Effect of weight loss by a low-fat diet and a low-carbohydrate diet on peptide YY levels.

OBJECTIVE: To compare the effects of weight loss by an energy-restricted low-fat diet vs low-carbohydrate diet on serum peptide YY (PYY) levels. DESIGN: 8-Week prospective study of 30 obese adults (mean age: 42.8+/-2.0 years, mean body mass index 35.5+/-0.6 kg m(-2)). RESULTS: After 8 weeks, subjects on the low-carbohydrate diet lost substantially more weight than those on the low-fat diet (5.8 vs 0.99 kg, P<0.001). Weight loss by either diet resulted in a 9% reduction in both mean fasting serum PYY levels (baseline: 103.5+/-8.8 pg ml(-1), after weight loss: 94.1+/-6.5 pg ml(-1), P<0.01) and postprandial area under the curve (AUC) PYY (baseline: (20.5+/-1.5) x 10(3) pg h(-1) ml(-1), after weight loss: mean AUC PYY (18.8+/-1.4) x 10(3) pg h(-1) ml(-1), P<0.001). There was a trend towards lower levels of PYY with greater degrees of weight loss. CONCLUSIONS: Reduced PYY levels after weight loss by an energy-restricted low-fat or low-carbohydrate diet likely represents a compensatory response to maintain energy homeostasis and contributes to difficulty in weight loss during energy-restricted diets.

The effects of insulin, glucose, and pyruvate on the kinetics of leptin secretion.

Leptin is a hormone that is secreted by fat cells and has roles in body weight regulation, glucose metabolism, reproduction, and other neuroendocrine functions. The purpose of this study was to determine whether the secretagogues, insulin, glucose, and pyruvate, enhance leptin secretion by increasing leptin synthesis, or whether these secretagogues stimulate the quantal release of a stored cytosolic pool of leptin. We found that in the absence of secretagogues, the rate of leptin secretion from isolated rat adipocytes approximately equals the rate of leptin synthesis. For 60 min after the addition of secretagogues, leptin synthesis rapidly increases, with little or no leptin secretion; leptin increases intracellularly by approximately 60% (P < 0.05). After 60 min, leptin is significantly released from cells. At 120 and 240 min, secretagogues enhance leptin secretion into the medium by 35% (P < 0.05) and 40% (P < 0.01), respectively. Cycloheximide prevents the synthesis and the secretagogue-mediated secretion of leptin. Monensin, an inhibitor of protein translocation, has no effect on leptin synthesis, but it blocks the secretagogue-mediated secretion of leptin. These findings suggest that secretagogues enhance leptin release by increasing leptin synthesis, rather than by enhancing the release of a preexisting cytosolic pool of leptin.

Hepatitis C virus infection: prevalence, risk factors, and prevention opportunities among young injection drug users in Chicago, 1997-1999.

The prevalence, risk factors, and prevention opportunities of hepatitis C virus (HCV) infection were studied in a large sample of 698 young adult injection drug users (IDUs) in Chicago, 18-30 years old. Participants were recruited between 1997 and 1999 by using street outreach, targeted advertising, and chain-referral methods. HCV infection prevalence was 27% and was strongly associated with both age and duration of injecting (P<.001). In multivariable analysis, sexual behaviors were unrelated to seropositivity. Independent drug-related risk factors included frequent injection, heavy crack smoking, injecting in a shooting gallery, and syringe-mediated sharing. Urban residents were more likely than suburban residents to be infected. Most research on hepatitis C has shown rapid spread of infection among IDUs, but these findings underscore that opportunities to identify IDUs uninfected with HCV may be greater than assumed and emphasize the need to target younger, newer IDUs.

Leptin responses to glucose infusions in obesity-prone rats.

The secretion of leptin is dually regulated. In fasting animals, plasma leptin concentrations reflect body fat stores, whereas the incremental leptin response to fasting or refeeding most likely reflects insulin-mediated energy flux and metabolism within adipocytes. Impaired secretion of leptin in either pathway could result in obesity. We therefore measured plasma leptin concentrations in fasted animals and plasma leptin concentrations after an intravenous glucose infusion in a rat model of obesity. Young Sprague-Dawley (S-D) and Fischer 344 (F344) rats had similar percent body fat and fasting glucose and fasting leptin concentrations. However, F344 animals had higher insulin concentrations and leptin responses to intravenous glucose than did the S-D animals. The animals were then fed a control or high-fat diet for 6 wk. High-fat fed animals gained more weight and body fat than did the control fed animals. Control and high-fat fed F344 animals gained approximately 40% (P < 0.0001) more weight and >100% (P < 0.01) more body fat than did the S-D animals. Fasting leptin concentrations and leptin concentrations after intravenous glucose infusions and feeding were more than double (P < 0.05) in F344 animals compared with S-D animals. Whether an animal is fed a control or high-fat diet had little effect on the leptin response to intravenous glucose. In conclusion, young, lean F344 animals, before the onset of obesity, demonstrated a greater acute leptin response to intravenous glucose than similarly lean S-D animals. After a 6-wk diet, F344 animals had a greater percent increase in body weight and insulin resistance and exhibited higher fasting leptin concentrations and a greater absolute leptin response to intravenous glucose compared with the S-D animals. The chronic diet (control or high fat) had little impact on the acute leptin response to intravenous glucose. F344 animals exhibit leptin resistance in young, lean animals and after aging and fat accumulation.

Dual regulation of leptin secretion: intracellular energy and calcium dependence of regulated pathway.

Rodent leptin is secreted by adipocytes and acutely regulates appetite and chronically regulates body weight. Mechanisms for leptin secretion in cultured adipocytes were investigated. Acutely, energy-producing substrates stimulated leptin secretion about twofold. Biologically inert carbohydrates failed to stimulate leptin secretion, and depletion of intracellular energy inhibited leptin release. There appears to be a correlation between intracellular ATP concentration and the rate of leptin secretion. Insulin increased leptin secretion by an additional 25%. Acute leptin secretion is calcium dependent. When incubated in the absence of calcium or in the presence of intracellular calcium chelators, glucose plus insulin failed to stimulate leptin secretion. In contrast, basal leptin secretion is secreted spontaneously and is calcium independent. Adipocytes from fatter animals secrete more leptin, even in the absence of calcium, compared with cells from thinner animals. Acute stimulus-secretion coupling mechanisms were then investigated. The potassium channel activator diazoxide and the nonspecific calcium channel blockers nickel and cadmium inhibited acute leptin secretion. These studies demonstrate that intracellular energy production is important for acute leptin secretion and that potassium and calcium flux may play roles in coupling intracellular energy production to leptin secretion.

Total parenteral nutrition increases serum leptin concentration in hospitalized, undernourished patients.

BACKGROUND: The hormone leptin has putative roles in both body weight homeostasis (chronic) and satiety (acute). To determine if this dual regulation is observed in hospitalized, undernourished patients, serum leptin concentration was measured before and during total parenteral nutrition (TPN) infusion. METHODS: Six consecutive patients were considered undernourished, as assessed by an independent multidisciplinary nutrition team, and TPN was prescribed at an initial rate of between 5023.2 and 7333.2 kJ in the first 24 hours. Serum leptin, insulin, and glucose were measured before the infusion and at 3 and 22 hours after initiation of TPN. RESULTS: Baseline serum leptin concentrations correlated well with the patient's body mass index (BMI; r2 = .85, p<.05). Three hours of TPN infusion produced only modest changes in circulating leptin. However, after 22 hours, leptin concentrations increased by 1.8+/-0.5-fold (p<.05), and this increase was independent of any change in body weight. CONCLUSIONS: Basal leptin concentrations correlate well with BMI. TPN induces a rise in leptin concentration independent of body weight. Leptin secretion is dually regulated in hospitalized, undernourished patients.

Development of phantoms for spiral CT.

PURPOSE: This paper reports on the development of a new phantom for spiral CT. The phantom meets the increased demands on phantom z-axis uniformity in order that objects from the CT slice, immediately above and below the CT slice of interest, do not contribute perturbing information to the reconstructed CT slice. MATERIAL AND METHODS: The phantom depends on formulation of tissue-like materials that can be cast and produced in both geometric and anthropomorphic shapes with sufficient z-axis length to enable unperturbed CT slices of test objects of interest. These materials are then used to produce a series of test objects of CT image quality including low contrast samples that do not require volume averaging or mixing of solutions, and that can reflect sub-slice thickness test objects and supra-slice thickness test objects. RESULTS: The overall phantom and its individual test objects provides meaningful tests of spiral CT image quality including slice sensitivity, CT number linearity and tests of high and low contrast resolution. Schematic designs and actual CT scans are shown. CONCLUSION: The new spiral phantom appears to meet the increased demands of spiral CT on phantom design, particularly z-axis length, and requirements for low contrast resolution test objects.

Effect of bile acid composition and manipulation of enterohepatic circulation on leptin gene regulation.

In the rat, the ob gene product, leptin, putatively regulates energy balance via appetite control and energy expenditure. Bile acids in the intestinal lumen are necessary for efficient absorption of dietary lipids and may trigger the release of regulatory peptides. To investigate whether bile acids play a role in leptin gene expression, we altered the bile acid pool and then measured leptin mRNA levels in adipose tissue. Rats fed cholic acid (1% of chow wt/wt) for 2 weeks did not gain weight as rapidly as pair-fed control animals. Despite the lower weight, normalized leptin mRNA levels were 24% greater in cholic acid-fed rats compared with controls. Conversely, cholestyramine, a bile acid sequestrant, in chow (5% wt/wt) resulted in a 26% decline in leptin mRNA. Ligation of the common bile duct or chronic biliary diversion, experimental manipulations that decreased the intestinal concentration of bile salts, decreased leptin gene expression by 30% and 50%, respectively. A fluid and electrolyte (F/E) solution with and without taurocholate (36 micromol/h x 100 g rat[-1]) was then infused for 12 hours into the duodenum in animals with chronic biliary diversion. Taurocholate infusion resulted in a fourfold increase in steady-state adipocyte leptin mRNA levels compared with F/E infusion. Intravenous infusion of taurocholate or incubation of cultured adipocytes with taurocholate had no effect on leptin mRNA levels. We conclude that bile acids upregulate leptin gene expression indirectly, probably via effects on the absorption of dietary lipids or the release of neurohumoral mediators.

Electromyographic assessment of biofeedback training for fecal incontinence and chronic constipation.

INTRODUCTION: Biofeedback training is an effective modality for the treatment of chronic constipation and fecal incontinence. In general, patients express satisfaction and perceive functional improvement following biofeedback therapy; however, quantifying these observations has been difficult. AIM: This study was undertaken to evaluate the physiologic benefits of biofeedback therapy as reflected by noninvasive electromyography parameters. METHODS: Fifty-five patients who underwent computerized electromyography-based biofeedback treatment at our institution between July 1993 and July 1995 were identified. Noninvasive electromyographic testing was performed before, during (weekly), and at completion of training. Mean number of weekly sessions was seven (range, 5-11). Short-term and ten-second contractions (amplitude/microV), sustained contractions (endurance, in seconds), and net strength (microV) of the external anal sphincter before and after biofeedback were compared for differences. RESULTS: There were 30 patients with chronic constipation, mean age, 65.3 (range, 33-86) years, composed of 24 women, and 25 patients with fecal incontinence, mean age 66 (range, 34-85) years, composed of 12 males. Statistically significant improvement in endurance and net strength following biofeedback training was noted in both the constipated and the fecal incontinence groups. Fifty-three of 55 (96.4 percent) patients expressed 50 to 100 percent subjective satisfaction after biofeedback therapy. Forty-six of 55 (83.6 percent) patients demonstrated individually improved endurance. CONCLUSIONS: Sphincter endurance and net strength, as measured by noninvasive electromyography, significantly improve following biofeedback therapy in both constipated and fecal incontinence patients. These data suggest that endurance and net strength may be useful tools in assessing a benefit from biofeedback training in these patients.

Effect of enteral versus parenteral nutrition on leptin gene expression and release into the circulation.

Leptin, a putative satiety hormone in rodents, is acutely regulated by fasting and refeeding. To determine the role of satiety hormones that are secreted by the gastrointestinal tract on leptin regulation, leptin mRNA and serum concentrations were measured after feeding rats similar calories with standard chow or infusion of total parenteral nutrition into the duodenum or intravenously. We have demonstrated that leptin gene expression and hormone secretion into the circulation are stimulated equally in the three experimental paradigms; it is unlikely that satiety factors secreted by the intestinal tract play a significant role in leptin regulation. Furthermore, intravenous infusion of individual components of TPN demonstrated that intravenous glucose infusion was mostly responsible for stimulation of the leptin gene and hormone secretion.

Biofeedback in colorectal practice: a multicenter, statewide, three-year experience.

PURPOSE: Biofeedback treatment is often offered to patients in colorectal centers; however, standards of treatment are still lacking. A dedicated team approach is desirable but difficult to coordinate. We present our three-year experience of electromyographic-based biofeedback treatment offered within a multicenter, statewide organization. METHODS: Between October 1992 and October 1995, 188 patients completed a biofeedback treatment program in one of five coordinated centers within a 200-mile radius. A unified common database was established and continuously updated. A colorectal surgeon served as statewide director, and dedicated teams were established at each location. Each local team included the medical director and a certified biofeedback therapist and had access to a dietitian and a nurse data coordinator. Electromyographic-based biofeedback sessions were given weekly, and a home trainer program was established. RESULTS: A total of 116 patients with chronic constipation had a mean of eight (range, 2-14) weekly sessions. A total of 72 patients with fecal incontinence had a mean of seven (range, 2-11) weekly sessions. A total of 84 percent of the constipated and 85 percent of the incontinent patients had significant improvement with biofeedback treatment. Patient compliance and satisfaction were high. Constipated patients increased the mean number of weekly unassisted bowel movements from 0.8 to 6.5. Incontinent patients decreased the mean number of weekly gross incontinence episodes from 11.8 to 2. CONCLUSIONS: Biofeedback treatment can be extremely successful in both incontinent and constipated patients. A large geographic area can be covered with coordinated centers in which each dedicated team uses a unified treatment protocol, and a common database is established.

In-frame exon 2 deletion in insulin receptor RNA in a family with extreme insulin resistance in association with defective insulin binding: a case report.

The phenotype and allelic expression of the insulin receptor gene is presented in a family with a patient with type A insulin resistance. Compared to controls, insulin receptor binding in transformed lymphocytes was 100%. 33% and 13% in the father, mother and proband, respectively. Reduced insulin receptor binding co-segregated with altered insulin receptor mRNA expression; the mother and daughter expressed eight insulin receptor mRNA species, including a set of four normal sized and a set of four shorter mRNA transcripts. In the proband the levels of the normal sized mRNA transcripts were suppressed relative to the shorter transcripts. Reverse polymerase chain reaction (PCR) revealed that the shorter transcripts contained an in-frame deletion of exon 2. Sequencing of the entire insulin receptor coding region revealed a paternally inherited A to T substitution in nucleotide 3205, converting isoleucine 996 to phenylalanine, which does not co-segregate with reduced binding. Therefore, we hypothesize that two findings are necessary for the presentation of type A insulin resistance in this patient: an in-frame deletion of the insulin receptor exon 2 that codes for amino acids crucial for insulin binding: and an inhibition of expression of the paternal insulin receptor allele.

Sequence and functional characterization of the terminal exon of the human insulin receptor gene.

We present 5.1 kb of the 3' noncoding region sequence of the human insulin receptor gene and identification of four functional polyadenylation domains responsible for 3'-end processing of the 5.4, 6.9, 8.0 and 9.4 kb human insulin receptor mRNA, respectively. The insulin receptor gene contains five putative polyadenylation sites (P1-P5), located 5160, 6502, 7488, 8945 and 8957 base pairs (bp) downstream from the translational initiation site. All putative polyadenylation sites are flanked by upstream AU rich and downstream GU rich regions which regulate mRNA stability and mRNA cleavage, respectively. Also, two RNA stem-loop structures have been identified. To determine its role on gene expression, a reporter gene was constructed containing various lengths of the insulin receptor 3' UTR and transiently transfected into COS 7 cells. A 539 bp fragment (4897-5436 bp downstream from the IR translational initiation site) inhibited CAT expression by 5-6 fold. Further downstream addition of 1169 bp of the insulin receptor 3' untranslated region enhanced gene expression by 2-fold. These studies provide evidence that the insulin receptor 3' untranslated region can modulate gene expression.

The effect of prenatal exposure to the phytoestrogen genistein on sexual differentiation in rats.

Exposure to naturally occurring estrogens during critical periods of development can alter morphologic and physiologic markers of sexual differentiation. The current experiment characterizes the effects of in utero treatment with genistein, an isoflavonoid phytoestrogen, on birth weight, anogenital distance (AGD) at birth. GnRH stimulated luteinizing hormone (LH) secretion, volume of the sexually dimorphic nucleus in the preoptic area of the hypothalamus (SDN-POA), puberty onset, and vaginal cyclicity. Pregnant Charles River CD rats were injected sc daily on gestation day 16-20 with either 25,000 micrograms genistein (G25), 5,000 micrograms genistein (G5), 5 micrograms diethylstillbestrol (DES), 50 micrograms estradiol benzoate (E), or corn oil alone for controls. Birth weights and anogenital distance was taken and exposed progeny were subsequently used in two experiments. In Experiment 1 intra-atrial catheters were placed in adult castrated rats, GnRH was given iv, serial blood samples were drawn and sera were assayed for LH by radioimmunoassay (RIA). Brains obtained by subsequent decapitation were saved for histology. In Experiment 2, females were monitored for timing of vaginal opening as a marker of puberty onset, and vaginal smears were taken to monitor cyclicity. G25-treated females and DES- and E-treated animals of both sexes had decreased weights at birth compared with controls. G5- and E-treated animals of both sexes and DES males had smaller AGD than controls. No significant differences in pituitary responsiveness to GnRH were found among treatment groups. There was a nonsignificant decrease in SDN-POA volume in G5-treated females while DES- and E-treated females had increased SDN-POA volume compared with controls. G5-treated females had delayed puberty onset, and DES-treated females had atypical vaginal cycles in comparison with controls. The results confirm that prenatal exposure to estrogens in the environment can influence sexual differentiation. Our previous experiments have demonstrated that castrate female rats exposed as neonates to genistein have decreased pituitary responsiveness to GnRH challenge and enlarged SDN-POA volume in comparison with controls. Prenatal genistein at these dosages did not significantly alter these markers. However, genistein did mimic other estrogens' effects on AGD and birth weight and had a unique influence on puberty onset. Not only are genistein's effects different from other estrogens, but dosage and timing of exposure during development appear to be important factors in genistein's ability to modify these end points.

Dexamethasone mediated stabilization of insulin receptor mRNA.

To determine the mechanism of glucocorticoid mediated enhancement of insulin receptor (IR) gene expression, we cotransfected a glucocorticoid receptor expression vector and a plasmid containing a reporter gene driven by an MMTV or IR promoter into COS 7 cells. Dexamethasone (Dex) increased MMTV promoter activity by 100% but had no effect on IR promoter activity. In the glucocorticoid responsive breast cancer cell line, MCF-7, Dex increased IR mRNA by 60%, and increased the IR mRNA half-life from approximately 6hrs to > 24 hrs. No glucocorticoid responsive element could be located in the insulin receptor 3' untranslated region. Glucocorticoids stabilize IR mRNA.

Nuclear protein-binding analysis of a GC-rich insulin-receptor promoter regulatory region.

We previously demonstrated that activation of the insulin-receptor promoter occurs between Xho I and HindIII restriction enzyme sites located 877 and 578 bp upstream, respectively, from the translational initiation site. Deletion mutants 5' of this promoter region were constructed with the reporter gene, CAT, and transiently transfected into HepG2 and MCF-7 cells. This study demonstrated that most of the promoter activity could be localized to a 40-bp region between -618 and -578. When attached to a heterologous SV40 early promoter, this 40-bp insulin-receptor regulatory region, in either orientation, stimulated the SV40 early promoter by approximately two- to threefold after transfection into HepG2 cells. EMSA demonstrated that the purified transcription factor, Sp1, binds to this transcription activator. DNA binding of protein obtained from crude HepG2 nuclear extracts demonstrated electrophoretically retarded bands that competed for the consensus Sp1 element; these bands were not observed in a similar analysis with crude MCF-7 nuclear extracts. However, in both HepG2 and MCF-7 cells, a protein was identified that specifically binds to this important insulin-receptor promoter region, but does not bind to the Sp1 consensus element. We conclude that activation of insulin-receptor gene transcription occurs in a 40 bp region 578 bp upstream from the translational initiation site, and that Sp1 and another nuclear factor other than Sp1 may be important in regulating transcription in HepG2 cells.