Structural characteristics of endogenous sugar acids and relations to feeding modulation

Structural specificity among short-chain organic acids for effects on feeding behavior, blood glucose and insulin was investigated by infusion of 1 exogenous and 6 endogenous derivatives into the rat third cerebral ventricle. Glyceric acid (GEA) (1.0 mumol), 3,4-dihydroxybutanoic acid gamma-lactone (3,4-DB) and 3,4,5-trihydroxypentanoic acid gamma-lactone (3,4,5-TP) (2.50 mumol) decreased food intake for, at most, 24 h. These acids depressed the size of the first meal after infusion, but did not affect latency to the first meal, eating speed, drinking or ambulation. Infusion of 2,4-dihydroxybutanoic acid gamma-lactone (2,4-DB) (1.25 mumol), 2,4,5-trihydroxypentanoic acid gamma-lactone (2,4,5-TP), and an exogenous compound, 2,4,5,6-tetrahydroxyhexanoic acid gamma-lactone (2,4,5,6-TH) (2.50 mumol), induced transient initial feeding which was not necessarily accompanied by periprandial drinking. Ambulation was concomitantly increased. Of these organic acids, 3,4-DB and 2,4,5-TP were most potent in their effects on feeding. Hyperglycemia was induced by 2.50 mumol 3,4-DB leaving insulin unaffected; 2.50 mumol 2,4,5-TP caused hypoglycemia, with a persistent but not significant rise in insulin. The results suggest that slight structural differences of endogenous organic acids, in particular the positions of hydroxyl groups on the lactone ring of 4-butanolide, may be important in feeding modulation by conveying intrinsically reciprocal signals to neurons involved in feeding and satiety.

Effects of corticotropin-releasing factor on food intake and brown adipose tissue thermogenesis in rats

Corticotropin-releasing factor (CRF) has been administered into the third ventricle of rats in acute and chronic experiments. Following a single 5-micrograms injection of CRF, there was an acute reduction in food intake at 30 and 60 min that was no longer significant at 3 h. Guanosine 5'-diphosphate (GDP) binding to mitochondria from interscapular brown adipose tissue (IBAT) of 21-h deprived rats was significantly increased 30 min after the acute infusion of 5 micrograms of CRF. Serum corticosterone was elevated in both groups but was significantly higher in the group treated with CRF. Serum glucose was unchanged. During a 7-day infusion of CRF (4.8 micrograms/day) into the third ventricle, the treated animals showed a slight, but significant, decrease in food intake but a progressive decline in body weight of 53 g over 7 days. Mitochondrial GDP binding was increased in the ad libitum-fed rats chronically treated with CRF. Serum corticosterone levels, although significantly higher than controls, were lower than following acute administration of CRF. These data show that CRF can acutely reduce food intake and increase sympathetic activity and that chronically it reduces body weight and may increase sympathetic activity without any consistent decrease in food intake.

Effect of intrahypothalamic hydroxybutyrate on sympathetic firing rate

Following the microinjection of 3-hydroxybutyrate into either the paraventricular or ventomedial nucleus of the hypothalamus, there was a significant increase in firing rate of the sympathetic nerves to brown adipose tissue, with a peak increase in activity occurring three minutes following the injection. The response in both hypothalamic regions was dose-dependent. When injected into both regions at the same time, the increase in firing rate was additive. These studies suggest that ketone bodies in the central nervous system may activate the sympathetic nervous system.

Effect of starvation and food intake on sympathetic activity

These studies have examined the effect of fasting and nutrient loads on sympathetic firing rate in three groups of rats that develop widely divergent degrees of obesity when eating a high-fat diet. Starvation of Sprague-Dawley rats for 24 or 48 h was associated with a decrease in basal sympathetic activity of nearly 25% in the first 24 h and of slightly greater than 30% in 48 h. This decline in sympathetic activity paralleled the loss of body weight and reduction in adipose tissue mass. After starvation for 48 h, Osborne-Mendel rats, which readily develop obesity when eating a high-fat diet, showed a greater decrease in basal sympathetic activity than did the diet-resistant S 5B/P1 rats. A single liquid 36-kcal intragastric meal was associated with an acute 30% increase in sympathetic firing rate in the overnight-fasted Sprague-Dawley rats. The values 3 h after the meal had returned halfway to normal, and by 6 h they were more than 85% of the way to normal. An intravenous injection of glucose produced a greater rise in sympathetic activity in diet-resistant S 5B/P1 rats than in the diet-sensitive Osborne-Mendel rats. These data are consistent with the hypotheses that sympathetic activity is positively related to nutrient status, that it varies between strains of rats, and that it can be acutely increased by an intragastric meal or by intravenous glucose.

Effect of fenfluramine on sympathetic firing rate

The effects of acute and chronic treatment with fenfluramine have been explored in two experiments. Three and twenty-four hours following the injection of fenfluramine 20 mg/kg the firing rate of sympathetic efferent nerves to brown adipose tissue was significantly increased compared to sham injected controls. Body weight loss following acute treatment with fenfluramine was significantly greater at three and twenty-four hours than in the vehicle-treated controls. In the chronic experiment animals were treated once daily for 12 days with 20 mg/kg of fenfluramine. There were two control groups. One control group ate ad lib and a second control group was pair fed to maintain body weight comparable to that of the fenfluramine-treated animals. By the twelfth day food intake in the fenfluramine-treated animals had returned to control levels. Sympathetic firing rate after three days of treatment with fenfluramine was significantly higher in the treated animals than in ad lib fed controls. The ad lib fed controls were likewise significantly higher than the vehicle-treated, pair-gained controls. After 12 days of treatment fenfluramine treated animals had sympathetic firing rates which were still slightly but significantly higher than those of the vehicle-treated controls whereas the vehicle-treated, pair-gained animals had a small but significantly reduced firing rate. These data support the hypothesis that fenfluramine can increase peripheral sympathetic activity.

Effect of an amino group at carbon 2 of 1-deoxyglucose analogues on anorexia in the rat

A steric hindering group at carbon 2 of 1-deoxyglucose analogues was introduced by epimerization, deoxidation and substitution of a hydroxyl group with either an acetamido or a fluoro group. Injection of this analogue into the rat third cerebroventricle attenuated the feeding suppression produced by 1-deoxyglucose. In contrast, the replacement of a hydroxyl group at carbon 2 with an amino group produced anorexia of the same magnitude as that produced by 1-deoxyglucose. Amination at carbon 2 was more potent than that at carbon 3, 4 or 6. These results indicate that an amino group at carbon 2 of the glucose molecule is important to reinforce the feeding suppression caused by 1-deoxyglucose analogues.

Sympathetic activity and food intake of rats with ventromedial hypothalamic lesions

Following ventromedial hypothalamic lesions, food intake increased from 60 to slightly more than 77 kcal/day during the first 6 days. Body weight increased and sympathetic activity, as measured by the electrical firing rate of efferent nerves to interscapular brown adipose tissue, decreased significantly. During a 6-day period of intragastric overfeeding in which animals with hypothalamic lesions received 60 kcal for the first day and 80 kcal for the remaining 5 days, the VMH-lesioned animals gained significantly more weight than the intact, sham-lesioned controls. This difference in weight gain was paralleled by the increased weight of liver and white adipose tissue. The lesioned animals showed a highly significant reduction in sympathetic activity compared to the normal or slightly increased values observed in the sham-lesioned animals. These studies are consistent with the hypothesis that food-induced increases in sympathetic activity are modulated by the ventromedial hypothalamus.

Effects of feeding behavior of rats of a cryptic peptide from the C-terminal end on prepro-growth hormone-releasing factor

An amidated peptide derived from cleavage of the C-terminal of prepro-GRF [prepro-GRF-(78-107)NH2] and designated CTPG or anorectin was injected ip and into the third ventricle of rats, and food intake and body weight were measured. An acute injection of 0.2, 0.5, or 1.0 microgram CTPG (anorectin; 60, 150, or 300 pmol) into the third ventricle produced a significant dose-related reduction in food intake in the hungry rat during the 12-h dark period. Water intake was suppressed 30% by 1.0 microgram (300 pmol), but the lower doses had no effect. The highest dose (1 microgram or 300 pmol) produced a small rise in glucose concentration 5 min after injection into the third ventricle, which returned to the control value by 15 min. Anorectin increased the sympathetic efferent firing rate 3, 6, and 24 h after a single injection. Intraperitoneal injection of 2.0, 5.0, and 20 micrograms, however, had no significant effect on food or water intake. Chronic infusion into the third ventricle at a rate of 50 ng/h for 7 days produced a persistent reduction in food intake and a steady fall in body weight. The chronically infused rats had a significantly higher level of sympathetic activity, as measured by the firing rate of sympathetic nerves innervating the interscapular brown adipose tissue. These studies raise the possibility that anorectin released during processing of GRF might be involved in the modulation of feeding behavior.

Lateral hypothalamic lesions and activity of the sympathetic nervous system

The firing rate of efferent sympathetic nerves to brown adipose tissue was measured on 18 h or 18 d following lateral hypothalamic lesions (LH). Eighteen hours following acute lateral hypothalamic lesions, sympathetic firing rate was significantly increased. Following chronic LH lesions there was a decrease in food intake and a fall in body weight which had stabilized by four days. Eleven days after surgery a group of control animals were food restricted and subsequently pair fed twice daily to maintain a body weight comparable to that of the LH lesioned animals. Food intake was lower in the pair-gained animals on all but one day of the experiment. When studied 18 days following LH lesions, sympathetic firing rates were significantly higher than in either the ad lib or pair-fed controls. Sympathetic firing rate in pair fed rats, on the other hand, was significantly lower than in the sham lesioned rats. These data are consistent with the hypothesis that the LH lesion removes an inhibitory control over sympathetic firing rate both acutely and in chronically lesioned animals and that this increased sympathetic firing rate may play an important role in the maintenance of a lower body weight.

Corticosterone inhibition of the intracerebroventricular effect of 2-deoxy-D-glucose on brown adipose tissue thermogenesis

The effects on food intake, blood glucose and the binding of guanosine 5-diphosphate (GDP) to mitochondria from interscapular brown adipose tissue (IBAT) were examined following the injection of 2-deoxy-D-glucose (2-DOG) into the third ventricle of the brain. Microinjections of 2-DOG increased food intake and blood glucose within 30 to 60 min, but binding of GDP to mitochondria from IBAT, on the other hand, was reduced. The order of sensitivity to 2-DOG was IBAT--feeding--hyperglycemia. Implantation of a 50 mg pellet of corticosterone inhibited the stimulatory effect of 2-DOG on feeding and hyperglycemia and prevented the inhibition of GDP binding to mitochondria from IBAT. These data are consistent with the hypothesis that glucocorticoid may inhibit glucose metabolism at multiple sites in the hypothalamus.

Hypophagia induced by endogenous or liposome-encapsulated 3,4-dihydroxybutanoic acid

Hypophagia induced by 3,4-dihydroxybutanoic acid (2-deoxytetronic acid, 2-DTA), an endogenous short-chain polyhydroxymonocarboxylic acid, was investigated in rats. Intraperitoneal injection of 2500 mumol 2-DTA did not suppress feeding, but 2.5 mumol 2-DTA injected into the third cerebroventricle did. To efficiently transport exogenous 2-DTA into the brain, its encapsulation and delivery in specially made sulfatide liposomes was attempted. Feeding was suppressed dose-dependently by intraperitoneally injected 2-DTA in liposomes. Injection of 2500 mumol 2-DTA into the common carotid artery also suppressed feeding. Administration by either route prolonged postprandial intermeal interval with no change in meal size, as was observed after central administration of 2-DTA. Injection of 2.5 mumol 2-DTA into the third cerebroventricle elevated plasma glucose level, leaving insulin and free fatty acids unaffected. These findings, together with previous results, indicate that at least one site for the physiological action of 2-DTA is in the hypothalamic centers for food intake.

Administration of D-glucosamine into the third cerebroventricle induced feeding accompanied by hyperglycemia in rats

D-glucosamine, 2-amino-2-deoxy-D-glucose, is known to be an endogenous glucose analogue and to antagonize glucose uptake and metabolism. The present experiments were aimed to clarify effects of glucosamine and related chemical substances on ingestive behavior, as well as its direct effects on hypothalamic neurons. Infusion of 24 mumole glucosamine into the third cerebroventricle induced feeding within 30 min in 5 rats out of 7 tested, accompanied by increased ambulatory activity. No periprandial drinking was observed. Plasma glucose level increased, peaking at 30 min after the injection. Plasma insulin level tended to increase, but not significantly. Electrophoretic application of glucosamine activated glucose-sensitive neurons in the lateral hypothalamus and suppressed glucoreceptors in the ventromedial hypothalamus. These facts, together with other reported results, suggest that glucosamine can modulate physiological feeding and that carbon 2 of the glucose molecule is important in feeding modulation by glucose analogues.

1-Deoxy-glucosamine initiates, then effectively suppresses feeding in the rat

The deoxy analogues of D-glucose, 1-deoxy-D-glucosamine and D-glucosamine, are biochemically and structurally similar to 1-deoxy-D-glucose, so their direct effects on food intake were studied. Both 12 and 24 mumol 1-deoxy-glucosamine potently decreased feeding and body weight after an initial transient elicitation of food intake. The suppression included decreased meal size and prolonged postprandial intermeal interval which persisted for at least 3 days after injection. Ambulatory activity was unaffected. The initial elicitation of feeding was not accompanied by drinking episodes, and subsequent drinking suppression was persisted. These findings, plus other biochemical evidence, suggest that inversion with an amino group or removal of a hydroxyl group from C-2 and/or C-1 may affect feeding.

Structural evaluation of anorectic action induced by 1,5-anhydro-D-glucitol

In previous studies, 1,5-anhydro-D-glucitol (1-DG), an endogenous glucose analog, was found to significantly influence physiological feeding behavior. The relationships between the hydroxyl group positions on the pyranose ring carbons and the anorectic action induced by 1-DG and its analogs are discussed. To investigate the effects of these glucose analogs on ingestive behavior, 24 mumole of test solution was injected into the rat third cerebral ventricle immediately before normal eating time, which starts at the beginning of the dark. After initial transient hyperphagia, 1-DG suppressed feeding during the first 12-hr dark period. It prolonged postprandial intermeal interval beginning shortly after injection, but eating rate was not affected and meal size did not decrease until near the end of the normal feeding period. The incidence of drinking episodes decreased concomitant with feeding suppression. Feeding and drinking suppression were also produced by 1,2-dideoxy-D-glucose, 1,3-dideoxy-D-glucose, and 1,4-dideoxy-D-glucose, although they were less potent than 1-DG. They suppressed feeding by prolonging the postprandial intermeal interval, but did not change meal size or eating rate. The anorectic effects of 1-DG were abolished by removal of the hydroxyl group at carbon 6 and by epimerization at carbons 2, 3, and 4. These findings indicate that feeding suppression induced by 1-DG and its analogs is induced mainly by prolongation of the postprandial intermeal interval, and the presence or absence of a hydroxyl group on each carbon of 1-DG is important for its feeding suppression.

Short-chain polyhydroxymonocarboxylic acids as physiological signals for food intake

In order to clarify the effects of endogenous organic acids on short and long-term feeding behavior, ingestive behavior was monitored for 2 hr before and after intra-third ventricular infusions of 3,4-dihydroxybutyric acid (2-deoxytetronic acid, 2-DTA), 2,4,5-trihydroxypentanoic acid (3-deoxypentonic acid, 3-DPA), and 3-hydroxybutyric acid (3-HBA). In addition, meal patterns were recorded for 2 days before and after the ventricular infusions. 2-DTA suppressed both short and long-term feeding by decreasing meal size (MS). 3-DPA elicited transient feeding behavior, but caused no change in long-term feeding. 3-HBA initially stimulated feeding, but subsequently suppressed long-term feeding by decreasing MS and prolonging postprandial intermeal interval (IMI). The suppressive effects of 3-HBA on feeding behavior lasted about 24 hr longer than those of 2-DTA. Based upon these observations as well as our previous reports, it appears that some of the processes affecting hunger and satiation are mediated by changes in central and peripheral concentrations of these organic acids.

Changes in meal pattern and endogenous feeding related substances following mazindol administration

In order to ascertain direct central anorectic actions of mazindol (MZD), subtle changes in meal patterns and endogenous feeding related chemical substances were examined in rats following intra-third ventricle injection of 0.03 mumole MZD. In ad lib feeding, MZD decreased meal size and prolonged postprandial intermeal interval during a 4 hr period starting 2 hr after injection. The magnitude of anorectic actions of MZD was depressed by hunger. Although the action of MZD is short in duration, long duration anorexia was achieved by chronic infusion for 8 days. Infusion of MZD starting at 5:50 p.m. decreased plasma insulin, leaving glucose and glucagon unaffected, although no change in plasma glucose or insulin was observed following injection at 11:30 a.m. These findings, together with other reports, can be explained by MZD's direct effects on the hypothalamic hunger and satiation centers.

[Changes in meal patterns and endogenous chemical determinants related to food intake following intra-ventricle III infusion of mazindol]

To clarify suppressive effects of mazindol on food intake in rats, changes in body weight, meal patterns as well as 24-hr food intake, and endogenous chemical substances were investigated following the intra-ventricle III infusion of 0.03 mumole mazindol. Experiments were carried out under the condition of a 12: 12 light-dark cycle (light: 0800-2000 hr). Mazindol decreased food intake as well as body weight after a 12 hr starvation. Reduced food consumption was observed during 12 hr following the injection. Weight reduction, however, lasted over all 3-tested days. When food was available ad. lib., mazindol decreased meal size during the 4 hr after injection and prolonged postprandial intermeal interval during the 4 hr period starting 2 hr after the injection. The infusion of mazindol also produced relative hyperglycemia and decreased free fatty acids, which was not accompanied with hyperinsulinemia. These findings, together with other reports, indicates that mazindol, unlike amphetamine and fenfluramine, possesses inhibitory actions on the hypothalamic feeding center.