Effects of central oxytocin administration on intraoral intake of glucose in deprived and nondeprived rats

We evaluated the effects of lateral intracerebroventricular administration of oxytocin (OT) and/or a selective oxytocin-receptor antagonist (OTX), 1-deamino-2-D-Tyr-(OEt)-4-Thr-8-Orn-OT, on ingestion of intraorally delivered 12.5% glucose in rats that were either nondeprived or deprived of food for 20 h. In deprived rats, OT delivered 30 min before an initial intake test yielded a dose-related reduction of intraoral glucose intake. The highest dose tested, 20 nmol, reduced intraoral glucose intake by 45%. The effect was short-lived, however. Intraoral intake for a second test, initiated 60 min after the termination of the first, increased as a function of OT dose so that total session intake was unaffected by OT treatment. The suppression of intraoral intake by 20 nmol OT was reversed by pretreatment (45 min before testing) with OTX. In nondeprived rats, by contrast, OT yielded no effect on first-test, second-test, or total session intakes. Significant increases in first-test and total session intakes were obtained when OTX (20 nmol) was administered alone both in deprived (32% increase in first-test intake) and nondeprived (31% increase) rats. In general, the results obtained are consistent with the suggestion that OT contributes to the control of meal size and, in particular, to the process of satiation, which is the aspect of ingestive control highlighted by the specialized intake test used in the present study.     

Effects of concentration presentation order and intraoral delivery on sucrose intake.

In this article, intraoral intake of an ascending concentration series of sucrose was found to plateau between concentrations of 0.3 M and 2.0 M, and thus failed to show the typical inverted U-shaped intake function found in standard intake tests. Two experiments were conducted to explain this result. In Exp 1, intraoral and standard 30-min, 1-bottle intake of ascending sucrose concentrations (0.03, 0.1, 0.3 1.0, 1.3, and 2.0 M) were compared. Sucrose intake was similar for both delivery methods. In a second experiment we examined the effect of the order of sucrose concentration presentation on the 1-bottle 30-min intake of nondeprived intact rats. An ascending concentration order of the solutions produced a significantly greater intake of concentrated sucrose solutions than did a random order. This result strongly suggests that the standard decline in sucrose intake at higher concentrations is determined not only by postoral factors but also by experiential factors (i.e., order of presentation). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of food recognition in young chicks: III. Discrimination.

Previous studies show that the pecking rate of naive 3-day-old chicks increases after ingestion of food and decreases after ingestion of sand, but these changes have not been specific to the stimulus that was ingested. In the present experiments with a total of 450 Burmese Red Junglefowl chicks, Exps I and II showed that neither 1 nor 4 10-min simultaneous-choice tests were sufficient for discrimination to be shown between food and sand. Exp III showed that many hours of experience with food or sand were sufficient for discrimination if Ss were tested for 10 min with only 1 stimulus at a time. Similar results were found in Exp IV in which Ss had only 10 min of experience with food or sand. Pecking rates to food and sand were the same during the 1st 2 min of the test and only later diverged. These results imply that the discrimination is based on feedback that develops 2-3 min after ingestion but develops only if chicks have had previous experience with food or sand. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chylomicron beta-carotene and retinyl palmitate responses are dramatically diminished when men ingest beta-carotene with medium-chain rather than long-chain triglycerides

The effect of the ingestion of beta-carotene with medium-chain triglycerides (MCT) or long-chain triglycerides (LCT) on the bioavailability and the provitamin A activity of beta-carotene was investigated in humans. Sixteen healthy young men ingested, on two different days, a test meal containing 120 mg beta-carotene incorporated into 40 g LCT (LCT meal) or 40 g MCT (MCT meal). This meal was followed 6 h later by a beta-carotene-free meal containing 40 g LCT. Chylomicron beta-carotene, retinyl palmitate and triglycerides were measured every hour for 12.5 h after the first meal. No significant increase in chylomicron triglycerides was detected for the 6 h after the MCT meal intake, whereas a significant increase in chylomicron triglycerides was observed after the LCT meal intake. The chylomicron beta-carotene and retinyl palmitate responses to the MCT meal (0-6 h area under the curves, AUC) were significantly (P < 0.05) lower [AUC = 68.1 +/- 26.8 and 43. 4 +/- 10.4 nmol/(L.h), for beta-carotene and retinyl palmitate, respectively] than those obtained after the LCT meal [301.4 +/- 64.0 and 166.0 +/- 29.0 nmol/(L.h), respectively]. The chylomicron beta-carotene and retinyl palmitate responses obtained after the beta-carotene-free meal (6-12.5 h AUC) were also significantly lower when the first meal provided MCT rather than LCT. The chylomicron (retinyl palmitate/beta-carotene) ratios were constant during the postprandial periods, whatever the meal ingested. We conclude that the chylomicron beta-carotene response is markedly diminished when beta-carotene is absorbed with MCT instead of LCT. This phenomenon is apparently due to the lack of secretion of chylomicrons in response to MCT; however, a lower intestinal absorption of beta-carotene or a higher transport of beta-carotene via the portal way in the presence of MCT cannot be ruled out. Finally, the data obtained show that MCT do not affect the rate of intestinal conversion of beta-carotene into vitamin A.     

Studies in early infant learning: Classical conditioning of the neonatal heart rate.

Three experiments demonstrated that human newborn heart rate level can be reliably modified through classical conditioning procedures. The theory of sensitization served as a frame of reference for Exps I and II, and drive reduction served for Exp III. In Exp I the delay, delay-trace, and control groups, with 10 2-day-old newborns in each, received 5 preconditioning trials of the CS alone, 16 conditioning trials with CS–UCS pairings differing for each group, and 5 extinction trials. Exp II was a replication of the 1st study and involved only the delay and delay-trace groups with 10 infants each. In both studies the delay group curves showed significant monophasic acceleratory responses during extinction. Results support the sensitization hypothesis (i.e., the CR occurring in the interstimulus interval was fashioned out of the response to the CS). In Exp III, the measure of conditioning was the response to the probe technique. 10 experimental Ss received preconditioning trials of nitrogen puff (UCS?) administered to the abdomen, followed by 10 CS–UCS? (500-Hz tone acetic acid) pairings with an interstimulus interval of 3 sec. 10 controls received the same design with a CS–UCS? interval of 40 sec. Analyses of the probe stimulus trials showed significant changes for the control group and none for the experimental group. The CS–UCS? pairings in the experimental group are interpreted as producing increased drive and adaptive damping of the heart rate response. Findings show that early learning may occur under a variety of conditions and that the results can be incorporated by different theories. (79 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dietary triglycerides, up to 40 g/meal, do not affect preformed vitamin A bioavailability in humans

OBJECTIVE: Assessing the effect of the dose of dietary triglycerides on preformed vitamin A (retinyl esters) bioavailability in humans. DESIGN: Four test meals containing 15,000 RE retinyl-palmitate and either 0, 15, 30 or 40 g added triglycerides were ingested by eight healthy volunteers, at different days and in a randomized order. SETTING: The study was done in the Hospital Sainte Marguerite, Marseille, France. SUBJECTS: Eight healthy male volunteers were recruited by advertisement. INTERVENTION: Blood samples were collected every hour for seven hours after the test meals intake. Serum and chylomicron (Svedberg flotation unit > 1000) were prepared by centrifugation and retinyl esters were measured by HPLC. RESULTS: The serum retinyl ester response was not significantly lower after the intake of the meal without added triglycerides (7944 +/- 3262 nmol/L h) than after the intake of the fat meals (10012 +/- 2182, 7869 +/- 3157 and 10777 +/- 2067 nmol/L h for the 15, 30 and 40 g-fat meal, respectively), indicating that the serum retinyl ester response was not related to the amount of meal triglycerides. Chylomicron retinyl linoleate response stepwise increased when the amount of meal triglycerides increased while retinyl palmitate and retinyl stearate responses reached a maximum since 15 g triglycerides. Postprandial serum retinol concentration did not change whatever the meal ingested. CONCLUSIONS: (i) a significant amount of preformed vitamin A is apparently absorbed when ingested with trace amount of meal triglycerides only; (ii) meal triglycerides, up to 40 g/meal, do not increase preformed vitamin A bioavailability; (iii) the retinyl ester pattern recovered in the chylomicrons, and probably the esterification process of retinol, is affected by the amount of meal triglycerides; (iv) postprandial retinol homeostasis is not affected by dietary triglycerides.     

Plasma concentrations of prolactin, glucose, insulin, urea nitrogen, and total amino acids in stallions after ingestion of feed or gastric administration of feed components

Concentrations of prolactin, glucose, insulin, urea N, and total amino acids in plasma of stallions after ingestion of pelleted feed were compared to those after direct gastric administration of water, NaCl, egg albumin, or corn starch (Exp. 1) or water, egg albumin, hydrolyzed casein (Amicase), or a mixture of indispensable amino acids (Exp. 2). Stallions were fed once daily (75% pellet and 25% hay) at 1500 for 30 d. On d 22, 24, 26, 28, and 30, blood samples were collected every 30 min from 1 h before through 4 h after treatment, which occurred at 1100. In Exp. 1, there was a positive secretory response for prolactin (P = .013) only after the meal. Positive glucose and insulin responses were observed after the meal (P < .055) and after gastric administration of corn starch (P < .001). Total amino acids increased (P = .008) only after the meal. In Exp. 2, a positive prolactin response (P < .001) occurred after the meal and a negative response (P = .023) after administration of water; administration of Amicase increased (P = .061) prolactin concentrations after a 2.5-h delay. Positive responses were observed for glucose, insulin, and total amino acids after the meal (P < .001) and after administration of Amicase or the amino acid mixture (P < .026). Positive urea N responses were observed after administration of Amicase and the amino acid mixture (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Abdominal vagotomy disrupts food-related drinking in the rat.

In 2 experiments with a total of 41 Sprague-Dawley albino rats, Ss with complete subdiaphragmatic bilateral transection of the abdominal vagus (Vgx-C) showed disordered food-related drinking when drinking water in temporal association with a meal of dry food after 5-hr food deprivation and when drinking water in association with a liquid meal after 24-hr food deprivation. The Vgx-C Ss drank after significantly longer latencies and drank significantly less water in 1 hr than did sham-vagotomized (Sham) Ss after eating the same size meal (solid or liquid). Ss with incomplete vagal transection (Vgx-I) ate and drank like Shams. Water intake of Sham and Vgx-I Ss correlated positively with the meal size of solid food, but the water intake of Vgx-C Ss did not. The failure of Vgx-C Ss to drink water normally when food was ingested was not due to failure of a food stimulus to reach the intestine, because Vgx-C and Sham Ss emptied equivalent volumes of liquid food from the stomach into the intestine within 10 min of food entering the stomach. Results indicate that the abdominal vagus is an important neurological substrate for food-related drinking in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

State-space models of insulin and glucose responses to diets of varying nutrient content in men and women

Discrete-time state-space models were developed to describe contemporaneous responses of plasma insulin and glucose of normal human subjects. Male and female subjects ingested three consecutive identical meals from isocaloric diets classified as high-carbohydrate, high-fat, high-protein, or standard. Distinctly different glucose and insulin responses were measured in men and women. A seven-state system of linear equations, three in insulin and four in glucose, was identified and estimated to describe responses in men. A six-state system, three in insulin and three in glucose, describes responses in women. Model simulations at 15-min intervals closely match measured concentrations over a 12-h period. Effects of diet content and meal timing on insulin and glucose concentrations were quantified. Dynamic insulin and glucose responses to isocaloric meals of pure carbohydrate, fat, and protein diets were projected on the basis of models developed from mixed diets. The symmetry of the projections indicates that positive excursions in glucose concentrations associated with carbohydrate intake may be matched with negative excursions associated with fat and protein intake to help manage postmeal glucose excursions.     

Intraventricular insulin enhances the meal-suppressive efficacy of intraventricular cholecystokinin octapeptide in the baboon.

Chronic intraventricular (IVT) insulin infusion suppresses food intake and body weight in the baboon. It has been hypothesized that one mechanism of this action may be enhancement of the effectiveness of satiety factors that regulate meal size. This hypothesis was supported by prior demonstration of a shift in the meal-suppressive effectiveness of cholecystokinin octapeptide (CCK-8) which was given intravenously. The authors tested the effectiveness of a near threshold dose of CCK-8 (25 ng/kg) given via the lateral ventricles (IVT) prior to a 30-min meal, while baboons were chronically infused with cerebrospinal fluid or insulin (100 μU/day) via the lateral ventricles. IVT CCK-8 infusion resulted in meal size changes of –44?±?7% and –75?±?9% in the absence and presence of insulin, respectively; this was observed in each of the three animals studied. These results provide further support for the hypothesis that IVT insulin can interact with other, meal-regulatory, peptides. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parabrachial gustatory lesions impair taste aversion learning in rats.

Lesions in the gustatory zone of the parabrachial nuclei (PBN) severely impair acquisition of a conditioned taste aversion (CTA) in rats. To test whether this deficit has a memorial basis, 15 intact rats and 10 rats with PBN lesions (PBNX) received 7 intraoral taste stimulus infusions (30 sec, 0.5 ml) distributed over a 30.5-min period after either LiCl or NaCl injection. This task measures the rapid formation of a CTA and has minimum demands on memory. LiCl-injected intact rats progressively changed their oromotor response profiles from one of ingestion to one of aversion. NaCl-injected intact rats did not change their ingestive pattern of responding. In contrast, there was no difference between LiCl- and NaCl-injected PBNX rats. These same PBNX rats failed to avoid licking the taste stimulus when tested in a different paradigm. A simple impairment in a memorial process is not likely the basis for the CTA deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Caloric regulation of food intake in man.

Investigated caloric regulation in normal 18-36 yr old human Ss on a liquid diet. In Exp I, 8 Ss failed to compensate for changes in the caloric density of a preload (.25-1.8 kcal/ml) by adjusting meal size within 1 meal or from 1 meal to the next. In Exp II, 15 Ss were required to ingest nothing but the liquid diet for 10-21 days. They were given adlib access to a standard liquid diet (1.0 kcal/ml) for 4-9 days followed by 4-14 days on a diluted diet (.5 kcal/ml). 9 Ss failed to regulate their caloric intake in the time allowed. 6 Ss failed to regulate their caloric intake in the time allowed. 6 Ss compensated dramatically for the caloric dilution by increasing both meal size and meal frequency. Regulation was slow to occur (2-5 days) and usually was not perfect (mean level of 87%). Results are discussed in the light of work with animals and man on the mechanisms controlling regulation of food intake. (30 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The autonomic innervation of the human male and female bladder neck and proximal urethra

This study was undertaken to determine whether the increase in plasma glucagon concentration that occurs in response to prolonged exercise is modified by endurance exercise training. Eight subjects participated in an exercise program, consisting of running and bicycling, 4 days/wk for 10 wk. The training program resulted in an average increase in VO2 max of 18%. The average increase in plasma glucagon during a 60-min long bicycle exercise test that required 60% of the subjects' VO2 max was 107+/-28 pg/ml, from 116+/-14 pg/ml at rest to 223+/-37 pg/ml after 60 min of exercise, prior to training. After training the same absolute work rate resulted in an increase in plasma glucagon of only 20+/-6 pg/ml, from 125+/-20 to 145+/-16 pg/ml (P less than 0.02). A similar blunting of the glucagon response to exercise was seen during work of the same relative intensity after training. Plasma insulin concentration decreased from 18.1+/-2.5 to 7.6+/-1.6 muunits/ml during the 60 min of exercise before training. A similar decrease in insulin concentration was seen at the same relative work rate after training. However, the decrease in plasma insulin at the same absolute work rate, from 18.5+/-3.0 to 12.5+/-1.8 muunits/ml, was significantly smaller after training (P less than 0.05).     

Dissociation of licking and volume intake controls in rats ingesting glucose and maltodextrin.

The volume of fluid that rats acquire with each lick was systematically varied across short-term tests with 12.5% glucose (Experiment 1) or 12.5% maltodextrin (Experiment 2). For glucose, rats increased the number of licks emitted as lick volume was reduced such that meal size remained remarkably stable across all (8, 4, and 2 μl) but the smallest (1 μl) lick volume conditions tested. Rats similarly compensated for lick volume reduction (8 to 4 μl) with maltodextrin by approximately doubling the number of licks emitted. Meal duration and a number of lick-microstructural parameters (initial ingestion rate, mean burst duration, terminal lick and ingestion rates and burst duration) were not correlated with the intake outcome insofar as they varied significantly across conditions over which intake remained stable. Thus, in response to lick volume manipulation, rats demonstrated an impressive degree of behavioral flexibility in what may be regarded as a defense of meal size. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Oxidation of exogenous [13C]galactose and [13C]glucose during exercise

The present study examined the oxidation of exogenous galactose or glucose during prolonged submaximal cycling exercise. Eight highly trained volunteers exercised on two occasions on a cycle ergometer at 65% of maximal workload for 120 min, followed by a 60-min rest period and a second exercise bout of 30 min at 60% maximal workload. At random, subjects ingested a 8% galactose solution to which an [1-13C]galactose tracer was added or a 8% glucose solution to which an [U-13C]glucose tracer was added. Drinks were provided at the end of the warm-up period (8 ml/kg) and every 15 min (2 ml/kg) during the first 120 min of the test. Blood and breath samples were collected every 30 and 15 min, respectively, during the test. The exogenous carbohydrate (CHO) oxidation was calculated from the 13CO2/12CO2 ratio and CO2 production of the expired air. Peak exogenous CHO oxidation during exercise for galactose and glucose was 0.41 +/- 0.03 and 0.85 +/- 0.04 g/min, respectively. Total CHO and fat oxidation were not significantly different between the treatments. Forty-six percent of the ingested glucose was oxidized, whereas only 21% of the ingested galactose was oxidized. As a consequence, more endogenous CHO was utilized with galactose than with glucose (124.4 +/- 6.7 and 100.1 +/- 3.6 g, respectively). These results indicate that the oxidation rate of orally ingested galactose is maximally approximately 50% of the oxidation rate of a comparable amount of orally ingested glucose during 120 min of exercise.     

Chlordiazepoxide attenuates activity-induced anorexia and weight loss in rats.

Studied the effects of chlordiazepoxide (CDP) on body weight and food intake in male rats. In Exp 1, the effect of repeated injections of 2.5, 5.0, or 10.0 mg/kg of CDP on food intake and body weight was studied in rats on an activity anorexia (AA) regimen. For several days before CDP testing began, rats lived in activity wheels and had one 60-min meal/day. During CDP testing, this regimen continued except that each rat was injected with an appropriate dose of CDP or saline 30 min before each meal. CDP enhanced food intake; 5.0 mg/kg seemed most effective. However, the CDP-induced increase in eating did not noticeably stem weight loss. In Exp 2, after several days of AA training, CDP (5.0 mg/kg) was tested under less severe conditions; food remained restricted, but access to the wheels was discontinued. Rats given CDP ate more and gained more weight than controls. These findings suggest that benzodiazepines such as CDP may help in treating anorexia nervosa and other anorectic conditions in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Volatile N-nitrosamine formation after intake of nitrate at the ADI level in combination with an amine-rich diet

Formation of nitrite from ingested nitrate can result in several adverse health effects and implies a genotoxic risk as a consequence of endogenous formation of carcinogenic N-nitroso compounds. We studied the formation of volatile N-nitrosamines after intake of nitrate at the acceptable daily intake (ADI) level in combination with a fish meal rich in amines as nitrosatable precursors. Twenty-five volunteers consumed this meal during 7 consecutive days; a diet low in nitrate was consumed during 1 week before and 1 week after the test week. Nitrate intake at the ADI level resulted in a significant rise in mean salivary nitrate and nitrite concentrations. Mean urinary nitrate excretion increased from 76 mg/24 hr in the first control week to 194 and 165 mg/24 hr in the test week, followed by a decline to 77 mg/24 hr in the second control week. The urine samples were analyzed for volatile N-nitrosamines, and both N-nitrosodimethylamine (NDMA) and N-nitrosopiperidine (NPIP) were detected in the samples. Mean urinary NDMA excretion significantly increased from 287 ng/24 hr in the control week to 871 and 640 ng/24 hr in the test week and declined to 383 ng/24 hr in the second control week. Excretion of NPIP was not directly related to the nitrate intake and composition of the diet. Nitrate excretion and NDMA excretion were significantly correlated, as well as salivary nitrate and nitrite concentration and NDMA excretion. We conclude that nitrate intake at the ADI level in combination with a fish meal containing nitrosatable precursors increases NDMA excretion in urine and thus demonstrates increased formation of carcinogenic N-nitrosamines.     

Effects of gastric loading on the sucking response and voluntary milk intake in neonatal piglets.

Studied the effects of loading the stomach of piglets with 100 ml of milk after 6 hrs of fasting and immediately before allowing them access to the dam. Ss were a total of 77 piglets from the experimenting institute's herd. Results show Ss gained less weight and rested more often on preloaded days. This suggests that gastric receptors exist and signal distension of the stomach. Monitoring sucking responses to a rubber teat revealed that although preloading the stomach substantially reduced voluntary milk intake during the initial 10-min period of the test, the vigorous oral activity continued largely unabated. Isometric saline suppressed voluntary milk intake for a shorter period than milk or isotonic glucose solution. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory aversive conditioning in the newborn (3-hr-old) rat impairs later suckling for water and milk.

An olfactory conditioning paradigm tested whether newborn rats can acquire a conditioned aversion to olfactory events associated with their first postnatal meal 3-5 hr after birth. Exposure to lemon odor (conditioned stimulus [CS]) paired with intraoral infusions of 0.1% quinine (unconditioned stimulus) resulted in explicit conditioning. Responsiveness to a surrogate nipple providing water in the presence of the CS was significantly lower than the 3 control conditions. The conditioning dramatically suppressed responsiveness to a surrogate nipple providing milk, which normally is expressed voraciously in terms of sustained nipple attachment and milk intake. These findings suggest that as early as 3-5 hr after birth newborn rats are capable of aversive conditioning to odors in the context of suckling behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Utilization of a low-lactose milk

This study was undertaken to determine if a milk containing prehydrolyzed lactose, yet affording full nutritional benefits, could be ingested by a milk intolerant (MI) population without the symptoms of lactose intolerance. MI was defined by the failure of serum glucose to rise greater than 20 mg/100 ml after ingestion of 50 gm of lactose as well as by subjective and objective symptoms and signs after consumption of both 12.5 gm of lactose in water and 250 ml of skim milk. Lactose tolerance (LT) was evidenced by both lack of symptoms and a concomitant rise in serum glucose of greater than 20 mg/100 ml after ingestion of 50 gm lactose in water. A series of four, two hr tolerance tests were given to 12 MI patients and 12 LT controls. The following solutions were employed: 12.5 gm lactose, 250 ml skim milk. 250 ml low-lactose skim milk, and 6 gm glucose plus 6 gm galactose. In the MI group, significant differences were apparent between the tolerance test utilizing skim milk and that using low-lactose skim milk; no such differences were observed in the LT group. These observations indicate that in the MI population the lactose in skim milk was poorly absorbed or tolerated, but after hydrolysis the low-lactose skim milk was well tolerated. A MI individual then, appears able to absorb the monosaccharides of the prehydrolyzed milk and can, furthermore, tolerate the low-lactose skim milk without suffering from symptoms normally associated with lactose intolerance.