The association of macro- and micronutrient intake with growth hormone secretion.

CONTEXT: Growth hormone (GH) is known to be nutritionally regulated, but the effect of dietary composition on detailed GH secretion parameters has not previously been comprehensively evaluated. OBJECTIVE: The objective of the study was to determine whether specific macro- and micronutrients are associated with discrete parameters of GH secretion among subjects with wide ranges of body mass index. DESIGN: Detailed macro- and micronutrient intake was assessed by 4-day food records while GH secretion was assessed by standard stimulation testing in 108 men and women in one study (Study 1), and by overnight frequent blood sampling in 12 men in another study (Study 2). RESULTS: Peak stimulated GH was positively associated with vitamin C (r=+0.29; P=0.003), dietary fiber (r=+0.27; P=0.004), arachidic acid (r=+0.25; P=0.008), and behenic acid (r=+0.30; P=0.002) intake in univariate analysis. Controlling for age, gender, race/ethnicity, visceral fat, HOMA-IR, total caloric intake and these four dietary factors in step-wise multivariate modeling, peak GH remained significantly associated with vitamin C and visceral fat (both P<0.05). In addition, vitamin C intake was associated with various parameters of endogenous GH secretion including basal GH secretion (r=+0.95; P<0.0001), GH half-life (r=+.75; P=0.005), total GH production (r=+0.76; P=0.004), GH area-under-the-curve (r=+0.89; P=0.0001), mean log(10) GH pulse area (r=+0.67; P=0.02), and overnight maximum (r=+0.62; P=0.03), nadir (r=+0.97; P<0.0001), and mean GH secretion (r=+0.89; P=0.0001). CONCLUSIONS: These results suggest that certain micronutrients such as vitamin C intake are strongly and uniquely associated with stimulated and endogenous spontaneous GH secretion.

Relationship of adiponectin to endogenous GH pulse secretion parameters in response to stimulation with a growth hormone releasing factor.

OBJECTIVE: Obesity is associated with both reduced growth hormone (GH) and adiponectin. However, the relationship between adiponectin and parameters of endogenous GH secretion remains unknown. The aim of this study was to determine the relationship between total and high molecular weight (HMW) adiponectin and parameters of endogenous pulsatile GH secretion and the effects of tesamorelin, a synthetic GH releasing hormone (GHRH(1-44)), on total and HMW adiponectin. DESIGN: A 2-week interventional study with tesamorelin was conducted at an academic medical center in 13 men with BMI 20-35 kg/m(2). Overnight frequent blood sampling and measurement of total and HMW adiponectin at baseline and after treatment were performed to assess the effects of augmenting endogenous pulsatile GH secretion. RESULTS: Total, but not HMW, adiponectin was positively associated with log(10)Peak GH area (r=+0.73; P=0.005), basal GH secretion (r=+0.67; P=0.01), and total GH production (r=+0.57; P=0.04), but was not associated with the number of secretion events (P=0.85). Two-week treatment with tesamorelin increased endogenous GH release and IGF-1, but neither total (change -0.16±0.64; P=0.40), nor HMW (change +0.03±0.70; P=0.87) adiponectin changed significantly with treatment. Sub-analyses in overweight and obese men yielded similar results. CONCLUSIONS: Our study demonstrates a strong relationship between specific parameters of endogenous GH pulsatility and adiponectin. However, short-term augmentation of GH pulsatility over 2-weeks does not change adiponectin. Therefore, the relationship between GH and adiponectin is most likely mediated by specific covariates related to adiposity or other factors.

Cerulenin mimics effects of leptin on metabolic rate, food intake, and body weight independent of the melanocortin system, but unlike leptin, cerulenin fails to block neuroendocrine effects of fasting.

Cerulenin and a related compound, C75, have recently been reported to reduce food intake and body weight independent of leptin through a mechanism hypothesized, like leptin, to involve hypothalamic nutrition-sensitive neurons. To assess whether these inhibitors act through mechanisms similar to mechanisms engaged by leptin, ob/ob and Ay (agouti) mice, as well as fed and fasted wild-type mice, were treated with cerulenin. Like leptin, cerulenin reduced body weight and food intake and increased metabolic rate in ob/ob mice, and cerulenin produced the same effects in wild-type mice, whereas lithium chloride, at doses that produce conditioned taste aversion, reduced metabolic rate. However, in contrast to leptin, cerulenin did not prevent effects of fasting on plasma corticosterone or hypothalamic levels of neuropeptide Y, agouti-related peptide, pro-opiomelanocortin, or cocaine- and amphetamine-related peptide mRNA. Also, in contrast to leptin, cerulenin was highly effective to reduce body weight in Ay mice, in which obesity is caused by blockade of the melanocortin receptor. These data demonstrate that cerulenin produces metabolic effects similar to effects of leptin, but through mechanisms that are independent of, or down-stream from, both leptin and melanocortin receptors.

Adrenalectomy reverses obese phenotype and restores hypothalamic melanocortin tone in leptin-deficient ob/ob mice.

In genetically obese leptin-deficient ob/ob mice, adrenalectomy reverses or attenuates the obese phenotype. Relative to lean controls, ob/ob mice also exhibit decreased hypothalamic proopiomelanocortin (POMC) mRNA and increased hypothalamic agouti-related peptide (AGRP) mRNA and neuropeptide Y (NPY) mRNA. It has been hypothesized that this profile of hypothalamic gene expression contributes to the obese phenotype caused by leptin deficiency. To assess if reversal of obese phenotype by adrenalectomy entails normalization of hypothalamic gene expression, male wild-type and ob/ob mice were adrenalectomized (with saline supplementation) or sham adrenalectomized at 2 months of age. Mice were sacrificed 2 weeks after adrenalectomy, during which time food intake and body weight were monitored daily. After sacrifice, hypothalamic gene expression was assessed by Northern blot analysis as well as in situ hybridization. In wild-type mice, adrenalectomy significantly decreased AGRP mRNA but did not significantly influence POMC or NPY mRNA. In ob/ob mice, adrenalectomy reduced the levels of plasma glucose, serum insulin and corticosterone, and food intake toward or below wild-type levels, and it restored hypothalamic POMC and AGRP mRNA but not NPY mRNA to wild-type levels. These studies suggest that adrenalectomy reverses or attenuates the obese phenotype in ob/ob mice, in part by restoring hypothalamic melanocortin tone toward wild-type levels. These studies also demonstrate that factors other than leptin may play a major role in regulating hypothalamic melanocortin function.

Fasting regulates hypothalamic neuropeptide Y, agouti-related peptide, and proopiomelanocortin in diabetic mice independent of changes in leptin or insulin.

Fasting increases hypothalamic neuropeptide Y (NPY) and agouti-related peptide (AGRP) messenger RNA (mRNA) and reduces hypothalamic POMC mRNA, and is also characterized by a reduction in plasma leptin, insulin, and glucose, each of which has been implicated in the regulation of hypothalamic gene expression. To further evaluate the roles of leptin, insulin, and glucose in mediating effects of fasting, we examined hypothalamic gene expression in nondiabetic and streptozotocin (STZ)-induced diabetic mice both under ad lib fed and 48-h fasted conditions. In both diabetic and nondiabetic mice, fasting stimulated hypothalamic NPY and AGRP mRNA and inhibited hypothalamic POMC mRNA and adipose leptin mRNA. However, in diabetic mice fasting had no effect on plasma leptin and insulin while decreasing plasma glucose, whereas in nondiabetic mice fasting decreased plasma leptin, insulin, and glucose. Furthermore, in nondiabetic fasted mice, NPY and AGRP mRNA were higher, and POMC mRNA and plasma glucose were lower, than in diabetic ad lib fed mice, even though insulin and leptin were similar in these two groups. These data are consistent with the hypothesis that although leptin and insulin regulate hypothalamic gene expression, glucose or other factors may have independent effects on hypothalamic and adipose gene expression under conditions of low insulin and leptin.

Vector autoregressive modeling analysis of frequently sampled oral glucose tolerance test results. 2. Insulin resistance and secretion after gastrectomy.

Using the method of vector autoregressive modeling (VAR) analysis of frequently sampled oral glucose tolerance test (OGTT) results, we evaluated abnormalities in the feedback relationships between plasma glucose and insulin in gastrectomized patients to assess insulin secretion capacity and insulin resistance following gastrectomy. VAR modeling analysis was applied to the plasma glucose and insulin level data from the frequently-sampled 75g-OGTT results of 38 subjects who had undergone total or subtotal gastrectomy and 977 controls without gastrectomy. After gastrectomy, the predicted response of insulin to a glucose challenge was excessive in normal subjects and those with slightly impaired glucose tolerance. Furthermore, the glucose response to insulin was clearly positive in gastrectomized subjects with moderately to severely impaired glucose tolerance, i.e., diabetics, indicating strong insulin resistance. The insulin resistance in this situation cannot be explained by decreased peripheral glucose disposal. Our results suggest that the lowered glucose tolerance which follows gastrectomy results from disturbance of the hormonal relationship between pancreas and intestine (entero-insular axis), which causes increased intestinal glucose absorption, and the insulin resistance which occurs in response to hyperinsulinemia in patients with normal fasting plasma glucose. Disturbance of the entero-insular axis may cause not only increased glucose absorption but also hyperglucagonemia, both of which contribute to hyperglycemia in diabetic patients after gastrectomy.

Vector autoregressive modeling analysis of frequently sampled oral glucose tolerance test results. 1. A new method for quantifying insulin resistance and secretion.

To elucidate abnormalities in the feedback relationships between plasma glucose and plasma insulin levels in diabetic patients, we have introduced the vector autoregressive modeling method as a new for tool feedback analysis. This technique was applied to plasma glucose and insulin level data from a series of 977 frequently-sampled oral glucose tolerance tests (FS-OGTT). Neither special instruments nor medications were used in FS-OGTT. We were able to predict the degree of the plasma glucose response occurring after an impulse-like increase in plasma insulin at 1 mU/mL, as well as the plasma insulin response triggered by an impulse-like increase in plasma glucose at 1 mg/dL, in the form of "impulse response curves". The predicted impulse response curve of glucose to insulin gradually changed from negative to positive with incremental changes in the fasting plasma glucose level, reflecting increased insulin resistance. Furthermore, the response of insulin to glucose decreased in a stepwise fashion with the incremental changes in the fasting plasma glucose level. Our findings confirm the usefulness of impulse response curves as clinical indicators. In addition, analytical data point to a possible contribution of excessive hepatic glucose production to the pathogenesis of the insulin resistance in non-insulin-dependent diabetes mellitus.

Defective viral vectors as agents for gene transfer in the nervous system.

Viral vectors have attracted great interest as vehicles for gene therapy. Due to concerns regarding continued viral gene expression in several systems, new approaches have been sought for gene transfer in the nervous system. This article reviews the general concepts and basic biology of defective viral vectors. These are vectors which can package into a viral coat but contain no viral genes, thereby allowing efficient gene transfer in the absence of viral gene expression in target cells. The defective herpes simplex virus (HSV) vector has been applied to numerous interesting questions in neurobiology. The inability to completely eliminate helper viruses has raised concern regarding the application of this vector to human disease. The adeno-associated virus (AAV) vector has recently been introduced into the nervous system. This vector harbors no viral genes, however helper viruses can also be completely eliminated from the system. Although the smaller size may limit the range of applications for this vector, it has received great interest as a potential agent for gene therapy in the nervous system. Potential future directions are discussed as well.

Long-term gene transfer in porcine myocardium after coronary infusion of an adeno-associated virus vector.

BACKGROUND: Viral vector-mediated gene transfer into the heart represents a potentially powerful tool for studying both cardiac physiology as well as gene therapy of cardiac disease. We report here the use of a defective viral vector, which expresses no viral gene products, for gene transfer into the mammalian heart. Previous studies have used recombinant viral vectors, which retained viral genes and yielded mostly short-term expression, often with significant inflammation. METHODS: An adeno-associated virus vector was used that contains no viral genes and is completely free of contaminating helper viruses. The adeno-associated virus vector was applied to rat hearts by direct intramuscular injection; adeno-associated virus was also infused into pig hearts in vivo via percutaneous intraarterial infusion into the coronary vasculature using routine catheterization techniques. RESULTS: Gene transfer into rat heart yielded no apparent inflammation, and expression was observed for at least 2 months after injection. Infusion into pig circumflex coronary arteries resulted in successful transfer and expression of the reporter gene in cardiac myocytes without apparent toxicity or inflammation; gene expression was observed for at least 6 months after infusion. CONCLUSIONS: We report the use of adeno-associated virus vectors in the cardiovascular system as well as successful myocardial gene transfer after percutaneous coronary artery infusion of viral vectors in a large, clinically relevant mammalian model. These results suggest that safe and stable gene transfer can be achieved in the heart using standard outpatient cardiac catheterization techniques.

Correlation between glycated lipoproteins and fructosamine level in serum.

The correlation between the level of fructosamine and glycated proteins, including glycated lipoproteins, in serum from diabetic and nondiabetic subjects was studied. Assay of glycated proteins in serum was performed using an agarose gel film electrophoresis with nitroblue tetrazolium coloration. Glycated albumin correlated well with the fructosamine level in the diabetics (r = 0.83-0.92, p less than 0.01) but showed no correlation with the nondiabetics (r = 0.25-0.26). Also, a high correlation between the glycated beta-lipoprotein and fructosamine levels was observed in diabetic patients with hyperglycemia and in nondiabetic subjects with a high risk of atherogenesis (atherogenic index, low-density lipoprotein-cholesterol/high-density lipoprotein-cholesterol greater than 2.8) (r = 0.51-0.66, p less than 0.01). Nondiabetics with a high level of beta-lipoprotein, which is well known to cause high atherogenesity, showed a high level of glycated beta-lipoprotein similar to that in the diabetic groups with hyperglycemia; therefore, the high level of glycated beta-lipoprotein seems to be attributable not only to the hyperglycemia-accelerated glycation of beta-lipoprotein but also to an increase in the level of beta-lipoprotein in serum. Consequently, the present results show that the fructosamine level in serum reflects not only the glycation of albumin but also that of lipoproteins which are known to increase in diabetes mellitus.

Thyrotropin-releasing hormone and insulin in chemically induced pancreatic islet cell tumors in rats.

Thyrotropin-releasing hormone (TRH) and insulin were measured by radioimmunoassay in acetic-acid extracts of 19 pancreatic islet cell tumors induced by streptozotocin and nicotinamide in rats. In addition, gel filtration properties of TRH-immunoreactivity and immunoreactive insulin (IRI) were examined in 5 and 14 tumors, respectively. TRH was demonstrated in 10 of 19 tumors, with a mean of 166 +/- 47 (SEM) pg/mg wet weight, whereas the concentration was less than 3 pg/mg wet weight in the other tumors. In contrast, all tumors contained IRI, with a mean of 11.0 +/- 1.6 micrograms/mg wet weight. Ten tumors in which TRH was demonstrated contained more IRI than those in which TRH was not detected (13.1 +/- 1.8 vs 6.5 +/- 1.7 micrograms/mg wet weight, P less than 0.02). After gel filtration, all TRH immunoreactivity was eluted at the same place as synthetic TRH in the 5 tumors. In addition, gel filtration elutes showed essentially the same pattern of IRI in the 14 tumors, with 3 peaks. The predominant IRI peak comigrated with marker insulin (95.7 +/- 0.8%), another prominent peak occurred coincident with proinsulin standard (3.3 +/- 0.5%), a third peak was present in the void volume (0.28 +/- 0.04%). These distributions of IRI were similar to those in extracts of normal pancreases. The present studies demonstrate TRH immunoreactivity in pancreatic islet cell tumors induced by streptozotocin and nicotinamide in rats. Chemically induced insulinomas can serve as a model for insulin storage which is analogous to islet B cells.

[Experimental study on diabetes and pregnancy: with special reference to the effects of insulin treatment on fetuses of diabetic dams].

Through the development of treatment of diabetes mellitus, diabetic cases of pregnancy have been increasing, and the effects of maternal hyperglycemia and insulin-treated hypoglycemia on the growth and life of fetuses and newborns are becoming very important problems. However, it is difficult for us to investigate the fetuses of human diabetic mothers as experimental models. Although many reports deal with the development of newborns of diabetic mothers and about their secretory changes of insulin and C-peptide reactivity, there have been few reports concerning the effects of severe diabetes on pregnancy and the effects of insulin treatment on fetuses. Concerning experimental animals, there are also few reports about the effects of insulin treatment on diabetic pregnant animals. We conducted the present investigation to determine the effects of insulin treatment on the growth and metabolism of the fetuses of diabetic pregnant rats. Virgin female Wistar rats weighing 200 approximately 300 g were caged overnight with male rats. The mated females were isolated and the gestational age was calculated from noon of this day (zero). Seventeen of 24 pregnant rats received a rapid intravenous injection of 50 mg/kg body weight of streptozotocin (STZ) in 0.4 ml of 0.01 M citrate buffer (pH 4.5) immediately after blood samples were collected through the jugular vein under light ether anaesthesia on the 5th day of gestation. Seven pregnant rats were injected with only 0.4 ml of citrate buffer and served as the controls. These rats were divided into four groups, and each group was named as follows: Normal pregnant rats group (group I, n = 7), diabetic pregnant rats group (group II, n = 6) and insulin-treated diabetic pregnant rats group (group III: plasma glucose level 60 approximately 300 mg/dl, n = 6 and group IV: plasma glucose level below 60 mg/dl, n = 5). Group III and IV rats were treated with a subcutaneous injection of Lente Insulin (from 2 u. to 6 u.) every day from the 13th to the 19th day of gestation. Group II rats were injected with saline every day in the same way. Maternal blood samples were collected under light ether anaesthesia after feeding ad libitum on the 5th and 12th days of gestation. On the 20th day of gestation, the pregnant rats were anaesthetized by an intraperitoneal injection of sodium pentobarbital, and blood samples were collected in the manner stated above. Each fetus and placenta was taken out individually by hysterotomy.(ABSTRACT TRUNCATED AT 400 WORDS)

Protection by nicotinamide against streptozotocin-induced reduction in pancreatic TRH.

The concentration of thyrotrophin-releasing hormone (TRH) immunoreactivity was determined in pancreatic islets and acini in the rat. In addition, time-course changes in TRH in response to an iv injection of streptozotocin (65 mg/kg body weight) with or without nicotinamide (500 mg/kg body weight) were examined in the whole pancreas. Furthermore, pancreatic TRH was measured in diabetic rats treated with insulin for 3 weeks. The TRH concentration in rat islets was 42-fold higher than in exocrine glands, indicating that the majority of pancreatic TRH is of islet origin. The mean concentration of pancreatic TRH decreased to 60 and 65% of the respective control values at 4 and 7 h after administration of streptozotocin, respectively. AT 24 h, it fell to 10% of control values without significant changes in TRH levels in the hypothalamus and gastrointestinal tract. In contrast, no significant change in pancreatic TRH was noted in rats given combined treatment with streptozotocin and nicotinamide. The injection of streptozotocin alone resulted in severe hypoglycaemia at 7 h and hyperglycaemia at 24 h, whereas neither resulted from the combined treatment. Insulin therapy had no influence on the decreased TRH concentrations in the diabetic pancreas. These results suggest that TRH may be localized to the B cells of pancreatic islets, and that the marked reduction in TRH in diabetic pancreases is not a metabolic consequence of insulin deficiency.

Portal somatostatin responds to intragastric glucose: effects of streptozotocin diabetes.

Changes in somatostatin levels in portal response to intragastric glucose loading were examined in normal controls and streptozotocin diabetic rats for one week duration. The mean (+/- SEM) basal level of somatostatin was more significantly elevated in diabetic rats (401 +/- 62 pg/ml) than in controls (171 +/- 13 pg/ml). However, no significant difference in somatostatin concentrations 30 min after glucose loading was found between diabetic and control animals (587 +/- 113 vs. 443 +/- 47 pg/ml). Glucose loading caused a significant elevation of somatostatin in controls, but not in diabetic rats. These results suggest a physiologic role of somatostatin in nutrient homeostasis, and that abnormalities in D cell function are present in streptozotocin diabetes of short duration.

Pancreatic insulin, glucagon and somatostatin concentrations in rats with islet cell tumors induced by streptozotocin.

Hyperinsulinemic and hypoglycemic rats with islet tumors induced by streptozotocin were shown to have significantly decreased immunoreactive insulin and somatostatin concentration (expressed as per g wet weight (w. wt) and content (expressed as per whole pancreas) in the pancreas surrounding the tumor as compared to those of age and weight adjusted controls. The pancreatic glucagon concentration of the former was significantly lower than that of the latter but no significant difference between glucagon content in the two groups was observed. Thus, inverse relationships were demonstrated between circulating insulin and somatostatin as well as insulin in the pancreas. It is suggested that a large amount of insulin in plasma results in a decrease in pancreatic insulin and somatostatin.

Increase of pancreatic somatostatin concentration in early phases of streptozotocin diabetes in rats.

A small yet significant increase of immunoassayable pancreatic somatostatin concentration (0.107 +/- 0.005 vs. 0.156 +/- 0.017 microgram/g at 24 hr, p less than 0.05) was found in rats, 24 hr as well as 7 days after treatment with a diabetogenic dose of streptozotocin (65 mg/kg BW). These animals were characterized by marked decreases of insulin in the pancreas without any significant changes in pancreatic glucagon concentration. These results suggest that an abrupt deprivation of insulin from islets results in an elevation of pancreatic somatostatin concentration, and that glucagon in the pancreas plays a minor role in determining pancreatic somatostatin concentration in rats with insulin-deprived diabetes of short duration.

Somatostatin concentration responds to arginine in portal plasma: effects of fasting, streptozotocin diabetes, and insulin administration in diabetic rats.

Changes of somatostatin concentration in response to a single i.v. injection of arginine (400 mg/kg body weight) were examined in extracted portal plasma of normal and diabetic rats in the fully fed state and after 24 h or fasting, as well as in diabetic rats treated with insulin for one week. In both normal and diabetic animals fasted for 24 h, the basal level of somatostatin declined but the magnitude of the arginine-induced elevation of somatostatin was not affected, suggesting a physiologic role of the tetradecapeptide in nutrient homeostasis. When compared with intact rats, diabetic animals were shown to have increased levels of somatostatin before and after arginine administration, both of which were attenuated by insulin replacement therapy. These findings suggest that alterations of D cell function in streptozotocin diabetes may be related to either insulin deficiency or its metabolic consequences.