[Myoelectric function, metabolism, intestinal circulation and vagal activity after chemical sympathectomy]

Abstract

Adrenergic innervation plays an important role in the control of electric activity and circulatory parameters of the gut. Importance of adrenergic system as a modulator of motor, neural and metabolic activity of the intestine is studied extensively but still not well understood. We use 6-OHDA a neurotoxin and a blocking agent of adrenergic fibers, to evaluate their exact role in the control of vital parameters of the intestine and vagal nerves. 50 Wistar rats were used. Animals were fasted 24 h prior to experiment with free access to water allowed. Acute experiments were performed on 30 rats, divided in the three groups. Four experimental groups were established. I--sham operated. II and III--pretreated with 6-ODHA (25 mg//kg/24 h s.c.) 3 days before experiment. IV group were used for chronic procedure. Thiopental anesthesia (Vetbutal Biovet) was applied. Animals were artificially ventilated with positive pressure rodent ventilator (Ugo Basile), and heated with continuous temperature control by rectal thermistor (FST). Left carotid artery was cannulated and connected with electro manometer--arterial pressure (AP) was expressed in mm Hg. Right jugular vein was cannulated for continuous saline administration 0.2 ml/h. Mesenteric blood flow (MBF) was recorded with use of ultrasonic probe (Transonic systems T206). Microcirculatory blood Flow (LDBF) was estimated by laser Doppler flowmetry (Periflux 2001 Master). Arterio-venous difference (AVO2) was estimated from whole blood (AVOXimeter 1000 E). Oxygen uptake was calculated from MBF and AVO2 and expressed in ml/min/100 g tissue. Chronic experiments were performed on conscious animals with electrodes implanted to the serosal surface of the intestinal wall. Measurements of intestinal myoelectric parameters were performed one, two and three weeks after 6-OHDA administration. Vagal activity was recorded in left vagus nerve in the neck with suction electrodes (one month after 6-OHDA). 6-OHDA pretreatment evoked increase of dominant slow wave frequency by 0.1 Hz from 0.62 +/- 0.10 to 0.74 (+/- 0.03) Hz in the first week after treatment (p < 0.05). Slow wave frequency was no markedly influenced in acute experiments. In the chronic experiments after initial increase gradual decrease of slow wave frequency was observed reaching control values of 0.62 +/- 0.17 Hz after 28 days. After 6-OHDA administration in chronic experiments no substantial changes in slow waves amplitude was observed. Frequency and amplitude of spikes activity in vagus nerve after sympatectomy increased from 7.96 +/- 1.3 to 10.3 +/- 2/min and 0.18 +/- 0.09 to 1.13 +/- 0.8/mV. Chemical denervation evoked increase of MBF and LDBF by 18 +/- 3.6% and 22 +/- 6.4% respectively. Intestinal oxygen uptake (VO2) was increased by 10.2 +/- 1.2% in comparison to control. Heart rate and arterial pressure was decreased by 18 +/- 4% and 12 +/- 2.4% respectively in comparison to control. Adrenergic system plays profound role in the modulation of both myoelectric and motor activity of the intestine in the rat. Continuous activity of adrenergic neurons affects vascular conductance, capillary density and oxygen diffusion parameters.