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B Ahren and M Gutniak

OBJECTIVES: To examine whether glucagon-like peptide-1 (GLP-1), which has been suggested as a new therapeutic agent in type 2 diabetes, affects circulating islet amyloid polypeptide (IAPP), a B-cell peptide of potential importance for diabetes pathophysiology. DESIGN: GLP-1 was administered in a buccal tablet (400 micrograms) to seven healthy subjects and nine subjects with type 2 diabetes. Serum IAPP and insulin levels were measured before and after GLP-1 administration. RESULTS: In the fasting state, serum IAPP was 4.1 +/- 0.3 pmol/l in the controls vs 9.8 +/- 0.9 pmol/l in the subjects with type 2 diabetes (P < 0.001). IAPP correlated with insulin only in controls (r = 0.74, P = 0.002) but not in type 2 diabetes (r = 0.26, NS). At 15 min after GLP-1, circulating IAPP increased to (6.0 +/- 0.5 pmol/l in controls P = 0.009) and to 13.8 +/- 1.2 pmol/l in type 2 diabetes (P = 0.021). In both groups, serum insulin increased and blood glucose decreased compared with placebo. In controls serum IAPP increased in parallel with insulin (r = 0.79, P = 0.032), whereas in type 2 diabetes the increase in IAPP did not correlate with the increase in insulin. CONCLUSION: Type 2 diabetes is associated with elevated circulating IAPP; GLP-1stimulates IAPP secretion both in healthy human subjects and in type 2 diabetes; IAPP secretion correlates with insulin secretion only in healthy subjects and not in type 2 diabetes.

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B Ahren and AJ Scheurink

We asked whether the likelihood for mice of the C57BL/6J strain to develop glucose intolerance when fed a high-fat diet is related to the increase in circulating levels of leptin or free fatty acids (FFA). We therefore administered a high-fat diet (58% fat) or a control diet (11% fat) for 1.5 years. NMRI mice were used as a more glucose-tolerant control group. After a high-fat diet, the area under the glucose curve following an intraperitoneal glucose challenge (1 g/kg) increased more markedly in C57BL/6J mice (by 42+/-8%) than in NMRI mice (by 21+/-3%, P = 0.007). Plasma levels of insulin, leptin and FFA increased in both strains of mice, whereas plasma glucose levels were elevated after the high-fat diet only in C57BL/6J mice. The slope of the relationship between body weight and plasma leptin was higher in C57BL/6J mice than in NMRI mice. suggesting leptin insensitivity. Circulating leptin correlated to circulating insulin in both strains of mice, whereas plasma FFA correlated to plasma insulin in NMRI mice but not in C57BL/6J mice. These correlations remained significant after adjustment for body weight. The results show that elevated leptin and FFA levels evolve after high-fat feeding in mice, in conjunction with evolvement of glucose intolerance and hyperglycemia.

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B Ahren and G Pacini

Insulin sensitivity and insulin secretion are mutually related such that insulin resistance is compensated by increased insulin secretion. A correct judgement of insulin secretion therefore requires validation in relation to the insulin sensitivity in the same subject. Mathematical analyses of the relationship between insulin sensitivity and insulin secretion has revealed a hyperbolic function, such that the product of the two variables is constant. This product is usually called the disposition index. Several techniques may be used for its estimation such as data derived from the frequently sampled i.v. glucose tolerance test, the oral glucose tolerance test or the glucose-dependent arginine stimulation test or the euglycemic hyperinsulinemic clamp technique in combination with a test on insulin secretion. Using these techniques the compensatory increase in beta cell function in insulin resistance has been verified in obesity, in pregnancy and after glucocorticoid administration as has the defective beta cell function as the underlying cause of impaired glucose tolerance and type 2 diabetes. Similarly, combined analysis of insulin sensitivity and insulin secretion has shown a down-regulation of beta cell function in increased insulin sensitivity accompanying weight reduction in obesity and following exercise. Acknowledging this inverse relationship between insulin secretion and insulin sensitivity therefore requires estimation of both variables for correct assessment in any individual.

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B. Månsson, B. Ahrén and A. Nobin

Abstract. Calcitonin is secreted from the thyroidal C-cells. Except that calcitonin secretion is stimulated by calcium, little is known of its regulation. Vasoactive intestinal peptide (VIP), substance P, and calcitonin gene related peptide (CGRP) have recently been detected within intrathyroidal neurons, and CGRP also within the C-cells, and may therefore affect calcitonin secretion. In this study, we investigated whether VIP, substance P or CGRP could influence calcitonin secretion in the rat. Each of these peptides was administered as a single injection (1.5 nmol/animal) or as a 30-min infusion (1.5 nmol/animal per 30 min) during which calcium chloride, 456 μmol/animal, was injected iv. We found that the peptides had no effect on basal calcitonin secretion, but that VIP potentiated the calcium-induced calcitonin release. Thus, the peak plasma calcitonin level following calcium chloride injection was doubled by the infusion of VIP (P < 0.001). In contrast, neither substance P nor CGRP significantly influenced the calcium-induced calcitonin release. We conclude that VIP, a neuropeptide within intrathyroidal nerves, has the capacity to augment calcium-induced calcitonin secretion in the rat and we therefore suggest that VIP is a regulator of calcitonin secretion.

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B Bulow, B Ahren and EM Erfurth

BACKGROUND: The adipocyte products, leptin and tumour necrosis factor (TNF)alpha, are associated with atherosclerotic diseases and may be factors contributing to the enhanced cardiovascular risk in hypopituitary patients with growth hormone (GH) deficiency. OBJECTIVE: To investigate whether leptin and TNFalpha are increased in a group of hypopituitary women previously found to have increased cardiovascular morbidity, and to compare them with matched individuals of the same sex and age and with similar body composition. DESIGN AND PATIENTS: Thirty-three GH-deficient women with a median age of 64 years (range 39-77 years) were investigated cross-sectionally. The patients were compared with 33 controls matched for sex, age, smoking habits, educational level and residence. METHODS: Body composition was measured by bioimpedance analysis. Fasting concentrations of leptin, TNFalpha and insulin were analysed in patients and controls. RESULTS: There was no significant difference in body mass index or fat mass between patients and controls (both P > or =0.4). Serum leptin did not differ significantly between patients and controls. However, when serum leptin concentrations were expressed per kilogram fat mass, the patients had significantly greater concentrations (P=0.01). Serum TNFalpha and TNFalpha per kilogram fat mass were also significantly greater in the patients (both P=0.001). In contrast, serum insulin did not differ significantly between patients and controls. In the patients, serum leptin concentrations correlated positively with kilogram fat mass (r=0.54, P=0.002). Leptin concentration per kilogram fat mass was positively correlated with insulin (r=0.40, P=0.03). CONCLUSIONS: In contrast to serum concentrations of TNFalpha, serum leptin did not differ from that in controls, implying that leptin is not a major contributor to the previously found increase in cardiovascular morbidity in the hypopituitary women investigated. However, the patients had increased leptin concentrations per unit fat mass, indicating an altered adipocyte secretory function in this group.

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T. Perklev, H.-B. Berglund and K. Ahrén

ABSTRACT

Human chorionic gonadotrophin (HCG) and ovine luteinizing hormone (LH) were administered intravenously (iv) to prepubertal rats 5 min before sacrifice, and the lactic acid production by the isolated ovaries was measured during a subsequent 2 h incubation period. HCG (2.5 and 5 IU) and LH (0.5–2 IU) produced a dose-related, significant increase in lactic acid production. Injections of 8 IU HCG, 1, 5 and 30 min, respectively, before sacrifice significantly enhanced the subsequent ovarian in vitro glycolysis. No difference in lactic acid production was seen between ovaries exposed to HCG for 5 or 30 min. The 1 min exposure was too short to induce maximum stimulation of the ovaries.

When 10 μl of an antiserum against HCG was injected iv 10 min before the administration of 8 IU HCG, the hormonal effect on the subsequent ovarian lactic acid production was completely neutralized. Ten μl and 100 μl of anti-HCG serum injected 1 min and 18 h, respectively, before the injection of HCG, also produced a complete neutralizing action. When 10 μ1 and 100 μ1 anti-HCG serum was administered 5 min after an injection of 8 IU HCG, the subsequent ovarian lactic acid production was not influenced. Anti-HCG serum injected before the injection of ovine LH evoked no inhibition of the ovarian glycolysis.

The present data are in agreement with those previously reported when HCG, bovine LH and anti-HCG serum were added directly to an incubation medium containing isolated, prepubertal rat ovaries. i. e. in a completely in vitro system.

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B Ahren, H Larsson and JJ Holst

OBJECTIVE: The gastrointestinal hormones, gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), are both released from the gut after oral glucose ingestion and stimulate insulin secretion. This study examined the release of these hormones in subjects with impaired glucose tolerance (IGT), which precedes the development of non-insulin-dependent diabetes. DESIGN AND METHODS: Six postmenopausal women with IGT, aged 59 years, underwent a 75 g oral glucose tolerance test and plasma levels of GIP and GLP-1 were determined regularly during the following 2 h. The results were compared with those in seven age- and weight-matched women with normal glucose tolerance (NGT). RESULTS: Basal plasma levels of GIP and GLP-1 were not different between the groups. In response to the oral glucose ingestion, plasma levels of both GIP and GLP-1 increased in both groups. The plasma GIP increase after glucose ingestion was, however, reduced in women with IGT. Thus, the GIP response as determined as the area under the curve for the 60 min after oral glucose was 34.8 +/- 3.2 pmol/l per min in women with IGT versus 56.4 +/- 7.8 pmol/l per min in those with NGT (P = 0.021). In contrast, the GLP-1 response to oral glucose was not different between the groups. By definition, the glucose response to oral glucose was markedly increased in women with IGT, and the insulin response during the second hour after glucose ingestion was exaggerated. CONCLUSIONS: The GIP response to oral glucose is impaired in postmenopausal women with IGT, whereas the plasma GLP-1 response is not affected.

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MK Reimer, JJ Holst and B Ahren

OBJECTIVES: Inhibitors of the glucagon-like peptide-1 (GLP-1)-degrading enzyme, dipeptidyl peptidase IV (DPPIV), are being explored in the treatment of diabetes. We examined the long-term influence of a selective, orally active inhibitor of DPPIV (NVP DPP728), in normal female C57BL/6J mice and such mice rendered glucose-intolerant and insulin-resistant by feeding a high-fat diet. DESIGN: In mice fed a standard diet (11% fat) or a high-fat diet (58% fat), NVP DPP728 (0.12 micromol/g body weight) was administered in the drinking water for an 8 week period. RESULTS: DPPIV inhibition reduced plasma DPPIV activity to 0.01+/-0.03 mU/ml vs 3.26+/-0.19 mU/ml in controls (P<0.001). Glucose tolerance after gastric glucose gavage, as judged by the area under the curve for plasma glucose levels over the 120 min study period, was increased after 8 weeks by NVP DPP728 in mice fed normal diet (P=0.029) and in mice fed a high-fat diet (P=0.036). This was accompanied by increased plasma levels of insulin and intact GLP-1. Glucose-stimulated insulin secretion from islets isolated from NVP DPP728-treated animals after 8 weeks of treatment was increased as compared with islets from control animals at 5.6, 8.3 and 11.1 mmol/l glucose both in mice fed normal diet and in mice fed a high-fat diet (both P<0.05). Islet insulin and glucagon immunocytochemistry revealed that NVP DPP728 did not affect the islet architecture. However, the expression of immunoreactive glucose transporter isoform-2 (GLUT-2) was increased by DPPIV inhibition, and in mice fed a high-fat diet, islet size was reduced after treatment with NVP DPP728 from 16.7+/-2.6 x 10(3) microm(2) in controls to 7.6+/-1.0 x 10(3) microm(2) (P=0.0019). CONCLUSION: Long-term DPPIV inhibition improves glucose tolerance in both normal and glucose-intolerant mice through improved islet function as judged by increased GLUT-2 expression, increased insulin secretion and protection from increased islet size in insulin resistance.

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B. Ahrén, P. Hedner, A. Melander and U. Westgren

ABSTRACT

The recent discovery of somatostatin-containing cells within the thyroid gland infers that somatostatin may influence thyroid activity. This possibility was investigated by measurements of radio-iodine release in mice pre-treated with 125I and T4. The animals were treated with TSH, isoprenaline or dibutyryl-cyclic AMP with and without concomitant injection of somatostatin. It was found that somatostatin reduced the blood 125I increase in response to each of the three thyroid-stimulating agents. The elimination rates of 125I-labelled T4 and T3 were unaffected by somatostatin.

The observations suggests that somatostatin may participate in the regulation of thyroid hormone secretion, by an inhibitory effect exerted within the thyroid gland.

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Monica G. Sender Baum and Kurt E. B. Ahrén

Abstract. The diterpene forskolin increased in a dosedependent way cyclic AMP (cAMP) accumulation in isolated corpora lutea from immature rats injected with an ovulatory dose of pregnant mare's serum gonadotropin (PMSG). The cAMP increase was significant already after 1 min of incubation with forskolin, and cAMP continued to rise to a maximum at about 30–60 min, with a clear decrease after 240 min of incubation. The forskolin effect was more pronounced in very young corpora lutea (1-day-old) than in older corpora lutea. There was a clear discrepancy between the marked effect on cAMP accumulation by forskolin and the steroidogenic response when compared with the corresponding effects of LH. Forskolin also increased progesterone production, but this effect was marginal compared with that of LH. Prostaglandin F (PGF) did not influence the forskolin stimulated cAMP increase. PGF has previously been shown to inhibit the stimulatory effect of LH on cAMP formation in this type of corpora lutea. The fact that PGF did not inhibit the forskolin stimulated cAMP production indicates that PGF does not act directly on the adenylate cyclase.