Janet M. Bryson

Development of the Diabetes Knowledge (DKN) Scales: Forms DKNA, DKNB, and DKNC

The Diabetes Knowledge Assessment (DKN) scales were developed to meet a specific need for rapid and reliable knowledge assessment in diabetic patients. Item format and item selection from an initial pool of 89 items were determined by pilot-testing over 300 diabetic subjects. Reliability analysis of the resulting 40 multiple-choice items, with a further sample of 56 subjects, gave a Cronbachs alpha coefficient of 0.92. Parallel forms DKNA, DKNB, and DKNC, each of 15 items selected from the parent set, had alpha coefficients above 0.82 and correlated 0.90 with each other. A full clinical trial, using DKNA, DKNB, and DKNC in randomized order of presentation, was conducted with 219 subjects attending a 2-day diabetes education program. Overall DKN scores improved from 7.6 (51%) to 11.3 (75%). Analysis of variance confirmed that DKNA, DKNB, and DKNC were equivalent forms at pretest. Mean posttest scores on DKNB were lower than the other scales (P < 0.001), but variances were equivalent for all three. A specific local change in the education program format was found to account for this discrepancy in the DKNB posttest mean. In situations where comprehensive assessment of diabetes knowledge would be time-consuming and unnecessary, these results indicate that rapid and reliable assessment is possible with a scale of only 15 validated items. The development of parallel forms of the scale extends the range of retesting possibilities for diagnosis and research.

The effect of fasting on liver receptors for prolactin and growth hormone

The effects of 3 day fasting on liver prolactin and growth hormone receptors have been investigated in male and female rats. Fasting caused a significant fall in serum immunoreactive insulin (67% decrease), while receptor-reactive somatomedin fell 82% when measured in whole serum and by 72% when measured in serum fractions following gel chromatography at low pH. Tracer ovine prolactin binding to liver microsomal membranes was reduced by 55% on fasting in females, but unchanged in males. Tracer bovine growth hormone binding fell significantly in both sexes. Analysis of competitive binding curves showed the decrease binding to be due to a loss of prolactin receptors in females, and of high affinity (but not low affinity) growth hormone receptors in males and females. Significant correlations were seen between serum insulin and tracer prolactin (females) and growth hormone (males and females) binding to liver membranes. Correlations between serum insulin and liver high affinity growth hormone binding sites were particularly significant (r = 0.899 in females, r = 0.910 in males). It is proposed that the hypoinsulinemia of fasting causes a loss of high affinity growth hormone receptors in the liver, which could result in a relative hepatic resistance to growth hormone and a decreased hepatic generation of somatomedin.

Leptin has acute effects on glucose and lipid metabolism in both lean and gold thioglucose-obese mice

Leptin is reported to have effects in peripheral tissues that are independent of its central effects on food intake and body weight. In this study, the acute effects of a single dose of recombinant mouse leptin on lipid and glucose metabolism in lean and gold thioglucose-injected obese mice were examined. Changes were measured 2 h after leptin injection. In lean mice, liver and white adipose tissue (WAT) lipogenesis was inhibited. The activity of the pyruvate dehydrogenase complex (PDHCa), the rate-determining step for glucose oxidation, was reduced in heart, liver, quadriceps muscle, and both brown and white adipose tissues. Muscle and liver glycogen and liver triglyceride (TG) content was unchanged, but muscle TG was decreased. In obese mice, liver and WAT lipogenesis was inhibited and PDHCa reduced in heart and quadriceps muscle. Muscle and liver glycogen was decreased but not TG. Serum insulin was reduced in obese but not lean mice. These results are consistent with a role for leptin in the maintenance of steady-state energy stores by decreasing lipid synthesis and increasing fat mobilization, with decreased glucose oxidation occurring as a result of increased fatty acid oxidation.

Leptin as a Potential Treatment for Obesity

Despite significant reductions in the consumption of dietary fat, the prevalence of obesity is steadily rising in western civilization. Of particular concern is the recent epidemic of childhood obesity, which is expected to increase the incidence of obesity-related disorders. The obese gene (ob) protein product leptin is a hormone that is secreted from adipocytes and functions to suppress appetite and increase energy expenditure. Leptin is an attractive candidate for the treatment of obesity as it is an endogenous protein and has been demonstrated to have potent effects on bodyweight and adiposity in rodents.Whereas leptin has been successfully used in the treatment of leptin-deficient obese patients, trials in hyperleptinemic obese patients have yielded variable results. Long-acting leptins have been tried but with no greater success. Other strategies including the use of leptin analogs and other factors that bypass normal leptin delivery systems are being developed. Identifying the mechanisms at the molecular level by which leptin functions will create new avenues for pharmaceutical targeting to simulate the intracellular effects of leptin.

Maternal Protein Restriction Increases Hepatic Glycogen Storage in Young Rats

This study aimed to determine whether maternal protein restriction alters hepatic glycogen metabolism. Mated female rats were fed diets containing 20% protein throughout pregnancy and lactation (CONT), 8% protein throughout pregnancy and lactation (LP), or 8% protein during the last week of pregnancy only and lactation (LLP). Weights and lengths were reduced in the LLP and LP offspring compared with the CONT offspring. The LLP and LP offspring demonstrated reduced insulin concentrations at both 10 and 26 d and also failed to show the increase in insulin seen with time in the CONT offspring. Serum glucose and leptin levels increased with time but were not different among the groups; however, in relation to adiposity leptin levels were greater in the LLP and LP offspring at 26 d. The LLP and LP offspring had increased hepatic glycogen at day 10 (CONT, 75.1 ± 9.8; LLP, 103.4 ± 11.0; LP, 116.0 ± 18.4 glucose residues/g tissue) and d 26 (CONT, 183.1 ± 38.9; LLP, 395.3 ± 16.8; LP, 396.6 ± 15.1 glucose residues/g tissue). Glycogen synthase expression was increased in the LLP and LP offspring at 10 d but not 26 d; glucose transporter 2 and glycogen phosphorylase expressions were not different at either time. At 26 d glycogen synthase activity was not different; however, glycogen phosphorylase a activity was reduced. The enhanced capacity to store glycogen despite reductions in insulin secretion suggests increased insulin sensitivity possibly acting with an alternative non–insulin-dependent glycogen storage mechanism.

Postnatal nutrition alters body composition in adult offspring exposed to maternal protein restriction

The insulin-like growth factor (IGF) system is altered with intra-uterine growth retardation and in adult metabolic disease. The aim of the present study was to observe effects of continued protein restriction on the IGF-I system and body composition in offspring of mothers fed a low-protein (LP) diet. Offspring from Wistar dams fed either a 20 % (CON) or 8 % (LP) protein diet during gestation and lactation were studied at birth, 10 d, weaning and at 12 weeks after maintenance on either the 8 % (lp) or 20 % (con) protein diet from weaning. LP offspring had reduced weaning weights (P < 0.05) and reduced serum insulin (P < 0.005). Serum IGF-I (P < 0.001) and acid-labile subunit (ALS) (P < 0.0001) were reduced at 10 and 21 d. Hepatic expression of IGF-I (P < 0.05) and ALS (P < 0.005) were reduced at 10 and 21 d. IGF binding protein (IGFBP)-1 hepatic expression was elevated at 10 d (P < 0.001) but not at 21 d. Adult LP-con offspring had reduced body weight (P < 0.05), lean (P < 0.0001) and bone (P < 0.0001) but not fat (P = 0.6) mass with no persistent effects on IGF-I, ALS and IGFBP-1.Postnatal lp feeding reduced lean mass (P < 0.0001) and bone mass (P < 0.0001) in CON and LP animals. Percentage fat (LP P = 0.04; CON P = 0.6) and IGFBP-1 (LP P = 0.01; CON P = 0.2) were increased in LP-lp but not CON-lp offspring. This suggests that postnatal nutrition is important in the effects of maternal protein restriction on adult body composition and that IGFBP-1 may be involved.

Changes in rat liver prolactin binding sites in diabetes are sex dependent.

The effect of streptozotocin-induced diabetes (100 mg/kg) on lactogenic binding sites, measured by iodinated ovine prolactin (PRL) binding, has been studied in liver microsomal membranes from males and female rats. In females, specific binding was reduced in diabetes from 13% to 4.5% of total tracer, while in males specific binding increased from 0.5% to 2.5%. Similar results were obtained using iodinated human growth hormone as tracer, through overall binding was higher. Scatchard plots of binding curves in females showed that changes in binding were due to changes in receptor concentration, while affinity remained unchanged at 2 X 10(9) M-1. In diabetes, serum PRL and estradiol levels fell by 60% in males but showed no significant change in females, and could therefore not account for receptor changes. In contrast, mean testosterone levels fell in diabetic males from 9.0 to 3.9 nM, and rose in diabetic females from 2.1 to 5.8 nM. Estrogen treatment of male rats caused a marked induction of binding in nondiabetic animals, and a change from the male to the female response to diabetes. Testosterone treatment of nondiabetic females suppressed binding, although not to the male levels, and diabetes caused further suppression. These results are consistent with a role for testosterone in regulating PRL receptors in experimental diabetes, but suggest that other hormonal influences are also involved.

Insulin determines leptin responses during a glucose challenge in fed and fasted rats

OBJECTIVE:Leptin secretion has been shown to respond acutely to changes in blood glucose and insulin. Nutritional state also has a marked effect on both the level of circulating leptin protein and leptin gene expression. The aim of this study was to assess whether the prior nutritional state altered the leptin secretory response to an acute glucose challenge, and to determine potential mechanisms.DESIGN:Male fed or fasted rats (200–250 g) were administered a single intravenous glucose bolus (1, 4 or 7 g/kg). The serum leptin, glucose, insulin and free fatty acid responses were studied over the following 5 h. The level of leptin gene expression and leptin protein was then determined in the epididymal fat pads, and in fed and fasted untreated rats for basal comparison.RESULTS:Leptin secretion in response to glucose was suppressed in fasted rats following all glucose doses. The total leptin response was correlated with the total insulin response in all conditions (r=0.85) and with the glucose response in fed rats (r=0.69). Both leptin gene expression and leptin protein content were lower in basal fasted rats. Leptin gene expression and leptin protein content still remained lower 5 h following a glucose bolus but there was partial reversal of the effects of fasting following the 7 g/kg glucose dose.CONCLUSIONS:Leptin secretion in response to an intravenous glucose bolus was determined by the insulin response and was significantly suppressed in fasted compared to fed rats. In addition to differences in the total insulin response of the animals, lower leptin responses may be facilitated by lower levels of both leptin gene mRNA and pre-existing leptin protein in epididymal adipose tissue of fasted rats.

Creatine Supplementation Affects Glucose Homeostasis but Not Insulin Secretion in Humans

Aims: In this study, it was investigated whether the glucose homeostasis is affected by dietary creatine supplementation. For this purpose, the plasma glucose concentration and the plasma insulin response to an oral glucose load were measured in creatine-supplemented vegetarians. Methods: The subjects were supplemented with either 5 g of creatine monohydrate (creatine-treated group, CREAT) or 5 g of maltodextrin (control group, CON) per day for 42 days. On days 0 and 43, blood samples were collected before as well as 10, 20, and 30 min following an oral glucose load and analyzed for plasma creatine, insulin, and glucose levels. Results: Creatine supplementation resulted in an increase in plasma creatine (CREAT 92.7 ± 14.6 µM vs. CON 31.2 ± 3.2 µM; p = 0.001). There was a trend (p = 0.07) towards elevated fasting plasma glucose levels following creatine supplementation, while the plasma glucose response to the glucose load was enhanced (CREAT 168.2 ± 5.3 mM· min vs. CON 129.6 ± 14.7 mM ·min; p = 0.05). There was no difference observed in the plasma insulin response to the glucose load between the groups. Conclusion: This study shows that creatine supplementation may result in abnormalities in glucose homeostasis in the absence of changes in insulin secretion.

Adrenal involvement in the diabetes-induced loss of growth hormone and prolactin receptors in the livers of female rats

SummaryStreptozotocin-induced diabetes causes a decrease in growth hormone and prolactin receptors in the livers of female rats, and in the serum concentration of somatomedin-C/insulin-like growth factor-1, concomitantly with an increase in the serum testosterone levels. In this study, a possible role for adrenal androgens in the loss of receptors was examined. Rats were adrenalectomised bilaterally 3 days after the induction of diabetes with streptozotocin (100 mg/kg intravenously), and livers were removed 3 days later. Adrenalectomy had no effect on binding of ovine prolactin or bovine growth hormone to liver microsomal membranes from non-diabetic rats, but in diabetic rats it entirely abolished the 56% decrease in prolactin binding and significantly reversed the 66% decrease in growth hormone binding and the parallel fall in serum levels of somatomedin-C/insulin-like growth factor-I (p<0.05). Adrenalectomy also prevented the diabetes-induced rise in serum testosterone. Daily injection of testosterone to normal and diabetic rats for 12 days significantly reduced both prolactin and growth hormone binding (p<0.001), with the effect of diabetes being additive upon the testosterone effect. Implantation of testosterone-filled silastic capsules at the time of adrenalectomy (i. e. for 3 days) did not prevent the adrenalectomy-induced restoration of both growth hormone and prolactin receptors. The resulting high serum testosterone level did not reduce binding to growth hormone receptors in control rats over the 3 day period, and caused no further decrease in diabetic rats. However, binding to prolactin receptors was reduced by 47% in control animals with no further loss in diabetic animals (p<0.001). Adrenalectomy prevented the loss of prolactin receptors in both testosterone-treated and diabetic rats. These results indicate that, whether or not the rise in testosterone of adrenal origin contributes to the receptor loss in diabetes, the effect also depends on another factor of adrenal origin.