Acta physiol. scand. 1975. 93. 500-504 From the Department of Pharmacology, School of Medicine, Linkoping, Sweden
Effect of Alloxan-diabetes on the Metabolism of Rabbit Colon Smooth Muscle BY HANSJ. ARNQVIST Received 14 October 1974
Abstract ARNQVIST, H. J. Effect of alloxan-diabetes on the metabolism of rabbit colon smooth mrrscle. Acta physiol. scand. 1975. 93. 500-504. The metabolism of colon smooth muscle from normal and alloxan-diabetic rabbits was studied in virro. Glucose uptake, incorporation of glucose-'*C into glycogen and incorporation of leucine-14Ci n t o protein were determined. These three parameters were all depressed in diabetic smooth muscle incubated in a medium containing 5.6 mM glucose. Raising the glucose concentration in the medium to 22.2 mM almost doubled the glucose uptake both in diabetic and normal smooth muscle and at this glucose concentration no significant difference in this parameter was found. Insulin (0.1 U/ml) added in v i m ) stimulated glucose C glycogen and incorporation of leucine-"C into protein in diabetic uptake, incorporation of g l ~ c o s e - ~ *into colon smooth muscle. Insulin stimulated glucose uptake to the same degree in normal and diabetic colon and Ieucine-lT incorporation tended to be somewhat more smooth muscle, while its effect on glu~ose-'~C pronounced in diabetic colon muscle.
The metabolic activity of smooth muscle cells is probably of importance for the development of vascular diseases (Adams and Bayliss 1969, Wissler 1968, Wolinsky 1973). Since diabetes mellitus is associated with an increased frequency of disorders of the vascular system it is of interest to know how insulin and the diabetic state influence the metabolism of smooth muscle. In previous investigations (Arnqvist 1973 a, 1974) the effect of insulin on smooth muscle metabolism was studied in oitro in bovine mesenteric arteries and rabbit colon smooth muscle. Insulin stimulated glucose uptake, glycogen synthesis, amino acid transport and the incorporation of amino acid into protein in these preparations. In comparison with the corresponding effects in rat skeletal muscle the effects of insulin on the smooth muscle were weaker and appeared later. The effects on smooth muscle could only be demonstrated at insulin concentrations above the physiological range (Arnqvist 1971, 1974). Alloxan-diabetes has been reported to decrease the metabolism of glucose in rat and rabbit aorta (Wertheimer and Ben-Tor 1962, Urrutiaer al. 1962, Mulcahyand Winegrad 1962) and the incorporation of amino acid into protein in rat aorta (Ben-Tor and Wertheimer 1964). 500
DIABETES AND SMOOTH MUSCLE
50 1
In the present investigation the effect of diabetes on smooth muscle metabolism was &died in rabbit colon smooth muscle. Glucose uptake, glycogen synthesis and incorporation of amino acid into protein were determined and were found to be depressed in smooth muscle from alloxan-diabetic animals.
Material and Methods Animals. Male rabbits weighing 2-3 kg were used. In order to decrease the biological variation and make it possible to detect small differences in metabolism between normal and diabetic animals the rabbits were divided into pairs. Each pair consisted of siblings of the same weight, one of which was randomly chosen for alloxan treatment, while the other served as a control. Diabetes was induced by i.v. injection of alloxan monohydrate 125-150 mg/kg. Control animals were injected with saline. The rabbits were considered diabetic if random blood glucose determinations 2 weeks after alloxan administration showed values greater than 300 mg/100 ml. N o insulin treatment was given to the diabetic animals. Before the experiments the rabbits were starved for 20-24 h. Both rabbits in each pair were sacrificed o n the same day by a blow on the neck and colon smooth muscle was dissected out as previously described (Arnqvist 1973 b). The in oitro incubations of normal and diabetic smooth muscle were run in parallel. Incubation technique. The incubation procedure has been described in detail earlier (Arnqvist 1973 b). The tissue samples were incubated in 25 ml flasks containing 4 ml Krebs-Henseleit bicarbonate buffer and a gas phase of 95% 0,and 5 % CO,. For determination of glucose uptake 10 ml flasks containing 2.3 ml of the buffer were used. When added, the concentration of insulin (pork monocomponent insulin from Novo) in the medium was 0.1 U/ml. After the incubation period the tissue samples to be analyzed were frozen at - 80°C in Frigen (CFCI,) containing solid CO,. Analytical. The analytical methods were the same as used previously (Arnqvist 1973 a, 1974). In short, glucose was determined enzymatically by hexokinase and glucose-6-phosphate dehydrogenase (Slein 1962). The incorporation of g I u c o ~ e - ~into ~ C glycogen was measured after digestion of the tissue with KOH and precipitation of glycogen by ethanol. For determination of incorporation of leucine-"C into protein the tissue samples were homogenized in trichloroacetic acid and the precipitated protein was purified according to Arvill and A h r h (1967). The radioactivity of the glycogen and protein was counted in a liquid scintillation detector. Statistics. The significance of the effect was calculated from the differences between paired observations, using Students t-test.
Results The glucose uptake in rabbit colon smooth muscle was determined after an incubation period of 180 min in a medium containing 5.6 mM glucose with and without added insulin (0.1 U/ml). From Fig. 1 A it is seen that the glucose uptake was significantly lower (p < 0.001) in smooth muscle from alloxan-diabetic rabbits than in that from normal rabbits. Insulin moderately increased the glucose uptake in both normal and diabetic tissue (Fig. 1 A, Fig. 2). In the presence of insulin the glucose uptake was still significantly lower in the diabetic tissue. To test how variations of the glucose concentration in the medium influenced the glucose uptake of colon smooth muscle the glucose uptake was also determined at a glucose concentration of 22.2 mM in the incubation medium. Fig. 3 shows that raising the glucose concentration from 5.6 to 22.2 mM markedly increased the glucose uptake both in the diabetic and normal colon smooth muscle. At this glucose concentration no difference in glucose uptake was found between normal and diabetic smooth muscle. The incorporation of l4C-labelled glucose into glycogen was depressed in colon smooth muscle from diabetic rabbits when measured after incubation for 180 min in 5.6 mM
502
HANS J. ARNQVIST A. 40
0 CONTROL +
DIABETIC
+++
I I
30
I 20 10
0
1.5
1.0
Fig. I. Glucose uptake (A), incorporation of gIucose-lT into glycogen (B) and incorporation of I e ~ c i n e - ~into ~C protein (C) were determined in rabbit colon smooth muscle from normal and diabetic animals. All tissue samples were incubated for 180 min in a medium containing 5.6 mM glucose with and without added insulin (0.1 U/ml). Tracer amounts of g l ~ c o s e - ~were ~ C added when the gl~cose-'~C incorporation was measured. 0.01 mM leucine-14C was present i n the incubation medium in the experiments on leucine-I4C incorporation. The asterisks denote the significance of the differences between normal and diabetic colon muscle. * = p c: 0.05; **=pi-JO1; ***: piO.001. Vertical bars indicate one S.E. (n = 17 in Fig. 1 A; n = 12 in Fig. 1 B and C).
I
1
BASAL
+INSULIN
0 CONTROL 0
CONTROL DIABETIC
1
b
t
,
801
:putcaOksee
glucose-14~
ieucina-14~ incorporation
I incorporation
I
I
m-
c
"1
DIABETIC
40
5.6rnM glucose
I 22.2 mM glucose
Fig. 3 Fig. 2 Fig. 2. The effect of insulin on glucose uptake, gIucose-l4C incorporation and leucine-14C incorporation in normal and diabetic colon muscle, expressed in percent of the basal values. The figure is based on the data presented in Fig. 1. The asterisks denote the significance of the effect of insulin. Fig. 3. Effect of glucose concentration on glucose uptake in normal and diabetic rabbit colon smooth muscle. Glucose uptake was determined after incubation for 180 min in 5.6 mM o r 22.2 mM glucose. Vertical bars indicate one S.E. Significance is denoted as in Fig. 1 (n= 12).
DIABETES AND SMOOTH MUSCLE
503
g l u ~ o s e - ~(Fig. T 1 B). Addition of insulin stimulated the gIucoseJ4C incorporation in muscle from both diabetic and control animals. The effect of insulin was most pronounced on the diabetic colon muscle (Fig. 2). In the presence of insulin the glucose-14Cincorporation was not significantly lower in the diabetic muscle. The incorporation of I e u ~ i n e - ~into ~ C protein in colon smooth muscle was determined after an incubation time of 180 min in a medium containing 5.6 mM glucose and 0.01 mM leucine-W. From Fig. 1 C it is seen that the leucine-14C incorporation was decreased in diabetic smooth muscle. Insulin augmented the incorporation of leucine-14C in diabetic as well as in normal colon smooth muscle (Fig. 2) and when insulin was present the leucine incorporation was not significantly depressed in diabetic muscle.
Discussion The results of this investigation indicate that the metabolism of rabbit colon smooth muscle is influenced by alloxan-diabetes. Glucose uptake, incorporation of glucose into glycogen and incorporation of leucine into protein were all decreased in diabetic smooth muscle. Similar metabolic changes are caused by alloxan-diabetes in intima-media preparations from rat and rabbit aorta (see introduction) of which smooth muscle is a major cellular constituent. This suggests that diabetes affects the metabolism of vascular and intestinal smooth muscle. The glucose uptake in diabetic colon muscle was decreased in comparison with colon muscle from control animals when the glucose concentration of the incubation medium was 5.6 mM. Raising the glucose concentration of the incubation medium from 5.6 to 22.2 mM almost doubled the glucose uptake in diabetic smooth muscle. The glucose uptake was also augmented in normal smooth muscle, in agreement with earlier observations (Arnqvist 1973 b). At the glucose concentration of 22.2 mM the glucose uptake did not differ significantly between normal and diabetic tissue. The smooth muscle of the diabetic animal is exposed to an elevated blood glucose concentration in uivo and the glucose uptake of diabetic smooth muscle in uiuo may rather be elevated than depressed. In alloxan-diabetic rat aorta glucose uptake is stimulated by insulin (Wertheimer and Ben-Tor 1962) and in diabetic rabbit aorta the incorporation of glucose into glycogen and lipids is augmented by insulin (Mulcahy and Winegrad 1962). Mulcahy and Winegrad (1962) found no effect of insulin on glucose uptake in normal or diabetic rabbit aorta in uitro but the reduced glucose uptake in diabetic aorta could be restored by administration of insulin in uiuo. In this study insulin was found to stimulate glucose uptake, incorporation of glucose into glycogen and incorporation of leucine into protein in diabetic and normal rabbit colon smooth muscle. In the presence of insulin the glucose uptake was still slightly lower in diabetic than in normal colon muscle while the incorporation of glucose into glycogen and the incorporation of leucine into protein were not significantly depressed. Expressed as percentual increase the effect of insulin on glucose uptake was of similar magnitude in normal and diabetic colon muscle (Fig. 2) while the effects on glucose and leucine incorporation tended to be relatively larger in the diabetic muscle. This suggests that diabetic colon smooth muscle is at least as sensitive as normal colon smooth muscle to the action of insulin.
504
HANS J. ARNQVlST
The fact that insulin counteracted the metabolic changes produced by alloxan-diabetes suggests that they were caused by insulin deficiency. This interpretation must, however, be regarded with some caution as other hormones such as growth hormone and cortisone are known to be of importance for the metabolic changes in diabetes (Krahl 1961). Thus it cannot be excluded that the metabolic alterations in diabetic smooth muscle are secondary to the hormonal imbalance in the diabetic state and not a direct effect of insulin deficiency. The excellent technical assistance of Mrs Lena Burlin is gratefully acknowledged. Financial support was given by Nordisk lnsulinfond and by the Swedish Medical Research Council (14X-101).
References ADAMS,S. W. M. and 0. 9. BAVLISS, The relationship between diffuse intimal thickening, medial enzyme failure and intimal lipid deposition in various arteries. J . Atherosrler. Res. 1969.10. 327-339. ARNQVIST, H. J., Studies of monosaccharide permeability of arterial tissue and intestinal smooth muscle; effects of insulin. Acfa physiol. scand. 1971.83. 247-256. ARNQVIST, H. J., Effects of insulin on glucose metabolism in vascular and intestinal smooth muscle. Acta pharmacol. (Kbh.) 1973 a. 33. 459470. ARNQVIST, H. J., Effects of increasing glucose concentrations on the glucose metabolism in arterial tissue and intestinal smooth muscle. Acfa physiol. scand. 1973 b. 88. 481-490. ARNQVIST, H. J., Action of insulin on vascular and intestinal smooth muscle. Effects on amino acid transport, protein synthesis and the accumulation of glucose carbon. Acfa physiol. scand. 1974.90. 132-142. ARVILL, A. and K. AHREN,Effects of insulin on the intact levator ani muscle of the rat. 11. Relationship between the effects on amino acid transport, RNA synthesis and protein synthesis. Acfa endoer. (Kbh.) 1967.56. 295-307. BEN-TOR,V. and H. E. WERTHEIMER, Transport and incorporation of amino acids into the aortic wall: Influence of age and hormones. Angiologica 1964. 1. 41-48. KRAHL,M. E., Insulin and muscle. In The action of insulin on cells. Acad. Press New York 1961. 15-39. MULCAHY, P. D. and A. I. WINEGARD, Effects of insulin and alloxan diabetes on glucose metabolism in rabbit aortic tissue. Amer. J. fhysiol. 1962. 203. 1038-1042. SLEIN.M. W., D-glucose Bestimmung mit Hexokinase und Glucose-6-phosphate-Dehydrogenase. In Mefhoden der enzj,mafischen Analyse. (H. Bergmeyer ed.) Verlag Chemie 1962. 117-123. URRUTIA,B., D. W. BEAVAN and F. G. CAHILLJr., Metabolism of g1u~ose-U-C'~in rat aorta in vitroMetabolism 1962. 11. 530-534. H. E. and V. BEN-TOR,Influence of diabetes on carbohydrate metabolism of aortic tissue. WERTHEIMER, Diabetes 1962. I I. 422425. WISSLER, R. W., The arterial medial cell, smooth muscle or multifunctional mesenchyme? J. Atherosrler. Res. 1968.8.201-213. WOLINSKY, H., Mesenchymal response of the blood vessel wall. Circular. Res. 1973. 32. 543-549.
Effect of Alloxan-diabetes on the Metabolism of Rabbit Colon Smooth Muscle BY HANSJ. ARNQVIST Received 14 October 1974
Abstract ARNQVIST, H. J. Effect of alloxan-diabetes on the metabolism of rabbit colon smooth mrrscle. Acta physiol. scand. 1975. 93. 500-504. The metabolism of colon smooth muscle from normal and alloxan-diabetic rabbits was studied in virro. Glucose uptake, incorporation of glucose-'*C into glycogen and incorporation of leucine-14Ci n t o protein were determined. These three parameters were all depressed in diabetic smooth muscle incubated in a medium containing 5.6 mM glucose. Raising the glucose concentration in the medium to 22.2 mM almost doubled the glucose uptake both in diabetic and normal smooth muscle and at this glucose concentration no significant difference in this parameter was found. Insulin (0.1 U/ml) added in v i m ) stimulated glucose C glycogen and incorporation of leucine-"C into protein in diabetic uptake, incorporation of g l ~ c o s e - ~ *into colon smooth muscle. Insulin stimulated glucose uptake to the same degree in normal and diabetic colon and Ieucine-lT incorporation tended to be somewhat more smooth muscle, while its effect on glu~ose-'~C pronounced in diabetic colon muscle.
The metabolic activity of smooth muscle cells is probably of importance for the development of vascular diseases (Adams and Bayliss 1969, Wissler 1968, Wolinsky 1973). Since diabetes mellitus is associated with an increased frequency of disorders of the vascular system it is of interest to know how insulin and the diabetic state influence the metabolism of smooth muscle. In previous investigations (Arnqvist 1973 a, 1974) the effect of insulin on smooth muscle metabolism was studied in oitro in bovine mesenteric arteries and rabbit colon smooth muscle. Insulin stimulated glucose uptake, glycogen synthesis, amino acid transport and the incorporation of amino acid into protein in these preparations. In comparison with the corresponding effects in rat skeletal muscle the effects of insulin on the smooth muscle were weaker and appeared later. The effects on smooth muscle could only be demonstrated at insulin concentrations above the physiological range (Arnqvist 1971, 1974). Alloxan-diabetes has been reported to decrease the metabolism of glucose in rat and rabbit aorta (Wertheimer and Ben-Tor 1962, Urrutiaer al. 1962, Mulcahyand Winegrad 1962) and the incorporation of amino acid into protein in rat aorta (Ben-Tor and Wertheimer 1964). 500
DIABETES AND SMOOTH MUSCLE
50 1
In the present investigation the effect of diabetes on smooth muscle metabolism was &died in rabbit colon smooth muscle. Glucose uptake, glycogen synthesis and incorporation of amino acid into protein were determined and were found to be depressed in smooth muscle from alloxan-diabetic animals.
Material and Methods Animals. Male rabbits weighing 2-3 kg were used. In order to decrease the biological variation and make it possible to detect small differences in metabolism between normal and diabetic animals the rabbits were divided into pairs. Each pair consisted of siblings of the same weight, one of which was randomly chosen for alloxan treatment, while the other served as a control. Diabetes was induced by i.v. injection of alloxan monohydrate 125-150 mg/kg. Control animals were injected with saline. The rabbits were considered diabetic if random blood glucose determinations 2 weeks after alloxan administration showed values greater than 300 mg/100 ml. N o insulin treatment was given to the diabetic animals. Before the experiments the rabbits were starved for 20-24 h. Both rabbits in each pair were sacrificed o n the same day by a blow on the neck and colon smooth muscle was dissected out as previously described (Arnqvist 1973 b). The in oitro incubations of normal and diabetic smooth muscle were run in parallel. Incubation technique. The incubation procedure has been described in detail earlier (Arnqvist 1973 b). The tissue samples were incubated in 25 ml flasks containing 4 ml Krebs-Henseleit bicarbonate buffer and a gas phase of 95% 0,and 5 % CO,. For determination of glucose uptake 10 ml flasks containing 2.3 ml of the buffer were used. When added, the concentration of insulin (pork monocomponent insulin from Novo) in the medium was 0.1 U/ml. After the incubation period the tissue samples to be analyzed were frozen at - 80°C in Frigen (CFCI,) containing solid CO,. Analytical. The analytical methods were the same as used previously (Arnqvist 1973 a, 1974). In short, glucose was determined enzymatically by hexokinase and glucose-6-phosphate dehydrogenase (Slein 1962). The incorporation of g I u c o ~ e - ~into ~ C glycogen was measured after digestion of the tissue with KOH and precipitation of glycogen by ethanol. For determination of incorporation of leucine-"C into protein the tissue samples were homogenized in trichloroacetic acid and the precipitated protein was purified according to Arvill and A h r h (1967). The radioactivity of the glycogen and protein was counted in a liquid scintillation detector. Statistics. The significance of the effect was calculated from the differences between paired observations, using Students t-test.
Results The glucose uptake in rabbit colon smooth muscle was determined after an incubation period of 180 min in a medium containing 5.6 mM glucose with and without added insulin (0.1 U/ml). From Fig. 1 A it is seen that the glucose uptake was significantly lower (p < 0.001) in smooth muscle from alloxan-diabetic rabbits than in that from normal rabbits. Insulin moderately increased the glucose uptake in both normal and diabetic tissue (Fig. 1 A, Fig. 2). In the presence of insulin the glucose uptake was still significantly lower in the diabetic tissue. To test how variations of the glucose concentration in the medium influenced the glucose uptake of colon smooth muscle the glucose uptake was also determined at a glucose concentration of 22.2 mM in the incubation medium. Fig. 3 shows that raising the glucose concentration from 5.6 to 22.2 mM markedly increased the glucose uptake both in the diabetic and normal colon smooth muscle. At this glucose concentration no difference in glucose uptake was found between normal and diabetic smooth muscle. The incorporation of l4C-labelled glucose into glycogen was depressed in colon smooth muscle from diabetic rabbits when measured after incubation for 180 min in 5.6 mM
502
HANS J. ARNQVIST A. 40
0 CONTROL +
DIABETIC
+++
I I
30
I 20 10
0
1.5
1.0
Fig. I. Glucose uptake (A), incorporation of gIucose-lT into glycogen (B) and incorporation of I e ~ c i n e - ~into ~C protein (C) were determined in rabbit colon smooth muscle from normal and diabetic animals. All tissue samples were incubated for 180 min in a medium containing 5.6 mM glucose with and without added insulin (0.1 U/ml). Tracer amounts of g l ~ c o s e - ~were ~ C added when the gl~cose-'~C incorporation was measured. 0.01 mM leucine-14C was present i n the incubation medium in the experiments on leucine-I4C incorporation. The asterisks denote the significance of the differences between normal and diabetic colon muscle. * = p c: 0.05; **=pi-JO1; ***: piO.001. Vertical bars indicate one S.E. (n = 17 in Fig. 1 A; n = 12 in Fig. 1 B and C).
I
1
BASAL
+INSULIN
0 CONTROL 0
CONTROL DIABETIC
1
b
t
,
801
:putcaOksee
glucose-14~
ieucina-14~ incorporation
I incorporation
I
I
m-
c
"1
DIABETIC
40
5.6rnM glucose
I 22.2 mM glucose
Fig. 3 Fig. 2 Fig. 2. The effect of insulin on glucose uptake, gIucose-l4C incorporation and leucine-14C incorporation in normal and diabetic colon muscle, expressed in percent of the basal values. The figure is based on the data presented in Fig. 1. The asterisks denote the significance of the effect of insulin. Fig. 3. Effect of glucose concentration on glucose uptake in normal and diabetic rabbit colon smooth muscle. Glucose uptake was determined after incubation for 180 min in 5.6 mM o r 22.2 mM glucose. Vertical bars indicate one S.E. Significance is denoted as in Fig. 1 (n= 12).
DIABETES AND SMOOTH MUSCLE
503
g l u ~ o s e - ~(Fig. T 1 B). Addition of insulin stimulated the gIucoseJ4C incorporation in muscle from both diabetic and control animals. The effect of insulin was most pronounced on the diabetic colon muscle (Fig. 2). In the presence of insulin the glucose-14Cincorporation was not significantly lower in the diabetic muscle. The incorporation of I e u ~ i n e - ~into ~ C protein in colon smooth muscle was determined after an incubation time of 180 min in a medium containing 5.6 mM glucose and 0.01 mM leucine-W. From Fig. 1 C it is seen that the leucine-14C incorporation was decreased in diabetic smooth muscle. Insulin augmented the incorporation of leucine-14C in diabetic as well as in normal colon smooth muscle (Fig. 2) and when insulin was present the leucine incorporation was not significantly depressed in diabetic muscle.
Discussion The results of this investigation indicate that the metabolism of rabbit colon smooth muscle is influenced by alloxan-diabetes. Glucose uptake, incorporation of glucose into glycogen and incorporation of leucine into protein were all decreased in diabetic smooth muscle. Similar metabolic changes are caused by alloxan-diabetes in intima-media preparations from rat and rabbit aorta (see introduction) of which smooth muscle is a major cellular constituent. This suggests that diabetes affects the metabolism of vascular and intestinal smooth muscle. The glucose uptake in diabetic colon muscle was decreased in comparison with colon muscle from control animals when the glucose concentration of the incubation medium was 5.6 mM. Raising the glucose concentration of the incubation medium from 5.6 to 22.2 mM almost doubled the glucose uptake in diabetic smooth muscle. The glucose uptake was also augmented in normal smooth muscle, in agreement with earlier observations (Arnqvist 1973 b). At the glucose concentration of 22.2 mM the glucose uptake did not differ significantly between normal and diabetic tissue. The smooth muscle of the diabetic animal is exposed to an elevated blood glucose concentration in uivo and the glucose uptake of diabetic smooth muscle in uiuo may rather be elevated than depressed. In alloxan-diabetic rat aorta glucose uptake is stimulated by insulin (Wertheimer and Ben-Tor 1962) and in diabetic rabbit aorta the incorporation of glucose into glycogen and lipids is augmented by insulin (Mulcahy and Winegrad 1962). Mulcahy and Winegrad (1962) found no effect of insulin on glucose uptake in normal or diabetic rabbit aorta in uitro but the reduced glucose uptake in diabetic aorta could be restored by administration of insulin in uiuo. In this study insulin was found to stimulate glucose uptake, incorporation of glucose into glycogen and incorporation of leucine into protein in diabetic and normal rabbit colon smooth muscle. In the presence of insulin the glucose uptake was still slightly lower in diabetic than in normal colon muscle while the incorporation of glucose into glycogen and the incorporation of leucine into protein were not significantly depressed. Expressed as percentual increase the effect of insulin on glucose uptake was of similar magnitude in normal and diabetic colon muscle (Fig. 2) while the effects on glucose and leucine incorporation tended to be relatively larger in the diabetic muscle. This suggests that diabetic colon smooth muscle is at least as sensitive as normal colon smooth muscle to the action of insulin.
504
HANS J. ARNQVlST
The fact that insulin counteracted the metabolic changes produced by alloxan-diabetes suggests that they were caused by insulin deficiency. This interpretation must, however, be regarded with some caution as other hormones such as growth hormone and cortisone are known to be of importance for the metabolic changes in diabetes (Krahl 1961). Thus it cannot be excluded that the metabolic alterations in diabetic smooth muscle are secondary to the hormonal imbalance in the diabetic state and not a direct effect of insulin deficiency. The excellent technical assistance of Mrs Lena Burlin is gratefully acknowledged. Financial support was given by Nordisk lnsulinfond and by the Swedish Medical Research Council (14X-101).
References ADAMS,S. W. M. and 0. 9. BAVLISS, The relationship between diffuse intimal thickening, medial enzyme failure and intimal lipid deposition in various arteries. J . Atherosrler. Res. 1969.10. 327-339. ARNQVIST, H. J., Studies of monosaccharide permeability of arterial tissue and intestinal smooth muscle; effects of insulin. Acfa physiol. scand. 1971.83. 247-256. ARNQVIST, H. J., Effects of insulin on glucose metabolism in vascular and intestinal smooth muscle. Acta pharmacol. (Kbh.) 1973 a. 33. 459470. ARNQVIST, H. J., Effects of increasing glucose concentrations on the glucose metabolism in arterial tissue and intestinal smooth muscle. Acfa physiol. scand. 1973 b. 88. 481-490. ARNQVIST, H. J., Action of insulin on vascular and intestinal smooth muscle. Effects on amino acid transport, protein synthesis and the accumulation of glucose carbon. Acfa physiol. scand. 1974.90. 132-142. ARVILL, A. and K. AHREN,Effects of insulin on the intact levator ani muscle of the rat. 11. Relationship between the effects on amino acid transport, RNA synthesis and protein synthesis. Acfa endoer. (Kbh.) 1967.56. 295-307. BEN-TOR,V. and H. E. WERTHEIMER, Transport and incorporation of amino acids into the aortic wall: Influence of age and hormones. Angiologica 1964. 1. 41-48. KRAHL,M. E., Insulin and muscle. In The action of insulin on cells. Acad. Press New York 1961. 15-39. MULCAHY, P. D. and A. I. WINEGARD, Effects of insulin and alloxan diabetes on glucose metabolism in rabbit aortic tissue. Amer. J. fhysiol. 1962. 203. 1038-1042. SLEIN.M. W., D-glucose Bestimmung mit Hexokinase und Glucose-6-phosphate-Dehydrogenase. In Mefhoden der enzj,mafischen Analyse. (H. Bergmeyer ed.) Verlag Chemie 1962. 117-123. URRUTIA,B., D. W. BEAVAN and F. G. CAHILLJr., Metabolism of g1u~ose-U-C'~in rat aorta in vitroMetabolism 1962. 11. 530-534. H. E. and V. BEN-TOR,Influence of diabetes on carbohydrate metabolism of aortic tissue. WERTHEIMER, Diabetes 1962. I I. 422425. WISSLER, R. W., The arterial medial cell, smooth muscle or multifunctional mesenchyme? J. Atherosrler. Res. 1968.8.201-213. WOLINSKY, H., Mesenchymal response of the blood vessel wall. Circular. Res. 1973. 32. 543-549.
