Glucose-induced thermogenesis in tetraplegic patients with low sympathoadrenal activity

Exercise and Health-Related Risks of Physical Deconditioning After Spinal Cord Injury

A sedentary lifestyle occurring soon after spinal cord injury (SCI) may be in contrast to a preinjury history of active physical engagement and is thereafter associated with profound physical deconditioning sustained throughout the lifespan. This physical deconditioning contributes in varying degrees to lifelong medical complications, including accelerated cardiovascular disease, insulin resistance, osteopenia, and visceral obesity. Unlike persons without disability for whom exercise is readily available and easily accomplished, exercise options for persons with SCI are more limited. Depending on the level of injury, the metabolic responses to acute exercise may also be less robust than those accompanying exercise in persons without disability, the training benefits more difficult to achieve, and the risks of ill-considered exercise both greater and potentially irreversible. For exercise to ultimately promote benefit and not impose additional impairment, an understanding of exercise opportunities and risks if exercise is undertaken by those with SCI is important. The following monograph will thus address common medical challenges experienced by persons with SCI and typical modes and benefits of voluntary exercise conditioning.

Thermogenesis induced by intravenous infusion of hypertonic solutions in the rat

1. Intravenous administration of 20-60 % glucose, 3.2-9.7 % NaCl or 20 % mannitol solutions (1.66 ml kg(-1)) for 5 min increased oxygen consumption in urethane-anaesthetized rats, whereas administration of physiological saline had no effect. Administration of 7.7-18.3 % urea slightly increased the oxygen consumption, but the increase was significantly smaller than that measured after the administration of other hypertonic solutions. The magnitude of the thermogenic effect correlated with the osmolality of the applied solutions. These results suggest that the thermogenesis was caused mainly by changes in osmolality rather than by a specific action of the different solute molecules. 2. Neither pretreatment with the ganglion blocker hexamethonium (20 mg kg(-1), I.P.) or the beta-adrenergic antagonist propranolol (10 mg kg(-1), I.P.), nor bilateral cervical vagotomy or bilateral adrenalectomy had any effect on the osmotically induced thermogenesis. Therefore, the autonomic nervous system and the adrenal gland were not involved in this metabolic response. 3. In response to osmotic stimulation, the temperature of the skeletal muscle increased significantly, whereas that of brown adipose tissue did not change and that of the colon and liver decreased. Accordingly, the site of osmotic thermogenesis is probably in the skeletal muscle, although osmotic stimulation was not accompanied by electromyographic activity and was not blocked by pretreatment with muscle relaxants such as dantrolene sodium or pancuronium bromide, or with the Na(+)-Cl(-) co-transport inhibitor bumetanide. 4. The increases in plasma osmolality observed after the administration of 20 % (1.3 osmol kg(-1)) glucose and 4.1 % (1.3 osmol kg(-1)) NaCl were 4.50 +/- 0.88 and 5.57 +/- 0.71 mosmol kg(-1), respectively. Since the slight increase in osmolality is well within the physiological range of changes that occur after food ingestion, diet-induced thermogenesis may have a component that is mediated by an increase in plasma osmolality, which results from the prandial increase in circulating nutrients.

Thermogenesis induced by osmotic stimulation of the intestines in the rat

Infusion of 5-20% glucose, 1.8-3.6% NaCl, 20% methylglucose, 20% fructose, or 5-10% solutions of various amino acids (10 ml x kg(-1)) into the duodenum induced dose-dependent thermogenesis in urethane-anaesthetized rats. In contrast, infusion of 0.9% NaCl, distilled water, or safflower oil had no effect on the metabolic rate. Infusion of 7.2% urea induced a small and transient increase in the metabolic rate. These results suggested that the thermogenesis was caused mainly by changes in osmolality rather than by a specific action of the different solute molecules. The respiratory exchange ratio increased after the infusion of glucose, fructose, glycine, or serine, did not change after the infusion of NaCl, methylglucose, safflower oil, or distilled water, and decreased after infusion of arginine. Therefore, there was no relationship between substrate utilization and the occurrence of thermogenesis. Intestinal infusion of 3.6% NaCl elevated the plasma osmolality, with a plateau increase of approximately 20 mosmol x kg(-1). However, intravenous infusion of the same amount of NaCl induced a significantly smaller thermogenic response, although it elevated the plasma osmolality with a time course and magnitude similar to those obtained after the intestinal infusion. Infusion of NaCl into the hepatic portal vein or the peritoneal cavity also produced a significantly small thermogenic response. These results suggested an intestinal or mesenteric location for osmoreceptors. To test for possible stimulation of intestinal osmoreceptors after intake of a normal meal, we measured the osmolality of the intestinal contents. The osmolality of the duodeno-jejunal contents was 600-800 mosmol kg-1, whereas the plasma osmolality was 306 +/- 1 mosmol x kg(-1), which suggests that the intestinal osmoreceptors are stimulated after meals and are involved in diet-induced thermogenesis.