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To study the cell cycle and regulation by glucose of Bcell proliferation, B-cell-rich pancreatic islets of rat fetuses (22 days gestational age) were maintained in tissue culture at various glucose concentrations. The proliferating islet cells were synchronized with hydroxyurea and their rate of progress through the cell cycle studied by pulse labeling with 3 H-thymidine and after exposure to colchicine. 0.5 h. Although glucose significantly stimulated B-cell proliferation, the progression of cells through the cell cycle was similar at different glucose concentrations. The experiments furthermore suggested that only a limited pool of islet cells was able to proliferate. Glucose seemed to stimulate B-cell proliferation by increasing the number of cells entering the cell cycle.From the cell cycle data it was possible to calculate the rate of formation of new B-cells, which ranged from 4.2%/24 h in 2.7 mM glucose to 10.4%/24 h in 16.7 mM. When the accumulation of mitotic figures during colchicine treatment was used as an alternative method for estimation of newly formed B-cells the cell birth rates were found to be 3.1 and 6.0%/24 h at 2.7 and 16.7 mM glucose, respectively.The notion that only a small fraction of B-cells takes part in proliferation would explain the limited regenerative capacity of this cell type. It remains to be established whether such a limitation is of significance in the development of maturity-onset diabetes.

We review some key aspects of the maturation of stimulus-secretion coupling and the regulation of DNA replication in the fetal beta-cell. During fetal life, the beta-cell shows a poor insulin response to glucose, although it responds to several other nonnutrient stimuli. However, chronic exposure to glucose in excess of basal levels can induce maturation of the stimulus-secretion coupling. Studies of glucose metabolism and the transmembrane flow of K+ and Ca2+ indicate that the attenuated glucose-stimulated insulin release is due to an immature glucose metabolism resulting in impaired regulation of ATP-sensitive K+ channels in the plasma membrane of the fetal beta-cell. In late fetal life, glucose is also a strong stimulus to beta-cell replication, and metabolism of glucose is a prerequisite for this process. Glucose stimulates proliferation by recruiting beta-cells from a resting state into a proliferative compartment composed of cells in an active cell cycle. The proliferative compartment comprises less than 10% of the total islet cell population even at maximal stimulation. The proliferation of fetal beta-cells is also regulated by several peptide growth factors such as growth hormone, insulinlike growth factor I, and platelet-derived growth factor. The observation that glucose can both induce precocious maturation of the stimulus-secretion coupling and stimulate proliferation of the fetal beta-cell explains the intrauterine hyperinsulinemia and beta-cell hyperplasia of the offspring of diabetic mothers with relatively mild hyperglycemia. However, severe hyperglycemia, at least when induced in rats, seems to retard rather than stimulate beta-cell growth.

The effect of a limited period of protein-calorie malnutrition in young rats on glucose tolerance, insulin secretory response to glucose, and tissue composition in the adult was studied. Three-week-old rats were weaned onto semisynthetic diets containing either 5% protein (low protein; LP) or 15% protein (control; C) and maintained for 3 wk on their respective diets. At 6 wk of age all rats were returned to a commercial rat chow diet (18% protein). Glucose tolerance, insulin secretory response to glucose, and the protein/DNA ratio in liver, skeletal muscle, heart, kidney, small intestine, and lung were investigated at 3, 6, and 12 wk of age. Rats receiving LP diet failed to gain weight, but growth resumed immediately when they were transferred to commercial rat chow. They did not, however, catch up with C rats. Glucose tolerance and insulin secretory response to glucose remained similar between 3 and 12 wk in C rats. In 6-wk-old LP rats, glucose tolerance was impaired, and the insulin secretory response to glucose was absent. At 12 wk of age the glucose tolerance of the LP rats had normalized, but the insulin secretory response was still blunted. In 6-wk-old LP rats there was an inhibition of the age-dependent increase in cell size, shown by lowered protein/DNA ratios in all tissues studied. This decrease in cell size persisted at 12 wk in liver, skeletal muscle, heart, and lung. We conclude that protein-calorie malnutrition early in life persistently impairs the insulin secretion. The persistently lowered protein/DNA ratios in many tissues may be related to this lowered capacity for insulin secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

The regulation of DNA replication by growth hormone and the production of somatomedin C/insulin-like growth factor I (SM-C/IGF-I) and insulin by fetal rat islets in culture has been studied. Islets were cultured for 3 days in medium containing 2.7 or 16.7 mM glucose, various concentrations of fetal calf serum (FCS), and 100-1000 ng/ml human growth hormone (GH). DNA replication was determined by incorporation of [3H]thymidine into islet DNA; SM-C/IGF-I and insulin secreted into the medium were measured by specific radioimmunoassays. Glucose caused a twofold stimulation of islet DNA replication in medium containing greater than or equal to 1% FCS but failed to stimulate DNA replication at lower serum concentrations. In the presence of 16.7 mM glucose, GH (100-1000 ng/ml) stimulated DNA replication at all serum concentrations. In medium containing 2.7 mM glucose, GH was stimulatory only in the presence of 1% FCS. Somatomedin C/IGF-I release into the culture medium could be detected in all experimental groups. Glucose alone did not affect SM-C/IGF-I release, and in serum concentrations less than 0.1% FCS, GH also failed to increase the release of the peptide. In medium containing 1% FCS and 16.7 mM glucose, 100-1000 ng/ml GH caused a 50-100% increase in SM-C/IGF-I release into the medium. Addition of 100 ng/ml exogenous SM-C/IGF-I to medium containing 16.7 mM glucose and 0.1-1.0% FCS caused a twofold stimulation of the islet DNA replication. This effect could be abolished by the addition of an antibody to SM-C/IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Swenne I, Larsson PT. Heart risk associated with weight loss in anorexia nervosa and eating disorders: risk factors for QTc interval prolongation and dispersion. Acta Paediatr 1999; 88: 304-9. Stockholm. ISSN 0803-5253Risk factors for QT c interval prolongation and dispersion, indicators of an increased risk for cardiac arrhythmia and sudden death, have been investigated in patients with eating disorders (ED) and ongoing weight loss. Patients were characterized with regard to weight, body mass index (BMI; weight/length 2 ), duration of weight loss, rate of weight loss and rate of weight loss immediately preceding examination. At examination, a 12-lead electrocardiographic (ECG) registration and blood samples for analysis of serum electrolytes were obtained. In total, 92 examinations in 58 female patients aged 15.5 AE 1.7 (mean AE SD) y were analysed. Control ECG recordings were obtained from 38 normal-weight teenage girls with no known heart disease. Patients with ED weighed 40.7 AE 7.8 kg, corresponding to BMI 15.2 AE 2.4 kg/m 2 following a weight loss of 11.8 AE 6.5 kg. In ED patients, the ECG showed bradycardia, a shift to the right of the QRS axis, diminished amplitudes of the QRS complex and T wave, and prolongation and increased dispersion of the QT c interval. In multiple regression analyses low weight, low BMI and rapid weight loss immediately preceding the examination were the most important independent predictors of QT c interval prolongation and dispersion. It is concluded that an ECG examination is an important part of the assessment of patients with ED and ongoing weight loss, even in the absence of electrolyte disturbances, and especially if the patient is severely underweight or weight loss is rapid.

Summary. Proliferation of islet cells may compensate for bothan increased peripheral insulin resistance and islet cell destruction but the capacity for regeneration may be genetically determined. For the latter reason, glucose-stimulated islet cell replication was estimated in both inbred C57BL/6J (BL/6) and C57BL/KsJ (BL/Ks) mice. Islets isolated from both strains were exposed to high concentrations of glucose in vitro or in vivo for a prolonged time period. This was achieved either by culturing the islets free-floating in a high glucose concentration medium for 3 days or implanting the islets intrasplenically in insufficient numbers to cure alloxan-diabetic syngeneic recipients. In both strains high glucose concentration culture was found to increase the autoradiographic labelling index of the islets but the replicatory activity decreased with age. The proliferative rate of the islet cells of the BL/6 mice was about twice as high as that of the BL/Ks mice irrespective of age and glucose concentration. Likewise, the labelling index of intrasplenic BL/6 islets implanted into alloxan-diabetic mice was twice as high as that of the islets implanted into alloxan-diabetic BL/Ks mice. The replicatory activity of the latter islets did not differ statistically from that of islets implanted into non-diabetic control BL/Ks mice. No differences in the rates of proinsulin and total protein biosynthetic rates were observed between high glucose concentration-cultured islets of the two mouse strains. The present resuits indicate that the proliferative response of pancreatic islets to a prolonged glucose stimulation may be genetically determined. This may play a significant role in the development of different diabetic syndromes both in laboratory animals and man.Key words: Inbred mouse strains, alloxan diabetes, islet culture, islet implantation, islet cell replication, autoradiographic labelling index, proinsulin biosynthesis.We have reported that intrasplenic transplantation of syngeneic pancreatic islets isolated from lean mice failed to cure obese hyperglycaemic mice, despite a considerable growth of the grafted islets [1]. In an attempt to elucidate the influence of hyperglycaemia on the growth of these islet grafts, syngeneic islets in numbers insufficient to cure diabetes (approximately 150) were implanted into alloxan-diabetic mice of two different inbred strains, C57BL/6J (BL/6) and C57BL/KsJ (BL/ Ks) [2]. The volume of the islets implanted intrasplenically into alloxan-diabetic BL/Ks mice decreased markedly, whereas that of islets implanted into BL/6 mice was usually unaffected. Some mice of the latter strain, however, became normoglycaemic and indeed, in these particular mice an increase of the volume of the implanted islets was found.The present study was carried out in order to elucidate to what extent a difference in islet cell replicatory activity of these two mouse strains contributes to the fate of intrasplenically implanted islets. For this purpose islets either were exposed to a high glucose environment in v...

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