Neurochemical, neuroautonomic and neuropharmacological acute effects of sibutramine in healthy subjects

Sibutramine, a serotonin-norepinephrine reuptake inhibitor, causes fibrosis in rats

Sibutramine hydrochloride monohydrate is a weight loss agent indicated for the treatment of obesity. Although it has been banned from most markets, studies are still relevant as it is often a hidden ingredient in herbal and over the counter slimming products. Sibutramine induces liver fibrosis with steatosis in female Sprague-Dawley rats fed a high-energy diet without significant weight gain. In this study, using the same animal model, the effect of Sibutramine on lung morphology was investigated using histological evaluation of the terminal bronchiole and transmission electron microscopy evaluation of the respiratory tissue. From these results Sibutramine was found to induce lung fibrosis in Sprague-Dawley rats as increased collagen synthesis, mast cell accumulation and aggregates of Bronchus Associated Lymphoid Tissue (BALT) in the terminal bronchiole as well as increased collagen deposition in the respiratory tissue was seen.

Non-invasive management of vasovagal syncope

Vasovagal syncope (VVS) is a common disorder of the autonomic nervous system. While recurrent syncope can cause very impaired quality of life, the spells are not generally life-threatening. Both non-pharmacological and pharmacological approaches can be used to treat patients. Conservative management with education, exercise and physical maneuvers, and aggressive volume repletion is adequate for controlling symptoms in most patients. Unfortunately, a minority of patients will continue to have recurrent syncope despite conservative therapy, and they may require medications. These could include vasopressor agents, beta-blockers, or neurohormonal agents. Some patients may require more aggressive device based therapy with pacemakers or radiofrequency ablation, which are emerging therapies for VVS. This paper will review non-procedure based treatments for VVS.

Contrasting effects of systemic and central sibutramine administration on the intake of a palatable diet in the rat

Sibutramine hydrochloride monohydrate is the only centrally active weight-modifying agent currently approved by the FDA for long-term use in the treatment of obesity. Systemic sibutramine treatment has been shown to reduce food intake in humans and rodent models in a manner that is consistent with the enhancement of satiety mechanisms. Although it is generally assumed that the hypophagic effects of the drug are mediated by actions within the brain, the locus or loci of these effects remains unclear. These experiments compared the effects of systemic and intracranial injections of sibutramine on the intake of a palatable diet in non-deprived animals. Consistent with prior reports, systemic injections of sibutramine hydrochloride (at 0, 0.5, 1.0, or 3.0mg/kg sibutramine i.p.) dose-dependently reduced feeding on a high fat/high sucrose diet across a 2-h feeding session, but did not alter water intake or locomotor activity. In contrast, bilateral injections of sibutramine (at 0.0, 2.0, 4.0 and 10.0μg/0.5μl/side) into either the paraventricular nucleus of the hypothalamus (PVN) or the medial nucleus accumbens shell (ACb) significantly and dose-dependently increased food intake of the sweetened fat diet. ACb treatment also modestly inhibited locomotor behavior; intracranial injections had no effect on water consumption. These experiments are the first to suggest that sibutramine treatment may have distinct actions upon separate neural circuits that modulate food intake behavior in the rat.

Central nervous system plus autonomic nervous system disorders responsible for gastrointestinal and pancreatobiliary diseases

Clinical digestive disorders depend on the non-adequate coupling of functioning of the gastrointestinal tract with that of its affluent systems, namely, the pancreatic exocrine and the hepato-biliary secretions. The secretion of gastrointestinal hormones is monitored by the peripheral autonomic nervous system. However, the latter is regulated by the central nervous system (CNS) circuitry localized at the medullary pontine segment of the CNS. In turn, both parasympathetic and adrenergic medullary circuitries are regulated by the pontine A5 noradrenergic (NA) and the dorsal raphe serotonergic nuclei, respectively. DR-5HT is positively correlated with the C1-Ad medullary nuclei (responsible for adrenal gland secretion), whereas the MR-5HT nucleus is positively correlated with the A5-NA pontomedullary nucleus. The latter is responsible for neural sympathetic activity (sympathetic nerves). Both types of sympathetic activities maintain an alternation with the peripheral parasympathetic branch, which is positively correlated with the enterochromaffin cells that secrete serotonin. Serotonin displays hormonal antagonism to the circulating catecholamines.

Impact of weight-loss medications on the cardiovascular system: focus on current and future anti-obesity drugs

Overweight and obesity have been rising dramatically worldwide and are associated with numerous co-morbidities such as cardiovascular disease (CVD), type 2 diabetes mellitus, hypertension, certain cancers, and sleep apnea. In fact, obesity is an independent risk factor for CVD and CVD risks have also been documented in obese children. The majority of overweight and obese patients who achieve a significant short-term weight loss do not maintain their lower bodyweight in the long term. This may be due to a lack of intensive counseling and support from a facilitating environment including dedicated healthcare professionals such as nutritionists, kinesiologists, and behavior specialists. As a result, there has been a considerable focus on the role of adjunctive therapy such as pharmacotherapy for long-term weight loss and weight maintenance. Beyond an unfavorable risk factor profile, overweight and obesity also impact upon heart structure and function. Since the beginning, the quest for weight loss drugs has encountered warnings from regulatory agencies and the withdrawal from the market of efficient but unsafe medications. Fenfluramine was withdrawn from the market because of unacceptable pulmonary and cardiac adverse effects. Nevertheless, there is extensive research directed at the development of new anti-obesity compounds. The effect of these molecules on CVD risk factors has been studied and reported but information regarding their impact on the cardiovascular system is sparse. Thus, instead of looking at the benefit of weight loss on metabolism and risk factor management, this article discusses the impact of weight loss medications on the cardiovascular system. The potential interaction of available and potential new weight loss drugs with heart function and structure is reviewed.

Locomotor and peripheral effects of sibutramine modulated by 5-HT2 receptors

Sibutramine has been described as an anti-obesity drug with the ability to inhibit serotonin (5-HT), noradrenaline, and dopamine re-uptake, but without affinity to histamine and muscarinic receptors. On the other hand, cyproheptadine antagonizes serotonin 5-HT2A, 5-HT2B, and 5-HT2C, histamine H1, and muscarinic (M) receptors. There are many reports concerning the influence of sibutramine on central serotoninergic pathways. In this study, we suggest that peripheral pathways may also be involved in the serotoninergic effects of sibutramine. In vivo experiments were undertaken to investigate the serotoninergic effects of sibutramine on body mass, the glycogen concentration in the diaphragm of rats, and locomotor behaviour. Rats were submitted to oral treatment with sibutramine, cyproheptadine, or sibutramine applied in combination with cyproheptadine, for a period of 2 months to investigate the 5-HT2 effects of sibutramine on these parameters. As the results demonstrated, the lower increase in body mass and the increased glycogen levels in the diaphragm muscle of rats treated with sibutramine seem to be modulated by 5-HT2 receptors, since these effects were completely antagonized by cyproheptadine in the group treated with the 2 drugs co-applied. Furthermore, the behavioural results also suggest that mechanisms modulated by 5-HT2 receptors are involved in the increase of locomotion in the rats treated with sibutramine, since the effect did not occur in the rats treated with sibutramine co-applied with the 5-HT2 receptor antagonist, cyproheptadine. The results suggest that sibutramine modifies energy-related parameters such as body mass, diaphragm glycogen, and locomotor behaviour in rats via 5-HT2 serotoninergic pathways.

Central nervous system circuitry involved in the hyperinsulinism syndrome

Raised plasma levels of insulin, glucose and glucagon are found in patients affected by 'hyperinsulinism'. Obesity, hypertension, mammary plus ovary cysts and rheumatic symptoms are frequently observed in these patients. Sleep disorders and depression are also present in most subjects affected by this polysymptomatic disorder. The simultaneous increases of glucose, insulin and glucagon plasma levels seen in these patients indicate that the normal crosstalk between A cells, B cells and D cells is disrupted. With respect to this, it is well known that glucose excites B cells (which secrete insulin) and inhibits A cells (which secrete glucagon), which in turn excites D cells (which secrete somatostatin). Gastrointestinal hormones (incretins) modulate this crosstalk both directly and indirectly throughout pancreatic and hepatobiliary mechanisms. The above factors depend on autonomic nervous system mediation. For instance, acetylcholine released from parasympathetic nerves excites both B and A cells. Noradrenaline released from sympathetic nerves and adrenaline secreted from the adrenal glands inhibit B cells and excite A cells, which are crowded with beta(2)- and alpha(2)-receptors, respectively. Noradrenaline released from sympathetic nerves also excites A cells by acting at alpha(1)-receptors located at this level. According to this, the excessive release of noradrenaline from these nerves should provoke an enhancement of glucagon secretion which will result in overexcitation of insulin secretion from B cells. That is the disorder seen in the so-called 'hyperinsulinism', in which raised plasma levels of glucose, insulin and glucagon coexist. Taking into account that neural sympathetic activity is positively correlated to the A5 noradrenergic nucleus and median raphe serotonergic neurons, and negatively correlated to the A6 noradrenergic, the dorsal raphe serotonergic and the C1 adrenergic neurons, we postulate that this unbalanced central nervous system circuitry is responsible for the hyperinsulinism syndrome.