Fasting Healthy Subjects Research Articles

Modulatory influences on antegrade and retrograde tonic reflexes in the colon and rectum.

Tonic reflexes in the colon and rectum are likely to be important in health and in disorders of gastrointestinal function. The aim of this study was to evaluate the fasting and postprandial "colorectal" and "rectocolic" reflexes in response to 2-min isobaric distensions of the colon and rectum, accounting for enteric sensation, compliance, and distending balloon volume. In 14 healthy fasting subjects, a dual barostat assembly was positioned (descending colon and rectum). A 2-min phasic distension was performed in the colon and rectum in random order while the opposing balloon volume was recorded. Sensation (phasic distension) and compliance (ramp distension) were also determined. The experiment was repeated postprandially. Colonic distension resulted in significant rectal tonic contraction in the fasting (rectal volume change: -35.4 +/- 8.4 ml, P < 0.01) and postprandial (-22.2 +/- 8.4 ml, P < 0.01) states. After adjustment for colonic sensitivity, for compliance, and for distending balloon volume, the rectal volume change remained significant; the extent of the tonic response, however, correlated significantly with increasing pain score (P < 0.01). In contrast, rectal distension did not produce a significant tonic response in the colon (fasting: -6.5 +/- 7.3 ml; postprandial: 2.7 +/- 7.3 ml), either unadjusted or adjusted for rectal sensitivity, compliance, and distending balloon volume. In conclusion, the colorectal reflex, but not the rectocolic reflex, can be readily demonstrated both before and after a meal in response to a 2-min isobaric distension in the colon and rectum, respectively. Although the presence of the colorectal reflex does not depend on colonic sensitivity or the volume of the distending colonic balloon, these factors modulate the reflex, especially in the fasting state.

Ghrelin levels are not regulated by recombinant leptin administration and/or three days of fasting in healthy subjects.

Ghrelin, a stomach-derived orexigenic peptide, and leptin, a fat-derived anorexigenic hormone, act primarily in the hypothalamus to regulate energy homeostasis and have been reported to be regulated in opposite directions by acute and chronic changes in nutritional state. Nutritional, anthropometric, and hormonal predictors of circulating ghrelin have not yet been fully elucidated, and whether ghrelin is regulated by leptin in humans remains unknown. To address these questions, we performed cross-sectional and interventional studies. In 120 healthy men and women, ghrelin was negatively associated with leptin as well as overall and central adiposity, but not with total energy or specific macronutrient intake. The sexual dimorphism in ghrelin levels (higher levels in women than in men) and the negative correlation between ghrelin and insulin are largely mediated by central adiposity. In six lean men, complete fasting for 3 d resulted in a low leptin state without a major change in fat mass and abolished the meal-related secretory pattern of ghrelin without increasing 24-h ghrelin levels. In addition, recombinant human leptin administration in physiological and pharmacological doses did not regulate ghrelin over several hours to a few days. These data do not support a role for regulation of circulating ghrelin by leptin levels independently of changes in adiposity and suggest that the leptin and ghrelin systems for energy homeostasis function independently of each other in healthy humans.

Effect of Ramadan Fasting on Clinical and Biochemical Parameters in Healthy Adults

Effect of Ramadan Fasting on Clinical and Biochemical Parameters in Healthy Adults

Strain during gastric contractions can be measured using Doppler ultrasonography

This study was undertaken to explore if strain of the muscle layers within the gastric wall could be measured by transabdominal strain rate imaging (SRI), a novel Doppler ultrasound (US) method. A total of 9 healthy fasting subjects (8 women, 1 man; ages 22 to 55 years) were studied and both grey-scale and Doppler US data were acquired with a 5- to 8-MHz linear transducer in cineloops of 97 to 256 frames. Rapid stepwise inflation (5 to 60 mL) of an intragastric bag was carried out and bag pressure and SRI were measured simultaneously. SRI enabled detailed studies of layers within the gastric wall in all subjects. Great variations in strain distribution of the muscle layers were found. Radial strain was much higher in the circular than in the longitudinal muscle layer. Strains derived from SRI correlated well with strains obtained with B-mode measurements (r = 0.98, p < 0.05). During balloon distension, we found an inverse correlation between pressure and radial strain (r = −0.87, p < 0.05). Intraobserver correlation of strain estimation was r = 0.98 ( p < 0.05) and intraobserver agreement was 0.2% ± 18.6% (mean difference ± 2SD, % strain). Interobserver correlation was r = 0.84 ( p < 0.05) and interobserver agreement was 6.9% ± 56.8%. SRI enables detailed mapping of radial strain distribution of the gastric wall and correlates well with B-mode measurements and pressure increments. (E-mail: Odd.Gilja@med.uib.no)

Splanchnic extraction and clearance of tissue plasminogen activator (t-PA) after injection of recombinant t-PA (Actilyse) in resting healthy subjects is proportional to the arterial concentration.

The purpose of the study was to evaluate the splanchnic extraction of tissue plasminogen activator (t-PA) in normal healthy fasting subjects after the injection of recombinant t-PA (rt-PA; Actilyse). In nine healthy volunteers (five male, four female), 21-29 years of age, the concentration of t-PA was determined in plasma samples taken simultaneously from a femoral artery and a large liver vein after a bolus injection (5, 10 or 20 mg) of rt-PA. The splanchnic plasma flow rate, the plasma volume, and the splanchnic extraction fraction of t-PA were determined. After the rt-PA injection, the measured arterial concentration of t-PA decreased from 36 750 to 45 pmol/l for t-PA antigen and from 50 700 to 17 pmol/l for active t-PA. The splanchnic extraction fraction decreased from 0.95 to 0.02 for t-PA antigen and from 0.78 to 0.08 (n = 3) for active t-PA. The extraction fraction was proportional to the arterial concentration of t-PA when the arterial concentration of t-PA was above about 300 pmol/l (both t-PA antigen and active t-PA). The median splanchnic plasma flow rate was 911 ml/min (range, 651-1149 ml/min). In the individual subject, the splanchnic plasma flow rate remained constant during the experimental period. The main conclusion of the study is that the splanchnic clearance and extraction fraction of t-PA, following an injection of rt-PA in the resting fasting steady state, depends on the arterial concentration of t-PA. The higher the arterial concentration of t-PA, the higher the extraction fraction of t-PA.

Plasma L-5-oxoproline kinetics and whole blood glutathione synthesis rates in severely burned adult humans.

Compromised glutathione homeostasis is associated with increased morbidity in various disease states. We evaluated the kinetics of L-5-oxoproline, an intermediate in the gamma-glutamyl cycle of glutathione production, in fourteen severely burned adults by use of a primed, constant intravenous infusion of L-5-[1-(13)C]oxoproline. In nine of these patients, whole blood glutathione synthesis and plasma kinetics of glycine and leucine were also measured with [(15)N]glycine and L-[(2)H(3)]leucine tracers. Patients were studied under a "basal" condition that provided a low dose of glucose and total parenteral nutrition. For comparison with control subjects, whole blood glutathione synthesis was estimated in six healthy adults. Burn patients in a basal condition showed significantly higher rates of plasma oxoproline clearance and urinary D- and L-oxoproline excretion compared with fasting healthy control subjects. Whole blood glutathione concentration and absolute synthesis rate in the basal state were lower than for control subjects. Total parenteral feeding without cysteine but with generous methionine did not affect oxoproline kinetics or whole blood glutathione synthesis. The estimated rate of glycine de novo synthesis was also lower in burn patients, suggesting a possible change in glycine availability for glutathione synthesis. The roles of precursor amino acid availability, as well as alterations in metabolic capacity, in modulating whole blood glutathione production in burns now require investigation.

Glycemic response to a rapidly digested starch is not affected by the addition of an indigestible dextrin in humans

To evaluate the effect of supplemental indigestible dextrin on the glycemic response to a rapidly digested starch, 30 healthy nondiabetic adult subjects were studied in a double-blind crossover design. After an overnight fast, subjects consumed a product containing either 67.5 g of corn syrup solids or the same plus 16 g of indigestible dextrin. Finger-prick capillary blood was obtained at baseline, 15, 30, 45, 60, 90, and 120 min postprandial for glucose measurement. The postprandial incremental change from baseline did not differ (P > 0.10) between treatments across all time points. Mean peak incremental change from baseline and net incremental area under the curve did not differ (P > 0.10) between treatments. Minimal effects on gastrointestinal symptoms (intensity and frequency of nausea, cramping, distention, and flatulence) were noted for both products, with no clinically significant difference between products. In conclusion, an acute challenge of 16 g supplemental indigestible dextrin did not affect the postprandial glycemic response to a rapidly digested starch and was well tolerated by fasting healthy adult subjects.

Interdigestive gallbladder emptying, antroduodenal motility, and motilin release patterns are altered in cholesterol gallstone patients.

The role of interdigestive gallbladder emptying in gallstone formation is unknown. In fasting healthy subjects, gallbladder emptying is associated with antral phase III of the migrating motor complex (MMC) and high plasma motilin. Therefore, gallbladder volumes and motilin levels were measured during 13 MMC cycles in 10 cholesterol gallstone patients and compared with 20 MMC cycles in 10 healthy subjects. MMC cycle length was longer in gallstone patients than in healthy subjects (158.2 +/- 17.0 vs 105.5 +/- 10.4 min, respectively; P < 0.05), due to longer phase I (39.8 +/- 5.7 vs 17.2 +/- 3.7 min, respectively; P < 0.05). In contrast to healthy subjects, gallstone patients had no significant fluctuations of gallbladder volume during the MMC cycle, and motilin concentrations were not different in MMC cycles with phase III originating in antrum or duodenum. During MMC cycles with phase III originating in the duodenum, motilin levels were twice as high in gallstone patients as in healthy subjects (P < 0.002). In conclusion, cholesterol gallstone patients have an abnormal MMC and motilin release pattern. Their interdigestive gallbladder emptying is reduced and dissociated from the MMC. These disturbances may contribute to gallstone formation.

First direct assay for intact human proinsulin

We describe a sensitive two-site sandwich enzyme-linked immunosorbent assay for the measurement of intact human proinsulin in 100 microL of serum or plasma. The assay is based on the use of two monoclonal antibodies specific for epitopes at the C-peptide/insulin A chain junction and at the insulin B chain/C-peptide junction, respectively. Cross-reactivities with insulin, C-peptide, and the four proinsulin conversion intermediates were negligible. The detection limit in buffer was 0.2 pmol/L (3 standard deviations from zero). The working range was 0.2-100 pmol/L. The mean intra- and interassay coefficients of variation were 2.4% and 8.9%, respectively. The mean recovery of added proinsulin was 103%. Dilution curves of 40 serum samples are parallel to the proinsulin calibration curve. Proinsulin concentrations in 20 fasting healthy subjects were all above the limit of detection: median (range), 2.7 pmol/L (1.1-6.9 pmol/L). Six fasting non-insulin-dependent diabetes mellitus and five insulinoma patients had proinsulin concentrations significantly higher than healthy subjects: median (range), 7.7 pmol/L (3.2-18 pmol/L) and 153 pmol/L (98-320 pmol/L), respectively.

Small bowel transit of a bran meal residue in humans: sieving of solids from liquids and response to feeding

Background—Ileal motor patterns are adapted to the propulsion of viscous meal residue, such as bran, which accumulates in the distal ileum postprandially.Aims—To examine the effects of a second liquid/solid meal...

Immunoluminometric assay (ILMA) for intact human proinsulin and its conversion intermediates

We describe an immunoluminometric assay (ILMA) for determination of intact proinsulin and its conversion intermediates, 32,33-split and 65,66-split proinsulin, in human serum. After incubation of the serum samples with the IgG fraction of a guinea pig antiserum against human insulin coated to the surface of polystyrene beads, a sandwich complex was formed using a monoclonal antibody against human C-peptide labelled with acridinium ester as second antibody, yielding a detection limit of 0.11 pmol/l. Mean proinsulin concentration in the serum of 38 healthy fasting subjects was 7.3 pmol/l (S.D. ± 5 pmol/l, median 5 pmol/l, 95th percentile 15 pmol/l); maximum serum proinsulin after oral glucose stimulation never exceeded 40 pmol/l. Eighteen of 20 patients with confirmed insulinoma had proinsulin concentrations over 50 pmol/l (mean 261 pmol/l, S.D. ± 248 pmol/l, median 170 pmol/l, 95th percentile 663 pmol/l); serum proinsulin in two patients with completely enucleated B-cell adenoma declined to normal values after surgery.

Immunoradiometric assay of human intact proinsulin applied to patients with type 2 diabetes, impaired glucose tolerance, and hyperandrogenism

We describe an immunoradiometric assay for human intact proinsulin in serum. In this method, one monoclonal antibody, coated onto polyacrylamide beads, cross-reacts with proinsulins and insulin. A sandwich is formed with intact proinsulin, split (65-66) proinsulin, and des (64-65) proinsulin binding with an 125I-labeled monoclonal antibody specific for an epitope at the intact B-C junction of proinsulin. Because split (65-66) and des (64-65) proinsulin concentrations are very low in serum, this assay essentially measures intact proinsulin. When we used 1-mL serum samples, the mean detection limit was 0.4 pmol/L. Mean proinsulin concentrations (pmol/L) were 3.4 (range 1-9.1) in healthy fasting subjects, 28.5 (9.7-101) in patients with type 2 diabetes (treated with metformin and sulfonylureas), 5.0 (1.6-9.3) in women with hyperandrogenism and normal insulinemia, 10.3 (2.6-36) in women with hyperandrogenism and hyperinsulinemia, and 8.5 (4.8-21.3) in patients with impaired glucose tolerance.

Comparativein vitro andin vivo bioavailability of naproxen from tablet and caplet formulations

A 500 mg dose of naproxen in a caplet formulation (product A) or a tablet (Naprosyn 500, product B) was administered to 14 fasting healthy subjects on two separate occasions, separated by a 1-2 week washout period in an open, randomized crossover. Blood samples were drawn periodically and plasma naproxen concentrations measured by HPLC. The median time Tmax to reach peak concentration for product A was shorter than that for product B (1.025 h versus 1.5 h) but A and B were similar with respect to median peak plasma concentration Cmax (77.9 mg l-1 versus 71.4 mg l-1), and average area AUC0-infinity under the plasma concentration-time curve (1210.2 mg l-1 h versus 1211.0 mg l-1 h). In vitro parameters (A versus B) of mean dissolution time MDT (5.03 min versus 15.0 min), and time for 70% dissolution T70 (6.67 min versus 20.2 min), differed significantly.

Highly sensitive enzyme immunoassay of proinsulin immunoreactivity with use of two monoclonal antibodies

A highly sensitive two-site sandwich ELISA measuring total proinsulin immunoreactive material in serum or plasma was developed. The assay was based on two monoclonal antibodies, an anti-C-peptide antibody bound to a microtest plate and a biotin-labeled anti-insulin antibody. The detection limit (3 SD above zero value) in buffer was 0.05 pmol/L, corresponding to 0.25 pmol/L in human serum (diluted 1:5). The linear calibrator range was 0.05-20 pmol/L. Interassay CVs were 4.7% at a median (range) of 2.3 pmol/L (1.4-2.8 pmol/L, n = 8), 6.7% at 5.1 pmol/L (3.3-8.0 pmol/L, n = 8), and 8.7% at 10.0 pmol/L (8-12 pmol/L, n = 10). Mean analytical recovery of added human proinsulin (hPI) (2, 5, and 10 pmol/L) to serum was 84% (range 68-128%, n = 9). Human insulin and human C-peptide did not cross-react at 5000 and 10,000 pmol/L, respectively. The four major proinsulin conversion intermediates reacted 65-99%: split(32-33)hPI 74%, des-(31,32)hPI 65%, split(65-66)hPI 78%, and des(64,65)hPI 99%. All serum values from 38 fasting healthy subjects were above the detection limit: median (range) 4.0 (2.1-12.6) pmol/L.

Cholinergic regulation of phase II interdigestive pancreatic secretion in humans.

Small fluctuations in cholinergic input may be involved in the regulation of human interdigestive pancreatic secretion. To determine the effects of small changes in cholinergic tone on phase II interdigestive trypsin secretion, we gave cholinergic agonists or antagonists to 17 healthy fasting subjects who underwent gastrointestinal intubation. Duodenal trypsin outputs, gastroduodenal motility, and plasma levels of pancreatic polypeptide (PP) as a marker of cholinergic tone were measured during intravenous infusion of bethanechol (0, 5, or 40 micrograms.kg-1.h-1) or atropine (0, 4, or 16 micrograms.kg-1.h-1) given during phase II alone or in combination based on a 3 x 3 factorial design. Data were evaluated by a response surface analysis of the average log values for the test period (using the average of log values of the control period as a covariate). Bethanechol increased trypsin output (p < 0.05) and plasma concentrations of PP (p < 0.05) within the ranges of spontaneous fluctuations of trypsin output and PP during phase II, but did not disrupt the periodicity of pancreatic secretion or the characteristic cyclical pattern of interdigestive motility and induction of phase III activity. Atropine markedly decreased trypsin output (p < 0.05) and plasma concentrations of PP (p < 0.05) and abolished the cycling of interdigestive pancreatic secretion and motor activity. These data suggest the hypothesis that cholinergic pathways participate in the control of interdigestive pancreatic secretion during phase II, while enzyme secretion during phase III may be regulated by other mechanisms.

Application of new fluorescent thiol reagent to diagnosis of homocystinuria

A new fluorescent thiol reagent, dansylaminophenylmercuric acetate (DAPMA), was applied to the diagnosis of homocystinuria, a disorder which can be associated with vascular disease at an early age. DAPMA was added to urine containing metabisulphite and the resulting fluorescent derivatives were extracted on a cyclohexyl silica column and separated by thin-layer chromatography. 102 coded samples were tested. The derivative of homocysteine was easily identified in samples from 4 children with homocystinuria but was absent from all samples from normal subjects and patients with unrelated disorders. Other thiols (cysteine, acetylcysteine, mercaptolactate, thiosulphate, and thiocyanate) were also identified in urine from healthy fasting subjects.

An investigation of the role of lecithin: cholesterol acyltransferase and triglyceride-rich lipoproteins in the metabolism of pre-beta high density lipoproteins

Small high density lipoproteins (HDL) with pre-beta electrophoretic mobility (pre-beta HDL) have recently been shown to be the primary acceptor of cholesterol from cultured cells. We studied the metabolism of these particles by incubating serum at 37°C in the presence and absence of active lecithin: cholesterol acyltransferase (LCAT). We found that the serum pre-beta HDL concentration decreased in the presence of LCAT, but when LCAT was inhibited the concentration remained constant, or increased, depending on the method of inhibition. This suggests that pre-beta HDL are a substrate for LCAT. We also found a significant negative correlation between levels of LCAT activity and pre-beta HDL in 28 fasting healthy subjects, this provides evidence that the activity of LCAT regulates, at least in part the concentration of these particles in vivo. During the early phase of incubation there was a more rapid decrease in pre-beta HDL concentration which was greater in the post-prandial than fasting state. When we infused a triglyceride emulsion into 6 subjects or added this to serum in vitro we observed an immediate fall in pre-beta HDL concentration. These findings suggest that pre-beta HDL interact with triglyceride rich particles. We investigated the origin of pre-beta HDL from blood lipoproteins during their lipolysis, in vivo and in vitro and found that they were produced from both triglyceride-rich and high-density lipoproteins. Formation from triglyceride-rich lipoproteins was evident by the rise in pre-beta HDL concentration during heparin-induced lipolysis when fasting and post-prandially. The rise was greater post-prandially and particularly marked in 4 hypertriglyceridaemic patients following a fat load. Generation from alpha-HDL was evident when we prolonged the action of the heparin-released lipases by incubation of post-heparin sera at 37°C. Continued formation of pre-beta HDL occurred at an equal rate in the fasting and post-prandial samples suggesting release by lipolysis of alpha-HDL. This was supported by the action of lipases on serum and isolated HDL in vitro, where triglyceride lipase rather than phospholipase activity appeared more effective at releasing pre-beta HDL. These findings suggest binding and release of pre-beta HDL by triglyceride-rich lipoproteins depending on the prandial state and production from alpha-HDL through the action of lipases.

Plasma Motilin Variation During the Interdigestive and Digestive States in Man

To evaluate the role of motilin in human physiology, we measured plasma motilin during the inter digestive and digestive states while recording antroduodenal contractile activity. In 24 healthy fasting subjects, 51 migrating periods of phase III activity were recognized, 42 of them started from the antral region and nine from the duodenum. A definite association was noted between circulating motilin and the gastric migrating motor complex. Significant peak elevations in plasma motilin were associated with phase Ills initiated from the antrum, but not with those originating from the duodenum. Exogenous synthetic motilin, when administered in supraphysiologic amounts, induced premature periods of front activity in fasting subjects. A test meal administered 30 minutes after a front of antral activity induced a significant release of motilin. Elevated plasma motilin levels were detected postprandially for a period of 30 minutes. Postprandial motilin increases were comparable in amplitude to the cyclic peak increases observed during the fasting period. Our study brings support for the argument that the contractile activity of the fasting stomach is regulated by circulating motilin in man, as it is in animals. The documented postprandial release of motilin is, however, unique to man and suggests that motilin could also be active during the digestive period in this species.

The absorption of bismuth and salicylate from oral doses of Pepto‐Bismol (bismuth salicylate)

Plasma bismuth and plasma salicylate concentrations were measured before and after three 30-ml oral doses of bismuth salicylate (Pepto-Bismol liquid) in 10 fasting healthy subjects. From 0 to 120 min following the first dose of bismuth salicylate, the plasma bismuth concentration was less than 1 ng/ml. The peak median plasma bismuth concentration was at +240 min (1.7 ng/ml; range 0.8-5.3 ng/ml). Salicylate appeared in the plasma of all subjects at +30 min, and it reached a peak at +120 min (median 61 mg/L; range 46-104 mg/L). The study demonstrates that, despite rapid and substantial absorption of salicylate, there is negligible absorption of bismuth into the bloodstream from standard oral doses of bismuth salicylate.

Action of ornithine alpha-ketoglutarate, ornithine hydrochloride, and calcium alpha-ketoglutarate on plasma amino acid and hormonal patterns in healthy subjects.

Ornithine alpha-ketoglutarate (OKG) has been useful as an adjuvant of enteral and parenteral nutrition. However, its metabolism and mechanism of action remain unclear although it is known that alpha-ketoglutarate (alpha KG) and ornithine (ORN) follow, in part, common metabolic pathways. Six fasting healthy male subjects underwent three separate oral load tests: (i) they received 10 g of OKG (i.e., 3.6 g of alpha KG and 6.4 g of ORN); (ii) 6.4 g of ORN as ornithine hydrochloride, and (iii) 3.6 g of alpha KG as calcium alpha-ketoglutarate. Blood was drawn 15 times over a five-hour period for measurements of plasma amino acids, alpha KG, insulin, and glucagon. After OKG and ORN administration, plasma ORN peaked at 60-75 min (494 +/- 91 and 541 +/- 85 mumol/L). The increase in plasma alpha KG was very small. OKG, alpha KG, and ORN all increased glutamate concentrations at 60 min (mean: +43%, +68%, +68%, respectively, p less than 0.05 compared to basal values). However, only OKG increased proline and arginine levels at 60 min (mean: +35%, p less than 0.01 and mean: +41%, p less than 0.05). Furthermore, glutamate, proline, and arginine concentrations correlated linearly with ornithine levels at 60 min. Finally, OKG increased insulinemia and glucagonemia (mean: +24% at 15 min, p less than 0.05 and +30% at 60 min, p less than 0.01, respectively). These data provide evidence that the combination of ORN and alpha KG modifies amino acid metabolism in a way which is not observed when they are administered separately. In addition, the OKG-mediated increase in insulin levels probably does not appear to result from a direct action of ORN on pancreatic secretion.