Myenteric neurons in diabetic rats 105 Braz. J. morphol. Sci. (2004) 21(2), 105-110 ISSN- 0102-9010 EVALUATION OF THE NITRERGIC MYENTERIC NEURONS IN THE DISTAL COLON OF DIABETIC RATS TREATED WITH ACETYL-L-CARNITINE Marcílio Hubner de Miranda Neto 1 , Cristina Elena Prado Teles Fregonesi 3 , Sônia Lucy Molinari 1 , Ângela Maria Pereira Alves 4 , Marli Aparecida Defani 1 , Jacqueline Nelisis Zanoni 1 and Roberto Barbosa Bazotte 2 1 Department of Morphophysiological Sciences (DCM/UEM) and 2 Department of Pharmacology, State University of Maringá, Maringá, PR, 3 Department of Physiotherapy, Faculty of Sciences and Technology, Paulista State University (FCT/UNESP), Presidente Prudente, SP, 4 West Paraná State University, Cascavel, PR, Brazil. ABSTRACT In this work, we evaluated the effect of acetyl-L-carnitine supplementation on the presence of NADPH-diaphorase positive myenteric neurons in the distal colon of rats with diabetes mellitus induced by streptozotocin. Rats 105 days old were divided into four groups: normoglycemic, normoglycemic supplemented with acetyl-L-carnitine, diabetic and diabetic supplemented with acetyl-L-carnitine. Diabetes was induced by the administration of streptozotocin (35 mg/kg, i.v.). Supplementation with acetyl-L-carnitine was done for 105 days. The neuronal density was similar in all groups. In diabetic rats, the area of the neuronal cell body profile was greater (p<0.05) than in normoglycemic rats, whereas in diabetic rats receiving acetyl-L-carnitine the areas were smaller than in the non-supplemented diabetic rats (p<0.05). The increase in the colonic area of diabetic rats was greater than in diabetic rats treated with acetyl-L- carnitine (p<0.05), indicating that the increment in the population of these neurons was higher in treated diabetic rats. These results suggest that the beneficial effect of carnitine is restricted to preventing an excessive increase in neuronal area. The greater dilatation of the distal colon seen in diabetic rats supplemented with acetyl-L-carnitine probably represents an adverse effect of this compound. Key words: Acetyl-L-carnitine, diabetes mellitus, distal colon, myenteric neurons, NADPH-diaphorase Correspondence to: Dr. Cristina Elena Prado Teles Fregonesi Departamento de Fisioterapia, Universidade Estadual Paulista, Campus de Presidente Prudente, Rua Roberto Simonsen, 305, CEP 19060-900, Presidente Prudente, SP, Brasil. Tel: (55) (18) 229-5365, Fax: (55) (18) 229-5353, E-mail: cristina@prudente.unesp.br INTRODUCTION Diabetes mellitus (DM) is a high-prevalence disease [29]. With the discovery of insulin in 1921 [39], and its therapeutic use in 1922 [18], the life expectancy of diabetic patients improved significantly because of a reduction in acute complications, especially cetoacidosis [11]. Although additional advances in the diagnosis and treatment of DM have prolonged the lifespan of these patients, ironically they continue to be affected by late chronic-degenerative complications [11,18], includind macroangiopathies, microangiopathies (retinopathy and nephropathy) and neuropathies [8], all of which have been increasing in prevalence [13] and are frequently observed 10 - 15 years after the beginning of the disease [8]. Although diabetic neuropathies are extremely common and represent one of the major complications of DM, the mechanisms producing the nerve lesion still remain poorly understood and investigated [2]. Several hypotheses have been proposed to explain the physiopathological mechanisms that trigger the neuropathies, and include hyperactivity of the polyol pathway, non-enzymatic glycation of structural proteins, impairment in the action of trophic and nerve growth factors [2,34,36], vascular changes and endoneural hypoxia [34,36,42], immune mechanisms [31], oxidative stress [2,17,34] and lipid metabolism [2,28,34,36], particularly alterations in the levels of carnitine [16,20,22,27,38]. The onset of diabetic gastrointestinal autonomic neuropathy has been investigated by studying the behavior of myenteric plexus neurons in rats with streptozotocin-induced diabetes. In addition to decreased neuronal activity and the development of chromatolysis followed by degenerative changes [24], there is also a reduction in the density of neurons in the stomach [12], duodenum [5], ileum [19,41], cecum [40] and proximal colon [14,30], all of which indicate a variable response in the gastrointestinal tract [3]. In view of the association between decreased levels of serum and tissue carnitine and the pathogenesis of diabetic neuropathy, in this study, we examined the morphometric and quantitative alterations in NADPH-