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Persons with spinal cord injury (SCI) have been recognized to have several metabolic changes that adversely impact their risk for cardiovascular disease. An increased prevalence of disorders of carbohydrate metabolism and dyslipidemia may be related predominantly to paralysis with immobilization and associated loss of lean body tissue and gain in relative adiposity. Studies have reported an increased risk of vascular disease in those with SCI. As such, an understanding of the constellation of carbohydrate and lipid changes that occur after SCI is relevant to the clinical practice of medicine in this population. Oral glucose tolerance testing and associated studiesImpaired glucose tolerance and diabetes mellitus are more prevalent in individuals with SCI than in those who are able-bodied. 1 ± 4 In most of the individuals with SCI and abnormal carbohydrate tolerance, resistance to insulin mediation of glucose uptake by peripheral tissues may be demonstrable. In the presence of insulin resistance, the normal homeostatic response to glucose challenge is increased pancreatic b-cell secretion of insulin. If the compensatory response of the pancreas is insu cient to control the serum glucose concentration, worsening of carbohydrate tolerance will ensue.Bauman et al 3 performed a 75 g oral glucose tolerance test in 100 male veterans with SCI and in 50 able-bodied veteran controls. According to criteria established by the World Health Organization, 5 22% of those with SCI were diabetic whereas only 6% of the control group were diabetic. Eighty-two per cent of the controls had normal oral glucose tolerance, compared with 38% of those with quadriplegia and 50% of those with paraplegia. Subjects with SCI had signi®cantly higher mean plasma glucose and insulin values at several points during the oral glucose tolerance test when compared with controls ( Figure 1). In subgroups, determinants of insulin sensitivity were measured: per cent lean body mass, per cent fat mass, and cardiopulmonary ®tness. Values for insulin sensitivity were linearly related with those of ®tness (VO 2 max) determined from a progressive incremental upper-body exercise stress test. Insulin sensitivity was suggestively correlated with lean body mass, and negatively correlated with body fat. Thus, in a relatively small subgroup of untrained subjects with paraplegia, the strongest determinant of insulin sensitivity was cardiopulmonary ®tness.In 201 non-veteran subjects with SCI, Bauman et al 2 studied the relationship of oral carbohydrate tolerance after a 75 g glucose load to several variables, including level and completeness of lesion, gender, ethnicity, age, duration of injury, and anthropometric measures. Of the total group, 27 (13%) had diabetes mellitus and 56 (29%) had impaired glucose tolerance. 2,6 The subjects with complete tetraplegia had sign®cantly worse carbohydrate tolerance (Figure 2) and were more frequently classi®ed with a disorder of carbohydrate tolerance than the other neurological de®cit subgroups. 2 There were no signi®cant gend...

A membrane bound form of nitric oxide synthase of human erythrocytes that could be activated by insulin was purified to homogeneity by detergent solubilization of the purified membrane preparation of these cells. The purified enzyme (M(r) 230 KD) was found to be composed of one heavy chain (M(r) 135 KD) and one light chain (Mr 95 KD) held together by disulphide bond(s). Scatchard plot analysis of insulin binding to the purified enzyme showed the presence of 2 different populations of the binding sites and the activation were directly related to the hormone binding to the protein. Line weaver Burk plot of the purified enzyme showed that the stimulation of the enzymic activity by insulin was related to the decrease of K(m) with simultaneous increase of V(max). Treatment of the purified enzyme with anti insulin receptor antibody inhibited the activation of the enzyme and the binding of the hormone to the protein. Furthermore NO itself, at low concentration (<0.4 microM) activated the enzyme, but at higher concentration (>0.8 microM) had no effect on the activation. Incubation of the purified enzyme with insulin simultaneously stimulated the tyrosine kinase and nitric oxide synthase activities of the preparations, that could be inhibited by genistein (an inhibitor of tyrosine kinase). These results indicated that the insulin activated nitric oxide synthase could be the insulin receptor itself.

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