstrate that IAPP and insulin gene expression are differentially regulated; the over-expression of IAPP relative to insulin is augmented when the beta-cell insult is aggravated, in our experiments represented by massive beta-cell destruction (high streptozotocin dose) or a combination of moderate beta-cell damage and peripheral insulin resistance (low streptozotocin dose and dexamethasone). An over-expression of IAPP relative to insulin may therefore be involved in diabetes pathogenesis, contributing to its metabolic perturbations, possibly through the capacity of IAPP to restrain insulin release and action and to form islet amyloid.

The oxytocin receptor antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin inhibits effects of the 5-HT1A receptor agonist 8-OH-DPAT on plasma levels of insulin, cholecystokinin and somatostatin

The aim of the present study was to investigate whether the 5-HT1A receptor agonist 8-OH-DPAT, which previously has been shown to release oxytocin, also influences plasma levels of gastrointestinal and pancreatic hormones, and if so, whether such an effect is mediated by an oxytocinergic mechanism. For this purpose 8-OH-DPAT (0.5 mg/kg s.c.) was injected to male rats pretreated with the oxytocin receptor antagonist 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-oxytocin (1 mg/kg s.c.), or vehicle. Thirty min after injection of 8-OH-DPAT, plasma levels of oxytocin were significantly increased. 8-OH-DPAT also increased insulin and decreased CCK and somatostatin levels, effects that were blocked by pretreatment with the oxytocin antagonist. Taken together, these data suggest that the effect of 8-OH-DPAT on plasma levels of insulin, somatostatin and CCK may be mediated by oxytocin. In previous experiments, we have shown that following i.c.v. application of oxytocin, plasma levels of insulin are increased through a cholinergic mechanism. In this study, 2 ng of oxytocin decreased plasma levels of CCK, gastrin and somatostatin, effects that were blocked by pretreatment with atropine. Since oxytocinergic fibers which originate in the PVN project to the DMX, we suggest that the effect on the release of insulin, CCK and somatostatin induced by the 5 HT1A receptor agonist 8-OH-DPAT may be mediated by an oxytocinergic activation of a vagal mechanism.

Comparison of cholecystokinin, pentagastrin, and duodenal oleate in gastroprotection in rats

BACKGROUND

Cholecystokinin (CCK) and gastrin show a potent influence on gastric secretion and motility, but their role in mucosal integrity has been little studied.

METHODS

In this study the effects of CCK-8, pentagastrin, and duodenal oleate on acute gastric lesions induced by 100% ethanol were studied in rats.

RESULTS

CCK-8 was about 13 times more potent than pentagastrin in protecting the gastric mucosa against ethanol damage. CCK released by duodenal oleate also protected gastric mucosa against this damage. The protective effects of CCK-8 were almost completely abolished by the blockage of CCK-A receptors with loxiglumide, whereas the protective effect of pentagastrin was completely abolished by L-365,260. The protective effects of CCK, pentagastrin, or duodenal oleate against ethanol injury were accompanied by a marked increase in luminal content of somatostatin, suggesting that this peptide is implicated in this protection. The protective activity of CCK and pentagastrin against ethanol injury was accompanied by a significant increase in gastric blood flow. Inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine methyl ester abolished almost completely both gastric protection and hyperemia induced by CCK and pentagastrin. Addition of L-arginine, but not D-arginine, restored the protective and hyperemic effects of CCK and pentagastrin. Pretreatment with the sulfhydryl blocking agent N-ethylmaleimide also abolished the protective and hyperemic effects of CCK and pentagastrin. The hyperemia, but not the protection, afforded by CCK and pentagastrin was reduced after sensory nerve deactivation with capsaicin.

CONCLUSIONS

Both exogenous and endogenous CCK and pentagastrin exert protective activity against ethanol damage, and this effect is mediated through separate receptors, NO, and sulfhydryl-sensitive pathway.

Secretory and biosynthetic responses of gastrin and somatostatin to acute changes in gastric acidity

The activity of gastric parietal cells in terms of hydrochloric acid (HCl) secretion is regulated by the interaction of stimulatory substances (e.g. gastrin) and inhibitors (e.g. somatostatin) acting in an endocrine and paracrine mode, as well as luminal factors. In the present study the following parameters were measured: the synthesis (mRNA), storage (tissue peptide concentration) and secretion (plasma peptide concentration) of somatostatin and gastrin following short-term treatment of rats with pentagastrin (acid stimulant), secretin, omeprazole (reduces gastric acidity by inactivating gastric H/K ATPase) and the somatostatin analogue octreotide (reduces gastric acidity by inhibiting both the parietal cell and gastrin). The mRNA coding for H/K ATPase and carbonic anhydrase II (CA II), the two enzymes responsible for the generation of hydrogen ions from the parietal cell, were also quantitated. In response to octreotide, somatostatin peptide and mRNA levels in the fundus rose to 180 +/- 16% (P < 0.001) and 1073 +/- 356% (P < 0.05) of control, respectively. In contrast, octreotide caused a decrease in antral somatostatin peptide and its mRNA did not change significantly. No significant changes in synthesis, secretion or storage of gastrin were observed except for omeprazole induced hypergastrinaemia (580 +/- 76%, P < 0.001). H/K ATPase and CA II mRNA were largely unaffected except for an increase in CA II mRNA following octreotide and a decrease in H/K ATPase mRNA after pentagastrin. These data support the concept of the differential control of antral and fundic somatostatin synthesis and provide evidence for a regulatory loop by which somatostatin can influence its own synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of gastrin receptor blockade on gastrin and histidine decarboxylase gene expression in rats during achlorhydria

BACKGROUND

Gastrin stimulates histidine decarboxylase (HDC) activity and proliferation of enterochromaffin-like (ECL) cells. Furthermore, it has been suggested that gastrin controls HDC gene expression. We therefore analysed the effect of gastrin receptor blockade by PD 136 450 (CAM 1189) on HDC gene expression. The influence of PD 136 450 on gastrin, somatostatin, and chromogranin A was also evaluated.

METHODS

Gene expression of HDC, gastrin, somatostatin, and chromogranin A (CgA) was analysed by Northern blot analyses after 14 days' application of the proton pump inhibitor BY 308 and/or the gastrin/cholecystokinin B receptor antagonist PD 136 450.

RESULTS

PD 136 450 had no significant effect on gastrin mRNA or somatostatin mRNA in controls and during proton pump inhibition. BY 308 treatment resulted in a marked induction of HDC and CgA mRNA, whereas concomitant PD 136 450 in a concentration previously shown to suppress maximal pentagastrin-induced gastric acid secretion and to prevent BY 308-induced ECL cell proliferation did not result in significant alteration. PD 136 450 increased HDC significantly and CgA mRNA to a lesser extent in normogastrinaemic rats, whereas previous work showed a decreased ECL cell labelling index.

CONCLUSIONS

These data suggest that there are independent regulatory pathways for ECL cell proliferation and gene expression. Other factors besides gastrin may act through PD 136 450-insensitive pathways to control HDC and CgA gene expression.

Effect of systemic gastric acid stimulation and intragastric pH changes on synchronous antral gastrin and somatostatin release in anesthetized, nonatropinized duodenal ulcer patients and controls

The synchronous changes in antral gastrin and somatostatin release in anesthetized, nonatropinized duodenal ulcer patients and control subjects were investigated by serial intraoperative blood sampling from the right gastroepiploic vein. The mean basal antral plasma gastrin and somatostatin concentrations of the two groups did not differ significantly. The significantly greater gastric acid secretory response to systemic gastric acid stimulation (pentagastrin stimulation) in duodenal ulcer patients compared with that of control subjects was not linked to any difference in antral somatostatin release pattern. The decrease in antral plasma gastrin release was significantly lower after acid instillation and the increase was significantly higher after alkali instillation in duodenal ulcer patients compared with those of controls, indicating an abnormal gastrin response to intragastric pH changes in duodenal ulcer patients, which was again not found to be coupled to any significant difference in antral somatostatin release. The results suggest that an abnormal somatostatin-mediated inhibition of gastrin release and/or gastric acid secretion does not exist in duodenal ulcer patients.

Different effects of pyridostigmine on growth hormone (GH) response to GH-releasing hormone in endogenous and exogenous hypercortisolemic patients

1. Somatostatin may play a role in the inhibition of growth hormone (GH) response to GH-releasing hormone (GHRH) in hypercortisolism. To examine this hypothesis we studied the effect of pyridostigmine, a cholinergic agonist that decreases hypothalamic somatostatin, on the GH response to GHRH in 8 controls, in 6 patients with endogenous hypercortisolism (3 with Cushing's disease and 3 with adrenal adenomas) and in 8 patients with exogenous hypercortisolism (lupus erythematosus chronically treated with 20-60 mg/day of prednisone). Each subject received GHRH(1-29)NH2,100 micrograms iv twice, preceded by pyridostigmine (120 mg) or placebo, orally. 2. The GH response to GHRH was significantly blunted in all hypercortisolemic patients compared to controls both after placebo (GH peak, 5.8 +/- 1.6 vs 46.2 +/- 15.9 micrograms/l, mean +/- SEM) and after pyridostigmine (15.7 +/- 5.6 vs 77.2 +/- 19.8 micrograms/l). 3. The GH response was absent in endogenous hypercortisolemic patients compared to the exogenous group, both after placebo (2.2 +/- 0.3 vs 8.5 +/- 2.4 micrograms/l) and after pyridostigmine (4.9 +/- 2.5 vs 23.8 +/- 8.7 micrograms/l). The GH release after GHRH/pyridostigmine for the exogenous group was similar to the response of controls treated with GHRH/placebo. 4. These results confirm that the GH response to GHRH is blunted in hypercortisolism, although more pronounced in the endogenous group. Pyridostigmine partially reversed this inhibition in the exogenous group. Therefore, somatostatin may play a role in the inhibition of GHRH-induced GH release in exogenous hypercortisolemic states.

Neurotransmitter regulation of somatostatin secretion by fetal rat cerebral cortical cells in culture

Extensive studies exploring the regulation of hypothalamic somatostatin GHRIH release have been reported, but the factors regulating GHRIH release in the cerebral cortex have not been well defined. We have studied the effects of central neurotransmitters on GHRIH secretion by cultured fetal rat cerebral cortical cells and on intracellular GHRIH levels. Cells maintained in vitro for 15-20 days were incubated with dopamine (DA), acetylcholine (ACh), gamma-aminobutyric acid (GABA), norepinephrine (NE), serotonin (SE) or histamine (His) (10(-11) M to 10(3) M) for 30 minutes. Following incubation, immunoreactive GHRIH was measured by RIA in cell extracts and incubation media. DA increased intracellular GHRIH content but have no effect on GHRIH in the media. Both media and intracellular GHRIH content were significantly reduced by GABA and SE. The effect of NE was stimulatory at low (10(-9) M) and inhibitory at high (10(-5) M to 10(-3) M) concentrations. ACh was found to increase media GHRIH and to decrease intracellular GHRIH content; 30 min exposure to His did not significantly modify either media or intracellular GHRH. Our findings with fetal rat cerebral cortical cells in culture demonstrate that endogenous neurotransmitters do have the capacity to directly influence GHRIH regulation.

Chronic growth hormone (GH) hypersecretion induces reciprocal and reversible changes in mRNA levels from hypothalamic GH-releasing hormone and somatostatin neurons in the rat

Effects of growth hormone (GH) hypersecretion on somatostatin-(SRIH) and GH-releasing hormone (GHRH) were studied by in situ hybridization and receptor autoradiography in rats bearing a GH-secreting tumor. 6 and 18 wk after tumor induction, animals displayed a sharp increase in body weight and GH plasma levels; pituitary GH content was reduced by 47 and 55%, while that of prolactin and thyrotropin was unchanged. At 18 wk, hypothalamic GHRH and SRIH levels had fallen by 84 and 52%, respectively. In parallel, the density of GHRH mRNA per arcuate neuron was reduced by 52 and 50% at 6 and 18 wk, while SRIH mRNA levels increased by 71 and 83% in the periventricular nucleus (with no alteration in the hilus of the dentate gyrus). The numbers of GHRH- and SRIH-synthetizing neurons in the hypothalamus were not altered in GH-hypersecreting rats. Resection of the tumor restored hypothalamic GHRH and SRIH mRNAs to control levels. GH hypersecretion did not modify 125I-SRIH binding sites on GHRH neurons. Thus, chronic GH hypersecretion affects the expression of the genes encoding for GHRH and SRIH. The effect is long lasting, not desensitizable and reversible.

Blockade of galanin-induced inhibition of insulin secretion from isolated mouse islets by the non-methionine containing antagonist M35

The neuropeptide galanin occurs in pancreatic adrenergic nerves and has been suggested to be the adrenergic mediator of the stress-induced inhibition of insulin release. To study its physiological function, we recently synthesized a galanin-like galanin receptor antagonist, galantide. However, this antagonist contains a methionine moiety, and is therefore easily oxidized. We have now synthesized another galanin antagonist which does not contain methionine. This peptide, M35, is a chimeric 21 amino acid peptide in which galanin-(1-13) is coupled to bradykinin-(2-9). M35 (10 microM to 1 pM) had no effect by itself on glucose (11.1 mM)-stimulated insulin secretion in isolated mouse islets, but potently counteracted the inhibitory action of galanin (100 nM). The lowest effective dose of M35 was 10 nM. M35 did not counteract the inhibitory action of clonidine (1 microM) or somatostatin (1 microM) on insulin secretion. Furthermore, M35 displaced 125I-monoiodo-[Tyr26]galanin from membranes of insulin producing RINm5F cells. The displacement curve fitted to a two-site model in which 60% of label bound with a K1 of 0.1 +/- 0.01 nM and 40% with a K2 of 3 +/- 0.5 nM. In conclusion, M35 is a specific, non-methionine-containing galanin receptor antagonist on insulin-producing cells.

Effects of aging on gastrin and somatostatin secretion from isolated perfused rat stomach

We have examined the release of gastrin and somatostatin from the isolated perfused stomach of rats of three different age groups (4 months, 12 months, and 24 months old) in response to bombesin and carbachol. The basal release of gastrin was diminished in 24-month-old rats. Basal somatostatin release showed an age-related decrease. Bombesin (10(-10) and 10(-9) M) and carbachol (10(-8) and 10(-7) M) stimulated gastrin release in each age group. The integrated release of gastrin in response to bombesin (10(-10) and 10(-9) M) or carbachol (10(-8) M) did not differ among the three age groups, although integrated gastrin release in response to carbachol (10(-7) M) decreased in 24-month-old rats. Bombesin-stimulated release of somatostatin decreased in 12- and 24-month-old rats. Carbachol inhibited release of somatostatin in each age group. Compared with 4-month-old rats, the inhibition of somatostatin release by carbachol was less in 24-month-old rats at 10(-8) and 10(-7) M, and less in 12-month-old rats at 10(-7) M. The decreased basal gastrin secretion and well-preserved gastrin response were further confirmed in conscious aged rats tested by means of oral gavage with 10% peptone. Our findings indicate that gastrin response to the stimuli is well preserved with aging, whereas the response of somatostatin diminishes in an age-related manner. Aging has different effects on the release of gastrin and somatostatin from the rat stomach.

The effect of galanin on growth hormone-releasing factor and somatostatin release from median eminence fragments in vitro

Galanin has been reported to stimulate secretion of GH in humans and rats. Thus, to investigate whether the effect of galanin on GH release is the result of either a stimulation of GH-releasing factor (GRF) and/or an inhibition of somatostatin (SRIF) release, we have evaluated the action of galanin on the release of SRIF and GRF from median eminence (ME) fragments in vitro. The MEs from adult male rats were incubated in Krebs-Ringer bicarbonate-glucose buffer, pH 7.4, at 37 degrees C, in an atmosphere of 95% O2, 5% CO2 with constant shaking for 30 min. Medium was discarded and replaced by medium containing various concentrations of galanin (10(-10)-10(-7) M). Galanin stimulated SRIF and GRF release in a dose-related manner. This effect was significant at concentrations varying from 10(-8) to 10(-7) M. To determine the mechanism by which galanin stimulated SRIF and GRF release, MEs were incubated with pimozide (dopaminergic blocker), phentolamine (alpha-adrenergic blocker) or naloxone (opioid blocker), at concentrations of 10(-6) M, and the effect of galanin was then evaluated. Phentolamine and naloxone did not alter the stimulatory effect of galanin, but when galanin was tested with pimozide, the galanin-induced release of SRIF and GRF was blocked. To determine whether the effect of galanin is mediated through D-1 and/or D-2 dopamine receptors, selective antagonists of D-1 (SCH 23390) and D-2 receptors (domperidone) were used (10(-7) M) in the presence of galanin (10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of somatostatin and growth hormone-releasing factor by gonadal steroids in fetal rat hypothalamic cells in culture

The mechanism underlying the sexually dimorphic pattern of growth hormone (GH) secretion in the rat has not been clearly elucidated. In the present study, we assayed the possible direct effect of gonadal steroids on both somatostatin (SS) and growth hormone-releasing factor (GRF) in fetal rat hypothalamic cells in culture. Hypothalamic cells, obtained by mechanical dispersion, were maintained as monolayer cultures in serum-supplemented medium. After 20 days in culture, cells were incubated with serum free medium containing testosterone (T, 10, 20, 40 ng/dl) or estradiol (E, 0.1, 1, 10 ng/dl) for 48 h. At the end of the experiments, immunoreactive SS (IR-SS) and immunoreactive GRF (IR-GRF) were measured by specific radioimmunoassays (RIAs) in media and cell extracts. After 48 h of incubation with testosterone, somatostatin in both media and cells was significantly reduced. On the contrary, this treatment lead to a dose-dependent increase in media and cell GRF content. When cells were incubated with estradiol for 48 h, a significant inhibition in medium SS release was observed, whereas intracellular SS slightly increased at the highest concentration of 10 ng/dl. Estradiol treatment resulted in an inconsistent decrease in media and cells IR-GRF. Our results indicate that both SS and GRF are under the influence of testosterone and estradiol acting at the hypothalamic level, and furthermore suggest that at this stage of brain development, gonadal steroids may regulate GH secretion through their ability to modulate hypothalamic SS and GRF.

[Lack of effect of the administration of TRH on growth hormone secretion induced by dexamethasone]

The usually accepted effect of corticosteroids on growth hormone secretion (GH) is the reduction or blockage of secretion. Our laboratory has previously reported that corticosteroids could have an acute stimulatory effect on this secretion; we have now studied the effect of administering THR on corticosteroids induced GH secretion. Three stimulatory tests were performed to three healthy volunteers on different days. Saline administration on time 0 and time 120 minutes (control test) did not modify GH levels. On the contrary, the administration of 4 mg Dexamethasone i.v. on time 0 induced an increase in GH with a maximum peak of 10 = 3.3 micrograms/L after three hours being these differences statistically significant (p less than 0.05) when referred to the control test from 120 to 240 minutes. The corticosteroid GH stimulus presented a peculiar secretion pattern: During two hours there were no changes in basal values and afterwards the values were maintained in maximum peak values during two hours, with a great net release of GH. The administration of THR (400 micrograms iv) 120 minutes after the administration of Dexamethasone did not notify GH secretion pattern when compared with the group receiving only Dexamethasone. To conclude, the administration of corticosteroids is a new and peculiar stimulus for GH secretion. Lack of THR inhibitory function suggests that the corticosteroid stimulatory function is probably at the hypothalamus level.

Effect of ingested carbohydrate, fat, and protein on the release of somatostatin-28 in humans

The level of somatostatin-28, a bioactive peptide derived from pro-somatostatin in gastrointestinal epithelial cells, increases in human plasma after food intake. To determine if an equivalent response occurs with individual components of a mixed meal, somatostatin-28 and prosomatostatin, somatostatin-14, and somatostatin-13, in combination, were measured in healthy men before and after intake of (a) a mixed meal (715 kcal), (b) carbohydrate (100 g equivalent glucose), (c) protein (22 and 45 g), and (d) fat (25 and 50 g). After the mixed meal, somatostatin-28 levels doubled within 120 min and gradually declined by 4 h. With carbohydrate, somatostatin-28 levels were unaltered. After 22 and 45 g of protein, somatostatin-28 increased equivalently within 60 min, representing 30% of the amount with the mixed meal. With 25 g fat, a somatostatin-28 increase similar to that with the meal was seen; this response was doubled with 50 g fat. No changes in prosomatostatin, somatostatin-14, or somatostatin-13 were observed with the mixed meal or with the separate macronutrients. The authors conclude that fat is the major stimulus for somatostatin-28 secretion in humans and hypothesize that somatostatin-28 is an inhibitor of the endocrine and exocrine pancreas during nutrient absorption.