Metabolic Fate of the Glucose Taken up by the Intestine During Induced Hyperglycaemia in Dogs.

Available data showed that the intestine increases it glucose uptake in response to hyperglycemia induced by anycause. However, what the intestine does with the glucose is not known. This study investigated the metabolic fate of theglucose taken up by the intestine during hyperglycaemia in dogs. Experiments were carried out on fasted, male, anaesthetizedmongrel dogs divided into 4 groups. The control (group 1, n=5) received normal saline (0.2 ml/kg) while groups 2-4(subdivided into two as low or high dose, n=5 each) received adrenaline (1 µg/kg or 5 µg/kg), glucagon (3 ng/kg or 8 ng/kg)and glucose (10 mg/kg/min or 20 mg/kg/min). Through a midline laparatomy, the upper jejunum was cannulated for IntestinalBlood Flow (IBF) measurement. Blood glucose and lactate levels were determined using glucose oxidase and lactatedehydrogenase methods, respectively. Intestinal Glucose/Lactate Uptake (IGU/ILU) was calculated as the product of IBFand arterio-venous glucose /lactate difference [(A-V) glucose/lactate]. Jejunal tissue samples were obtained for the determinationof Glycogen Content (GC) and activities of Glycogen Synthase (GS), Glycogen Phosphorylase 'a' (GPa), hexokinase andglucose-6-phosphatase. Anthrone method was used to determine GC while activities of GS, GPa, hexokinase and glucose-6-phosphatase were determined spectrophotometrically. Data were subjected to descriptive statistics and analyzed usingstudent's t-test and ANOVA at α0.05. Arterial and venous blood glucose and lactate were increased by adrenaline, glucagonand glucose. Venous lactate was higher than arterial lactate in all groups. Intestinal blood flow, (A-V) glucose and (A-V)lactate were increased in all the experimental groups. Intestinal glucose uptake increased by 624% (adrenaline), 705%(glucagon) and 589% (glucose) while intestinal lactate release increased by 422%, 459% and 272% respectively. IntestinalGC increased from 138.72 ± 4.58 mg/100 g to 167.17 ± 4.20 mg/100 g (adrenaline), 229.21 ± 6.25 mg/100 g (glucagon) and165.17 ± 4.20 mg/100 g (glucose). Adrenaline and glucose had no effect on GS activity but it was increased by glucagon;GPa was decreased while hexokinase activity was increased by adrenaline, glucagon, and glucose. Glucose-6-phosphataseactivity was not affected by adrenaline and glucagon but decreased by glucose. The intestine modulates blood glucose levelsthrough lactate formation, glycogen formation and most probably conversion of lactate to glucose through gluconeogenesis.

Intestinal glucose uptake responses to infusion of glucose, fructose and galactose in dogs Intestinal glucose uptake responses to infusion of glucose, fructose and galactose in dogs.

The present study was designed to investigate the effects of intravanous (i.v) infusion of fructose, galactose and glucose on canine IGU during postprandial state. Experiments were carried out on fasted, male, anaesthethized adult mongrel dogs divided into four groups with 5 dogs per group. Each of the groups was given i.v infusion of normal saline, fructose (0.15, 0.55 and 1.1mg/dl/min), galactose (0.15, 0.55 and 1.1mg/dl/min) and glucose (0.15, 0.55 and 1.1mg/dl/min) respectively. Through a midline laparatomy, the upper jejunum was secured and cannulated for blood flow measurement. Blood samples were obtained for measurement of glucose content of arterial and venous blood from the upper jejunal segment. The blood glucose was determined by glucose oxidase method and intestinal glucose uptake was calculated as the product of jejunal blood flow and arterio-venous glucose difference. Values are means ± S.E.M, compared by ANOVA and Student t-test. Fructose, galactose and glucose significantly increased arterial blood glucose from 97.60 ± 1.78 mg/dl to 114.20 ± 1.88, 109.80 ± 1.43, and 141.20 ± 5.65 mg/dl, respectively. Glucose also significantly increased jejunal blood flow from 10.0 ± 0.32 ml/min to 14.40 ± 0.93 ml/min, however, fructose and galactose did not produce any significant effect on intestinal blood flow. IGU increased by 600%, 350%, and 700% in response to fructose, galactose and glucose respectively. There is no correlation between the increase in blood glucose levels induced by each of the sugars and its corresponding rise in IGU. The data suggest that the intestine responds to fructose and galactose in a similar manner as glucose probably through similar mechanism.

Role of Adrenergic Receptors in Glucose, Fructose and Galactose-Induced Increases in Intestinal Glucose Uptake in Dogs.

The study investigated the role of adrenergic receptors in glucose, fructose-, and galactose- induced increases in intestinal glucose uptake. Experiments were carried out on fasted male anaesthetized Nigerian local dogs divided into seven groups (with five dogs per group). Group I dogs were administered normal saline and served as control. Dogs in groups II, III and IV were intravenously infused with glucose (1.1 mg/kg/min), fructose (1.1 mg/kg/min) and galactose (1.1 mg/kg/min) respectively. Another three groups, V, VI and VII were pretreated with prazosin (0.2mg/kg), propranolol (0.5mg/kg) or a combination of prazosin (0.2mg/kg) and propranolol (0.5mg/kg) followed by glucose infusion, frutose infusion or galactose infusion respectively. Through a midline laparatomy, the upper jejunum was cannulated for blood flow measurement and blood samples were obtained for measurement of glucose content of the arterial blood and venous blood from the upper jejunal segment. Glucose uptake was calculated as the product of jejunal blood flow and the difference between arterial and venous glucose levels (A-V glucose). The results showed that pretreatment of the animal with prazosin had no effect on glucose and galactose induced increases in glucose uptake. However, pretreatment with propranolol completely abolished glucose, fructose and galactose-induced increases in intestinal glucose uptake. Prazosin also significantly reduced galactose-induced increase in intestinal glucose uptake. The results suggest that the increases in intestinal glucose uptake induced by glucose and fructose are mediated mostly by beta adrenergic receptors while that of galactose is mediated by both alpha and beta adrenergic receptors.

Effect of adrenaline on glucose uptake in the rabbit small intestine.

OBJECTIVES: Previous study had shown that nicotine acts on blood glucose through release of adrenaline. While there are reports on the hyperglyceic effect of adrenaline in rabbits, there is no information on the effect of adrenaline on intestinal glucose uptake of rabbits. The present study was carried out to find out if adrenaline has any effect on glucose uptake in the rabbit small intestine. MATERIALS AND METHODS: Experiments were carried out on fasted anaesthetized male rabbits. Five groups of rabbits (6 rabbits per group) were studied. A vein draining a segment of the upper jejunum was cannulated for blood flow and venous glucose measurements. The left femoral artery and vein were cannulated for arterial blood sampling and drug infusion respectively. Glucose uptake was calculated as a product of jejunal blood flow and the glucose difference between arterial (A) and venous (V) blood. RESULTS: The fasting venous blood glucose levels were 151.8 +/- 4.4mg/dl and 164.0 + 2.3mg/dl in Groups I and V that were not given adrenoceptor blockers. The upper jejunum had a resting (or basal) glucose uptake of 38.3 +/- 1.6mg/min in the control group. When adrenaline (2ug/kg) was injected intravenously, arterial blood glucose rose from a basal value of 245.5 +/- 4.6mg/dl to 307.5+4.7mg/dl at the peak of response while venous glucose rose from 151.8+4.4mg/dl to 275.8 +/- 4.2mg/dl at the peak of response. Glucose uptake increased to 107.4 +/- 2.5mg/ min at the peak of response. The hyperglycaemic response to adrenaline injection was abolished by propranolol but not by prazosin indicating that this effect of adrenaline is mediated through beta adrenoceptor. Both prazosin and propranolol reduced considerably adrenaline-induced increase in blood flow and glucose uptake, prazosin being more potent in flow reduction. CONCLUSION: This study showed that the resting small intestine of rabbits took up large amounts of glucose. The intestinal glucose uptake was markedly increased by adrenaline injection. The response to adrenaline was mediated through alpha and beta adrenoceptors. The responses to adrenaline are different in many respects from those induced by nicotine in rabbits in our earlier study. The reason for the differences is obscure.

Effect of nicotine on glucose uptake in the rabbit small intestine.

A technique for measuring glucose uptake in the small intestine of rabbits was developed. Using this technique, the glucose uptake in the resting jejunum of rabbits and the effect of nicotine infusion on glucose uptake were studied. Experiments were carried out on fasted anaesthetized male rabbits. Four groups of rabbits (6 per group) were studied. A vein draining segment of the upper jejunum was cannulated for blood flow and venous glucose measurements. The left femoral artery and vein were cannulated for arterial blood sampling and drug infusion respectively. Glucose uptake was calculated as a product of jejunal blood flow and the (A-V) glucose difference. The fasting blood glucose levels were 101.0 +/- 8.4 mg/dl and 127.0 +/- 11.3 mg/dl before and after anaesthesia respectively. Basal blood glucose was much higher than this following surgery. The upper jejunum had a resting glucose uptake of 24.1 +/- 7.0 mg/min. When nicotine (50 ug/kg) was infused intravenously, blood glucose rose from a basal value of 253.8 +/- 9.5 mg/dl to 379.8 +/- 20.3 mg/dl at the peak of response. Glucose uptake increased to 73.1 +/- 11.3 mg/min at the peak of response. These effects of nicotine are mediated through both beta and alpha adrenoceptors. Comparison with previous studies in dogs and rats showed that different adrenoceptors are involved in nicotine hyperglycaemia in fasted dogs, rats and rabbits.

Intestinal glucose uptake in normal, untreated and insulin-treated diabetic dogs.

The study was carried out on fasted, anaesthetized diabetic and non-diabetic dogs. Diabetes was induced by i.v injection of alloxan (60 mg/kg). A vein draining a segment of the upper jejunum was cannulated for blood flow measurements, and blood samples were obtained for determination of glucose content of arterial and venous blood. Glucose uptake was calculated as the product of jejunal blood flow and arterio-venous glucose difference ((A-V) glucose. The results showed that following induction of diabetes, there were significant increases in jejunal blood flow, (A-V) glucose and jejunal glucose uptake when compared with non-diabetic dogs. For instance, the glucose uptake increased from 23.10+/-2.34 to 178.40+/-6.93 mg/min. When the diabetic dog was challenged with different doses of insulin (2.5, 5.0, 7.5, 10.0 iu/kg), the blood glucose levels and the intestinal glucose uptake decreased in a dose-dependent manner. In normal dogs, insulin administration caused negative glucose uptake at the lower dose (5.0 iu/ kg) while at the higher dose, 8.0 iu/kg, insulin caused just a transient negative glucose uptake. From the results, it was concluded that the small intestine increased its glucose uptake in response to the hyperglycemia in alloxan-induced diabetes and when the blood glucose was reduced with insulin the intestine also reduced its glucose uptake accordingly. The result of insulin administration in normal dogs suggests that glucose uptake by the gut cannot be explained on the basis of blood glucose concentration alone.

A comparative study of students' performance in preclinical physiology assessed by multiple choice and short essay questions.

This study was designed to compare the performance of medical students in physiology when assessed by multiple choice questions (MCQs) and short essay questions (SEQs). The study also examined the influence of factors such as age, sex, O/level grades and JAMB scores on performance in the MCQs and SEQs. A structured questionnaire was administered to 264 medical students' four months before the Part I MBBS examination. Apart from personal data of each student, the questionnaire sought information on the JAMB scores and GCE O' Level grades of each student in English Language, Biology, Chemistry, Physics and Mathematics. The physiology syllabus was divided into five parts and the students were administered separate examinations (tests) on each part. Each test consisted of MCQs and SEQs. The performance in MCQs and SEQs were compared. Also, the effects of JAMB scores and GCE O/level grades on the performance in both the MCQs and SEQs were assessed. The results showed that the students performed better in all MCQ tests than in the SEQs. JAMB scores and O' level English Language grade had no significant effect on students' performance in MCQs and SEQs. However O' level grades in Biology, Chemistry, Physics and Mathematics had significant effects on performance in MCQs and SEQs. Inadequate knowledge of physiology and inability to present information in a logical sequence are believed to be major factors contributing to the poorer performance in the SEQs compared with MCQs. In view of the finding of significant association between performance in MCQs and SEQs and GCE O/level grades in science subjects and mathematics, it was recommended that both JAMB results and the GCE results in the four O/level subjects above may be considered when selecting candidates for admission into the medical schools.

Preference of preclinical medical students for medical specialties and the basic medical sciences.

A structured questionnaire was administered to 346 medical and dental students who were about to take the Part I MBBS/BDS degree examination. Apart from personal data of each student, the questionnaire sought information on their post-graduation career preferences in ten medical specialties, lectureship in anatomy, physiology or biochemistry, career in the armed forces, politics or business. They were required to give reasons for their choices. The results showed that 89.6% of the students were aged 19 to 24 years and 94.8% were admitted via concessional entry. Forty-one percent of the students preferred surgery, while 15%, 11% and 7.8% chose careers in obstetrics and gynaecology, paediatrics and internal medicine respectively. The specialties of radiology, anaesthesia, psychiatry, pathology, community medicine and general practice were unattractive to most students. Only 1.5% of the students wanted to become lecturers in anatomy and physiology while none wanted to lecture in biochemistry. Choice of career in the armed forces, politics and business was low. Nine students (2.6%) wanted to be pastors/missionary doctors. The main reasons for the choices are personal interest (73.7) and better financial reward 11.8%. Sex had a significant effect on choices. The results were discussed and their implications were highlighted. Suggestions on how to solve the problems identified were made.

Effects of glucagon, glucose, adrenaline and insulin infusion on blood glucose level in the common African toad (bufo regularis).

Male toads, weighing 70-123 g, were divided into 13 groups with 8 toad in each group. Animals in each group were fasted overnight before the experiments. Toads in groups 1 to 4 were infused for 30 minutes with adrenaline, 5 ugkg-1 min-1, glucose, 5.5 mg kg-1 min-1; glucagon 2 ugkg-1 min-1; and insulin 2000 uU kg-1 min-1, respectively. Blood samples for blood glucose measurement were taken before, during and after each infusion. The experiment was repeated in groups 5 and 6 using 3.5 mg kg-1 min-1 and 7.5 mg kg-1 min-1 of glucose respectively. Toads in groups 7 to 9 were pretreated with prazosin, 0.2 mg/kg and those in groups 10 to 12 were pretreated with propranolol, 0.5 mg/kg. After pretreatment, glucose, glucagon and insulin infusions were repeated in the alpha-blocked and beta-blocked toads, respectively. Group 13 was infused with 0.7% saline and served as the control. The results showed that infusions of adrenaline, glucose and glucagon resulted in significant hyperglycaemia while insulin caused hypoglycaemia. The hyperglycaemic response to glucose was dose-dependent. The experiments using blockers showed that the glycaemic effects of glucagon and insulin are mediated via beta adrenoceptors, that for glucose is via alpha adrenoceptors and from an earlier study, the glycaemic response of adrenaline is through both alpha and beta adrenoceptors.

The role of adrenergic receptors in the increased glucose uptake by the canine gut.

The study was carried out on fasted anaesthetized dogs. A vein draining a segment of the upper jejunum was cannulated for blood flow measurement. Arterial blood and venous blood from the upper jejunal segment, were obtained for measurement of glucose content. Glucose uptake was calculated as the product of jejunal blood flow and the difference between arterial and venous glucose levels. Prazosin, (0.2 mg/kg) had no effect on the glucose uptake induced by insulin and glucagon injections and glucose infusion. However, prazosin reduced the glucose uptake by about 50% during adrenaline-induced hyperglycaemia. Pretreatment of the animal with propranolol (0.5 mg/kg) significantly reduced the increased glucose uptake caused by adrenaline, glucagon and glucose hyperglycaemia. Propranolol also reduced by half the negative glucose uptake during insulin-hypoglycaemia. Since both the alpha and beta adrenergic receptor blocking agents did not abolish the induced glucose uptake, it was concluded that the effects of adrenaline, glucagon, glucose and insulin on intestinal glucose uptake are mediated in part by beta adrenergic receptors.

Evidence that the gastrointestinal tract is involved in glucose homeostasis.

Experiments were carried out on fasted anaesthetized dogs. A vein draining a segment of the upper jejunum was cannulated for blood flow measurement and blood samples were obtained for measurement of glucose content of the arterial blood and venous blood from the upper jejunal segment. Glucose uptake was calculated as the product of jejunal blood flow and the difference between arterial and venous glucose levels (A-V glucose). Blood pressure was recorded continuously. The upper jejunum had a resting glucose uptake of 16 +/- 28 mg/min. When adrenaline (1 microgram/kg or 5 micrograms/kg) injection, glucagon (3 micrograms/kg or 8 micrograms/kg) injection or glucose (10 mg/kg/min or 20 mg/kg/min) infusion was given intravenously, glucose uptake increased 600-700%, 700-900%, and 560-600%, respectively at the peak of their responses. These increases in glucose uptake were much greater than increases in blood flow at the peak of responses to adrenaline, glucagon or glucose. Insulin (5 i.mu/kg or 8 i.mu/kg) injection, however, caused a negative glucose uptake of about 400%, i.e., the gut pushed glucose into the blood stream in response to insulin-induced hypoglycaemia. These results indicate that the jejunum plays a modulatory role in glucose homeostasis.

Electrolyte loss during exercise in apparently healthy Nigerians.

Treadmill exercise was performed and electrolyte loss estimated in apparently healthy young adult males. Subjects walked at four mph for 20 minutes at 28.9 +/- 0.2 degrees C (SEM) ambient temperature and 75.3 pc relative humidity. Gradient was incrementally increased from 0 degrees to 4 degrees (0 pc-7 pc) during the 20 minutes. Mean concentrations of sodium, potassium, and chloride in the sweat were 67 +/- 0.1 meg/litre (SEM), 4.3 +/- 0.1 meg/litre (SEM) and 55 +/- 0.9 meg/litre (SEM) respectively. The electrolyte concentration was significantly related to work load and body surface area (p < 0.001). The results indicate that the quantity of electrolytes lost in the sweat of Nigerian males during exercise is close to those of Caucasians under similar conditions.

Effects of adrenergic receptor blockers on adrenaline and nicotine-induced hyperglycaemia in the rat.

Studies in fasted, anaesthetized rats have shown that adrenaline and nicotine-induced hyperglycaemia is mediated via activation of beta-adrenoceptors. The hyperglycaemic response to nicotine is different from that of adrenaline in that, unlike adrenaline hyperglycaemia, nicotine hyperglycaemia is characterized by a long latent period, delayed attainment of peak of response and sustained hyperglycaemia throughout the 120 minutes post-injection observation. Comparison with previous studies in dogs showed that different receptors are involved in nicotine hyperglycaemia in fasted dogs and fasted rats.

Effects of adrenoceptor blockers on the cardiorespiratory response to nicotine in rats.

Three groups of anaesthetized rats, consisting of 8 rats per group, were studied. Group 1 was the control and received intravenous injection of nicotine, 50 micrograms/kg, only. Groups II and III were pretreated with propranolol, 0.5mg/kg and prazosin, 1mg/kg respectively before 50 micrograms/kg of nicotine was injected i.v. Blood pressure, heart rate, respiratory rate and amplitude of respiratory excursion were monitored continuously before and for 1 hr after the injections. Index of Pulmonary Ventilation Rate was computed as a product of amplitude of respiratory excursion and respiratory rate. The results showed that nicotine caused an initial fall in blood pressure followed by a rise. The initial fall in blood pressure was abolished by prazosin, while propranolol abolished the pressor response. Nicotine had no effect on heart rate in the three groups. Nicotine caused an increase in respiratory rate and this effect was abolished by prazosin. Nicotine also caused an initial increase in pulmonary ventilation which was due mainly to increase in respiratory rate. It was concluded that nicotine exerts most of its cardiorespiratory effect via stimulation of alpha and beta adrenoceptors.

Factors influencing academic achievement of medical students in the basic medical sciences.

A structured questionnaire was administered to 236 medical and dental students who had just finished the Part I M.B.B.S./B.D.S. degree examination. Apart from personal data of each student, the questionnaire sought information on issues that may affect the student's learning of Anatomy, Biochemistry and Physiology. The scores of all the students in their continuous assessment tests and the finals of the Part I M.B.B.S./B.D.S. examinations in the three subjects were recorded. The results showed that age, repeating the year, performance in continuous assessment tests, having one, seven or eight 'A' grades in the Ordinary Level (O/L) examination significantly affected the overall performance of the students. On the other hand, likeness for a particular subject, mode of entry of the student whether direct or concessional, types of books read, time spent on each subject, having between two and six 'A' grades in O/L, access to hostel accommodation, adequacy or otherwise of financial support and the student's rating of his/her state of health did not significantly influence the performance of the students. The students gained most from lectures while tutorials were rated as being more helpful than practical classes. Multiple choice questions (MCQs) is the preferred mode of assessment. The possible explanation for these findings and their implications for medical education are discussed.

Effects of cows' urine concoction with and without tobacco leaves on plasma glucose concentration in fasted rats.

The effects of a full preparation (FP) and a modified preparation (MP) of cows' urine concoction (CUC) on the level of plasma glucose in fasted male Wistar rats were investigated. The results showed that FP caused significant hyperglycaemia; while the MP and a control injection using 0.9% saline had no effect on plasma glucose. Hexamethonium, prazosin, propranolol and combined prazosin and propranolol did not abolish the hyperglycaemic response to FP. The mechanism of the hyperglcaemic response to FP and the reason why MP did not produce hypoglycaemia are obscure. The result of this study did not agree with the findings of CUC-induced hypoglycaemia reported by earlier workers.

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

Resting blood flow, arterio-venous glucose and oxygen (A-V)O2 differences, glucose uptake and oxygen consumption by a segment of the upper jejunum were measured in anaesthetized dogs. Systemic arterial pressure was also measured. The effect of nicotine infusion (25 micrograms kg-1 i.v., over 10 min) on these measurements was recorded in untreated dogs, in dogs treated with propranolol (0.5 mg kg-1) to produce beta-adrenoceptor blockade and in dogs after alpha 1-adrenoceptor blockade with prazosin (0.2 mg kg-1). 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 beta-blocked animals. Vascular resistance was reduced during nicotine infusion and the decrease persisted post infusion in the beta-blocked group. In the untreated group (A-V)O2 was significantly reduced during the first 5 min of nicotine infusion, thereafter it returned to control levels, then rose significantly above control level, post infusion. beta-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. Nicotine caused significant hyperglycaemia during and for about 1 h after infusion. Tissue release of glucose was occasionally observed following the infusion. beta-Adrenoceptor blockade reduced the hyperglycaemia caused by nicotine. beta-Blockade alone increased uptake and nicotine caused a further three to four fold increase. Prazosin abolished the effects that were observed in the untreated and the alpha-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 beta-adrenoceptors. The responses are not related to oxygen utilization.

Effect of adrenergic receptor blockers on the cardio-respiratory response to cow's urine concoction in rats.

The influence of alpha and beta adrenoceptor blockers on the cardio-respiratory effects of cow's urine concoction (CUC) in rats was studied. The study showed that phenoxybenzamine abolished the pressor response observed in the untreated animal while propranolol had no effect on blood pressure response. The alpha-blocked animals also developed significant post-injection hypotension. Electrocardiographic abnormalities seen in the control group were ameliorated by beta-blockers but alpha-blockers had no such effect. CUC caused an initial depression of respiration with short apnoeic phases and an increase in pulmonary ventilation. The latter was significantly decreased by alpha and beta adrenoceptor blockers. It was concluded that adrenoceptors play an important role in the cardio-respiratory effects of CUC.