Persistence of rhythmic human growth hormone release during sheep in fasted and nonisocalorically fed normal subjects

The effects of nonisocaloric feeding and fasting on rhythmic release of HGH in sleep were examined in three normal women. Each was studied on two nights during a base-line-isocaloric period, on the second and third nights of an 80-hr fast, and on the third and sixth nights of a 600-g CHO, 4000-calorie diet. Plasma HGH, insulin, and glucose were determined at 20-min intervals and NEFA at hourly intervals during polygraphically monitored sleep. Normal repetitive patterns of HGH release in sleep occurred in all three subjects during base-line and high-CHO diet periods. No suppression of release occurred in any subject during the 6 days of excessive caloric intake and weight gain of 2.8–3.5% above mean basal weight. Fasting resulted in increased peak HGH concentrations in sleep, but each subject continued her same pattern of release, frequency of peaks, and sequential damping of release during sleep, as did a fourth male subject during a 60-hr fast. HGH release in sleep in fasting exhibited amplification of the normal rhythm. This occurred despite a significant glucose fall to below normal range, undetectable insulins, elevated NEFAs, and weight losses of 4.6–9.4%. NEFA fell sharply at sleep onset on 5 of 6 fast nights suggesting an adrenergic mechanism had been altered at entry into sleep. No pattern of rise in glucose or NEFA comparable to classic HGH effects on substrate followed the early sleep HGH peak in any study period. The data suggest that sleep release of HGH is a primary neural rhythm relatively independent of substrate concentration. Neuronal adaption to utilization of nonglucose substrates in fasting may lead to enhanced rhythmic activity and increased amplitude of the HGH release rhythm in sleep.     

Leucine metabolism in stable cirrhosis

Alterations in protein and amino acid metabolism have been postulated to explain the frequent observations of muscle wasting and decreased plasma branched-chain amino acid concentrations in cirrhosis. In order to investigate the changes in protein metabolism, we have measured the rates of leucine turnover and oxidation in six stable, biopsy-proven cirrhotics and six age and sex-matched healthy control subjects after an overnight fast, using [1-13C]leucine tracer. Following a primed constant-rate infusion of [1-13C]leucine, the 13C enrichments of plasma leucine and expired CO2 were used to estimate leucine turnover and oxidation, respectively. Fat-free body mass was estimated from the measurements of total body water as quantified by H2[18O] tracer dilution. The rates of CO2 production and oxygen consumption were measured hourly during the study period, using open-circuit respiratory calorimetry. Urinary urea, ammonia and total nitrogen excretion rates were quantified from timed urine samples. Even though the plasma leucine levels were lower in cirrhotics as compared with controls (100.5 +/- 17.1 vs. 138.3 +/- 20.4 mumoles per liter, mean +/- S.D., p less than 0.001), the rates of leucine turnover were not significantly different in the two groups (89.4 +/- 19.0 vs. 87.8 +/- 19.0 mumoles per kg X hr). In contrast, the rates of leucine oxidation were significantly reduced in cirrhosis (8.1 +/- 2.5 vs. 12.7 +/- 3.1 mumoles per kg X hr, p less than 0.01). When all subjects were considered, the leucine oxidation rate was correlated with plasma leucine concentration (r = 0.62, p less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)     

Brain/gut peptides in fed and fasted rats

The concentrations and contents of vasoactive intestinal peptide (VIP) and cholecystokinin (CCK) in the brain and of these peptides along with secretin and glucagon-like immunoreactivity (GLI) in the gut were compared in a group of 16 5-day fasted adult Sprague-Dawley rats with the corresponding peptides in a group of 16 nonfasted littermates. The mean weight of the fasted rats at the beginning of the study was 263 +/- 10 g (+/- SEM) and was 177 +/- 7 g before killing, for a net loss of 33% of initial body weight; the 16 fed rats increased their mean weight from 225 +/- 11 to 284 +/- 12 g, for a net gain of 12%. During the 5-day fast there was no change in the weight of the cortex, hypothalamus, or brain stem. However, the weight of tissues from the gut decreased to about half the weight of the corresponding tissues in the fed animals. There was no significant change in brain VIP or CCK. VIP content in the gut was unchanged. However, because of the decrease in organ weight, its concentration almost doubled. Secretin concentrations in the gut of fasted rats did not change significantly, but organ contents fell to about half. The gut content of GLI also fell by half or more. The concentrations of CCK in methanol extracts of the duodenum and jejunum remained relatively constant, but those in acid extracts fell by 40% in the fasted animals. This represents an approximately 70% decrease in organ content of CCK. These findings are interpretable as demonstrating that during a prolonged fast neuronal CCK and VIP are well conserved, but endocrine CCK, secretin, and GLI are markedly decreased because of loss of intestinal mucosa.     

Ghrelin and leptin pulse discharge in fed and fasted rats.

Ghrelin stimulates and leptin inhibits appetite by modulating neuropeptide Y (NPY) signaling in the hypothalamus. Analysis of plasma ghrelin and leptin by sensitive radioimmunoassays showed that the two peripheral hormones are secreted in pulsatile fashion in rats consuming ad libitum rat chow. Fasting augmented all parameters of ghrelin pulsatile secretion and diminished leptin secretion by selectively attenuating the pulse amplitude; concomitantly it produced synchrony in ghrelin and leptin pulse discharge. These studies imply that a synchronous leptin restraint and ghrelin stimulus on NPYergic signaling may underlie robust appetitive drive.     

Urinary excretion rate of C-peptide in fed and fasted obese humans

The aim of the study was to evaluate the reliability of urinary excretion rate of C-peptide as a marker of B-cell function during fasting. Ten obese subjects of both sexes fasted for 5 days. Diurnal serum C-peptide was collected before and on the 5th day; morning serum samples (for glucose, insulin and C-peptide) and 12-h urine samples (7.00 to 19.00 h) were collected daily. Body weight decreased from 138.7 +/- 15.9 to 132.9 +/- 15.6 kg. Morning glucose, insulin (-40%) and C-peptide (-50%) fell significantly throughout the study. Mean diurnal C-peptide values were 2.19 +/- 0.69 nmol/l before and 0.60 +/- 0.19 nmol/l after fasting (P less than 0.0001) and its secretion rate was 909.4 +/- 297.9 and 244.4 +/- 83.9 nmol/12 h (P less than 0.005), respectively. Excretion rate of C-peptide fell progressively from basal (11.2 +/- 4.2 nmol/12 h) to a nadir value of 1.3 +/- 0.8 nmol/12 h (P less than 0.0005); similarly, the C-peptide to creatinine clearance ratio fell from 0.062 +/- 0.035 to 0.028 +/- 0.015 (P less than 0.05). These results indicate that fasting modifies renal metabolism of C-peptide thus creating several complications in the quantitative interpretation of urinary levels as an index of its secretion rate from the B-cell.     

Fenofibrate raises plasma homocysteine levels in the fasted and fed states

The effect of fenofibrate (FEN), compared with placebo (PL), on total plasma homocysteine (tHcy) levels in the fasted and fed states has been examined. Twenty men with established coronary artery disease (CAD) or with at least two cardiovascular risk factors, who had elevated plasma triglyceride levels (> 2.3 mmol/l) and reduced HDL-C levels (< 0.91 mmol/l), and in whom a fibric acid derivative was clinically indicated were studied. The study was a randomized, PL controlled, double-blind study designed to test the effect of micronized FEN on postprandial lipemia. Plasma tHcy levels were investigated as a post-hoc analysis. After a 4-week dietary stabilization period, patients were randomized to PL or FEN (200 mg/day) for 8 weeks, followed by an 8-h postprandial study, consisting of 1 g fat/kg body weight (35% cream). The methionine content of cream was approximately 0.53 mg/ml. A 5-week washout period was then followed by a second 8-week treatment period (FEN or PL), at the end of which a second postprandial study was undertaken. Blood was sampled in the fasted state (0 h) and postprandially at 2, 4, 6 and 8 h. Plasma was stored at -80 degrees C for homocysteine, vitamins B(6), B(12) and folate measurements. FEN caused a marked decrease in all triglyceride-rich lipoprotein parameters, no change in LDL-C, and an increase in HDL-C levels. Fen treatment was associated with an increase in fasting tHcy (PL: 10.3+/-3.3 micromol/l to FEN: 14.1+/-3.8 micromol/l, 40.4+/-20.5%, P < 0.001) and fed tHcy levels 6 h post-fat load (PL: 11.6+/-3.3 micromol/l vs. FEN: 17.1+/-5.4 micromol/l, P < 0.001). Homocysteine levels were increased by the fat load; PL: 14% (P < 0.001) and FEN: 21%, P < 0.001 at the 2, 4, 6 and 8 h time points. Change in tHcy level on FEN was not associated with changes in plasma levels of folate, vitamins B(6) or B(12) or creatinine. Amino acid analysis revealed that methionine and cysteine were significantly increased on FEN (P < 0.005). The incidence of hyperhomocysteinemia (defined as tHcy level >14 micromol/l) was PL: 2/20 (10%) and FEN: 9/20 (45%) (chi(2) = 4.51, P = 0.034). There was no correlation between changes in plasma triglyceride levels and tHcy levels. Since tHcy is considered an emerging cardiovascular risk factor, the ability of FEN to increase plasma tHcy levels could potentially mitigate the potential of this drug to protect against cardiovascular disease.     

Trophic effects of pentagastrin on gastrointestinal tract in fed and fasted rats

In rats injected with pentagastrin (2-500 micrograms/kg subcutaneously) in saline, peak gastric acid responses occurred after 31 (30-min output) or 63 micrograms/kg (60-min output). Rats were fed or fasted for 48 h and injected every 8 h with 63, 250, or 1000 micrograms/kg pentagastrin. Fasting decreased body weight (30% versus fed), serum gastrin (90%), and weight and protein content of oxyntic and pyloric gland areas, pancreas, small intestine, and colon. Deoxyribonucleic acid content or [3H]thymidine incorporation was decreased in all organs except colon. The lowest dose of pentagastrin significantly increased [3H]thymidine incorporation in the oxyntic gland area of fed rats and the small intestine of fasted rats, although organ weight, protein, or deoxyribonucleic acid content did not increase. These data indicate that short-term fasting has dramatic effects on gastrointestinal organ growth in rats and that pentagastrin reverses some of these changes.     

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.     

Central nervous system control of glycogenolysis and gluconeogenesis in fed and fasted rat liver

The influence of brain cholinergic activation on hepatic glycogenolysis and gluconeogenesis was studied in fed and 48-hour fasted rats. Neostigmine was injected into the third cerebral ventricle and hepatic venous plasma glucose, glucagon, insulin, and epinephrine were measured. The activity of hepatic phosphorylase-a and phosphoenolpyruvate-carboxykinase (PEP-CK) was also measured. Experimental groups: 1, intact rats; 2, rats infused with somatostatin through the femoral vein; 3, bilateral adrenodemedullated (ADMX) rats; 4, somatostatin infused ADMX rats; 5, 5-methoxyindole-2-carboxylic acid (MICA) was injected intraperitoneally 30 minutes before injection of neostigmine into the third cerebral ventricle of intact rats. MICA treatment completely suppressed the increase in hepatic glucose in fasted rats, but had no effect in fed rats. Phosphorylase-a activity was not changed in fasted rats, but increased in fed rats, intact rats, somatostatin-infused rats, somatostatin-infused ADMX rats, and ADMX rats in that order. PEP-CK was not changed in fed rats, but increased at 60 and 120 minutes after neostigmine injection into the third cerebral ventricle in fasted rats. We conclude that, in fed states, brain cholinergic activation causes glycogenolysis by epinephrine, glucagon, and direct neural innervation. In fasted states, on the other hand, gluconeogenesis is dependent on epinephrine alone to increase hepatic glucose output.     

Glyceroneogenesis in rat and guinea pig adipose tissue during the fed and fasted states

While both pyruvate and lactate are good substrates for glyceride-glycerol synthesis in isolated adipocytes from fed rats and guinea pigs, neither alanine nor serine appear to support glyceroneogenesis. Fasting increases the proportion of radioactive pyruvate or lactate incorporated into glyceride-glycerol and reciprocally decreases the proportion incorporated into fatty acids. However, the total incorporation of radioactivity into triacylglycerol is considerably lower in isolated adipocytes from fasted than from fed animals. Addition of glucose to the incubation medium promotes the incorporation of radioactive lactate into both fatty acids and glyceride-glycerol by adipocytes from fasted as well as fed animals. The concentration of α-glycerolphosphate is considerably higher in adipose tissue of fed than fasted animals. In general, these results support the presence of a glyceroneogenic pathway in rat and guinea pig adipose tissue. However, it would appear that the physiologic significance of this pathway is less important in the fasted than the fed state, where it may play some role in the esterification of intracellular fatty acids.     

Metabolic balance of the ovine fetus during the fed and fasted states

The present study was performed in order to quantitate the uptake and excretion of a number of metabolic substrates by the sheep uterus as well as the fetus during the fed and fasted states within the same animals. 5 dated Suffolk sheep were studied initially at least 7 days after surgical placement of catheters in the fetal umbilical artery and vein, as well as the uterine veins and maternal artery. During the fed state and after 5 days of complete maternal fasting, measurements were made of uterine and umbilical blood flow by the steady-state antipyrine method, and the concentrations of whole blood glucose, oxygen, ammonia, 23 amino acids and plasma urea nitrogen were assessed. The results indicate that free amino acids and glucose comprise the major substrates required by the fetal lamb during both the fed and fasted states. While a number of amino acids changed in concentration in both the maternal and fetal circulations, few amino acids demonstrated a significant change in uptake in either the umbilical or uterine circulations. Similarly, no changes were observed in the uptake of oxygen by either the fetus or the uterus, while glucose consumption by the fetus decreased substantially with a concomitant increase in urea production. Consumption of both glucose and oxygen by the uteroplacenta remained unchanged during fasting. Leucine is one of several amino acids which is metabolized to a significant extent within the uteroplacenta, and theoretically may play a role in modulating glucose metabolism within the placenta and fetus.     

Insulin clearance and microsomal glutathione-insulin transhydrogenase in perfused livers of fed and fasted rats

Clearance of exogenous insulin measured in perfused livers from rats fed ad lib or fasted X 24 or X 48 h was correlated with changes in activity and distribution of the insulin-degrading enzyme glutathione-insulin transhydrogenase measured in microsome fractions, post-perfusion. For comparison with endogenous insulin removal (Endocr. Res. Commun. 7: 231, 1980), a single-pass perfusion mode was used and clearance of insulin at levels (less than or equal to 15 ng/ml) typically observed in perfused rat liver-pancreases during glucose stimulation was studied. Similar to the endogenous data, exogenous insulin removal followed an ogival pattern during fasting. In the fed state, clearance was relatively low, corresponding to a hepatic extraction of approximately 29%. Insulin extraction increased nearly 2-fold after a 24 h fast to approximately 48% (p less than .01), declining to approximately 30% (p less than .025) when fasting was prolonged (X 48 h). At portal insulin concentrations greater than 8 ng/ml (approximately 200 microUnits/ml), clearance tended to decrease in all 3 nutritional states, with apparent saturation of the insulin capturing mechanism being strongest in the 24 h fasted state. In conjunction with these changes in whole organ insulin removal, GSH-insulin transhydrogenase nonlatency, viz., nonlatent activity in intact microsomes relative to total activity in disrupted microsomes, did not change during the first 24 h of fasting; whereas the proportion of nonlatent activity was significantly decreased (p less than .01) after 48 h. Homogenate activity remained essentially constant during the initial fasting period, and declined by approximately 16% (p less than .01) after 48 h of fasting.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of noncarbohydrate substrates on protein synthesis in hearts from fed and fasted rats

An overnight fast reduced RNA content and resulted in lower rates and efficiency of protein synthesis when rat hearts were perfused in vitro and supplied glucose as oxidizable substrate. Decreased efficiency of synthesis was associated with development of a block in peptide chain initiation in hearts of both fed and fasted rats. Provision of pyruvate increased the rate and efficiency of protein synthesis in fasted but not fed tissue, and partially overcame the initiation block in both groups. A mixture of glucose, pyruvate and insulin increased the efficiency of protein synthesis and decreased ribosomal subunit content to similar values in both groups of hearts. Noncarbohydrate substrates, including pyruvate, lactate, acetoacetate and beta-hydroxybutyrate, supported higher rates of protein synthesis than glucose in hearts of fasted, but not fed rats. However, mixtures of glucose and either pyruvate, acetoacetate or beta-hydroxybutyrate increased the synthetic rate in fed tissue. Provision of noncarbohydrate substrates increased energy availability, as indicated by higher creatine-P/creatine ratios in both groups of hearts, but the synthetic rate increased as a function of creatine-P/creatine ratio only in the fasted tissue. Octanoate and leucine accelerated protein synthesis and increased energy availability in the fed tissue. The mixtures of glucose and noncarbohydrate substrates or octanoate elevated glucose-6-P content. These studies indicate that an overnight fast decreased the capacity for protein synthesis and modified the regulation of synthesis by noncarbohydrate substrates.     

Sugar transport in the small intestine of obese hyperglycemic,fed and fasted mice

1. The in vitro transport of 3-0-methyl-D-glucose was measured in the small intestine of obses-hyperglycemic (ob/ob) mice and their lean littermates, fed or fasted for 48 hrs. 2. Transport was much increased in the jejunum of obese animals and, to a lesser extent, in obese mice on a chronic restricted diet. 3. Kinetic studies indicate that the Vmax of transport was significantly greater in obese than in lean mice, whether fed or fasting. Fasting increase the Vmax in lean but not in obese animals. These changes were more prominent in the jejunum. The apparent Km of transport was the same in all four groups. 4. These findings are discussed in relation to the increase in intestinal absorptive functions in diabetes and in some conditions of food restriction or starvation. The results are consistent with the hypothesis that the effects of diabetes and of starvation on intestinal sugar transport reflect an alteration in the same controlling factor.     

Effects of naloxone on glucose and insulin regulation during endotoxicosis in fed and fasted rats

This study examined the effects of naloxone on glucose and insulin dyshomeostasis during endotoxicosis in ad libitum fed and overnight-fasted rats. Plasma glucose levels were measured in vivo to assess the effects of naloxone on glucose regulation during endotoxicosis. Naloxone's effects on endotoxin-induced portal and systemic hyperinsulinemia were evaluated in vivo. In addition, the ability of naloxone to alter the insulin hypersecretory state of the endotoxic pancreas was evaluated using the in vitro perfused rat pancreas preparation. Naloxone did not alter endotoxin-induced glucose dyshomeostasis in fasted rats, but potentiated hypoglycemia in fed, endotoxic rats. Naloxone potentiated endotoxin-induced hyperinsulinemia and insulin hypersecretion from the endotoxic pancreas in fed, but not fasted, rats. Thus the results indicated that naloxone had no apparent beneficial effects on glucose and insulin dyshomeostasis during endotoxicosis in either fed or fasted rats, and potentiated glucose and insulin dyshomeostasis in fed, endotoxic rats. Since naloxone is a specific opiate antagonist, these results suggested that endogenous opiate systems do not play a significant deleterious role in the glucose and insulin dyshomeostasis of endotoxic shock. In addition, this study identified prior feeding history of rats (ad libitum feeding vs. overnight fasting) as an important variable relative to the study of naloxone's effects on glucose and insulin regulation during endotoxicosis.     

Diet-induced obesity alters protein synthesis: tissue-specific effects in fasted versus fed mice

The influence of obesity on protein dynamics is not clearly understood. We have designed experiments to test the hypothesis that obesity impairs the stimulation of tissue-specific protein synthesis after nutrient ingestion. C57BL/6J mice were randomized into 2 groups: group 1 (control, n = 16) was fed a low-fat, high-carbohydrate diet, whereas group 2 (experimental, n = 16) was fed a high-fat, low-carbohydrate diet ad libitum for 9 weeks. On the experiment day, all mice were fasted for 6 hours and given an intraperitoneal injection of (2)H(2)O. They were then randomized into 2 subgroups and either given a sham saline gavage or a liquid-meal challenge. Rates of protein synthesis were determined via the incorporation of [(2)H]alanine (5 hours postchallenge) into total gastrocnemius muscle protein, total liver protein, and plasma albumin. High-fat feeding led to an increase in total body fat (P < .001) and epididymal fat pad weights (P < .001) and elevated fasting plasma glucose levels (P < .01). Diet-induced obesity (a) did not affect basal rates of skeletal muscle protein synthesis, but did impair the activation of skeletal muscle protein synthesis in response to nutrient ingestion (P < .05), and (b) slightly reduced basal rates of synthesis of total hepatic proteins and plasma albumin (P = .10), but did not affect the synthesis of either in response to the meal challenge. In conclusion, there are alterations in tissue-specific protein metabolism in the C57BL/6J mouse model of diet-induced obesity. This model may prove to be helpful in future studies that explore the mechanisms that account for altered protein dynamics in obesity.     

Leucine metabolism in patients with Cushing's syndrome before and after successful treatment

OBJECTIVE Results from studies on the effect of glucocor-ticosteroids on protein turnover in both rat and man have been conflicting. The aim of this study was to investigate the primary cause of muscle wasting in patients with Cushing's syndrome. DESIGN Studies of whole body 1-¹⁴C-leucine turnover in patients with Cushing's syndrome before and after successful treatment, and in control subjects. PATIENTS Eleven patients with Cushing's syndrome before and after (n= 5) treatment and 11 control subjects. MEASUREMENTS Whole body 1-¹⁴C-leucine turnover to determine leucine metabolic clearance rate, leucine production rate, leucine oxidation rate and leucine incorporation into protein. RESULTS Plasma leucine concentration (mean ± SEM 100 ± 6 μ mol/l), leucine metabolic clearance rate (9.97 ± 0.11 μ mol/min/kg), leucine turnover (0.98 ± 0.11 μ mol/min/kg) and leucine incorporation into protein (0.71 ± 0.09 μ mol/min/kg) were all significantly reduced in patients with Cushing's syndrome compared with control subjects (122 ± 6 μ mol/l, P < 0.05; 13.61 ± 1.27 μ mol/min/kg, P < 0.05; 1.65 ± 0.12 μ mol/min/kg, P < 0.05; 1.46 ± 0.10 μ mol/min/kg, P < 0.001, respectively). Leucine oxidation rate was similar in the patients with Cushing's syndrome and control subjects. When leucine metabolism was expressed in terms of lean body mass (LBM) in five patients with Cushing's syndrome and 11 control subjects, leucine MCR, leucine turnover and leucine oxidation were not significantly different in the two groups. However, leucine incorporation into protein was significantly reduced (P< 0.001) in the patients with Cushing's syndrome (1.07 ± 0.20 μ mol/min kg LBM) compared with control subjects (1.95 ± 0.11 μ mol/min/kg LBM). CONCLUSION We conclude from these studies that the muscle wasting associated with Cushing's syndrome is primarily due to a reduction in protein synthesis.