Search

The action of insulin (0.1 U/ml) on the metabolism of human intestinal smooth muscle was studied in vitro. The experiments were performed on the muscle layer of human jujunum obtained from patients undergoing intestinal shunt operations because of obesity. Insulin significantly increased glucose uptake, glycogen content, the membrane transport of alpha-amino-isobutyric acid (AIB), the incorporation of leucine into protein and tended to increase the membrane transport of the nonutilizable model monosaccharide 3-0-methylglucose. The effects of insulin were moderate and appeared after incubation times of 120 to 180 min.

The incorporation of leucine-14C into protein in bovine mesenteric arteries was augmented by cyclic GMP (10-3 M) and decreased by cyclic AMP (10-3 M). There was no effect of 5'AMP (10-3 M). The phosphodiesterase inhibiting drugs theophylline (10-3 M) and papaverine (5 x 10-5 g/ml) both decreased the leucine-14C incorporation.

The influence of elevated substrates (glucose, beta-hydroxybutyrate and palmitate) on the gated. The oxidation of 14C-glucose to 14CO2 was depressed in diabetic aorta at a glucose concentration of 5.6 mM in the incubation medium. The glucose oxidation in normal and mM. The oxidation of 14C-beta-hydroxybutyrate (0.5 and 1.5 mM) to 14CO2 was impaired in diabetic aorta, while the oxidation of 14C-palmitate (0.5 and 1.0 mM) to 14CO2 was unaltered. The oxidation of both substrates was concentration dependent. The glucose oxidation in normal rat aorta was reduced by addition of 3.0 and 6.0 mM of beta-hydroxybutyrate to the incubation medium, while 1.5 mM palmitate had no effect on the glucose oxidation. After incubation of normal rat aorta in MEM with glucose (20.0 mM) for 46 h the subsequently determined glucose oxidation was not influenced in comparison to the aorta incubated in 5.6 mM glucose. Incubation with 6.0 mM beta-hydroxybutyrate or 1.5 mM palmitate did not affect the aortic glucose oxidation. In rats which were infused for 24 h with glucose or beta-hydroxybutyrate to obtain diabetic levels of these substrates, there was no change in the aortic glucose oxidation compared to saline-infused controls. The present results suggests that the lowered glucose oxidation in diabetic vascular tissue is not caused by hyperglycemia or high concentrations of ketone bodies or free fatty acids in the diabetic state.

The incorporation of 14C-labelled leucine or phenylalanine into alkali-soluble protein was determined under in vitro conditions in aortic intima-media of normal and streptozotocin-diabetic rats. Two weeks after the induction of diabetes the incorporation of the amino acids into aortic protein was reduced. When determined after diabetes of one week's duration the leucine-14C incorporation was not significantly reduced, while after 5 weeks of diabetes it was severely impaired. After administration of insulin to diabetic rats in vivo for 2 weeks there was no difference in leucine-14C incorporation between normal and diabetic rats. Addition of insulin (0.1 U/ml) in vitro had no effect on the leucine-14C incorporation in either normal or diabetic aorta during incubation times of 3 or 6 h. Elevation of the glucose concentration in vitro from 5.6 to 22.2 mmol/l did not influence the leucine incorporation in diabetic aorta. Both the aortic wet weight and the aortic content of alkali-soluble protein were decreased after 5 weeks of diabetes. The decrease in the protein content of aorta of diabetic animals suggest that the protein synthesis is impaired in vivo.

Binding of IGF-I to plasma membranes from bovine mesenteric arteries was studied. The maximal specific binding of IGF-I was found to be 7.4 +/- 1.7% of total 125I-IGF-I added to the incubation medium. Unlabelled IGF-I displaced 125I-IGF-I with an IC50 value of 0.5 nmol/l and a maximal displacement of 64.2 +/- 2.8% of total binding. The potency of insulin to displace 125I-IGF-I was 100-1000-fold lower. Cross-linking of 125I-IGF-I to the receptor with disuccinimidyl suberate, followed by SDS-polyacrylamide gel electrophoresis under reducing conditions showed an IGF-I binding protein with a molecular weight of 146,000 Dalton. In summary, we have shown the presence of receptors for IGF-I in plasma membranes isolated from macrovessels. The binding characteristics and the size of the binding unit were found to be similar to those of the IGF-I receptor found in cultured vascular smooth muscle cells. Furthermore, insulin at high concentrations was found to interact with the IGF-I receptor.

24 h profiles of free insulin and glucose were determined in insulin-dependent diabetic patients on intensive insulin regimens with biosynthetic human insulin, either as continuous subcutaneous insulin infusion (CSII) with mealtime bolus doses (n = 6), or intensified conventional insulin therapy (ICIT) with preprandial injections of regular insulin and intermediate-acting insulin at bedtime (n = 6). The free insulin profiles were similar to the normal profiles but there were some important differences: CSII gave hyperinsulinaemia at daytime compared to normal people (p less than 0.05) and also to ICIT (p less than 0.005); ICIT but not CSII gave hyperinsulinaemia at midnight (p less than 0.05) whereas fasting free insulin was too-low to keep blood glucose normal; the insulin peaks after the bolus doses were retarded with a maximum after 30-90 min and a return to the basal level after 5-7 h (ICIT) or 8-9 h (CSII). The height of the insulin peaks were of similar magnitude at all meals and did not differ significantly between ICIT, CSII, and normal people. Time-to-peak was dependent on the injection level. We conclude, that intensive regimens with biosynthetic hum insulin do not give normoinsulinaemia but insulin profiles that resemble physiology. Biosynthetic human NPH insulin may be rather short-acting for overnight glucose control. The interval that should be recommended between preprandial insulin dose and meal may vary depending on the preinjection insulin level.

The influence of diabetes on the oxidation of exogenous glucose, pyruvate, beta-hydroxybutyrate and palmitate was studied in rat aorta. Diabetes was induced by streptozotocin (65 mg/kg). The metabolic processes were measured during incubation in vitro for 90-180 min. After a diabetes duration of two weeks the oxidation of glucose, pyruvate and beta-hydroxybutyrate was lowered while the oxidation of palmitate was unaffected. The effect of diabetes on glucose oxidation appeared after 24 h and was more pronounced after 48 and 96 h. The lowered glucose oxidation in diabetic aorta was still present after incubation of rat aorta in organ culture for 48 h. Insulin treatment increased the glucose oxidation in diabetic aorta after 24 h and after 48 h the glucose oxidation in diabetic aorta was markedly increased. Incubation of diabetic aorta in organ culture for 48 h with insulin added to the incubation medium did not increase its glucose oxidation. Pretreatment of rats with diazepam and phentolamine before sacrifice, did not influence glucose oxidation or lactate production in vitro. Addition of albumin to the incubation medium slightly increased glucose oxidation but did not affect lactate production. The alternations in substrate oxidation in diabetic rat aorta found in this study are qualitatively similar to those found in diabetic striated muscle.

The oxidation of 14C-labelled glucose, beta-hydroxybutyrate and palmitate to CO2 and the incorporation of 14C-labelled amino acid into alkali-soluble protein were studied in aorta from fed and fasted male Sprague-Dawley rats, weighting about 200 g. Substrate oxidation and amino acid incorporation were measured during incubation of rat aorta in vitro for 2-3 h. After fasting for 6 h there was a slight but significant increase in the plasma concentration of beta-hydroxybutyrate. Blood glucose was lowered after 12 h while an increase in the plasma concentration of free fatty acids was found after 24 h. A decrease in the oxidation of glucose in rat aorta was found after fasting for 12 h and with prolonged fasting a further decrease in the aortic glucose oxidation was found. After fasting for 4 days the oxidation of beta-hydroxybutyrate and the incorporation of 14C-leucine and 14C-phenylalanine into protein were reduced in rat aorta while the oxidation of palmitate was not altered. The effects of fasting on substrate oxidation and amino acid incorporation in rat aorta, found in this study are similar to the known effects of diabetes on vascular metabolism.

Glucose metabolism is depressed in aortic intima-media of fasted and diabetic rats. The aim of this study was to elucidate the influence of diabetic and fasted plasma on glucose oxidation in rat aorta. Male Sprague-Dawley rats weighing about 200 g were used. Diabetes was induced by streptozotocin (65 mg/kg) and the rats were used after a diabetes duration of two weeks. Fasted rats were used after food deprivation for 3 days. Aortic intima-media was preincubated in plasma for 120 or 240 min. During a further incubation for 2 hours in Krebs-Henseleit bicarbonate buffer the oxidation of 14C-glucose to 14CO2 was measured. Preincubation of normal aorta in diabetic or fasted rat plasma and diabetic human plasma significantly depressed the subsequently determined glucose oxidation in comparison to aorta preincubated in normal plasma. Preincubation of aorta from diabetic or fasted rats in normal rat plasma enhanced the glucose oxidation compared with the glucose oxidation in aorta of diabetic or fasted rats after preincubation in the corresponding plasma. These results suggest that diabetic and fasted plasma contains factor(s) which in vitro depress glucose oxidation in vascular smooth muscle and, thus, may be of importance for the lowered glucose oxidation found in vascular smooth muscle preparations obtained from diabetic or fasted animals.

The metabolism of colon smooth muscle from normal and alloxan-diabetic rabbits was studied in vitro. Glucose uptake, incorporation of glucose minus14-C into glycogen and incorporation of leucine minus-14C into 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 vitro stimulated glucose uptake, incorporation of glucose minus14-C into glycogen and incorporation of leucine minus14-C into protein in diabetic colon smooth muscle. Insulin stimulated glucose uptake to the same degree in normal and diabetic colon smooth muscle, while its effect on glucose minus14-C and leucine minus14-C incorporation tended to be somewhat more pronounced in diabetic colon muscle.

Insulin-like growth factor-I (IGF-I) mRNA and GH receptor mRNA levels were analysed in different tissues from rats made diabetic with streptozotocin, fasted rats and rats fed with a protein-reduced diet. Diabetes decreased IGF-I mRNA levels in liver, heart, diaphragm, kidney and aorta, but not in brain. GH receptor mRNA levels were decreased in heart and diaphragm, but not in liver and kidney. Fasting decreased IGF-I mRNA in all tissues studied except brain, and decreased GH receptor mRNA in liver, heart and diaphragm, but not in kidney. A protein-reduced diet decreased hepatic IGF-I mRNA levels but did not significantly affect other tissues, while GH receptor mRNA levels were reduced in liver and diaphragm. In conclusion, both diabetes and limited nutrition affected IGF-I and GH receptor mRNA in different tissues, but the two mRNAs were not co-ordinately regulated in all tissues studied. While reduced GH receptor gene expression may thus be responsible for decreased IGF-I gene expression in some states and tissues, additional regulatory mechanisms may be of importance.

Glucose utilization and the conversion of glucose to lactate, CO2, glycogen and lipids are decreased in the aorta from diabetic rats and rabbits. In addition the incorporation of amino acid into protein is reduced in diabetic rat aorta. The metabolic changes produced by diabetes are counteracted by insulin treatment, but there is a time lag of about 2 days before the effect of insulin treatment appears. The membrane transport of glucose in smooth muscle is carried out by a specific transport system of the facilitated diffusion type. A rate limiting influence of membrane transport on glucose metabolism is found in bovine mesenteric arteries and rabbit colon smooth muscle. In these preparations the influence of glucose concentrations on glucose metabolism is most pronounced in the range 0-11.1 mmol exhibiting saturation at higher glucose concentrations. Insulin in a high concentration (0.1 U/ml) has acute (less than or equal to 3 h) metabolic effects in vitro on smooth muscle which are qualitatively similar to those in skeletal muscle, but are weaker and appear later. The threshold concentration for the acute metabolic effects of insulin on smooth muscle in vitro is 10-100 times above the physiological levels, indicating a low acute sensitivity to insulin.

Eight insulin-treated diabetic patients in good glycaemic control were studied as out-patients with frequent determinations of stable glycosylated haemoglobin (HbA1c) before, during and after 1 week of induced poor glycaemic control. Stable HbA1c was determined by cation exchange chromatography after elimination of the labile fraction by incubation in saline (0.15 mol/l). The increase in mean blood glucose was significant on the first day of reduced insulin therapy and greatest after 1 week (6.9 +/- 3.9 mmol/l above basal values). Stable HbA1c increased significantly on day 7 of the reduced insulin treatment. The increase represented, on average, 0.009% of total haemoglobin per mmol/l increase in mean blood glucose per 24 h during the period of induced hyperglycaemia. After restoring insulin therapy, a significant decrease in blood glucose was achieved on day 1 and after 2 days, the blood glucose level was similar to before the study. There was no significant decrease in stable HbA1c within the first 2 weeks of improved glycaemia.