Effect of l-NAME microinjected into the nucleus tractus solitarius on jejunal glucose and electrolyte absorption in anesthetized rats

The aim of the present study was to investigate the effects of NG-nitro-l-arginine-methyl-ester (l-NAME) microinjected into the rostral nucleus tractus solitarius (NTS) on jejunal glucose, sodium and potassium absorption. Male Wistar rats (210–250 g, n = 6–12) were anesthetized and submitted to midline laparotomy to expose and isolate 20 cm of jejunal loop and perform a subdiaphragmatic truncal vagotomy or sympathectomy. Either 0.9% NaCl or l-NAME (10 nmol 100 nl− 1) was microinjected into the rostral NTS using a stereotaxic instrument. Tyrode solution (pH 8) containing twice the usual concentrations of glucose, sodium and potassium was infused (0.5 ml min−1) into the jejunal loop and samples were taken at 10-min intervals during the 40-min experiment. Results were expressed by the difference between influx and efflux. l-NAME into the NTS increased glucose absorption and decreased potassium absorption when compared to the saline group (38.8 ± 3.8 vs. 50.3 ± 3.3 mg/dl and 0.6 ± 0.01 vs. 0.4 ± 0.03 mM, respectively; p < 0.05). Sympathectomy inhibited the glucose absorption caused by l-NAME alone (50.3 ± 3.3 vs. 30.7 ± 4.6 mg/dl; p < 0.05), whereas vagotomy inhibited the l-NAME effect on potassium absorption (0.40 ± 0.02 vs. 0.70 ± 0.05; p < 0.05). Moreover, increased sodium absorption was observed only in the group that received 30 nmol of l-NAME into NTS (33.0 ± 4.2 vs. 48.4 ± 3.9). In conclusion, the results suggest the participation of endogenous nitric oxide (NO) in the NTS in modulating intestinal glucose and potassium absorption mediated by the autonomic nervous system.

Research Highlights
► Participation of endogenous NO in the NTS in modulating jejunal absorption.
► l-NAME into the NTS increased glucose absorption and decreased potassium absorption.
► Sympathectomy inhibited the glucose absorption caused by l-NAME
► Vagotomy inhibited the l-NAME effect on potassium absorption.
► NO in the NTS modulating jejunal absorption is mediated by the autonomic nervous system.