Acid glycohydrolase in Chinese hamster with spontaneous diabetes. I. Depressed levels of renal alpha-galactosidase and beta-galactosidase.

The activites of alpha-and Beta-galactosidases (alpha-D-galactoside galactohydrolase, EC 3.2.1.22; beta-D-galactoside galactohydrolase, EC 3.2.1.23) were significantly lower in the kidneys of diabetic XA line than those in the nondiabetic M line Chinese hamsters. The depression of these enzymes was found only in the kidney but not in liver, spleen, hind leg muscle, cheek pouch or spinal cord. In young XA animals before onset of glycosuria, renal alpha-galactosidase level was similar to that in age-matched M animals; whereas, their renal beta-galactosidase activity was about 90% of those in the M animals. Partial purification and separation of these enzymes were achieved by chromatography on DEAE-Sepharose CL-6B columns. beta-galactosidase was separated into two isozymes and depression of activity in the XA kidneys was evident in both. alpha-galactosidase was recovered in a single peak. The pH optima of these enzymes from XA and M animals were identical. With p-nitrophenyl glycosides as substrates, the Michaelis constants of these enzymes were also the same of XA and M animals. Molecular weight estimation by gel filtration on Sepharose 6B yielded similar results between M and XA samples: 2.4-10(5) for alpha-galactosidase and 1.6.10(5) and 1.9.10(5) for beta-galactosidase isozymes. The data suggest that the diabetic animals had lower concentrations of alpha-and beta-galactosidase in their kidneys, probably as a consequence of hyperglycemia.     

Chronic hyperglycemia in experimental diabetes mellitus of short duration does not contribute to muscle capillary basement membrane thickening

The effect of chronic hyperglycemia on the relationship of nonenzymatic glycation and capillary basement membrane thickness in muscle was studied in streptozotocin-induced diabetic rats early in the course of diabetes mellitus. Diabetic animals were placed on either standard (24%) or restricted (8%) protein diet. The animals on 8% protein diet had elevated glycated hemoglobin levels (p less than 0.01) and increased levels of nonenzymatic glycation of basement membrane (p less than 0.01) as compared to insulin-treated diabetic (euglycemic), age-matched control, and streptozotocin-injected nondiabetic animals also on 8% protein diet. In contrast, diabetic animals on restricted (8%) protein diet and those on standard (24%) protein diet showed no statistical differences between them with regards to the above parameters. Moreover, there were no statistical differences among diabetic and control animals on either 8 or 24% protein diet with respect to muscle capillary membrane thickness. Even though the peripheral muscle biopsy study of capillary basement membrane is less invasive than kidney biopsy, the results of this study suggest that neither nonenzymatic glycation nor basement membrane thickness can be utilized as predictors of renal dysfunction during early onset of diabetes mellitus.     

Matrix metalloproteinase activity is required for activity-induced angiogenesis in rat skeletal muscle

Proteolysis of the capillary basement membrane is a hallmark of inflammation-mediated angiogenesis, but it is undetermined whether proteolysis plays a critical role in the process of activity-induced angiogenesis. Matrix metalloproteinases (MMPs) constitute the major class of proteases responsible for degradation of basement membrane proteins. We observed significant elevations of mRNA and protein levels of both MMP-2 and membrane type 1 (MT1)-MMP (2.9 +/- 0.7- and 1.5 +/- 0.1-fold above control, respectively) after 3 days of chronic electrical stimulation of rat skeletal muscle. Inhibition of MMP activity via the inhibitor GM-6001 prevented the growth of new capillaries as assessed by the capillary-to-fiber ratio (1.34 +/- 0.08 in GM-6001-treated muscles compared with 1.69 +/- 0.03 in control 7-day-stimulated muscles). This inhibition correlated with a significant reduction in the number of capillaries with observable breaks in the basement membrane, as assessed by electron microscopy (0.27 +/- 0.27% in GM-6001-treated muscles compared with 3.72 +/- 0.65% in control stimulated muscles). Proliferation of capillary-associated cells was significantly elevated by 2 days and remained elevated throughout 14 days of stimulation. Capillary-associated cell proliferation during muscle stimulation was not affected by MMP inhibition (80.3 +/- 9.3 nuclei in control and 63.5 +/- 8.5 nuclei in GM-6001-treated animals). We conclude that MMP proteolysis of capillary basement membrane proteins is a critical component of physiological angiogenesis, and we postulate that capillary-associated proliferation precedes and occurs independently of endothelial cell sprout formation.     

Hypertrophy of skeletal muscle in diabetic rats in response to chronic resistance exercise.

This study had the following objectives: 1) to determine whether diabetic rats could increase muscle mass due to a physiological manipulation (chronic resistance exercise), 2) to determine whether exercise training status modifies the effect of the last bout of exercise on elevations in rates of protein synthesis, and 3) to determine whether chronic resistance exercise alters basal glycemia. Groups consisted of diabetic or nondiabetic rats that performed progressive resistance exercise for 8 wk, performed acute resistance exercise, or remained sedentary. Arterial plasma insulin in diabetic groups was reduced by about one-half (P < 0.05) compared with nondiabetic groups. Soleus and gastrocnemius-plantaris complex muscle wet weights were lower because of diabetes, but in response to chronic exercise these muscles hypertrophied in diabetic (0.028 +/- 0.003 vs. 0.032 +/- 0.0015 g/cm for sedentary vs. exercised soleus and 0.42 +/- 0.068 vs. 0.53 +/- 0.041 g/cm for sedentary vs. exercised gastrocnemius-plantaris, both P < 0.05) but not in nondiabetic (0.041 +/- 0.0026 vs. 0.042 +/- 0.003 g/cm for sedentary vs. exercised soleus and 0.72 +/- 0.015 vs. 0.69 +/- 0.013 g/cm for sedentary vs. exercised gastrocnemius-plantaris) rats when muscle weight was expressed relative to tibial length or body weight (data not shown). Another group of diabetic rats that lifted heavier weights showed muscle hypertrophy. Rates of protein synthesis were higher in red gastrocnemius in chronically exercised than in sedentary rats: 155 +/- 11 and 170 +/- 7 nmol phenylalanine incorporated x g muscle(-1) x h(-1) in exercised diabetic and nondiabetic rats vs. 110 +/- 14 and 143 +/- 7 nmol phenylalanine incorporated x g muscle(-1) x h(-1) in sedentary diabetic and nondiabetic rats. These elevations, however, were lower than in acutely exercised (but untrained) rats: 176 +/- 15 and 193 +/- 8 nmol phenylalanine incorporated x g muscle(-1) x h(-1) in diabetic and nondiabetic rats. Finally, chronic exercise training in diabetic rats was associated with reductions in basal glycemia, and such reductions did not occur in sedentary diabetic groups. These data demonstrate that, despite lower circulating insulin concentrations, diabetic rats can increase muscle mass in response to a physiological stimulus.     

Diabetes mellitus in sand rats (Psammomys obesus): microangiopathy during development of the diabetic syndrome.

The purpose of the study was to investigate the development of microangiopathic complications in North African sand rats with diabetes induced by a long-term standard laboratory diet. Hyperinsulinaemic rats, whether non-diabetic obese or diabetic, developed capillary basement membrane (CBM) thickening in the skin; in insulin-dependent animals, this change was diffuse. Many PAS positive areas were demonstrated in skeletal muscle and myocardium, together with evidence of microangiopathy; the primary myocardial lesion in insulin-dependent disease was ischaemic fibrosis. The kidney was also affected with marked basement membrane thickening in Bowman's capsule and glomerular capillaries; glomerulosclerosis and tubular changes were found in insulin-dependent disease. No evidence of diabetic retinopathy was found, and there was a high incidence of cataract.     

Effects of Type II diabetes on capillary hemodynamics in skeletal muscle

Microcirculatory red blood cell (RBC) hemodynamics are impaired within skeletal muscle of Type I diabetic rats (Kindig CA, Sexton WL, Fedde MR, and Poole DC. Respir Physiol 111: 163-175, 1998). Whether muscle microcirculatory dysfunction occurs in Type II diabetes, the more prevalent form of the disease, is unknown. We hypothesized that Type II diabetes would reduce the proportion of capillaries supporting continuous RBC flow and RBC hemodynamics within the spinotrapezius muscle of the Goto-Kakizaki Type II diabetic rat (GK). With the use of intravital microscopy, muscle capillary diameter (d(c)), capillary lineal density, capillary tube hematocrit (Hct(cap)), RBC flux (F(RBC)), and velocity (V(RBC)) were measured in healthy male Wistar (control: n = 5, blood glucose, 105 +/- 5 mg/dl) and male GK (n = 7, blood glucose, 263 +/- 34 mg/dl) rats under resting conditions. Mean arterial pressure did not differ between groups (P > 0.05). Sarcomere length was set to a physiological length ( approximately 2.7 mum) to ensure that muscle stretching did not alter capillary hemodynamics; d(c) was not different between control and GK rats (P > 0.05), but the percentage of RBC-perfused capillaries (control: 93 +/- 3; GK: 66 +/- 5 %), Hct(cap), V(RBC), F(RBC), and O(2) delivery per unit of muscle were all decreased in GK rats (P < 0.05). This study indicates that Type II diabetes reduces both convective O(2) delivery and diffusive O(2) transport properties within muscle microcirculation. If these microcirculatory deficits are present during exercise, it may provide a basis for the reduced O(2) exchange characteristic of Type II diabetic patients.     

Effects of aging on capillary geometry and hemodynamics in rat spinotrapezius muscle

The effects of aging on muscle microvascular structure and function may play a key role in performance deficits and impairment of O2 exchange within skeletal muscle of senescent individuals. To determine the effects of aging on capillary geometry, red blood cell (RBC) hemodynamics, and hematocrit in a muscle of mixed fiber type, spinotrapezius muscles from Fischer 344 x Brown Norway hybrid rats aged 6-8 mo [young (Y); body mass 421 +/- 10 g, n = 6] and 26-28 mo [old (O); 561 +/- 12 g, n = 6] were observed by high-resolution transmission light microscopy under resting conditions. The percentage of RBC-perfused capillaries (Y: 78 +/- 3%; O: 75 +/- 2%) and degree of tortuosity and branching (Y: 13 +/- 2%; O: 13 +/- 2%, additional capillary length) were not different in O vs. Y muscles. Lineal density of RBC-perfused capillaries in O was significantly reduced (Y: 30.7 +/- 1.8, O: 22.8 +/- 3.1 capillaries/mm; P < 0.05). However, RBC-perfused capillaries from O rats (n = 78) exhibited increased RBC velocity (VRBC) (Y: 219 +/- 12, O: 310 +/- 14 microm/s; P < 0.05) and RBC flux (FRBC) (Y: 27 +/- 2, O: 41 +/- 2 RBC/s; P < 0.05) vs. Y rats (n = 66). Thus O2 delivery per unit of muscle was not different between groups (Y: 894 +/- 111, O: 887 +/- 118 RBC. s-1. mm muscle-1). Capillary hematocrit was not different in Y vs. O rats (Y: 26 +/- 1%, O: 28 +/- 1%: P > 0.05). These data indicate that in resting spinotrapezius muscle, aging decreases the lineal density of RBC-perfused capillaries while increasing mean VRBC and FRBC within those capillaries. Whereas muscle conductive O2 delivery and capillary hematocrit were unchanged, elevated VRBC reduces capillary RBC transit time and may impair the diffusive transport of O2 from blood to myocyte particularly under exercise conditions.     

Severe diabetes prohibits elevations in muscle protein synthesis after acute resistance exercise in rats.

This study determined whether rates of protein synthesis increase after acute resistance exercise in skeletal muscle from severely diabetic rats. Previous studies consistently show that postexercise rates of protein synthesis are elevated in nondiabetic and moderately diabetic rats. Severely diabetic rats performed acute resistance exercise (n = 8) or remained sedentary (n = 8). A group of nondiabetic age-matched rats served as controls (n = 9). Rates of protein synthesis were measured 16 h after exercise. Plasma glucose concentrations were >500 mg/dl in the diabetic rats. Rates of protein synthesis (nmol phenylalanine incorporated. g muscle(-1). h(-1), means +/- SE) were not different between exercised (117 +/- 7) and sedentary (106 +/- 9) diabetic rats but were significantly (P < 0.05) lower than in sedentary nondiabetic rats (162 +/- 9) and in exercised nondiabetic rats (197 +/- 7). Circulating insulin concentrations were 442 +/- 65 pM in nondiabetic rats and 53 +/- 11 and 72 +/- 19 pM in sedentary and exercised diabetic rats, respectively. Plasma insulin-like growth factor I concentrations were reduced by 33% in diabetic rats compared with nondiabetic rats, and there was no difference between exercised and sedentary diabetic rats. Muscle insulin-like growth factor I was not affected by resistance exercise in diabetic rats. The results show that there is a critical concentration of insulin below which rates of protein synthesis begin to decline in vivo. In contrast to previous studies using less diabetic rats, severely diabetic rats cannot increase rates of protein synthesis after acute resistance exercise.     

The postnatal development of capillaries in the triceps muscle of arm of the white rat. Light and electron microscopic studies]

This paper continues former ultrastructural investigations about fetal development of capillaries in the muscle anlage of the fore limb of white rats. Present investigations deal with postnatal ultrastructural changes of the capillaries of the triceps muscle of rats from the 4th up to the 23rd day p.p. Counting of the capillaries with light and electron microscope reveal a linear increase of the capillary to fiber ratio in this period proportional to the growth of the muscle. Related to a defined area however the number of capillaries remains constantly. Ultrastructural changes of capillaries consist in further flattening of the endothelial profiles, decrease in number or organelles (mitochondria and endoplasmic reticulum), while the number of pinocytotic vesicles remains highmthe endothelial joints become less interdigitated, the basement membrane shows an increase in density leading to a temporary decrease in thickness. Since the 9th postnatal day all of the capillaries including buds closely border upon the muscle fibres. The distance between endothelium and myofiber diminishes up to 0,1 mum.     

Morphometric study on the renal glomeruli of streptozotocin (SZ)-induced diabetic APA hamsters.

Morphometrical analysis was done on the renal glomeruli of streptozotocin (SZ)-induced diabetic and control APA hamsters. In coincidence with the histopathological and ultrastructural findings, the areas of whole glomerulus (WG) and mesangial region (MR) were significantly larger in diabetic animals than in controls at 1 and 3 months after SZ-injection (1 and 3MAI). The area of capillary lumen in diabetic animals was larger than that in controls at 1MAI but it became similar between both groups at 3MAI probably due to an increase in the area of MR. The thickness of basement membrane was significantly larger in diabetic animals than in controls at 3MAI. The present morphometrical findings, together with histological and ultrastructural ones, suggest that SZ-induced diabetic APA hamsters are useful as a model system for the investigation of focal and segmental glomerulosclerosis.     

Effects of benfluorex-vitamin C supplementation on cutaneous capillaries of diabetic rats

The ultrastructural changes on capillaries of the dermis in diabetic and benfluorex-vitamin C treated diabetic rats have been investigated. Three groups of 21 Wistar albino rats were used in the examination: control, diabetes, and benfluorex-vitamin C treated diabetic rats. Diabetes was induced by injection of streptozotocin. The streptozotocin-induced group was treated for 21 days with vitamin C and benfluorex, of which antidiabetic and antihyperlipidemic effects were experimentally proved. Samples taken from the skin of rats' legs were examined under transmission electron microscopy. Swollen endothelial cells, narrowed capillary lumens, a thickened basement membrane, and fusion of mitochondrial cristae in the capillaries of diabetic rat dermis were seen. In the benfluorex-vitamin C treated group, contrary to the diabetic group, neither signs of degeneration in endothelial cells nor a significant difference with the control group with regard to capillary structure were observed. Amelioration in capillaries appears to be due to benfluorex and vitamin C treatment in diabetes.     

Thiazolidinediones upregulate impaired fatty acid uptake in skeletal muscle of type 2 diabetic subjects

We examined the regulation of free fatty acid (FFA, palmitate) uptake into skeletal muscle cells of nondiabetic and type 2 diabetic subjects. Palmitate uptake included a protein-mediated component that was inhibited by phloretin. The protein-mediated component of uptake in muscle cells from type 2 diabetic subjects (78 +/- 13 nmol. mg protein-1. min-1) was reduced compared with that in nondiabetic muscle (150 +/- 17, P < 0.01). Acute insulin exposure caused a modest (16 +/- 5%, P < 0.025) but significant increase in protein-mediated uptake in nondiabetic muscle. There was no significant insulin effect in diabetic muscle (+19 +/- 19%, P = not significant). Chronic (4 day) treatment with a series of thiazolidinediones, troglitazone (Tgz), rosiglitazone (Rgz), and pioglitazone (Pio) increased FFA uptake. Only the phloretin-inhibitable component was increased by treatment, which normalized this activity in diabetic muscle cells. Under the same conditions, FFA oxidation was also increased by thiazolidinedione treatment. Increases in FFA uptake and oxidation were associated with upregulation of fatty acid translocase (FAT/CD36) expression. FAT/CD36 protein was increased by Tgz (90 +/- 22% over control), Rgz (146 +/- 42%), and Pio (111 +/- 37%, P < 0.05 for all 3) treatment. Tgz treatment had no effect on fatty acid transporter protein-1 and membrane-associated plasmalemmal fatty acid-binding protein mRNA expression. We conclude that FFA uptake into cultured muscle cells is, in part, protein mediated and acutely insulin responsive. The basal activity of FFA uptake is impaired in type 2 diabetes. In addition, chronic thiazolidinedione treatment increased FFA uptake and oxidation into cultured human skeletal muscle cells in concert with upregulation of FAT/CD36 expression. Increased FFA uptake and oxidation may contribute to lower circulating FFA levels and reduced insulin resistance in skeletal muscle of individuals with type 2 diabetes following thiazolidinedione treatment.     

Expression and regulation by insulin of low-density lipoprotein receptor-related protein mRNA in human skeletal muscle

Evidence suggests that increased hydrolysis and/or uptake of triglyceride-rich lipoprotein particles in skeletal muscle can be involved in insulin resistance. We determined the steady state mRNA levels of the low-density lipoprotein-related receptor (LRP) and lipoprotein lipase (LPL) in skeletal muscle of eight healthy lean control subjects, eight type 2 diabetic patients and eight nondiabetic obese individuals. The regulation by insulin of LRP and LPL mRNA expression was also investigated in biopsies taken before and at the end of a 3 h euglycemic hyperinsulinemic clamp (insulinemia of about 1 nM). LRP mRNA was expressed in human skeletal muscle (1.3+/-0.1 amol/microg total RNA in control subjects). Type 2 diabetic patients, but not nondiabetic obese subjects, were characterized by a reduced expression of LRP (0.8+/-0.2 and 1.3+/-0.3 amol/microg total RNA in diabetic and obese patients, respectively; P<0.05 in diabetic vs. control subjects). Insulin infusion decreased LRP mRNA levels in muscle of the control subjects but not in muscle of type 2 diabetic and nondiabetic obese patients. Similar results were found when investigating the regulation of the expression of LPL. Taken together, these results did not support the hypothesis that a higher capacity for clearance or hydrolysis of circulating triglycerides in skeletal muscle is present during obesity- or type 2 diabetes-associated insulin resistance.     

Impaired capillary hemodynamics in skeletal muscle of rats in chronic heart failure.

Skeletal muscle blood flow is reduced and O(2) extraction is increased at rest in chronic heart failure (CHF). Knowledge of red blood cell (RBC) flow distribution within the capillary network is necessary for modeling O(2) delivery and exchange in this disease. Intravital microscopy techniques were used to study the in vivo spinotrapezius muscle microcirculation in rats with CHF 7 wk after myocardial infarction and in sham-operated controls (sham). A decrease in mean muscle fiber width from 51.3 +/- 1.9 microm in sham to 42.6 +/- 1.4 microm in CHF rats (P < 0.01) resulted in an increased lineal density of capillaries in CHF rats (P < 0.05). CHF reduced (P < 0.05) the percentage of capillaries supporting continuous RBC flow from 87 +/- 5 to 66 +/- 5%, such that the lineal density of capillaries supporting continuous RBC flow remained unchanged. The percentage of capillaries supporting intermittent RBC flow was increased in CHF rats (8 and 27% in sham and CHF, respectively, P < 0.01); however, these capillaries contributed only 2.3 and 3.3% of the total RBC flux in sham and CHF rats, respectively. In continuously RBC-perfused capillaries, RBC velocity (252 +/- 20 and 144 +/- 9 microm/s in sham and CHF, respectively, P < 0.001) and flux (21.4 +/- 2.4 and 9.4 +/- 1.1 cells/s in sham and CHF, respectively, P < 0.01) were markedly reduced in CHF compared with sham rats. Capillary "tube" hematocrit remained unchanged (0.22 +/- 0.02 and 0.19 +/- 0.02 in sham and CHF, respectively, P > 0.05). We conclude that CHF causes spinotrapezius fiber atrophy and reduces the number of capillaries supporting continuous RBC flow per fiber. Within these capillaries supporting continuous RBC flow, RBC velocity and flux are reduced 45-55%. This decreases the potential for O(2) delivery but enhances fractional O(2) extraction by elevating RBC capillary residence time. The unchanged capillary tube hematocrit suggests that any alterations in muscle O(2) diffusing properties in CHF are mediated distal to the RBC.     

Fatty acid transport protein-1 mRNA expression in skeletal muscle and in adipose tissue in humans

Fatty acid transporter protein (FATP)-1 mRNA expression was investigated in skeletal muscle and in subcutaneous abdominal adipose tissue of 17 healthy lean, 13 nondiabetic obese, and 16 obese type 2 diabetic subjects. In muscle, FATP-1 mRNA levels were higher in lean women than in lean men (2.2 +/- 0.1 vs. 0.6 +/- 0.2 amol/microg total RNA, P < 0.01). FATP-1 mRNA expression was decreased in skeletal muscle in obese women both in nondiabetic and in type 2 diabetic patients (P < 0.02 vs. lean women in both groups), and in all women there was a negative correlation with basal FATP-1 mRNA level and body mass index (r = -0.74, P < 0.02). In men, FATP-1 mRNA was expressed at similar levels in the three groups both in skeletal muscle (0.6 +/- 0.2, 0.6 +/- 0.2, and 0.8 +/- 0.2 amol/microg total RNA in lean, obese, and type 2 diabetic male subjects) and in adipose tissue (0.9 +/- 0.2 amol/microg total RNA in the 3 groups). Insulin infusion (3 h) reduced FATP-1 mRNA levels in muscle in lean women but not in lean men. Insulin did not affect FATP-1 mRNA expression in skeletal muscle in obese nondiabetic or in type 2 diabetic subjects nor in subcutaneous adipose tissue in any of the three groups. These data show a gender-related difference in the expression of the fatty acid transporter FATP-1 in skeletal muscle of lean individuals and suggest that changes in FATP-1 expression may not contribute to a large extent to the alterations in fatty acid uptake in obesity and/or type 2 diabetes.     

Acid glycohydrolase in Chinese hamster with spontaneous diabetes II. N-acetyl-beta-D-hexosaminidase in plasma and tissues

Excessively high activity of N-acetyl-beta-D-hexosaminidase (2-acetamido-2-deoxy-beta-D-glucoside acetamidodeoxy-glucohydrolase, EC 3.2.1.30) was found in the plasma of hereditary diabetic XA line animals, which however showed similar activity of this enzyme in both 12 00 X g supernatant and precipitate fractions of kidney homogenates as the nondiabetic M line animals. 0.1% Triton X-100 extracts of kidney, spleen, hind leg muscle, cheek pouch and spinal cord of XA and M line animals also showed similar activities of this enzyme whereas the XA animal liver extracts showed significantly higher activity than the M extracts. On a Sepharose CL-6B column, plasma N-acetyl-beta-D-hexosaminidase was eluted as two major peaks at 0 and 0.05 M NaCl (isozyme B1 and B2). Both isozymes showed pH optima between 3.5 and 4.0 and the same Michaelis constants for p-nitrophenyl-N-acetyl-beta-D-glucosaminide at pH 4.5, i.e. 0.18 mM. Isozymes from XA and M animals showed identical properties. N-acetyl-beta-D-hexosaminidase in the liver extracts was separated into 3 isozymes, A, B1 and B2, by successive column chromatography runs on Sepharose 6B and DEAE-Sepharose CL-6B. At 49 degrees C, isozyme B1 showed thermostability whereas B2 and A lost 20% and 76% of their activities after 30 min incubation, pH optima for A, B1 and B2 were 4.0--4.5, 3.5 and 3.5--4.0 respectively. The Km values for p-nitrophenyl-N-acetyl-beta-D-glucosaminide were 0.48 mM for A and 0.19 for B1 and B2. The XA animal liver extracts showed higher activities in all three isozymes than the M animal livers. Identical results, however, were obtained for liver isozymes from M and XA animals with regard to thermostability, pH vs. activity, elution profile on ion exchange column and affinity to p-nitrophenyl-N-acetyl-beta-D-glucosaminide.     

Capillary supply of the tibialis anterior muscle in young, healthy, and moderately active men and women.

Tibialis anterior muscle biopsies from moderately active men and women (21-30 yr; n = 30) were examined to determine potential gender differences in capillarization. The fiber type proportions [type I (T1) approximately 73%] were unaffected by gender. The men (M) had significantly (P < 0.001) larger fibers than the women (W), with a greater gender effect for type II (T2) fibers (P < 0.001). The M and W had similar capillary densities (CD approximately 390 capillaries/mm2), but the capillaries-to-fiber ratio (C/F) was higher in the M (M = 2.20 +/- 0.35, W = 1.66 +/- 0.32; P < 0.01). Capillary contacts (CC) were higher in T2 than T1 for the M (P < 0.01), but not W, and M had greater CC (P < 0.001). Both fiber area per capillary (FA/C) and fiber perimeter per capillary (FP/C) indicated that T1 fibers had greater capillarization than T2 fibers (P < 0.001). There were no gender differences in T1 FA/C and T2 FA/C or T1 FP/C, but a gender difference existed for T2 FP/C (M = 60.5 +/- 10.9, W = 70.6 +/- 13.4; P < 0.01). The gender difference for C/F could be explained by fiber size; however, the physiological implications of the difference in T2 FP/C remains to be determined. In conclusion, despite gender differences for fiber size, overall, capillarization was similar between the men and women.     

Mechanism of dilation to reactive oxygen species in human coronary arterioles

We tested whether reactive oxygen species (ROS) generated from treatment with xanthine (XA) and xanthine oxidase (XO) alter vascular tone of human coronary arterioles (HCA). Fresh human coronary arterioles (HCA) from right atrial appendages were cannulated for video microscopy. ROS generated by XA (10(-4) M) + XO (10 mU/ml) dilated HCA (99 +/- 1%, 20 min after application of XA/XO). This dilation was not affected by denudation or superoxide dismutase (150 U/ml). Catalase (500 U/ml or 5,000 U/ml) attenuated the dilation early on, but a significant latent vasodilation appeared after 5 min peaking at 20 min (51 +/- 1%, 20 min after application of XA/XO + 500 U/ml catalase, P < 0.01 vs. control). KCl (40 mM) reduced the early and sustained vasodilation to XA/XO in the absence of catalase but 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 x 10(-5) M), diethyldithiocarbamate trihydrate (DDC, 10(-2) M), and deferoxamine (DFX, 10(-3) M) had no effect. In contrast, the catalase-resistant vasodilation was significantly attenuated by DDC, ODQ, and DFX as well as polyethylene-glycolated catalase (5,000 U/ml), but KCl had no effect. Confocal microscopy revealed that even in the presence of catalase, 2',7'-dichlorodihydrofluoresein diacetate fluorescence was observed in the vascular smooth muscle, but this was abolished by DDC. These data indicate that the exogenously generated superoxide anion (O2-*) by XA/XO is spontaneously converted to H2O2, which dilates HCA through vascular smooth muscle hyperpolarization. O2-* is also converted to H2O2 likely by superoxide dismustase within vascular cells and dilates HCA through a different pathway involving the activation of guanylate cyclase. These findings suggest that exogenously and endogenously produced H2O2 may elicit vasodilation by different mechanisms.     

Long-term isoprenaline administration produces an increase in capillarity in the soleus muscle of the rat

The effects of isoprenaline administration (300 micrograms/kg for 5 weeks) on rat soleus muscle capillarity and glycolytic and oxidative capacities were evaluated. The treatment resulted in ventricular hypertrophy. The activities of lactic dehydrogenase, pyruvate kinase, citrate synthase, and cytochrome c oxidase in soleus muscle homogenates were not different between control and isoprenaline-injected animals. Capillaries were visualized in muscle cross sections treated to demonstrate ATPase activity after acid preincubation. Capillary density was higher in the experimental (873 +/- 38 capillaries/mm2) than in the control (713 +/- 33 capillaries/mm2) animals. Capillary to fiber ratio was also higher in the experimental (2.47 +/- 0.10) than in control (2.09 +/- 0.08) animals, but fiber cross-sectional area was not changed by the treatment (2836 +/- 87 microns2 in controls and 2951 +/- 136 microns2 in experimental). A plot of capillary to fiber ratio vs. fiber cross-sectional area showed that at a given fiber cross-sectional area the value of capillary to fiber ratio of the treated animals was higher than that of the controls. This indicates that treatment resulted in the proliferation of microvessels. The results suggest that prolonged beta-adrenergic stimulation results in the development of new capillaries but that this is not accompanied by increases in the oxidative capacity of the soleus muscle of the rat.     

Vascular rarefaction in peripheral skeletal muscle after experimental heart failure

A decrease in vascular density in peripheral skeletal muscle has been associated with exercise intolerance in humans with congestive heart failure (CHF). The purpose of this study was to determine whether CHF results in a reduction in vascular density in peripheral skeletal muscle. In this established model, CHF was induced by coronary artery ligation in New Zealand White rabbits and sham rabbits that underwent an identical surgical procedure without ligation of the coronary artery. At study termination, rabbits underwent hemodynamic testing and skeletal muscle analysis. The first series of rabbits was divided into sham (n = 6) and CHF (n = 6) 21 days postoperatively. Ten CHF rabbits were then examined 3 (n = 3), 7 (n = 3), and 14 days (n = 4) postoperatively. Vascular density in sham tibialis anterior muscle was 347 +/- 41 capillaries/mm2 or 1.20 +/- 0.11 capillaries/muscle fiber. In 21-day CHF rabbits, the capillary density was significantly lower, 236 +/- 14 capillaries/mm2 or 0.84 +/- 0.04 capillaries/muscle fiber (both P < 0.00001 vs. sham); PECAM protein was 2-fold lower (P < 0.0001) in muscle protein lysates; the fraction of apoptotic cells was greater, 3.8 +/- 2.2 vs. 0.69 +/- 0.56 (P < 0.02 vs. sham) with many TdT-mediated dUTP-biotin nick-end labeling-positive endothelial cells; and Bax protein was 2.8-fold greater (P < 0.0001). By regression analysis, vascular density tended to decrease over time (r2 = 0.572, P < 0.0001). Vascular rarefaction and endothelial apoptosis develop after experimental CHF and may contribute to the skeletal muscle abnormalities in this disease. Modulating vascular density may provide new approaches to treat exercise intolerance in CHF.