Effect of nicotine on blood flow, oxygen consumption and glucose uptake in the canine small intestine

Abstract

1 Resting blood flow, arterio-venous glucose and oxygen (A-V)02 differences, glucose uptake and oxygen consumption by a segment of the upper jejunum were measured in anaesthetized dogs. Systemic arterial pressure was also measured. 2 The effect of nicotine infusion (25 pg kg-' i.v., over 10 min) on these measurements was recorded in untreated dogs, in dogs treated with propranolol (0.5 mg kg-') to produce P-adrenoceptor blockade and in dogs after a,-adrenoceptor blockade with prazosin (0.2 mg kg-').3 Nicotine cause a significant pressor response during infusion and a hypotensive response during the post infusion period. Propranolol did not significantly affect these results. Jejunal blood flow increased in the first half of nicotine infusion in both the untreated and P-blocked animals. Vascular resistance was reduced during nicotine infusion and the decrease persisted post infusion in the P-blocked group. 4 In the untreated group (A-V)O2 was significantly reduced during the first 5min of nicotine infusion, thereafter it returned to control levels, then rose significantly above control level, post infusion. P-Adrenoceptor blockade had little effect on these responses to nicotine. When oxygen consumption was calculated it was found that nicotine had little effect during or after infusion. 5 Nictine caused significant hyperglycaemia during and for about 1 h after infusion. Tissue release of glucose was occasionally observed following the infusion. 13-Adrenoceptor blockade reduced the hyperglycaemia caused by nicotine. P-Blockade alone increased glucose uptake and nicotine caused a further three to four fold increase. Prazosin abolished the effects that were observed in the untreated and the a-blocked animals. 6 The present findings, related to our previous observations on the effects of catecholamines on glucose uptake by the bowel, are consistent with the hypothesis that nicotine has its action on bowel glucose uptake or release through its well-established action in releasing catecholamines and in activating P-adrenoceptors. The responses are not related to oxygen utilization.

Evaluation of flash echo imaging of the canine gastrointestinal tract.

“…We also studied the effect of nicotine, which has been shown to reduce gastrointestinal tract blood flow. 31,32 As expected, we observed a reduction in the difference in gray scale amplitude after nicotine provocation. Since a prior report stated that microbubble concentration and videointensity in the cardiac left ventricular cavity are linearly related, 33 we considered the reduction in the gray scale amplitude after nicotine provocation to represent the reduction of focal blood flow in this study.…”

Effect of adrenaline on glucose uptake by the canine larger bowel

“…The resting blood flow of 10.1 + 0.2ml/min for the colon is similar to those reported for the upper jejunum (Grayson and Oyebola, 1983, 1985, Alada and Oyebola, 1996 and the terminal ileum (Pyebola and Durojaiye, 1988). However, the average resting glucose uptake of about 28.28 ± 1.2mg/min by the large intestine contrasts with an average of 17.77 ± 1.56mg/min in the upper jejunum (Alada and Oyebola, 1996) and the terminal ileum (Oyebola and Durosaiye, 1988).…”

“…However, while adrenaline caused an increase of about 700% in the jejunum (Grayson and Oyebola, 1983;1985;Alada and Oyebola (1996) and about 400% in the terminal ileum (Oyebola and Durosaiye, 1988) the percentage increase in glucose uptake by the large intestine in the present study is about 150%. In other words, the large intestine takes up less amount of glucose when compared with the small intestine in response to adrenaline induced hyperglycemia.…”

“…Simultaneous measurements of glucose uptake and oxygen consumption have shown that the glucose taken up by the small intestine is far in excess of what can be accounted for on the basis of oxidative metabolism (Durotoye and Grayson, 1971;Grayson and Oyebola, 1983;1985).…”

“…Studies on glucose uptake of the g.i.t. in dog have been confined mainly to the duodenum, upper jejunum (Durotoye and Grayson, 1971;1983;1985;Alada and Oyebola, 1996;1997) and the terminal ileum (Oyebola and Durosaiye, 1988). There has been no study on glucose uptake in the dog large intestine.…”