Altered endocrine pancreatic function following vagotomy: possible behavioral and metabolic bases for assessing completeness of vagotomy

The Vagus Nerve and Spleen: Influence on White Adipose Mass and Histology of Obese and Non-obese Rats

The vagus nerve (VN) and spleen represent a complex interface between neural and immunological functions, affecting both energy metabolism and white adipose tissue (WAT) content. Here, we evaluated whether vagal and splenic axis participates in WAT mass regulation in obese and non-obese male Wistar rats. High doses of monosodium glutamate (M; 4 g/Kg) were administered during the neonatal period to induce hypothalamic lesion and obesity (M-Obese rats). Non-obese or Control (CTL) rats received equimolar saline. At 60 days of life, M-Obese and CTL rats were randomly distributed into experimental subgroups according to the following surgical procedures: sham, subdiaphragmatic vagotomy (SV), splenectomy (SPL), and SV + SPL (n = 11 rats/group). At 150 days of life and after 12 h of fasting, rats were euthanized, blood was collected, and the plasma levels of glucose, triglycerides, cholesterol, insulin, and interleukin 10 (IL10) were analyzed. The visceral and subcutaneous WAT depots were excised, weighed, and histologically evaluated for number and size of adipocytes as well as IL10 protein expression. M-Obese rats showed higher adiposity, hyperinsulinemia, hypertriglyceridemia, and insulin resistance when compared with CTL groups (p < 0.05). In CTL and M-Obese rats, SV reduced body weight gain and triglycerides levels, diminishing adipocyte size without changes in IL10 expression in WAT (p< 0.05). The SV procedure resulted in high IL10 plasma levels in CTL rats, but not in the M-Obese group. The splenectomy prevented the SV anti-adiposity effects, as well as blocked the elevation of IL10 levels in plasma of CTL rats. In contrast, neither SV nor SPL surgeries modified the plasma levels of IL10 and IL10 protein expression in WAT from M-Obese rats. In conclusion, vagotomy promotes body weight and adiposity reduction, elevating IL10 plasma levels in non-obese animals, in a spleen-dependent manner. Under hypothalamic obesity conditions, VN ablation also reduces body weight gain and adiposity, improving insulin sensitivity without changes in IL10 protein expression in WAT or IL10 plasma levels, in a spleen-independent manner. Our findings indicate that the vagal-spleen axis influence the WAT mass in a health state, while this mechanism seems to be disturbed in hypothalamic obese animals.

Protein restriction during lactation alters the autonomic nervous system control on glucose-induced insulin secretion in adult rats

Involvement of autonomic nervous system (ANS) neurotransmitters on insulin secretion in rats submitted to protein malnutrition during lactation was studied. During the first 2/3 of lactation, mothers received a 4% protein diet (LP). Control group received normal diet (23% protein) (NP). After protein restriction, mothers received normal diets. At 81 days rats were submitted to intravenous glucose tolerance tests (ivGTT). Plasma glucose and insulin concentration (PIC) were measured. Glucose-induced insulin secretion (GIIS) was tested in pancreatic islets. Fasting normoglycemia and hypoinsulinemia were observed in LP rats. Glucose intolerance and low PIC in LP group were detected during ivGTT. Acetylcholine (Ach) or blockage of alpha-adrenoceptors induced high PIC increment in LP rats; atropine or stimulation of alpha-adrenoceptors did not change PIC. Insulin secretion of LP rat islets showed low glucose and carbachol responses. Epinephrine-inhibited GIIS in both islet groups. Hypoinsulinemia observed in lactation-malnourished rats might be caused by alterations in GIIS regulation, including ANS modulation.

Involvement of the cholinergic pathway in glucocorticoid-induced hyperinsulinemia in rats

AIMS

We investigated the contribution of the cholinergic nervous system to dexamethasone-induced insulin resistance and hyperinsulinemia in rats.

METHODS

Seventy-day-old Wistar male rats were distributed in groups: control (CTL), vagotomized (VAG), and sham operated (SHAM). On the 90th day of life, half of the rats were treated daily with 1mg/kg of dexamethasone for 5 days (CTL DEX, VAG DEX, and SHAM DEX).

RESULTS

In the presence of 8.3mM glucose plus 100microM carbachol (Cch), isolated islets from CTL DEX secreted significantly more insulin than CTL. Cch-enhancement of secretion was further increased in islets from VAG CTL and VAG DEX than SHAM CTL and SHAM DEX, respectively. In CTL DEX islets, M3R and PLCbeta1 and phosphorylated PKCalpha, but not PKCalpha, protein content was significantly higher compared with each respective control. In islets from VAG DEX, the expression of M3R protein increased significantly compared to VAG CTL and SHAM DEX. Vagotomy per se did not affect insulin resistance, but attenuated fasted and fed insulinemia in VAG DEX, compared with SHAM DEX rats.

CONCLUSION

These data indicate an important participation of the cholinergic nervous system through muscaric receptors in dexamethasone-induced hyperinsulinemia in rats.

Fat storage is partially dependent on vagal activity and insulin secretion of hypothalamic obese rat

Hypothalamic MSG-obese rats show hyperinsulinemia and tissue insulin resistance, and they display intense parasympathetic activity. Current analysis investigates whether early subdiaphragmatic vagotomy prevents tissue insulin sensitivity impairment in adult obese MSG-rats. Hypothalamic obesity was induced by MSG (4 mg/g BW), daily, from birth up to 5 days. Control animals receiving saline solution. On the 30th day rats underwent bilateral subdiaphragmatic vagotomy or sham surgery. An intravenous glucose tolerance test (i.v.GTT) was performed when rats turned 90 days old. Total white fat tissue (WAT) from rat carcass was extracted and isolated; the interscapular brown fat tissue (IBAT) was weighed. Rather than blocking obesity, vagotomy reduced WAT and IBAT in MSG-obese rats when the latter were compared to sham MSG-rats. High blood fasting insulin and normal glucose levels were also observed in MSG-obese rats. Although glucose intolerance, high insulin secretion, and significant insulin resistance were recorded, vagotomy improved fasting insulinemia, glucose tolerance and insulin tissue sensitivity in MSG-obese rats. Results suggest that increased fat accumulation is caused, at least in part, by high blood insulin concentration, and enhanced parasympathetic activity on MSG-obese rats.

Blood glucose dynamics and control of meal initiation: a pattern detection and recognition theory

A new framework for understanding the control of feeding behavior, with special emphasis on the evolution of hunger, the initiation of feeding, and its dependence on patterns of blood glucose, is the subject of this review. A perspective on the current status and future directions of this search for a more complete understanding of the regulation of feeding behavior in laboratory rats and humans is presented including theoretical and experimental components. First, a historical perspective on the role of blood glucose in the control of feeding is presented. Next, the theoretical approaches that have been applied to the control of feeding and had a strong influence on experimental feeding research are summarized. This is followed by a statement and overview of a current theory that has emerged from studies of the role of transient declines in blood glucose in the control of meal initiation. The current working hypothesis that transient declines in blood glucose are endogenous metabolic patterns that are detected and recognized by the central nervous system and are mapped into meal initiation in rats and are correlated with meal requests in humans are then presented. Then, the experimental studies on meal initiation and its dependence on patterns of blood glucose, first in rats and then in humans, are reviewed in detail. Finally, the future directions of the work, limitations, and the implications for the understanding of the control of feeding behavior and the regulation of energy balance are discussed.

Efeito da vagotomia troncular em ratos injetados na fase neonatal com glutamato monossódico: estudo biométrico

Obesidade hipotalâmica pode ocorrer em humanos e pode ser reproduzida, experimentalmente, por lesão do VMH em ratos. Esta obesidade pode ser revertida por vagotomia troncular (VT), devido à redução da ingestão alimentar e da insulinemia mediada pelo nervo vago. Experimentalmente, a injeção de MSG causa lesão em nível de ARC. O objetivo deste trabalho é avaliar os efeitos do MSG em ratos e se VT os altera. Estudou-se 52 ratos Wistar machos, divididos em dois grupos de 26 animais, um submetido à injeção de MSG na fase neonatal e outro à de solução salina. Aos 30 dias de vida, após nova divisão, obteve-se: grupo MSG, submetido à VT (VTMSG), e outro à laparotomia (LAPMSG); grupo SALINA, submetido à VT (VTSAL), e outro à laparotomia (LAPSAL). Obteve-se peso, CNA e índice de Lee. O consumo alimentar foi obtido dos 30 aos 90 dias de vida. Aos 90 dias, após eutanásia, mensurou-se peso, CNA, índice de Lee e gordura perigonadal. Análise estatística foi realizada pelo "t de Student". Constatou-se que o MSG provoca redução do CNA e aumento do índice de Lee aos 30 dias de vida, e provoca redução do peso e do CNA, aumento do índice de Lee e da gordura perigonadal aos 90 dias e aumento do consumo alimentar dos 30 aos 90 dias de vida. A VT provoca redução do peso, do índice de Lee e da gordura perigonadal, e tendência à redução do CNA no rato injetado com MSG. A VT provoca redução de consumo alimentar nos primeiros 30 dias de pós-operatório, mas com tendência a maior consumo nos 30 dias subseqüentes. Conclui-se que o MSG injetado na fase neonatal provoca aumento do consumo alimentar e da adiposidade e causa redução da estatura e do peso do animal dos 30 aos 90 dias de vida. E que a VT, realizada aos 30 dias de vida, provoca redução do consumo alimentar nos primeiros 30 dias de pós-operatório, da adiposidade e do peso.

Vagotomy does not affect thermal responsiveness to intrabrain prostaglandin E2 and cholecystokinin octapeptide

Subdiaphragmatic vagotomy has been repeatedly shown to attenuate the febrile response to peripherally injected pyrogens. In the present study, we investigated whether vagotomy-induced attenuation of febrile responsiveness reflects a decreased sensitivity of the brain to central fever mediators, prostaglandin E2 (PGE2) and cholecystokinin octapeptide (CCK-8). Male rats were subjected to subdiaphragmatic vagotomy (or sham surgery) on day 0 and had a cannula implanted into the lateral cerebral ventricle on day 24. On day 30-36, the thermal responsiveness of the rats to PGE2 or CCK-8 was tested. Each animal was injected in the ventricle with either PGE2 (0, 10, 100, or 500 ng) in pyrogen-free saline with 0.5% ethanol (5 microl) or CCK-8 (0 or 1.6 microg) in artificial cerebro-spinal fluid (5 microl). While the 0-dose of either PGE2 or CCK-8 (vehicle alone) induced no thermal response, all the higher doses of either agent caused a body temperature rise preceded by tail skin vasoconstriction. The vagotomized rats did not respond differently than their sham-operated counterparts to any dose of either drug. It is concluded that subdiaphragmatic vagotomy does not change the rat's thermal responsiveness to intrabrain PGE(2) and CCK-8.

Effect of chemical sympathectomy on serum levels of thyroid hormones and the biochemical profile of domestic pigeons

Recent studies have stressed the importance of the cholinergic system on avian metabolism. However, the role of the sympathetic nervous system (SNS) remains unclear. The present study was, therefore, aimed to probe the mechanisms for modulation of avian metabolism by the sympathetic nervous system after inhibition of the adrenergic responses. Activities of serum thyroid hormones (tri-iodothyronine, T3, and thyroxine, T4), body weight, hepatic weight, as well as total lipid and water content in the liver and body temperature were some of the parameters examined after chemical sympathectomy with 6-hydroxydopamine (6-OHDA) and reserpine treatment in 24-h starved pigeons. In addition, glucose was administered to the pigeons to identify the regulatory role played by glucose after disruption of the SNS. A reduction in body weight of the pigeons and an enhancement in the lipogenic machinery along with a corresponding increase in water content were some of the obvious effects in 6-OHDA+reserpine treated, as well as glucose-loaded sympathectomized birds. The cloacal temperature (Tc) and both the thyroid hormones showed a drastic decrease while the T3/T4 ratio was augmented as a result of sympathectomy. However, serum T3 and T4 levels were restored to control values when glucose load was given, indicating that glucose might be reversing some of the detrimental effects of 6-OHDA treatment by activating intrinsic autoregulatory mechanisms of thyroid gland, thereby reviving the levels of thyroid hormones. Thus, the influence of SNS appears to be crucial in the maintenance of serum thyroid hormones and body temperature, as well as metabolic activities of hepatic cells.

Gastric vagotomy blocks opioid analgesia enhancement produced by placenta ingestion

Ingestion of amniotic fluid or placenta by rats has been shown to enhance opioid-mediated analgesia induced by morphine injection, footshock, vaginal/cervical stimulation, or late pregnancy. This enhancement by ingestion appears to be specific to the central actions of opioids. The present study was designed to examine the possibility that information traveling via the vagus nerve might be involved in mediating this effect. Rats that had undergone either selective gastric vagotomy or sham vagotomy were injected with either morphine sulfate or vehicle and fed either placenta or a meat control. Enhancement was observed in rats that had undergone sham vagotomy but not in those that had undergone gastric vagotomy. These results support an interpretation of vagal involvement in the enhancement of opioid-mediated analgesia by placenta.

Immediate effect of vagotomy on pancreatic insulin secretion

The effect of vagotomy and gastric resection on insulin secretion was examined by the glucagon stimulated C-peptide test in gastrectomy patients (n = 11) without truncal vagotomy and in total gastrectomy patients (n = 10) with truncal vagotomy. The test was performed twice in each patient: 10 minutes after the midline incision was made and then 60 to 90 minutes later when gastric resection or total gastrectomy was completed, during the reconstructive phase of the operation. Gastric resection without truncal vagotomy was followed by a higher increase (48%) in serum C-peptide concentration caused by glucagon stimulation than total gastrectomy with truncal vagotomy (13%). There was a significant (p less than 0.05) increase in the glucagon stimulated glucose-related C-peptide concentration in patients without truncal vagotomy, whereas truncal vagotomy inhibited this increase. These results suggest that truncal vagotomy will produce a reduction in stimulated insulin secretion in humans.

Short term effects of fructose on blood glucose dynamics and meal initiation

We have previously shown that small (-11%) transient (approximately 18 min) declines in blood glucose which precede feeding are causally related to meal initiation under free-feeding conditions. We have also shown that IV infusions of glucose (20 mg) that blunt these declines can delay meal initiation. In order to test the specificity of exogenous glucose to delay meal initiation, the ability of another hexose, fructose, to block meal initiation was studied. Since oral and IV fructose have been reported to cause transient hypoglycemia, we also used fructose in an attempt to mimic transient declines in blood glucose and measure the latency to meal initiation. Continuous monitoring of blood glucose and meal pattern was performed in chronically cannulated female rats. When fructose (20 mg) was infused IV during transient declines in blood glucose, meal initiation occurred with a normal latency. During the early dark phase, IV fructose was followed by a slight decrease at the lowest dose or increase in blood glucose at higher doses and no feeding behavior was observed. In the light phase, however, a transient dose-dependent decrease in blood glucose was observed. Furthermore, three types of blood glucose response patterns were identified. Meal initiation occurred only following changes in the blood glucose trajectory that mimicked the spontaneous transient declines in blood glucose. The other two patterns were not followed by meal initiation. Similar effects on blood glucose were observed following oral administration of a range of fructose doses (0.25-0.75 g) in 2-hour fasted rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of atropine on insulin secretion in healthy subjects

The effect of an anti-cholinergic drug (atropine) on insulin secretion was studied in a double-blind manner by the glucagon C-peptide secretion test in five healthy subjects and controlled with saline only (placebo) in four subjects. Blood C-peptide increased only by 157% in the group given atropine and by 252% in the group given placebo. The blood glucose concentration increased by 25% and 32%, respectively. Thus, it is concluded that the cholinergic system, probably through the vagus nerve, has an insulin secretion stimulating effect. The results also suggest that denervation of the vagus nerve, e.g. in gastric surgery, may partly explain post-prandial hyperglycaemia particularly found in dumping.

Cardiorespiratory changes following chemical applications to gut serosa

Application of 0.2-0.3 ml of 1 M ammonium chloride, 100 mM citric acid, 100 mM hydrochloric acid, 1% potassium chloride, 1% ammonium oxalate, 1% oxalic acid, 0.5% sodium hydroxide, 200 micrograms% bradykinin or 20 mg% capsaicin to gastrointestinal serosa produced a fall in blood pressure and inhibition of respiration in hypertensive as well as normotensive rats. In 6 (8%) of the animals studied, a fall in heart rate was also seen which was blocked by atropine. The blood pressure changes were independent of changes in heart rate. After acute abdominal vagotomy, while the respiratory inhibition following chemical application on gut serosa was enhanced, the cardiovascular responses were the same as before. In animals subjected to sympathetic denervation by spinal section at T5, celiac ganglionectomy or splanchnicotomy, a similar application produced an augmented respiratory response while the cardiovascular parameters were unaffected. These results show that the above inhibitions were mediated through the sympathetic afferents and a minor stimulation of respiration, via vagal afferents. The efferent pathway for the cardiac changes seems to be via vagus and the vascular changes via the sympathetics. In chronic vagotomized animals, the same stimulation produced a response similar to that seen in animals with intact vagus. An adaptive response may be operating in chronic animals reverting the status back to normal.