Acute hyperglycemia depresses arteriolar NO formation in skeletal muscle.

In the rat intestinal and cerebral microvasculatures, acute D-glucose hyperglycemia suppresses endothelium-dependent dilation to ACh without affecting endothelium-independent dilation to nitroprusside. This study determined whether acute hyperglycemia suppressed arteriolar wall nitric oxide concentration ([NO]) at rest or during ACh stimulation and inhibited nitroprusside-, ACh- or contraction-induced dilation of rat spinotrapezius arterioles. Vascular responses were measured before and after 1 h of topical 300 mg/100 ml D-glucose; arteriolar [NO] was measured with NO-sensitive microelectrodes. Arteriolar dilation to ACh was not significantly altered after superfusion of 300 mg/100 ml D-glucose. However, after hyperglycemia, arteriolar [NO] was not increased by ACh, compared with a 300 nM increase attained during normoglycemia. Arteriolar dilation to submaximal nitroprusside and muscle contractions was enhanced by hyperglycemia. These results indicated that in the rat spinotrapezius muscle, acute hyperglycemia suppressed arteriolar NO production while simultaneously augmenting vascular smooth muscle responsiveness to nitroprusside, presumably through cGMP-mediated mechanisms. In effect, this may have allowed ACh- and muscle contraction-induced vasodilation to be maintained during hyperglycemia despite an impaired NO system.

Exercise training enhances adrenergic constriction and dilation in the rat spinotrapezius muscle.

Treadmill training increases functional vasodilation in the rat spinotrapezius muscle, although there is no acute increase in blood flow and no increase in oxidative capacity. To assess concurrent changes in vascular reactivity, we measured arterial diameters in the spinotrapezius muscle of sedentary (Sed) and treadmill-trained (Tr; 9-10 wk; terminal intensity 30 m/min, 1.5 degrees incline, for 90 min) rats during iontophoretic application of norepinephrine, epinephrine (Epi), and H+ (HCl) and during superfusion with adenosine. Terminal-feed arteries and first-order arterioles in Tr rats constricted more than those in Sed rats at the higher current doses of norepinephrine and Epi. In contrast, at low-current doses of Epi, first- and second-order arterioles dilated in Tr but not in Sed rats. The vascular responses to HCl were highly variable, but second-order arterioles of Tr rats constricted more than those of Sed rats at intermediate-current doses. There were no significant differences between Sed and Tr rats in the vascular responses to adenosine. Both adrenergic vasodilation and vasoconstriction were enhanced in the spinotrapezius muscle of Tr rats, and enhanced adrenergic vasodilation may contribute to increased functional vasodilation. These observations further demonstrate vascular adaptations in "nontrained" skeletal muscle tissues.

Training-induced alterations in contractile function and excitation-contraction coupling in vascular smooth muscle.

Aerobic training-induced changes in vascular reactivity have been evaluated in vessels of a variety of sizes and tissue origins. In trained animals large coronary arteries have increased responses to adenosine (Ad) and decreased responses to norepinephrine (NE) and nitroprusside (Np). Smaller coronary arterioles have increased responses to bradykinin (Bk) but not Ad; intermediate size vessels have enhanced responses to both Ad and Bk. A similar size dependence has been found in the vascular bed of the rat spinotrapezius muscle. The terminal feed arteries of trained animals demonstrate increased dilation in response to Np and increased constriction in response to epinephrine (Epi) and NE. Smaller arterioles demonstrate increased beta-dilation at low doses of Epi and decreased constriction at higher doses. Intermediate size vessels demonstrate adaptive responses that appear to be a combination of those in larger and smaller vessels. These vascular alterations are evident despite the fact that blood flow does not increase in this muscle during treadmill running and the oxidative capacity of this tissue is not enhanced by treadmill training. Recently, training-induced vascular adaptations have also been observed in the rat intestine; these adaptations include decreased responses to NE and acetylcholine and increased responses to Np. Experimental evidence suggests that vascular smooth muscle adaptations to training are highly dependent on the size and tissue location of the vessel and occur in tissues other than those activated during the training bout. Potential mediators of these adaptations are discussed.

Femoral artery ligation stimulates capillary growth and limits training-induced increases in oxidative capacity in rats.

OBJECTIVE: The purpose of this study was to assess the interaction of arterial insufficiency and exercise training on soleus and plantaris muscle capillarity and oxidative capacity in adult rats. METHODS: Arterial insufficiency was created by ligation (LIG) of the right femoral artery, and exercise training (TR) was performed on a rodent treadmill. The left hindlimb served as a normally (NORM) perfused control. Capillary:fiber ratio number of capillary contacts per fiber, and citrate synthase activity (CS) were evaluated in the plantaris (Plant) and soleus (Sol) muscles. RESULTS: In sedentary rats, CS was similar between LIG and NORM (Plant: 24.4 vs. 24.3 mumol.min-1.g-1; Sol: 16.6 vs. 16.9 mumol.min-1.g-1), but capillaries per fiber and capillary contacts per fiber were significantly elevated in the plantaris muscle of LIG (2.46 vs. 2.10 caps/fiber, 5.78 vs. 5.03 capillary contacts). CS was elevated in both limbs of TR but was lower in LIG than in NORM (Plant: 28.5 vs. 32.4 mumol.min-1.g-1; Sol: 21.1 vs. 24.9 mumol.min-1.g-1). Treadmill training did not significantly affect capillarity in NORM. However, muscles in the ligated limb of TR tended to have greater capillarity than comparable muscles in either NORM of TR of LIG in SED. CONCLUSIONS: These results demonstrate capillary proliferation in the plantaris but not soleus muscle of rat hindlimbs with femoral artery ligation. Capillarity and CS adaptations were not obligatorily related in LIG, and femoral artery ligation and exercise training appeared to have interactive effects on skeletal muscle capillarity.

Time- and order-dependent changes in functional and NO-mediated dilation during exercise training.

Arterial vessel responses to sodium nitroprusside (SNP) and acetylcholine (ACh) were measured in the spinotrapezius muscle of sedentary (Sed) and treadmill-trained (Tr) rats to determine whether these endothelium-dependent (ACh) and -independent (SNP) mechanisms contribute to the training-induced increase in functional vasodilation previously observed. Control and maximal vessel diameters were similar between Sed and Tr. After 8 wk of training, functional dilation (2-, 4-, and 8-Hz contractions) was enhanced in all orders of vessels studied [terminal feed artery (FA), largest arterioles (1A), and intermediate-sized arterioles (2A)], but responses to SNP were increased only in FA. Responses to ACh were not significantly increased in any vessel order. After 16 wk of training, functional dilation had regressed in Tr such that only the FA response to 4 Hz was significantly elevated relative to Sed. However, the FA and 1A responses to SNP were significantly greater in Tr than in Sed, as were the 1A and 2A responses to ACh. These results show a dissociation of functional dilation and SNP- or ACh-mediated responses, as well as age-dependent interactions, a time-dependent progression, and vessel order specificity in the adaptations to training.

Regulation of skeletal muscle blood flow during contractions.

Skeletal muscle blood flow increases nearly 20-fold during exercise. Despite experimental work in this area for more than a century, the physiological mechanisms responsible for the regulation of skeletal muscle blood flow during contractions remain relatively unknown. Historically, experiments have focused on identifying chemical factors associated with increased tissue metabolism that also act as vasodilators. However, functional vasodilation cannot be attributed to changes in the local concentration of any single metabolic factor. The rapid increase in muscle blood flow during the initial moments of exercise led others to consider a role for neural mechanisms in the development of functional hyperemia. However, a specific neural pathway has not been identified. Mechanical factors, such as vascular compression and increases in perfusion pressure, also affect vascular resistance and skeletal muscle blood flow. Yet the specific manner in which these mechanical factors interact during muscle contractions is not well understood. The recent determination that arterial feed vessels, upstream from the active tissue and microcirculation, also dilate during muscle contractions has led to the consideration that the vessels are primarily responsible for the regulation of bulk flow to the tissue. Since these vessels are anatomically separated from the active tissue, more complex, indirect regulatory mechanisms must be explored. It is also likely that the specific factors responsible for functional vasodilation and increased muscle blood during exercise differ between muscle fiber types and relative contraction intensities. Consideration of these factors may lead to a better understanding of the regulation of muscle blood flow.

Intestinal absorption of sodium and nitric oxide-dependent vasodilation interact to dominate resting vascular resistance.

The villi of the small intestine maintain a hypertonic interstitium at all times, and the submucosal glands constantly secrete ions and accompanying water into the lumen. Generation of the 400- to 600-mOsm interstitial fluid in the villus and secretion by glands may require a large expenditure of energy and, consequently, have major effects on intestinal vascular regulation to supply oxygen and nutrients. Blood flow and oxygen consumption were measured in the ileum of anesthetized rats during natural resting conditions with physiological sodium chloride in the bathing fluid and during isosmotic replacement of sodium chloride with mannitol. Microvascular pressures and blood flow were used to determine the changes in resistance of the major arterioles and the terminal vasculature. When mannitol replaced sodium chloride in contact with the villi, intestinal blood flow decreased to 58.6 +/- 2.8% of control, and oxygen consumption was 54.2 +/- 3.4% of control. Resistance of the major arterioles increased 101.7 +/- 9.9%, and that of the terminal vasculature increased 40.4 +/- 6.2%. The increased resistance appeared to be caused by suppression of a nitric oxide mechanism. Local application of 10(-4) mol/L NG-nitro-L-arginine methyl ester caused about the same reduction in flow and increases in regional vascular resistance as during replacement of sodium but did not alter the oxygen consumption. These data indicate that about half of the intestinal metabolic rate during natural resting conditions is devoted to sodium secretion/absorption. Large resistance vessels are dilated to maintain a high blood flow through release of nitric oxide. We propose that dilation of the terminal vasculature in the metabolically active tissues increased flow velocity sufficiently in the major resistance vessels to cause a flow-mediated release of nitric oxide.

Resting oxygenation of rat and rabbit intestine: arteriolar and capillary contributions.

Counter-current exchange of oxygen may occur between inflow and outflow microvessels of the small intestine and greatly influence the dominant sites of tissue oxygenation. To determine the location and magnitude of potential exchange, percent saturation of hemoglobin with oxygen (%SHb) was measured in microvessels throughout the intestine of rats and rabbits. Oxygen losses from systemic arterial blood through large and intermediate arterioles (second order, 2A) was 5-7%SHb in both species, and there was no evidence of an increase in percent saturation along intermediate and large venules. A larger loss of oxygen from arterioles and an increase in venous saturation would be evident if significant arteriolar to venular counter-current exchange of oxygen occurred in the submucosa. From 2A to the villus tip, arteriolar saturation decreased approximately 10%SHb in rabbits and approximately 15%SHb in rats; the villus tip percent saturation was 72.9 +/- 3.9%SHb in rabbits and 69.9 +/- 2.9%SHb in rats. An additional decrease of 5%SHb in rabbits and 15%SHb in rats occurred across the villus capillaries and smallest venules. Although the total reduction in percent saturation across the villi was different between the two species, 70-90% of the total arteriovenous oxygen losses occurred in the capillaries and small arterioles of the villi. We found no evidence of counter-current exchange of oxygen in villi or any other vascular region. Rather, as appears to occur in most organs, small arterioles in conjunction with capillaries dominate resting oxygen exchange to tissue.

Early adaptations in collateral and microvascular resistances after ligation of the rat femoral artery.

Collateral and microvascular (including feed artery) resistances in the rat hindlimb were determined immediately or 1 wk after ligation of the femoral artery. Collateral-to-microvascular resistance ratios were determined from in vivo pressure measurements proximal and distal to the ligation. Microvascular resistance was 32 +/- 2.5 and 41 +/- 1.5% of the total collateral-dependent vasculature in acutely and chronically ligated limbs, respectively, and decreased 20% in both groups during reactive hyperemia. Minimum resistances of collateral vessels and the microcirculation arising from arterial branches proximal and distal to the ligation were determined by using a modification of the standard hindquarter perfusion technique for determining maximum vascular conductance. One week postligation, minimum total hindquarter resistance was decreased by a reduction in the resistance of the collaterals (approximately 50%) and microcirculation (approximately 33%) proximal to the ligation. The results suggest that the microvasculature distal to the occlusion is able to increase flow by dilation both initially and at 1 wk postligation but that collateral adaptations are primarily responsible for decreases in the minimum total resistance of the collateral-dependent region.

Endothelial-dependent vasodilation is preserved in non-insulin-dependent Zucker fatty diabetic rats.

Alterations in the structural properties of the microvasculature and in vasodilation mediated by endothelial- and, to some extent, nonendothelial-dependent mechanisms occurs in insulin-dependent diabetic humans and animals. Less severe problems of this type appear to occur during non-insulin-dependent diabetes mellitus (NIDDM) in humans, but data based on animal models of NIDDM are not available. The endothelial- and nonendothelial-mediated dilation of intestinal arterioles was studied in insulin-resistant male Zucker fatty diabetic (DB) rats and their lean normal male littermates (LM) at ages 22-25 and 35-40 wk. DB become hyperglycemic (450-550 mg/100 ml) at age 9-10 wk. Microiontophoretic release of acetylcholine, ADP, and nitroprusside onto arterioles caused equivalent dilation in LM and DB for both large and intermediate diameter arterioles. Administration of streptozotocin (STZ) to DB at age 18-19 wk lowered their insulin concentration approximately 25% but did not significantly effect the resting plasma glucose concentration. However, endothelial-dependent vasodilation was attenuated by 70-80% within 8-10 wk. The overall results indicate that prolonged hyperglycemia in insulin-resistant but hyperinsulinemic rats does not impair the endothelial- and nonendothelial-dependent dilation of the intestinal microvasculature. However, compromising beta-cell function with STZ, as indicated by lowering the insulin concentration by one-fourth, substantially compromises endothelial-dependent dilation similar to that found in insulin-dependent diabetic rats and humans.

Excess oxygen delivery during muscle contractions in spontaneously hypertensive rats.

These experiments determined whether a deficit in oxygen supply relative to demand could account for the sustained decrease in tissue PO2 observed during contractions of the spinotrapezius muscle in spontaneously hypertensive rats (SHR). Relative changes in blood flow were determined from measurements of vessel diameter and red blood cell velocity. Venular hemoglobin oxygen saturation measurements were performed by using in vivo spectrophotometric techniques. The relative dilation [times control (xCT)] of arteriolar vessels during contractions was as large or greater in SHR than in normotensive rats (Wistar-Kyoto), as were the increases in blood flow (2 Hz, 3.50 +/- 0.69 vs. 3.00 +/- 1.05 xCT; 4 Hz, 10.20 +/- 3.06 vs. 9.00 +/- 1.48 xCT; 8 Hz, 16.40 +/- 3.95 vs. 10.70 +/- 2.48 xCT). Venular hemoglobin oxygen saturation was lower in the resting muscle of SHR than of Wistar-Kyoto rats (31.0 +/= 3.0 vs. 43.0 +/- 1.9%) but was higher in SHR after 4- and 8-Hz contractions (4 Hz, 52.0 +/- 4.8 vs. 43.0 +/- 3.6%; 8 Hz, 51.0 +/- 4.6 vs. 41.0 +/- 3.6%). Therefore, an excess in oxygen delivery occurs relative to oxygen use during muscle contractions in SHR. The previous and current results can be reconciled by considering the possibility that oxygen exchange is limited in SHR by a decrease in anatomic or perfused capillary density, arteriovenular shunting of blood, or decreased transit time of red blood cells through exchange vessels.

Exercise training effects on collateral and microvascular resistances in rat model of arterial insufficiency.

Experiments were performed to determine if exercise training reduces collateral or microvascular resistances in the hindlimb of rats with arterial insufficiency. After right femoral arterial ligation (age 10 wk), rats were divided into sedentary (Sed) and treadmill-trained (Tr) groups (7-9 wk, final intensity: 27 m/min, 6 degree grade, 60 min/day). Minimal resistances (mmHg.ml-1.min.100 g) of the total limb (RT), collateral vessels (RC), and the microcirculations distal (Rfmc) and proximal (Rimc) to the ligation site were determined during pump perfusion of the hindlimbs. RT was lower in nonligated (open) and acutely ligated limbs of Tr than Sed rats (open: 0.69 +/- 0.011 vs. 0.93 +/- 0.071; acute: 0.92 +/- 0.028 vs. 1.18 +/- 0.070 mmHg.ml-1.min.100 g) but not in chronically ligated limbs (chronic: 0.88 +/- 0.072 vs. 1.00 +/- 0.046 mmHg.ml-1.min.100 g). RC was similar between the chronically ligated limbs of Sed and Tr rats (1.69 +/- 0.165 vs. 1.97 +/- 0.227 mmHg.ml-1.min.100 g) and was approximately 70% lower than in acutely ligated limbs of both groups. Rfmc and Rimc were not affected by arterial ligation, but Rimc was significantly lower in Tr than in Sed rats (acute: 1.05 +/- 0.026 vs. 1.54 +/- 0.163; chronic: 1.24 +/- 0.071 vs. 1.81 +/- 0.202 mmHg.ml-1.min.100 g). These results indicate that the primary site of vascular adaptations to chronic arterial ligation is in the collateral vessels. Exercise training does not significantly alter the collateralization process but may provide protection against acute arterial occlusion by stimulating microvascular growth.

Arterial and arteriolar contributions to skeletal muscle functional hyperemia in spontaneously hypertensive rats.

During contractions of the spinotrapezius muscle in spontaneously hypertensive rats (SHR), arteriolar dilation is of normal magnitude but tissue PO2 is significantly depressed relative to normotensive [Wistar-Kyoto (WKY)] rats. This study examined the possibility that this low PO2 results from suppressed dilation of the upstream arterial feed vessels and a limitation of muscle blood flow. Contraction-induced changes in vascular resistances (R) and conductances (G) were calculated for upstream (Rup, Gup), microvascular (Rst, Gst), and downstream (Rdown, Gdown) vascular segments from measurements of pressure and flow in the rostral feed artery and vein. Feed arteries were smaller in SHR than in WKY rats at rest and after contractions (rest, 63.0 +/- 2.6 vs. 86.0 +/- 4.8 microns; 2 Hz 84.0 +/- 4.5 vs. 111.0 +/- 7.3 microns; 8 Hz, 130.0 +/- 5.9 vs. 144.0 +/- 7.1 microns). However, relative increases [times control (xCT)] in diameter and flow were greater in SHR (8 Hz diam, 2.080 +/- 0.072 vs. 1.690 +/- 0.042 xCT; 8 Hz flow, 15.700 +/- 2.057 vs. 8.170 +/- 0.752 xCT). In both groups, Rup and Rst decreased 60-70 and 85-90% after 2- and 8-Hz contractions, respectively. However, segmental vascular conductances increased more in SHR than in WKY rats (8 Hz: Gup, 18.50 +/- 3.76 vs. 8.00 +/- 1.26 xCT; Gst, 19.90 +/- 3.73 vs. 10.10 +/- 0.96 xCT; Gdown, 8.80 +/- 1.70 vs. 5.50 +/- 0.88 xCT). Therefore, upstream arterial dilation is not suppressed during muscle contractions in SHR, and deficits in muscle blood flow and oxygen delivery cannot account for the abnormally low tissue PO2 observed during muscle contractions in SHR.

Role of a lymphatic system in glucose absorption and the accompanying microvascular hyperemia.

In this study we evaluated the importance of a functional intestinal lymphatic system on changes in arteriolar and venular blood oxygen content, vasodilation, and elevation of venous blood osmolarity during glucose absorption. Glucose absorption was associated with a doubling of the arteriovenous oxygen difference [(A-V)O2], a 50 mosM increase in venous blood osmolarity, and 17% dilation of the intermediate-diameter arterioles. After the lymph vessels were mechanically blocked with mineral oil, glucose absorption again doubled the (A-V)O2, indicating that glucose was absorbed without a functional lymphatic system. Furthermore, venous blood osmolarity and arteriolar diameter increased similarly with and without a functional lymphatic system. This study indicates that even though the lymphatic system likely facilitates distribution of hypertonic material in the bowel wall during absorption, blockade of the lymphatics did not appreciably hinder vasodilation, glucose absorption, changes in intravascular oxygen content, or the elevation of tissue hyperosmolarity, as judged by the tonicity of the venular blood. Therefore, passage of materials absorbed or released in the mucosa to the submucosa through venular blood flow may be very important to the mechanism of absorptive hyperemia.

Active and passive arteriolar regulation in spontaneously hypertensive rats.

This study determined to what extent active and passive wall tensions increase in in vivo intestinal arterioles of 13- to 15-week-old and 25- to 27-week-old spontaneously hypertensive rats (SHR) to maintain normal or smaller arteriolar diameters during microvascular hypertension. Acetylcholine and nitroprusside were used to determine whether vascular muscle relaxation to endothelium-derived relaxing factor or cyclic GMP is impaired. Large arterioles of hypertensive rats have passive tension-circumference relations that are steeper and shifted to the left compared with those of age-matched controls; passive resistance to distension limits vasodilation in hypertensive rats except at their naturally elevated arteriolar pressure. Passive tension contributes approximately 30% of the total resting tension in arterioles of hypertensive and normotensive rats because a greater passive tension occurs at the 20% to 25% constricted resting diameter in hypertensive rats. Absolute and relative changes in the diameter of SHR arterioles during acetylcholine and nitroprusside application were equal to or greater than those in Wistar-Kyoto rats. However, reduction in active tension was suppressed in older SHR and remained approximately 50% higher than that found in older Wistar-Kyoto rats during drug application. Vasoconstriction and increased passive resistance to distension of the arteriolar wall diminish the active tension required to maintain normal or smaller resting diameters against microvascular hypertension. However, the elevated microvascular pressure in hypertensive rats is required to allow near-normal dilation to compensate for their increased passive resistance to stretch and decreased ability to relax active tension through cyclic GMP mechanisms.

Contribution of arterial feed vessels to skeletal muscle functional hyperemia.

The purpose of this study was to determine whether dilation of arterial vessels preceding the microcirculation contributes differentially to increases in skeletal muscle blood flow during contractions in anesthetized sedentary (SED) or trained (TR) rats. Experiments were performed in the spinotrapezius muscle of adult male Sprague-Dawley rats. Before and immediately after muscle contractions (2, 4, or 8 Hz), intravascular pressures, red blood cell velocities, and vessel diameters were measured in terminal feed arteries at a site before penetration into the tissue. Pressure was also measured in the accompanying vein. Contraction-induced changes in vascular resistance were calculated for upstream (Rup), spinotrapezius muscle microvascular (Rst), and downstream segments. At rest, Rup accounted for less (32 vs. 40%) and Rst for more (59 vs. 47%) of total resistance in TR than in SED rats. At 8 Hz, contractions produced significantly greater functional dilation (SED, 138 +/- 14 microns; TR, 178 +/- 12 microns) and hyperemia (SED, 11.9 +/- 3.2 x control; TR, 16.8 +/- 3.1 x control) in TR than in SED rats. Inflow pressures did not change, and outflow pressures increased significantly with contractions. Rup and Rst each decreased 60-80% after 2-Hz contractions and > 90% after 8-Hz contractions. Therefore, feed artery dilation contributes significantly to functional hyperemia in the rat spinotrapezius muscle. Furthermore, it appears that aerobic exercise training results in a redistribution of segmental vascular resistance between feed vessels and the microcirculation.

Adrenergic and pressure-dependent vascular regulation in sedentary and trained rats.

In this study, we determined if aerobic exercise training alters adrenergic or pressure-dependent vascular regulation in the rat hindlimb or intestine. Pressor responses to bilateral carotid artery occlusion and systemic phenylephrine (PE) infusion were not altered by training. During occlusion, peak and steady-state changes in hindlimb vascular resistance (HLR) were significantly greater in trained (24 and 13%) than in sedentary (8 and -3%) rats; a similar trend existed for intestinal vascular resistance (IR). The pressure-dependent contribution was consistent between groups (HLR: peak 55-85%, steady state 25-45%; IR: peak and steady state 40-65%). During PE infusion, increases in IR and HLR were similar between groups. The increase in HLR was substantially pressure dependent in both groups (approximately 50% at highest dose) as was the change in IR in trained rats. However, the IR response to PE was not pressure dependent in sedentary rats. The direct effects of PE were similar between sedentary and trained rats in the hindlimb but were suppressed in the intestine of trained rats compared with sedentary rats. Therefore, aerobic exercise training altered adrenergic and pressure-dependent vasoregulatory mechanisms in both skeletal muscle and intestinal tissues.

Topical hyperglycemia rapidly suppresses EDRF-mediated vasodilation of normal rat arterioles.

Arteriolar dilation to endothelium-derived relaxing factor (EDRF) is suppressed early in diabetes mellitus. The purpose of this study was to determine whether acute exposure to a hyperglycemic media can suppress EDRF function of normal arterioles. Dilation of intestinal arterioles to iontophoretically applied acetylcholine (ACh) and nitroprusside was measured in normoglycemic rats before and after 1 h of topical exposure to isotonic solutions containing D-glucose concentrations of 200, 300, and 500 mg/100 ml. Exposure to a D-glucose concentration of 200 mg/100 ml had no effect on vasodilation to ACh. D-Glucose concentrations of both 300 and 500 mg/100 ml caused significant suppression of the responses: for example, at the approximate 50% effective dosage (100 nA), the dilatory response was decreased by 60% at a D-glucose concentration of 300 mg/100 ml and 55% at a D-glucose concentration of 500 mg/100 ml. Responses to nitroprusside were not significantly (P < 0.05) impaired after exposure to D-glucose concentrations of 200, 300, or 500 mg/100 ml. Exposure to an isotonic L-glucose concentration of 500 mg/100 ml for 1 h had no significant (P > 0.05) effect on responses to ACh. Pretreatment with superoxide dismutase, catalase, indomethacin, or meclofenamic acid preserved EDRF-mediated vasodilation during exposure to a D-glucose concentration of 500 mg/100 ml at almost all the ACh dosages tested. These results indicate that oxygen radicals formed in part by increased eicosanoid synthesis during exposure to D-glucose hyperglycemia interfere with the EDRF mechanism before its action on the microvascular smooth muscle.

Evaluation of carbocyanine-labeled erythrocytes for microvascular measurements.

Red blood cells labeled with the carbocyanine dyes, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO), were evaluated for use in making microvascular measurements in rat small intestine and spinotrapezius muscle. We determined the minimum concentration of each dye which produced near maximal fluorescent intensity and labeled cell fraction. These dyes, which have excitation and emission spectra similar to fluorescein and rhodamine derivatives, have a number of advantages over the isothiocyanates: (1) the labeling procedure is quicker, easier, and less expensive; (2) the labeled cell fraction and the fluorescent intensity of DiI and DiO cells are stable for long periods of time in the rat circulation; and (3) DiI-labeled cells are brighter and transmit light through overlying erythrocytes better than rhodamine X isothiocyanate. However, in vitro and in vivo evaluations illustrate the potential limiting effects of vessel diameter and cell velocity on the accuracy of microvascular measurements made using this technique. In the small intestine and spinotrapezius muscle preparations, measurements of labeled cell flux were readily reproducible and could be partly automated with image analysis only in capillaries and small venules. Counting labeled cells in larger vessels by human observation or with automation was not reproducible, presumably due to absorption and dispersion of the fluorescent signal by overlying erythrocytes and smearing of the cell image at high cell velocities.

Effects of downhill running on the responses to an oral glucose challenge.

Because muscle damage from eccentric exercise has been associated with alterations in muscle glycogen metabolism, this study determined the effects of exercise on the insulin and glucose responses to an oral glucose tolerance test (OGTT). In a repeated-measures design, 11 subjects undertook either no exercise, 2 min of isokinetic leg exercise, or 50 min of level or downhill running. No exercise was performed and diet was controlled during the 48 hrs after the treatments and before the OGTT. Ratings of muscle soreness and CK activity were significantly elevated 48 hrs after downhill running. Level running also increased CK activity but did not induce muscle soreness. Isokinetic exercise did not affect either one. Blood glucose responses to the OGTT were similar among the treatments. In contrast, the insulin responses to the OGTT following downhill running were significantly increased. These results suggest that eccentric exercise associated with downhill running that results in delayed muscle soreness is associated with the development of a mild insulin-resistant condition.