Elevated plasma concentrations of beta-cell tropin (ACTH22-39) in diet-treated type II diabetic patients.

beta-Cell tropin, the pituitary peptide ACTH22-39, is a potent insulin secretagogue and stimulates lipogenesis in adipose tissue in rodents. Plasma beta-cell tropin was measured fasting and after glucose infusion (5 mg.kg glucose ideal body weight-1.min0-1 for 90 min) in 10 mild diet-treated non-insulin-dependent (type II) diabetic subjects and 10 control subjects (body mass index) (BMI): 26.4 +/- 3.2 and 24.1 +/- 2.0 kg/m-2, NS, fasting plasma glucose 7.8 +/- 2.7 mM and 4.7 +/- 0.3 mM, respectively). The diabetic subjects had raised fasting plasma beta-cell tropin compared with the normal subjects (geometric mean (1 SD range): 0.49 (0.25-0.96) nM and 0.17 (0.10-0.28) nM, respectively, P = 0.007). In response to the glucose infusion, plasma glucose rose higher in the diabetic subjects (mean +/- 1 SD: 13.7 +/- 3.1 and 9.6 +/- 0.9 mM, P = 0.007) and plasma insulin was impaired in the diabetic compared with the nondiabetic subjects (geometric mean (1 SD range): 14 (8-26) and 34 (18-63), P less than 0.01). beta-Cell tropin concentrations in the diabetic subjects rose to 1.31 (0.74-2.30) nM (P = 0.007), whereas beta-cell tropin did not change in the normal subjects at 0.19 (0.11-0.91) nM. There was no overlap between glucose-stimulated plasma beta-cell tropin in the two groups (P = 0.0002). Pituitary-adrenal function, as assessed by plasma cortisol, did not differ between the two groups when fasting and did not change after the glucose infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin release from the perfused rat pancreas, stimulated by perifusates of the pituitary neurointermediate lobes of genetically obese and lean mice.

The perfused rat pancreas has been used to study the dynamics of insulin release during stimulation with a perifusate of the pituitary neurointermediate lobe (NIP) of genetically obese mice (ob/ob) and their lean litter-mates (+/+). It has been shown that the NIP of ob/ob mice is more active. The remainder of the study was carried out with NIP from ob/ob mice. The results showed that both phases of insulin release stimulated by 16.6 mM-glucose were increased by NIP. When the pancrease was first stimulated with NIP in the presence of 5.5 mM-glucose, followed by a high concentration of glucose, it responded to the latter with a normal biphasic response. If, however, the pancreas was stimulated first with glucose the response to NIP was refractory. The results are discussed in relation to the possible significance of an insulin secretagogue from the pituitary pars intermedia in the hyperinsulinaemia associated with obesity.

Identification of beta-cell-trophin, a peptide of the pituitary pars intermedia which stimulates insulin secretion in plasma from genetically obese (ob/ob) mice.

The influence of plasma from genetically obese (ob/ob) and lean (+/+) mice on insulin secretion has been studied by perifusion of collagenase-prepared pancreatic islets maintained for 48 h in culture. Insulin secretion was measured at 2-min intervals and plasma from the ob/ob mice not from the +/+ mice rapidly stimulated insulin release, reaching a maximum in 2-4 min and falling to basal levels in about 10 min. Experimental evidence is given indicating that the plasma insulin secretagogue is identical to beta-cell-trophin, a peptide of the pituitary pars intermedia which stimulates insulin secretion. The evidence is based on (1) the antigenic properties of the peptides (both cross-react with a -COOH terminal ACTH antiserum raised to the 17-39 moiety of ACTH), (2) identical chromatographic separation on Biogel columns and on reverse-phase high pressure liquid chromatography and (3) the similarity of their insulin releasing action from perifused islets.

Acute regulation of insulin release by the pituitary gland in relation to hyperinsulinaemia and obesity.

The pituitary glands from mice rendered obese by gold thioglucose treatment and by dietary manipulation, and pituitary glands from lean mice after a high food intake or a glucose load, were shown to stimulate insulin secretion from isolated pancreatic islets. The insulin releasing activity of pituitary glands from obese (ob/ob) mice was reduced by fasting for 24 and 48 h. Results obtained with pituitary glands from ob/ob and from lean ob/+ and +/+ mice suggest that the insulin releasing property manifests a gene dosage effect. Pituitary glands from 3-week-old (young) ob/ob mice stimulated insulin secretion to the same extent as pituitary glands from 3-month-old (adult) ob/ob mice. The pancreatic islets of young ob/ob mice were shown to be somewhat more responsive to stimulation by the pituitary factor than were lean ob/+ or +/+ islets from this age group. The concept that high insulin level, partly under pituitary control, and high caloric intake may be interlinked and may, in combination, be a major factor in producing obesity is discussed. Furthermore, it is suggested that the pituitary insulin releasing factor may play a role in the early development of obesity in the animal models studied.

Influence of the pituitary gland on insulin secretion in the genetically obese (ob/ob) mouse.

The influence of the pituitary gland of lean and genetically obese (ob/ob) mice on insulin secretion from microdissected pancreatic islets of lean and ob/ob mice has been studied by perifusing the pituitaries of these animals in series with the isolated islets and measuring insulin secretion at 5-min intervals over a period of 60 min. It has been shown that the pituitary perifusate of both lean and obese mice stimulate insulin secretion from lean mouse islets but not from obese mouse islets. The maximum stimulation occurs in the first 10 min and with the lean mouse pituitaries returns to the basal level in about 20 min, whereas with the obese mouse pituitaries insulin secretion is about double that from the control islets even after 40 min. A concentration of pure porcine ACTH equivalent to about three times the amount released from the pituitary gland under the experimental conditions used, caused only a small stimulation of insulin release. Possible interpretations of these findings and further lines of investigation are discussed.

Beta-cell tropin- and glucose-induced hypersecretion of insulin and amylin from perfused fatty rat pancreas.

The neurointermediate pituitary peptide beta-cell tropin (BCT) has potent insulin-releasing and lipogenic properties and is elevated in obesity and type-2 diabetes. The effects of BCT and glucose on the release of insulin and amylin from the perfused pancreas of obese 'fatty' (fa/fa) rats and lean (Fa/?) controls were measured. Pancreata were perfused, sequentially, with buffer containing: 5.6 mmol glucose/l (basal); basal glucose +/- 0.5 nmol BCT/l; 16.7 mmol glucose/l (high). Insulin and amylin release during basal glucose treatment was eight to nine times greater from pancreata from fatty than from lean rats. BCT induced a fivefold greater monophasic insulin and amylin release from fatty compared with lean pancreata. When not preceded by BCT there was a twofold greater high glucose-induced amylin release from fatty pancreata but no difference in insulin secretion. When preceded by BCT stimulation, high glucose induced twofold greater insulin and fourfold larger amylin release from fatty compared with lean pancreata. Molar secretion ratios of insulin:amylin varied between 30:1 and 50:1. In view of the elevated levels of BCT found in the fatty rat and in the light of the above findings, it is concluded that the peptide may have a role in the development of hyperinsulinaemia, hyperamylinaemia and insulin resistance in this animal model of obesity and diabetes.

Evidence for the presence of the pituitary insulin secretagogue beta-cell trophin in human plasma.

It has been demonstrated that the insulin secretagogue beta-cell-trophin, ACTH(22-39), is present in human plasma. The hormone, separated from plasma by affinity chromatography on a corticotrophin-like intermediate-lobe peptide antibody column, behaves similarly to synthetic beta-cell-trophin on a gel filtration column and on reverse-phase high-performance liquid chromatography. Sufficient amounts of the hormone were isolated from the plasma of two patients with Nelson's syndrome to demonstrate its biological activity on the perfused rat pancreas.

The insulin-like action of beta-cell-tropin on glucose and lipid metabolism in adipocytes.

The insulin-like activity of the pituitary pars-intermedia insulin secretagogue beta-cell-tropin, ACTH22-39, has been studied on rat adipocytes. The peptide was prepared by tryptic digestion of synthetic human CLIP, ACTH18-39. beta-Cell-tropin stimulated the incorporation of 3H2O into total lipids. The 50% maximal activity concentration was 5 X 10(-2) ng/ml-1 about 2.5 X 10(-11) M. Iodination of tyrosine, the penultimate amino-acid of the N-terminal, eliminated lipogenic activity, and acetylation of the N-terminal valine reduced activity. ACTH and CLIP (ACTH18-39) had no lipogenic action on the adipocyte system studied. beta-Cell-tropin stimulated the oxidation of glucose and the conversion of glucose into saponified fatty acids and glyceride glycerol. The influence of beta-cell-tropin and insulin on the incorporation of glucose into total lipids, saponified fatty acids and glyceride glycerol was not additive. The results suggest that beta-cell-tropin is either a potent lipogenic hormone, stimulating the conversion of glucose into lipids or that it activates endogenous insulin. The biological activity is associated with the N-terminal amino-acids of the peptide. The possible significance of beta-cell-tropin in obesity is discussed.

The metabolism of glucose in diaphragm muscle from normal rats, from streptozotocin-treated diabetic rats and from rats treated with anti-insulin serum.

1. The metabolism of [U-(14)C]glucose by the isolated diaphragm muscle of normal rats, rats rendered diabetic with streptozotocin and rats with transitory insulin deficiency after an injection of anti-insulin serum was studied. 2. The incorporation of [(14)C]glucose into glycogen and oligosaccharides was significantly decreased in the diabetic diaphragm muscle and in the muscle from rats treated with anti-insulin serum. 3. Neither diabetes nor transitory insulin deficiency influenced the oxidation of glucose, or the formation of lactate and hexose phosphate esters from glucose. 4. Insulin fully restored the incorporation of glucose into glycogen and maltotetraose in the diabetic muscle, but the incorporation into oligosaccharides, although increased in the presence of insulin, was significantly lower than the values obtained with normal diaphragm in the presence of insulin.

Effect of substrate interactions on in vitro fatty acid synthesis in adipose tissue of normal and genetically obese mice.

Fatty acid synthesis was measured in vitro in pieces of adipose tissue from lean and obese-hyperglycaemic (ob/ob) mice, using 14C-glucose or 14C-lactate and 3H2O to obtain absolute rates of total fatty acid synthesis. In the presence of lipoprotein-triglyceride (2.5 mumol/l) metabolic interaction occurred which decreased glucose incorporation into fatty acids by 30% in lean mouse tissue, but not in obese mouse tissue. In the absence of added insulin, the contribution of glucose to total fatty acid synthesis was 69% in obese mouse tissue, significantly lower than the value of 87% obtained in lean mouse tissue. Insulin increased the contribution of glucose to total synthesis in both lean and obese mouse tissues, although the value in obese mouse tissue (83%) remained lower than the value in lean mouse tissue (100%). Lactate was not a major precursor for fatty acid synthesis. When both lactate (2 mmol/l) and glucose (15 mmol/l) were present, the contribution of lactate to total fatty acid synthesis was not increased in obese mouse tissue, suggesting that even in the presence of insulin, about 30% of the carbon was provided by intracellular precursors.

The influence of insulin and of contraction on glucose metabolism in the perfused diaphragm muscle from normal and streptozotocin-treated rats.

1. The metabolism of [U-(14)C]glucose in perfused resting and contracting diaphragm muscle from normal rats and rats made diabetic with streptozotocin was studied in the presence and absence of insulin. 2. The incorporation of [U-(14)C]-glucose into glycogen and oligosaccharides was stimulated by insulin under all experimental conditions studied. 3. In the normal perfused resting diaphragm muscle the incorporation of radioactivity from [(14)C]glucose into lactate and CO(2) was not affected by insulin. 4. Periodic contractions, induced by electrical stimulation of the perfused diaphragm muscle in the absence of insulin, caused an increased incorporation of (14)C into glycogen and hexose phosphate esters, whereas incorporation of (14)C into lactate was greatly decreased. Production of (14)CO(2) in the contracting muscle was not significantly different from that in resting muscle. Addition of insulin to the perfusion liquid caused a further increase in formation of [(14)C]-glycogen in contracting muscle to values reached in the resting muscle in the presence of insulin. Formation of [(14)C]lactate was also stimulated by insulin, to values close to those found in the resting muscle in the presence of insulin. 5. In the diabetic resting muscle the rate of glucose metabolism was very low in the absence of insulin. Insulin increased formation of [(14)C]glycogen to the value found in normal muscle in the absence of insulin. Production of (14)CO(2) and formation of [(14)C]hexose phosphate remained unchanged. 6. In the diabetic contracting muscle production of (14)CO(2) was increased to values approaching those found in normal contracting muscle. Formation of [(14)C]lactate and [(14)C]glycogen was also increased by contraction, to normal values. Only traces of [(14)C]hexose phosphate were detectable. Addition of insulin to the perfusion medium stimulated formation of [(14)C]glycogen, to values found in normal contracting muscle. Production of [(14)C]hexose phosphate was stimulated by insulin, to approximately the values found in the normal contracting muscle. Production of (14)CO(2) and [(14)C]lactate, however, was not significantly affected by insulin. 7. These results indicate that the defects of glucose metabolism observed in perfused resting diabetic diaphragm muscle can be partially corrected by contraction, and in the presence of insulin the contracting diabetic muscle has a completely normal pattern of glycogen synthesis and lactate production, but CO(2) production remains impaired.