Video Micrometer Research Articles

Severe Cerebrovascular Dysfunction in a Hypertensive Heart Failure Model

The spontaneously hypertensive, heart failure‐prone rat (SHHF) is a preclinical model of heart failure, and is available in both lean/hypertensive (SHHF‐L) and obese/hypertensive (SHHF‐Ob) strains. While cardiac mechanics have been studied extensively in this model, vascular reactivity of conduit and small arteries has not been evaluated. The aim of this study was to assess vasoreactivity in aortic rings, isolated middle cerebral arteries (MCA), and gracilis arterioles (GA) of adult male SHHF‐L and SHHF‐Ob animals.At 37‐40 weeks of age, vessels were harvested from SHHF animals for evaluation. Aortic rings were placed in a myobath, and MCA and GA into isolated microvessel chambers. Vascular reactivity to dilator/constrictor stimuli was measured by tension myograph or video micrometer. Vasodilation to ACh was significantly impaired in aortic rings and GA of SHHF‐L (70% compared to non‐hypertensive lean control) and SHHF‐Ob (60‐70% to control). However, dilation to ACh in MCAs was reduced more than 50 % to control in the SHHF‐L, and nearly ablated in SHHF‐Ob. Both GA and MCA of SHHF‐L and SHHF‐Ob were hyperconstrictive to adrenergic stimuli. Myogenic reactivity was significantly impaired in MCA of both SHHF‐L and SHHF‐Ob, even compared to GA from the same animals.Our findings reveal severe cerebrovascular dysfunction in both lean and obese SHHFs. SHHF rats are severely hypertensive (MAP>175 mmHg), which impacts vascular tone; however, the difference in reactivity between GA and MCA indicates a more complex pathology. Further investigation is needed to determine the physiological mechanisms of vascular dysfunction in this preclinical animal model.

Chronic AT(1) receptor blockade alters mechanisms mediating responses to hypoxia in rat skeletal muscle resistance arteries.

The goal of this study was to determine the effect of angiotensin type 1 (AT(1)) receptor antagonism on vasodilator responses in isolated skeletal muscle resistance arteries. Normotensive Sprague-Dawley rats were fed normal rat chow with the AT(1) receptor antagonist losartan (1mg/ml) in the drinking water for 7 days and compared with untreated control rats. Changes in the diameter of isolated resistance arteries supplying the gracilis muscle were assessed with a video micrometer. Arteriolar responses to acetylcholine, iloprost, and sodium nitroprusside were unaffected by losartan administration, whereas dilation to reduced Po(2) was converted into a constriction. Hypoxia-induced constriction of vessels from losartan-treated rats was inhibited by endothelium removal or indomethacin (1 microM). Blockade of the PGH(2)-thromboxane A(2) receptor with SQ-29548 (10 microM), thromboxane synthase inhibition with dazoxiben (10 microM), or the addition of the superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPOL, 100 microM) converted hypoxic vasoconstriction to a dilation that was blocked by inhibiting nitric oxide synthase with N(omega)-nitro-l-arginine methyl ester (100 microM). These data suggest that AT(1) receptor activation has an important role in maintaining the vascular release of prostaglandins responsible for mediating hypoxic dilation in skeletal muscle microvessels.

Pressure-diameter relationship in the human greater saphenous vein

Background Compliance of artificial and autologous vascular grafts is related to future patency. We investigated whether differences in compliance exist between saphenous vein grafts derived from the upper or lower leg, which might indicate upper or lower leg saphenous vein preference in coronary artery bypass surgery. Furthermore, the effect of perivenous application of fibrin glue on mechanical vein wall properties was studied to evaluate its possible use as perivenous graft support. Methods Vein segments (N = 10) from upper or lower leg saphenous vein grafts were collected for histopathologic examination and smooth muscle cell/extracellular matrix (SMC/ECM) ratio was calculated. This ratio is suggested to be related with vascular elastic compliance. In a second group vein graft segments (N = 6) from upper and lower leg were placed in an in vitro model generating stepwise increasing static pressure up to 150 cm H 2O. Outer diameter was measured continuously with a video micrometer system. Distensibility was calculated from the pressure-diameter curves. A third group of vein graft segments (N = 7) was pressurized after fibrin glue application to prevent overdistension, and studied in the same setup. Results Vein segments from the lower leg demonstrated a consistent higher relative response compared with the upper leg saphenous vein graft (0.9176 ± 0.03993 vs 0.5245 ± 0.02512). Both reach a plateau in the high-pressure range (> 100 cm H 2O). A significant difference in in vitro distensibility between upper and lower leg saphenous vein was only found at a pressure of 50 cm H 2O ( p < 0.05). With fibrin glue, support overdistension is prevented as revealed by the maximum relative response between fibrin glue supported upper and lower leg saphenous vein segments (0.4080 ± 0.02464 vs 0.582 ± 0.051), and no plateau is reached in the pressure range up to 150 cm H 2O. Conclusions No upper or lower leg saphenous vein preference could be deduced from the differences in pressure-diameter response due to loss of distensibility (and thus of compliance) in the high-pressure range. Fibrin glue effectively prevents overdistension and preserves some distensibility in the high-pressure range in both the upper and lower leg saphenous vein. This might provide a basis for clinical application of perivenous support.

Chronic intermittent hypoxia impairs endothelium-dependent dilation in rat cerebral and skeletal muscle resistance arteries.

The goal of the present study was to evaluate the effects of relatively short-term chronic intermittent hypoxia (CIH) on endothelial function of resistance vessels in the skeletal muscle and cerebral circulations. Sprague-Dawley rats were exposed to 14 days of CIH (10% fraction of inspired oxygen for 1 min at 4-min intervals, 12 h/day, n = 6). Control rats (n = 6) were housed under normoxic conditions. After 14 days, resistance arteries of the gracilis muscle (GA) and middle cerebral arteries (MCA) were isolated and cannulated with micropipettes, perfused and superfused with physiological salt solution, and equilibrated with 21% O2-5% CO2 in a heated chamber. The arteries were pressurized to 90 mmHg, and vessel diameters were measured via a video micrometer before and after exposure to ACh (10-7-10-4 M), sodium nitroprusside (10-6 M), and acute reduction of Po2 in the perfusate/superfusate (from 140 to 40 mmHg). ACh-induced dilations of GA and MCA from animals exposed to CIH were greatly attenuated, whereas responses to nitroprusside were similar to controls. Dilations of both GA and MCA in response to acute reductions in Po2 were virtually abolished in animals exposed to CIH compared with controls. These findings suggest that exposure to CIH reduces the bioavailability of nitric oxide in the cerebral and skeletal muscle circulations and severely blunts vasodilator responsiveness to acute hypoxia.

Augmented adrenergic vasoconstriction in hypertensive diabetic obese Zucker rats.

This study examined skeletal muscle microvessel reactivity to constrictor stimuli in obese (OZR) versus lean Zucker rats (LZR). Gracilis arteries from both rat groups were isolated, cannulated with glass micropipettes, and viewed via television microscopy. Changes in vessel diameter were measured with a video micrometer. Arterial constriction to norepinephrine was elevated in OZR versus LZR, although vasoconstrictor reactivity to endothelin and angiotensin II was unaltered. Differences in reactivity between vessels of LZR and OZR were not explained by the loss of either endothelial nitric oxide synthase or beta-adrenergic receptor function. Reactivity of in situ cremasteric arterioles of OZR to norepinephrine was elevated versus LZR. Treatment with prazosin increased the diameter of in vivo gracilis arteries of OZR to levels determined in LZR and also normalized blood pressure in OZR. These results suggest that the constrictor reactivity of skeletal muscle microvessels in OZR is heightened in response to alpha-adrenergic stimuli and that development of diabetes in OZR may be associated with impaired skeletal muscle perfusion and hypertension due to microvessel hyperreactivity in response to sympathetic stimulation.

Variation of proposed correlation indices of cerebrovascular reactivity with change of arteriolar diameter.

The purpose of this study was to examine the relationship between proposed correlation indices of cerebrovascular reserve and corresponding changes of cerebrovascular reserve as measured by changes of pial arteriolar diameter. Mild and severe physiologic challenge was produced in piglets by appropriate ventilation with foreign gas mixture and altered alveolar ventilation. Intracranial pressure (ICP), arterial blood pressure (ABP), and video micrometer recordings of pial arteriolar diameter were made. Serial values of ICP and ABP were used to compute the Correlation Coefficient index (Corrx) and the Pressure Reactivity Index (PrX). For the 10 mild physiologic challenge experiments, correlations between percent change index (% delta Corrx and % delta PrX) and percent change of pial arteriolar diameter (% delta dia.) induced by mild challenges (n = 40) were 0.51 (p < .005) and 0.097 (p n.s.) respectively. For 8 asphyxia experiments, serial values with respect to time of the correlation indices were correlated with % delta dia. obtained before, during induction and recovery. The grand mean (n = 8) correlation values (+/- S.D.) of the Corrx and PrX were 0.76 (+/- 0.18, p < .025) and 0.21 (+/- 0.38, p n.s.) respectively. In contrast to the PrX index, changes of the Corrx index significantly correlated with changes of pial arteriolar diameter. However, Corrx and PrX were simultaneously high only during a state of maximum dilation. These findings suggest that sudden salient increases of the Corrx and PrX indices induced by physiologic challenge are indicative of vigorous dilatory response of the cerebral arterioles and loss of cerebrovascular reserve.

Role of Prostanoids and 20-HETE in Mediating Oxygen-Induced Constriction of Skeletal Muscle Resistance Arteries

This study determined the contribution of cytochrome P450 (CP450) 4A enzyme metabolites of arachidonic acid in mediating the constriction of isolated rat skeletal muscle resistance arteries in response to elevated PO2. Gracilis arteries (GA) were viewed via television microscopy and constrictor responses to elevated PO2 were measured with a video micrometer. Endothelium removal and treatment of GA with 17-octadecynoic acid (17-ODYA; suicide substrate inhibitor of CP450 4A enzymes) impaired oxygen-induced constriction of the vessels; treatment of endothelium-denuded GA with 17-ODYA eliminated responses to elevated PO2. NOS inhibition and inhibition of EET production had no effect on oxygen-induced constriction of the vessels, although cyclooxygenase inhibition with indomethacin impaired GA responses to elevated PO2. Treatment of GA with dibromododecenyl methylsulfimide (DDMS; inhibitor of 20-hydroxyeicosatetraenoic acid (20-HETE) production) or 6(Z),15(Z)-20-HEDE (antagonist for 20-HETE receptors) mimicked the effects of 17-ODYA on GA responses to elevated PO2. Treatment of vessels with iberiotoxin or glibenclamide reduced the constriction of the vessels in response to elevated PO2 while treatment with both K+ channel blockers eliminated oxygen-induced constriction of the vessels. Following treatment of GA with indomethacin and 20-HETE, the vessels failed to respond to elevated PO2. These results suggest that oxygen-induced constriction of skeletal muscle resistance arteries represents the combined effects of reduced prostanoid release from the vascular endothelium and enhanced 20-HETE production in vascular smooth muscle cells.

Impaired NO-dependent dilation of skeletal muscle arterioles in hypertensive diabetic obese Zucker rats.

This study determined alterations to nitric oxide (NO)-dependent dilation of skeletal muscle arterioles from obese (OZR) versus lean Zucker rats (LZR). In situ cremaster muscle arterioles from both groups were viewed via television microscopy, and vessel dilation was measured with a video micrometer. Arteriolar dilation to acetylcholine and sodium nitroprusside was reduced in OZR versus LZR, although dilation to aprikalim was unaltered. NO-dependent flow-induced arteriolar dilation (via parallel microvessel occlusion) was attenuated in OZR, impairing arteriolar ability to regulate wall shear rate. Vascular superoxide levels, as assessed by dihydroethidine fluorescence, were elevated in OZR versus LZR. Treatment of cremaster muscles of OZR with the superoxide scavengers polyethylene glycol-superoxide dismutase and catalase improved arteriolar dilation to acetylcholine and sodium nitroprusside and restored flow-induced dilation and microvascular ability to regulate wall shear rate. These results suggest that NO-dependent dilation of skeletal muscle microvessels in OZR is impaired due to increased levels of superoxide. Taken together, these data suggest that the development of diabetes and hypertension in OZR may be associated with an impaired skeletal muscle perfusion via an elevated vascular oxidant stress.

Relative Contributions of Cyclooxygenase- and Cytochrome P450 ω-Hydroxylase-Dependent Pathways to Hypoxic Dilation of Skeletal Muscle Resistance Arteries

This study determined the contribution of prostanoids, cytochrome P450 (CP450) 4A enzyme metabolites of arachidonic acid, and other potential mediators of hypoxic dilation of isolated rat skeletal muscle resistance arteries. Gracilis arteries (GA) were viewed via television microscopy and dilator responses to hypoxia (reduction in superfusate and perfusate PO₂ from ∼145 to ∼40 mm Hg) were measured with a video micrometer. Hypoxic dilation of gracilis arteries was severely impaired by either endothelium removal or cyclooxygenase inhibition with indomethacin, but not by nitric oxide synthase inhibition with L-NAME. Treatment of GA with 17-octadecynoic acid (17-ODYA) alone to inhibit CP450 4A enzymes significantly reduced hypoxic dilation from control levels. Treatment of vessels with N-methylsulfonyl-6-(2-proparglyoxyphenyl)hexanoic acid (MS-PPOH) to inhibit the production of epoxyeicosatrienoic acids (EETs) did not alter hypoxic dilation, although treatment with dibromo-dodecenyl-methylsulfimide (DDMS) to inhibit 20-hydroxyeicosatetraenoic acid (20-HETE) production had similar effects as 17-ODYA. Treatment of GA with 6(Z),15(Z)-20-HEDE, a competitive antagonist of the actions of 20-HETE, mimicked the effects of 17-ODYA and DDMS treatment on hypoxic dilation. These results suggest that hypoxic dilation of skeletal muscle resistance arteries primarily represents the effects of enhanced prostanoid release from vascular endothelium, although a contribution of reduced 20-HETE production via CP450 ω-hydroxylase enzymes also regulates hypoxic dilation of these vessels.

Altered Mechanisms Underlying Hypoxic Dilation of Skeletal Muscle Resistance Arteries of Hypertensive versus Normotensive Dahl Rats

To determine mechanisms underlying hypoxic dilation of skeletal muscle resistance arteries from normotensive (NT) and hypertensive (HT) Dahl salt-sensitive (SS) rats. Isolated gracilis arteries (GA) from both rat groups were viewed via television microscopy and vascular responses to a reduction in PO2 from 145 mm Hg to 40 mm Hg were measured with a video micrometer. Responses were determined following endothelium removal and following inhibition of specific biochemical pathways regulating vascular tone. Hypoxic dilation was impaired in HT rats versus NT controls. Endothelium removal abolished hypoxic dilation in NT rats, although a significant dilation to hypoxia remained in vessels from HT animals. Inhibition of cytochrome P450 (CP450) 4A enzymes blunted hypoxic dilation in both groups, while inhibition of epoxyeicosatrienoic acid (EET) production impaired responses in NT rats only. Inhibition of 20-hydroxyeicosatetraenoic acid (20-HETE) production or blockade of membrane receptors for 20-HETE reduced hypoxic dilation in HT rats, with minimal effects in NT animals. Nitric oxide synthase inhibition had no effect on hypoxic dilation in either group, while cyclooxygenase inhibition significantly reduced this response in both groups. These results suggest that the mechanisms of hypoxic dilation in GA from NT Dahl-SS rats are altered with HT, impairing the response to reduced PO2. While hypoxia induces substantial prostanoid release in both groups, the role of CP450 4A enzymes is shifted from EET production in NT rats toward inhibition of 20-HETE production in HT rats.

20-HETE modulates myogenic response of skeletal muscle resistance arteries from hypertensive Dahl-SS rats.

The present study determined the role of 20-hydroxyeicosatetraenoic acid [20-HETE; produced by omega-hydroxylation of arachidonic acid via cytochrome P-450 (CP450) 4A enzymes] in regulating myogenic activation of skeletal muscle resistance arteries from normotensive (NT) and hypertensive (HT) Dahl salt-sensitive (SS) rats. Gracilis arteries (GA) were isolated from each rat and viewed via television microscopy, and changes in vessel diameter with altered transmural pressure were measured with a video micrometer. Under control conditions, GA from both groups exhibited strong, endothelium-independent myogenic activation. Treatment of GA with 17-octadecynoic acid (17-ODYA; inhibitor of CP450 4A enzymes) did not alter myogenic activation in NT rats, but impaired this response in HT animals. Treatment of GA from HT rats with dibromo-dodecynyl-methylsulfimide (DDMS; inhibitor of 20-HETE production) impaired myogenic activation, as did application of 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, an antagonist for 20-HETE receptors. Application of iberiotoxin, a Ca(2+)-activated potassium (K(Ca)) channel inhibitor, restored myogenic activation from HT rats treated with DDMS. These results suggest that myogenic activation of skeletal muscle resistance arteries from NT Dahl-SS rats does not depend on CP450, whereas myogenic activation of these vessels in HT Dahl-SS rats is partly a function of 20-HETE production, inhibiting K(Ca) channels through a receptor-mediated process.

20-HETE Contributes to Myogenic Activation of Skeletal Muscle Resistance Arteries in Brown Norway and Sprague-Dawley Rats

Objective: To evaluate the role of 20-hydroxyeicosatetraenoic acid (20-HETE), a product of arachidonic acid ω-hydroxylation via cytochrome P450 (CP450) 4A enzymes, in regulating myogenic activation of skeletal muscle resistance arteries from normotensive Brown Norway (BN) and Sprague-Dawley (SD) rats. Methods: Gracilis arteries (GA) were isolated from each animal, viewed via television microscopy, and vessel diameter responses to elevated transmural pressure were measured with a video micrometer under control conditions and following pharmacological inhibition of the CP450 4A enzyme system. Results: Under control conditions, GA from both rat groups exhibited strong, endothelium-independent myogenic activation, which was impaired following treatment with either 17-octadecynoic acid (17-ODYA) or dibromo-dodecenylmethylsulfimide (DDMS), two mechanistically different inhibitors of 20-HETE production. The addition of tetraethylammonium (KCa channel inhibitor) to 17-ODYA-treated GA restored myogenic reactivity to levels comparable to those under control conditions. Treatment of GA from BN and SD rats with 6(Z), 15(Z)-20-HEDE, a selective antagonist for 20-HETE receptors, mimicked the effects of 17-ODYA and DDMS treatment on myogenic reactivity. Conclusions: These results suggest that the production of 20-HETE via CP450 4A enzymes contributes to the myogenic activation of skeletal muscle resistance arteries from normotensive BN and SD rats. 20-HETE may act through a receptor-mediated process to block vascular smooth muscle KCa channels in response to the elevated transmural pressure.

Contribution of Extrinsic Factors and Intrinsic Vascular Alterations to Reduced Arteriolar Reactivity with High-Salt Diet and Hypertension

To determine whether the impaired relaxation of skeletal muscle arterioles of rats on high-salt diet or with reduced renal mass hypertension (RRM-HT) represents intrinsic alterations to microvessels alone, or whether extravascular influences also contribute to reduced dilator responses. Normotensive (NT) Sprague-Dawley rats were fed low-salt (LS) or high-salt (HS) diets, and RRM-HT rats were fed HS diet for 4-6 weeks. In situ and isolated cremaster muscle first-order arterioles (1A) were examined using television microscopy, and a video micrometer was used to measure diameter changes in response to acetylcholine (ACH), cholera toxin (CT), and sodium nitroprusside (SNP). Compared to normotensive low-salt (NT-LS) rats, responses of 1A to the agonists were reduced in normotensive high-salt (NT-HS) and RRM-HT rats. Arteriolar reactivity to the agonists in NT-LS rats aid in NT-HS rats was not different between in situ and in vitro environments. However, in RRM-HT rats, the reactivity of 1A to each agonist was greater in isolated arterioles than in in situ arterioles. These results suggest that the impaired response of skeletal muscle arterioles to vasodilator stimuli in normotensive rats on high-salt diet primarily reflects alterations to microvessels alone, while reduced dilator responses in RRM-HT rats represent a combination of extravascular influences and intrinsic alterations to arterioles themselves.

Impairment of Flow-Induced Dilation of Skeletal Muscle Arterioles with Elevated Oxygen in Normotensive and Hypertensive Rats

The effects of elevated PO2 on flow-induced dilation of in situ skeletal muscle arterioles was assessed in cremaster muscle preparations from spontaneously hypertensive rats (SHR) and normotensive Wistar–Kyoto (WKY) rats. Blood flow increases in selected arterioles were initiated by occlusion of a parallel daughter branch from a parent arteriole. Changes in the diameter of the perfused arteriole were measured with a video micrometer and erythrocyte velocity was measured using optical Doppler velocimetry. Superfusate PO2 was controlled by changing the O2 concentration (0% O2 or 21% O2) of the equilibration gas mixture. The increase in arteriolar diameter during occlusion was reduced in SHR compared to WKY rats, resulting in an elevated wall shear rate in SHR. Elevated PO2 decreased flow-induced dilation in both groups and increased wall shear rate during parallel occlusion. An inhibitor of the formation of 20-HETE via cytochrome P450-4A enzymes (P450), dibromododecenyl methylsulfimide, minimized O2-induced constriction of arterioles and prevented the O2-induced decrease in flow-induced dilation and the increase in wall shear rate in both SHR and WKY rats. These results suggest that: (1) flow-induced dilation of in situ skeletal muscle arterioles is impaired in SHR compared to WKY, (2) elevated O2 compromises flow-induced dilation in both groups, (3) 20-HETE contributes to both the O2-induced increases in resting tone and the reduced flow-induced dilation of cremasteric arterioles with elevated PO2.

Elevated Oxygen Tension Inhibits Flow-Induced Dilation of Skeletal Muscle Arterioles

The purpose of this study was to determine if elevated oxygen tension affects flow-induced dilation of in situ skeletal muscle arterioles. Cremaster muscle preparations from Sprague-Dawley rats were superfused with physiological salt solution (PSS) and viewed via television microscopy. A video micrometer was used to measure changes in arteriolar diameter in response to the increase in flow produced by occlusion of a parallel branch from the parent arteriole. Erythrocyte velocity was measured with an optical Doppler velocimeter. The superfusate PO2 was altered by changing the oxygen concentration of the equilibration gas between 0 and 21% O2. Elevation of superfusate PO2 to 10% O2 and 21% O2 significantly decreased arteriolar diameter compared to the control diameter during 0% O2 superfusion. Increases in arteriolar diameter during parallel arteriolar occlusion were reduced as superfusate PO2 was elevated. However, elevated PO2 had no significant effect on erythrocyte velocity through the perfused daughter vessel, either prior to or during parallel occlusion. As a result, blood flow through the dilating vessel was reduced with elevated PO2. As a result of the reduced arteriolar diameter, wall shear rate in the perfused daughter vessel was increased with elevated PO2, both prior to and during parallel occlusion. These observations demonstrate that elevated PO2 can override flow-induced vasodilation in the skeletal muscle microcirculation, leading to the persistence of an elevated wall shear rate.

Chronic captopril administration decreases vasodilator responses in skeletal muscle arterioles

Changes in arteriolar reactivity to dilator agonists were assessed in the cremaster muscle of Sprague-Dawley rats fed normal rat chow with captopril (100 mg/kg/day) in the drinking water for 8 weeks and in nontreated controls. The in situ cremaster muscle was prepared, superfused with physiologic salt solution, and arteriolar diameter was measured using television microscopy. Changes in the diameter of distal arterioles in response to topical application of iloprost, forskolin, cholera toxin, acetylcholine, and nitroprusside were measured with a video micrometer. Arteriolar responses to each of the vasodilator agonists used in this study were significantly reduced in the captopril-treated rats, relative to the untreated controls. The maximum dilation of the arterioles, determined during superfusion with Ca 2+-free physiologic salt solution containing 10 −4 mol/L adenosine, was also reduced in the captopril-treated rats, suggesting structural remodeling of the arteriolar wall. These observations indicate that chronic angiotensin converting enzyme inhibition with captopril leads to significant alterations in arteriolar structure and reactivity, and that angiotensin II may play a protective role in maintaining normal vascular structure and vasodilator reactivity in the microcirculation.

Chronic Elevations in Salt Intake and Reduced Renal Mass Hypertension Compromise Mechanisms of Arteriolar Dilation

Alterations in the reactivity of arterioles to vasodilator agonists were assessed in the skeletal muscle microcirculation of age-matched, normotensive male Sprague–Dawley rats fed either a high salt (4% NaCl, HS) or a low salt (0.4% NaCl, LS) diet and in reduced renal mass hypertensive rats on a high salt diet (HSRRM) for 4 weeks. Thein situsuperfused cremaster muscle was prepared for observation by television microscopy. Changes in the microvessel diameter in response to acetylcholine, iloprost, cholera toxin, forskolin, or sodium nitroprusside were measured with a video micrometer. Arteriolar responses to each of the agonists were decreased under both HS and HSRRM conditions. Maximum arteriolar diameter (determined during superfusion with Ca2+-free solution containing 10−4M adenosine) was reduced in HS and HSRRM rats, suggesting anatomic remodeling of the vessels. In normotensive animals on the HS diet, the decreased reactivity was in proportion to the remodeling so the sensitivity index (vascular reactivity corrected for the anatomic remodeling) was not altered. Vascular responses in HSRRM rats were depressed to an extent disproportionate to the remodeling, so that the sensitivity index to the vasodilator agonists was significantly reduced. We conclude that HSRRM hypertension and HS diet (independent of hypertension) can have significant effects on the structure of microvessels and on the reactivity of the arterioles to dilator agonists. The severity of these alterations is greater in HSRRM hypertension than in normotensive rats on HS diets.

チタンクラウンの辺縁部の鋳造性および金属構造に関する研究

Previous studies on dental applications of pure titanium were mainly focused on its mechanical properties rather than its clinical aspects. The purpose of this study was to evaluate the margin castability and mechanical properties of C. P. titanium for better understanding of its suitability for clinical application. To simulate the crown margins, flat wax patterns, which had two different margin thicknesses, i.e., 20 and 40 degrees sharp edges respectively, were used. These patterns were cast using two casting systems, centrifugal and pressure systems. There were statistically significant differences between the samples made from the two types of patterns in terms of cast deficiency at the margins observed with a light microscope and the increased length of the margins measured with a video micrometer, but not between the samples made with the two different systems. Both the thickness of layered structures measured by a metallurgical light microscope and the micro-hardness by a Dynamic Hardness Tester were lowest at the apex of the margins in all samples. These observations were more evident among 20 degree samples than 40 degree samples. The layered structures were different among the casting systems. In conclusion, pure titanium is suitable for clinical application as restorative material when used appropriately.

Immunocytochemical detection of enhanced expression of c-myc protein in the heart of cardiomyopathic hamster.

An immunocytochemical study was performed to examine the expression of cellular c-myc protein in the heart of 30-, 120- and 180-day-old cardiomyopathic Syrian UM-X7.1 hamsters. The heart of age- and sex-matched BIO-RB hamster was used as normal control. In paraffin sections, an immunostaining for c-myc was markedly increased in cytoplasm of cells from the UM-X7.1 heart as compared with that of the BIO-RB heart which showed a weak staining. However, c-myc was localized in nuclei of cells in frozen sections of the heart. Specific cell types of the heart were differentiated with anti-vimentin, and we found that the increased expression of c-myc was present in nuclei of muscle cells of the UM-X7.1 myocardium. A quantitative study of c-myc-positive nuclei of muscle and nonmuscle cells was carried out by a video micrometer. The mean number of c-myc-positive nuclei of muscle cells was significantly higher in the cardiomyopathic heart than in the control heart from hamsters of all ages studied. These results suggest that the increase of c-myc protein may relate to the pathological state or pathogenesis of the hereditary cardiomyopathy.

Two‐dimensional motion of DNA bands during 120° pulsed‐field gel electrophoresis. I. Effect of molecular weight

AbstractThe instantaneous position and velocity of bands of linear, double‐stranded DNA were measured during 120° pulsed‐field electrophoresis in 1% agarose gels, using a video micrometer capable of simultaneous measurements in two dimensions. When the direction of the field was switched, the band initially retraced the last portion of its path during the preceding pulse. The distance the band moved backward increased with DNA length: 48.5 kb (kilobase pair) DNA moved backward only 0.2 μm, but 1110 kb DNA moved backward 24 μm, before setting off in a positive direction. The velocity of the DNA band was particularly rapid during the backward movement: the magnitude of the velocity spike increased with M, reaching 2.4 μm/s for 1110 kb DNN, which was about 5 times the steady‐state velocity. The velocity in the y direction, perpendicular to the mean drift direction, allowed an even larger transient spike, which also increased with M.Simulation of the dynamics of long DNA chins undergoing gel electrophoresis by a dynamic Monte Carlo method gave instantaneous xy position and velocity in excellent agreement with experiment. The simulation included extensional motions of the DNA within the tube of interconnected agarose pores as well as the possibility of loops (hernias) that escape laterally from the tube. © 1995 John Wiley &amp; Sons, Inc.