Influence of Parenteral Feeding on Spontaneous Caloric Intake and Food Selection in Rats

A double-blind randomized trial comparing outpatient parenteral nutrition with intravenous hydration: effect on resumption of oral intake after marrow transplantation

BACKGROUND

Outpatient parenteral nutrition (PN) is often given to marrow transplant recipients after high-dose chemoradiotherapy until the resumption of adequate oral intake; however, it may adversely prolong resumption or oral calorie intake by contributing to early satiety.

METHODS

A double-blind, randomized study compared standard PN (final concentration 25% dextrose, 5% amino acids) with a hydration solution (5% dextrose) during the first 28 days of outpatient treatment. Patients were eligible for the study if they were > or = 2 years of age, < 65 days posttransplant, had < 70% oral caloric intake at hospital discharge, and required < or = 10 U insulin/L PN. Solutions were provided until the patient's oral intake met > or = 85% caloric requirements for 3 consecutive days.

RESULTS

Two hundred fifty-eight marrow transplant recipients (128, PN and 130, hydration solution) were studied. Age, donor type, and diagnoses were similar in the two groups. Time to resumption of > or = 85% oral caloric intake was 6 days sooner in the hydration group than in the PN group (median 10 vs 16 days, respectively; p = .049). When adjusting for sex, age, donor type, total body irradiation, previous oral intake, acute graft-versus-host disease, and prednisone therapy, the hydration group resumed oral intake sooner than the PN group (relative risk = 1.51; 95% confidence interval [CI] 1.04 to 2.19; p = .029). The percentage of weight change from pretransplant values, adjusted for the above covariates and the number of weeks of treatment, indicated that the hydration solution group lost weight (4.63%) compared with the PN group (1.27%) after 4 weeks of therapy (p = .004). Rates of hospital readmissions, relapse of malignancy, and survival did not differ between the two treatment groups.

CONCLUSIONS

We conclude that outpatient PN delays resumption of oral intake and that its replacement with hydration solution does not result in adverse patient outcome.

Studies on the regulation of food intake using rat total parenteral nutrition as a model

Total parenteral nutrition (TPN) is essential for maintaining the nutritional status of patients who are unable to eat sufficiently to meet their metabolic needs. However, TPN suppresses appetite and ultimately diminishes food intake. Theories concerning the role(s) of peripheral metabolites as signals, acting via the liver and the hypothalamus, for the metabolic control of food intake, have been put forward to explain the anorectic effect of TPN. In addition, it is postulated that changes in peripheral metabolites during TPN may be translated into changes in the levels of brain neurotransmitters known to decrease food intake. This review summarizes studies concerning the effect of TPN on food intake. These studies have involved: (1) characterizing the changes in feeding activity due to TPN; (2) investigating the involvement of the central nervous system; and (3) investigating the role of the periphery and its metabolites in the regulation of food intake during TPN. Some insight into the mechanism of action of TPN on food intake is provided.

An electrophysiological study on amino acid sensors in the hepato-portal system in the rat

The existence of amino acid sensors sensitive to arginine, alanine, leucine and glycine in the hepato-portal region was previously reported based on recording of the afferent signals from the hepatic branch of the vagus nerve. The present study was carried out to investigate the effects of fifteen different amino acids on the activity of the vagal hepatic afferents. Intraportal administration (10 mM, 0.1 mL) of alanine, arginine, histidine, leucine, lysine, serine, tryptophane and valine increased vagal afferent discharge rate, and that of cysteine, glycine, isoleucine, methionine, phenylalanine, proline and threonine suppressed it. The results indicate the existence of two groups of amino acids sensors which exhibit excitatory or inhibitory effect on the afferent activity of the hepatic branch of the vagus nerve. The change in afferent activity to the hypothalamus may affect reflex regulation of the visceral functions and thereby influence appetite.

The comparative effects of abrupt vs. stepwise discontinuation of TPN in rats

The comparative effects of discontinuing total parenteral nutrition (TPN: caloric ratio of glucose:fat:amino acid = 50:30:20) abruptly or in a stepwise manner on spontaneous food intake were investigated in two studies. Study 1: In 16 rats, TPN was given for 4 days, then stopped abruptly in eight rats. In the other eight rats, TPN was tapered; they received TPN at 75%, 50%, and 25% of their mean daily energy requirements per day for 3 consecutive days, and then switched to normal saline. Total parenteral nutrition induced a significant 60% reduction in spontaneous food intake (SFI) in both groups during the first TPN day. After 4 days of TPN, an 80% decrease in SFI had occurred in both groups. Resumption of SFI was significantly sooner in the abruptly-stopping group than in the stepwise-stopping group. But, in the latter group, there was a significantly greater cumulative caloric intake during the entire study. Study 2: In 32 rats, TPN providing either 100%, 50%, or 25% of their mean daily caloric requirements was given to three groups each of eight rats, for 3 days, then abruptly changed to normal saline; control rats received normal saline throughout. The TPN-induced decrease in SFI was proportional to the caloric density of the solution infused. Three days of 100%, 50%, or 25% TPN infusion led to an approximate 85%, 60%, or 35% decrease in SFI, respectively. Spontaneous food intake recovery was independent of the caloric density of TPN.(ABSTRACT TRUNCATED AT 250 WORDS)