Television Microscopy Research Articles

Фундаментальная и прикладная технологии диагностики нарушения двигательной активности реснитчатого эпителия верхних дыхательных путей

The modern development of computer and mathematical technologies makes it possible to improve the study of the movement of biological objects of extremely small sizes, including the cilia of epithelial cells of the upper respiratory tract. One of the directions of such research is the mathematical processing of video recordings that record the movement of the cilia of the epithelium of the respiratory tract. The methodology for conducting such studies is laborious and time-consuming. Such research is of a fundamental nature and is carried out primarily for scientific purposes. At the same time, clinical practice requires a fairly simple, objective method for diagnosing the disorder, which allows you to quickly obtain a result in inpatient and outpatient settings. The article presents the results of the development of algorithms for fundamental and applied research of the motor activity of the cilia of the epithelium of the upper respiratory tract using television microscopy and computer mathematical processing. The algorithms and integral criteria developed by the authors for an objective assessment of the motor activity of cilia make it possible to choose a research method depending on the goal. The use of an in-depth fundamental method in research work allows to reveal in detail the mechanism of impairment of motor activity of cilia beating. The use of the method of express diagnostics of cilia movements makes it possible to diagnose a violation, prescribe adequate treatment for correction and objectively evaluate its effectiveness.

Motor activity of ciliary epithelium of the auditory tube tympanic opening in the patients with the middle and the internal ear pathology

The work presents the results of study of the condition and function of the motor activity of the ciliary epithelium of the auditory tube and the middle ear in the patients with various forms of chronic otitis media and patients with non-inflammatory diseases of the middle ear. The method of television microscopy will provide the study of the mucosa structure and the operation of the ciliary epithelium of the auditory tube in various diseases, thus facilitating the prediction of the outcomes of diseases and developing the new techniques aimed at the favorable outcome of the middle ear diseases.

Evaluation of Vascular Control Mechanisms Utilizing Video Microscopy of Isolated Resistance Arteries of Rats.

This protocol describes the use of in vitro television microscopy to evaluate vascular function in isolated cerebral resistance arteries (and other vessels), and describes techniques for evaluating tissue perfusion using Laser Doppler Flowmetry (LDF) and microvessel density utilizing fluorescently labeled Griffonia simplicifolia (GS1) lectin. Current methods for studying isolated resistance arteries at transmural pressures encountered in vivo and in the absence of parenchymal cell influences provide a critical link between in vivo studies and information gained from molecular reductionist approaches that provide limited insight into integrative responses at the whole animal level. LDF and techniques to selectively identify arterioles and capillaries with fluorescently-labeled GS1 lectin provide practical solutions to enable investigators to extend the knowledge gained from studies of isolated resistance arteries. This paper describes the application of these techniques to gain fundamental knowledge of vascular physiology and pathology in the rat as a general experimental model, and in a variety of specialized genetically engineered "designer" rat strains that can provide important insight into the influence of specific genes on important vascular phenotypes. Utilizing these valuable experimental approaches in rat strains developed by selective breeding strategies and new technologies for producing gene knockout models in the rat, will expand the rigor of scientific premises developed in knockout mouse models and extend that knowledge to a more relevant animal model, with a well understood physiological background and suitability for physiological studies because of its larger size.

Mechanisms of electromechanical and electrochemical coupling in olfactory cilia of the frog (Rana temporaria)

The mechanisms of electromechanical and electrochemical coupling in olfactory cilia of the frog (Rana temporaria) have been investigated. High-resolution optical television microscopy of live tissue and pharmacological analysis have been used to reveal the regulation of the motility of olfactory cilia in the absence of odorants; the entry of Ca2+ ions mediated by three types of ion channels (mechanosensitive, cyclic nucleotide gated, and voltage-gated) was shown to determine the motility of cilia. Stimulation of the olfactory adenylate cyclase by movements of the cilia in the absence of odors has been demonstrated and the regulation of cilia motility by membrane potential has been revealed. Membrane potential can affect olfactory acuity and the ability to perceive weak olfactory stimuli in the absence of adequate stimulation.

The Empirical Foundations of Telepathology: Evidence of Feasibility and Intermediate Effects.

Telepathology evolved from video microscopy (i.e., "television microscopy") research in the early 1950s to video microscopy used in basic research in the biological sciences to a basic diagnostic tool in telemedicine clinical applications. Its genesis can be traced to pioneering feasibility studies regarding the importance of color and other image-based parameters for rendering diagnoses and a series of studies assessing concordance of virtual slide and light microscopy diagnoses. This article documents the empirical foundations of telepathology. A selective review of the research literature during the past decade (2005-2016) was conducted using robust research design and adequate sample size as criteria for inclusion. The evidence regarding feasibility/acceptance of telepathology and related information technology applications has been well documented for several decades. The majority of evidentiary studies focused on intermediate outcomes, as indicated by comparability between telepathology and conventional light microscopy. A consistent trend of concordance between the two modalities was observed in terms of diagnostic accuracy and reliability. Additional benefits include use of telepathology and whole slide imaging for teaching, research, and outreach to resource-limited countries. Challenges still exist, however, in terms of use of telepathology as an effective diagnostic modality in clinical practice.

Television pyrometry improvement

The article analyzes the problem of television pyrometry improvement by determination of the range of linearity of the television system luminous-signal characteristics. The contemporary scientific literature practically does not have any materials on the relevant research methods or their results. It places special emphasis on the importance of the problems, laid down in this article.If we consider characteristics, that determine accuracy of the temperature measurement in methods of the television bispectral pyrometry, the main characteristics shall be equivalent wavelength, effective to the noise difference of color temperatures and luminoussignal characteristic. Clearly, accuracy of the temperature measurement is affected by a dark signal range of the specific device. First of all, in such a case it is necessary to make experimental studies of performance of the facilities, which are used today or evaluated from the perspective of their use in the bispectral television pyrometry. We have accumulated a considerable amount of experimental materials in course of the experiments. They concern formation of signals both in the television information-measuring system parameters of zonal melting, and in the television equipment of another destination, particularly, in the television pyrometers that can be used for control over the temperature conditions for pipe rolling technologies, in the television devices for food product quality control, environmental monitoring, in the television microscopy etc.

Reduced angiotensin II levels cause generalized vascular dysfunction via oxidant stress in hamster cheek pouch arterioles

ObjectivesWe investigated the effect of suppressing plasma angiotensin II (ANG II) levels on arteriolar relaxation in the hamster cheek pouch. MethodsArteriolar diameters were measured via television microscopy during short-term (3–6days) high salt (HS; 4% NaCl) diet and angiotensin converting enzyme (ACE) inhibition with captopril (100mg/kg/day). ResultsACE inhibition and/or HS diet eliminated endothelium-dependent arteriolar dilation to acetylcholine, endothelium-independent dilation to the NO donor sodium nitroprusside, the prostacyclin analogs carbacyclin and iloprost, and the KATP channel opener cromakalim; and eliminated arteriolar constriction during KATP channel blockade with glibenclamide. Scavenging of superoxide radicals and low dose ANG II infusion (25ng/kg/min, subcutaneous) reduced oxidant stress and restored arteriolar dilation in arterioles of HS-fed hamsters. Vasoconstriction to topically-applied ANG II was unaffected by HS diet while arteriolar responses to elevation of superfusion solution PO2 were unaffected (5% O2, 10% O2) or reduced (21% O2) by HS diet. ConclusionsThese findings indicate that sustained exposure to low levels of circulating ANG II leads to widespread dysfunction in endothelium-dependent and independent vascular relaxation mechanisms in cheek pouch arterioles by increasing vascular oxidant stress, but does not potentiate O2- or ANG II-induced constriction of arterioles in the distal microcirculation of normotensive hamsters.

Restoration of Vascular Relaxation in Cerebral Arteries of Congenic Dahl Rats Receiving the Brown Norway (BN) Renin Gene

The Dahl Salt Sensitive (SS) rat exhibits impaired regulation of the renin‐angiotensin system (RAS), chronically low levels of angiotensin II, and impaired vascular relaxation in response to vasodilator stimuli. This impaired vascular relaxation is likely due to chronic exposure of the animals to low levels of ANG II. The present study investigates responses to vasodilator stimuli in two different congenic strains in which a portion of the BN chromosome 13 was inserted onto the SS genetic background. Congenic strain SS.BN‐(D13rat88‐D13rat105) contains a 2.9 Mbp portion of chromosome 13 which excludes the BN renin gene, and would not be expected to restore normal regulation of the RAS. Congenic strain SS.BN‐(D13hmgc41‐D13hmgc23) contains a 2.0 Mbp adjacent region that includes the BN renin gene, which should restore normal ANG II levels in animals fed low salt (LS) diet. Males from each congenic strain were fed a LS diet (0.4% NaCl) after weaning. At the age of 10–14 weeks, middle cerebral arteries (MCA) were isolated and cannulated and dilator responses to acetylcholine (10−10M–10−5M) and reduced PO2 were assessed using television microscopy. MCA from the congenic strain containing the BN allele for renin dilated in response to acetylcholine and reduced PO2 while the MCA from the congenic strain containing the SS renin allele did not. These results suggest that the presence of a normally functioning renin gene from the BN rat in the SS genetic background restores normal vasodilator responses in the MCA. [NIH #HL‐29587; #HL‐65289, and #HL‐72920].

SKELETAL MUSCLE ARTERIOLAR CONSTRICTION TO VASOPRESSIN AND ANGIOTENSIN II IS DEPENDENT ON PROTEIN KINASE C ACTIVATION

Arginine vasopressin (AVP) and angiotensin II (ANG II) regulate systemic vascular resistance and regional blood flow by virtue of their potent constrictor effects. In skeletal muscle, ANG II elicits a significant, but brief constriction of arterioles, whereas AVP causes a long-lasting contraction. PKC is known to mediate the effects of both agonists in cultured smooth muscle cells and isolated, pressurized skeletal muscle arterioles. We investigated the role of PKC to mediate constriction of in vivo skeletal muscle arterioles in response to both agonists. Male Sprague Dawley rats were anesthetized and the intact cremaster muscle was exteriorized and outstretched in a pH- and temperature-controlled bath for visualization of the microcirculation using in vivo television microscopy. The constriction of third-order arterioles to Ang II or AVP was quantified before and after treatment with PKC inhibitors (Calphostin C, staurosporine or bisindolylmaleimide I). Cremaster muscle PKC activity was measured. Staurosporine and bisindolylmaleimide I (BIM) inhibited PKC activity by >75% and inhibited arteriolar constriction to both agonists. Calphostin C failed to inhibit PKC activity or arteriolar constriction to either agonist. Thus PKC activation plays a significant role in the transient constriction elicted by Ang II and the sustained response to AVP in intact skeletal muscle arterioles.

Neurogenic vasoconstriction of pial arterial vessels of various branching orders in normotensive and spontaneously hypertensive rats

Intravital television microscopy was employed to study the reaction of pial arteries in normotensive and spontaneously hypertensive rats to stimulation of the superior cervical ganglion. The amplitude of constrictor response was similar in WKY and SHR animals. Under conditions of normal arterial pressure and arterial hypertension, the maximum constrictor effect was attained due to equal involvement of the arteries from all generations in the normotensive rats and predominant constriction of the precortical arterioles in SHR animals.

Chronic intermittent hypoxia alters NE reactivity and mechanics of skeletal muscle resistance arteries

Although arterial dilator reactivity is severely impaired during exposure of animals to chronic intermittent hypoxia (CIH), few studies have characterized vasoconstrictor responsiveness in resistance arteries of this model of sleep-disordered breathing. Sprague-Dawley rats were exposed to CIH (10% inspired O2 fraction for 1 min at 4-min intervals; 12 h/day) for 14 days. Control rats were housed under normoxic conditions. Diameters of isolated gracilis muscle resistance arteries (GA; 120-150 microm) were measured by television microscopy before and during exposure to norepinephrine (NE) and angiotensin II (ANG II) and at various intraluminal pressures between 20 and 140 mmHg in normal and Ca2+-free physiological salt solution. There was no difference in the ability of GA to constrict in response to ANG II (P = 0.42; not significant; 10(-10)-10(-7) M). However, resting tone, myogenic activation, and vasoconstrictor responses to NE (P < 0.001; 10(-9)-10(-6) M) were reduced in CIH vs. controls. Treatment of rats with the superoxide scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (tempol; 1 mM) in the drinking water restored myogenic responses and NE-induced constrictions of CIH rats, suggesting that elevated superoxide production during exposure to CIH attenuates vasoconstrictor responsiveness to NE and myogenic activation in skeletal muscle resistance arteries. CIH also leads to an increased stiffness and reduced vessel wall distensibility that were not correctable with oral tempol treatment.

Chronic At1 Receptor Blockade Alters the Mechanisms Mediating Hypoxic Dilation in Middle Cerebral Arteries

The purpose of this study was to determine whether chronic blockade of the angiotensin II (ANG II) AT1 receptor under normal physiological conditions impairs vascular relaxation mechanisms in isolated middle cerebral arteries (MCA). Male Sprague-Dawley rats on a standard diet were given losartan (1 mg/mL) in the drinking water or normal water ad libitum for 7 days. Vessel diameters were measured by television microscopy before and during exposure to various vasodilator agonists and reductions in PO2 from 140 mm Hg to 35-45 mm Hg. Dilations to acetylcholine (1 microM), the stable prostacyclin analogue iloprost (10 pg/mL), and the Gs protein activator cholera toxin (1 ng/mL) were completely eliminated in vessels from losartan-treated animals. However, middle cerebral arteries from control and losartan-treated rats still demonstrated significant dilations in response to reduced PO2. Hypoxic dilation of middle cerebral arteries from control rats was eliminated by indomethacin (1 microM) and unaffected by the NOS inhibitor L-NAME (100 microM) whereas dilation in response to reduced PO2 in middle cerebral arteries from losartan-treated rats was eliminated by L-NAME and unaffected by indomethacin. Middle cerebral arteries from control and losartan-treated animals exhibited similar dilations in response to the NO-donor sodium nitroprusside (1 microM). These data suggest that AT1 receptor activation is important in maintaining normal vascular relaxation mechanisms in cerebral resistance arteries during normal physiological conditions, and that AT1 receptor blockade causes a shift in the mechanisms of hypoxic dilation of middle cerebral arteries from cyclooxygenase metabolites to NO.

Enhanced arteriolar alpha-adrenergic constriction impairs dilator responses and skeletal muscle perfusion in obese Zucker rats.

The present study tested the hypothesis that enhanced vascular alpha-adrenergic constriction in obese Zucker rats (OZR) impairs arteriolar dilation and perfusion of skeletal muscle at rest and with increased metabolic demand. In lean Zucker rats (LZR) and OZR, isolated gracilis arterioles were viewed via television microscopy, and the contralateral cremaster muscle or gastrocnemius muscle was prepared for study in situ. Gracilis and cremasteric arterioles were challenged with dilator stimuli under control conditions and after blockade of alpha-adrenoreceptors with prazosin, phentolamine, or yohimbine. Gastrocnemius muscles performed isometric twitch contractions of increasing frequency, and perfusion was continuously monitored. In OZR, dilator responses of arterioles to hypoxia (gracilis), wall shear rate (cremaster), acetylcholine, and iloprost (both) were impaired vs. LZR. Treatment with prazosin and phentolamine (and in cremasteric arterioles only, yohimbine) improved arteriolar reactivity to these stimuli in OZR, although responses remained impaired vs. LZR. Gastrocnemius muscle blood flow was reduced at rest in OZR; this was corrected with intravenous infusion of phentolamine or prazosin. At all contraction frequencies, blood flow was reduced in OZR vs. LZR; this was improved by infusion of phentolamine or prazosin at low-moderate metabolic demand only (1 and 3 Hz). At 5 Hz, adrenoreceptor blockade did not alter blood flow in OZR from levels in untreated rats. These results suggest that enhanced alpha-adrenergic constriction of arterioles of OZR contributes to impaired dilator responses and reduced muscle blood flow at rest and with mild-moderate (although not with large) elevations in metabolic demand.

Myogenic responses of isolated adipose tissue arterioles

Previous in vivo studies indicate that vascular autoregulation does take place in adipose tissue. We tested the hypothesis that adipose tissue arterioles can develop a myogenic response to increases in transmural pressure. Arterioles, isolated from the inguinal fat pad of male Wistar rats, were placed in a microvessel chamber containing a Kreb’s bicarbonate-buffered solution (pH 7.4) gassed with 10% O 2 (5% CO 2; 85% N 2). Vessels were cannulated and pressurized to 100 mm Hg and studied under no-flow conditions. Control diameters were obtained at 100 mm Hg. Changes in arteriolar diameter were observed and measured by television microscopy and videocaliper. Diameters, in response to 20 mm Hg step increases in transmural pressure, were measured before and after removal either of extracellular calcium or of the endothelium, and administration of indomethacin (10 −5 M) or L-NAME (3 × 10 −4 M). Removal of calcium resulted in an increase in control diameter of 81% and completely eliminated the myogenic response. In contrast, administration of indomethacin increased control diameter by 13%. L-NAME significantly enhanced the myogenic response; however, neither endothelium removal nor indomethacin had any significant effect. These results indicate that adipose tissue arterioles are capable of eliciting a myogenic response that could contribute to the regulation of blood flow in vivo. Furthermore, it appears that calcium is essential for the myogenic response and that nitric oxide significantly contributes to the modulation of baseline myogenic tone, as well as the myogenic response.

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.

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 dilation of skeletal muscle microvessels to reduced oxygen tension in diabetic obese Zucker rats.

This study determined alterations to hypoxic dilation of isolated skeletal muscle resistance arteries (gracilis arteries; viewed via television microscopy) from obese Zucker rats (OZR) compared with lean Zucker rats (LZR). Hypoxic dilation was reduced in OZR compared with LZR. Endothelium removal and cyclooxygenase inhibition (indomethacin) severely reduced this response in both groups, although nitric oxide synthase inhibition (N(omega)-nitro-L-arginine methyl ester) reduced dilation in LZR only. Treatment of vessels with a PGH(2)-thromboxane A(2) receptor antagonist had no effect on hypoxic dilation in either group. Arterial dilation to arachidonic acid, iloprost, acetylcholine, and sodium nitroprusside was reduced in OZR versus LZR, although dilation to forskolin and aprikalim was unaltered. Treatment of arteries from OZR with oxidative radical scavengers increased dilation to hypoxia and agonists, with no effect on responses in LZR. The restored hypoxic dilation in OZR was abolished by indomethacin. These results suggest that hypoxic dilation of skeletal muscle microvessels from LZR represents the summated effects of prostanoid and nitric oxide release, whereas the impaired response of vessels in OZR may reflect scavenging of PGI(2) by superoxide anion.

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.