Biomedical subjects

I G Joshua

Publications and source records attributed to I G Joshua.

At least 19 recordsLinked to original sources

PubMed2001

Decreased influence of nitric oxide on deoxycorticosterone acetate (DOCA)-salt hypertension.

The response to exogenous administration of acetylcholine and the effects of nitric oxide (NO) synthesis blockade were assessed for small arterioles in the cremaster muscle of deoxycorticosterone acetate (DOCA)-salt hypertensive and normotensive rats using intravital microscopy. The NO synthesis inhibitor N omega-L-nitro-arginine methyl ester (L-NAME) produced significantly less constriction in the arterioles of DOCA-salt hypertensive rats. Exposure to increasing concentrations of acetylcholine (10(-10) to 10(-5) mol/L) or sodium nitroprusside (10(-10) to 10(-5) mol/L) produced similar arteriolar dilation in both groups. These results suggest that attenuated basal release of NO by arterioles may play a role in the development of increased peripheral resistance observed in DOCA-salt hypertension.

Acetylcholine↗

PubMed2001

Blood flow shear rates in arterioles of spontaneously hypertensive rats at early and established stages of hypertension.

Alterations of blood rheological properties can affect blood flow shear rates and therefore alter changes in the interactions between blood and vascular wall components during the development of hypertension. This study was done to evaluate alterations of blood flow shear rates in resistance vessels during the development of genetic hypertension in rats. In the current study, measurements were carried out on spontaneously hypertensive rats (SHR) during an early (3 weeks of age) and an established stage (12 weeks of age) of hypertension development. Age matched normotensive Wistar Kyoto (WKY) rats were used as controls. Intravital television microscopy was used to quantitate blood flow shear rates in first-(1A), second-(2A) and third-order (3A) arterioles of the cremaster muscle. In the young SHRs mean arterial blood pressure was not different from age matched WKY rats, but there was a significant increase of shear rate values in all observed (1A, 2A, 3A) arterioles of SHRs. However, shear rate values were significantly less in arterioles (1A, 2A, 3A) of SHRs with an established hypertension compared to the 3-week-old SHR group. We conclude that shear rates are elevated in resistance vessels prior to an increase in mean arterial pressure during the development of genetic hypertension. These results suggest that a change in blood rheology may cause a change in peripheral vascular resistance and thus contribute to the pathogenesis of hypertension.

Age Factors↗

PubMed2001

Enhanced PKC beta II translocation and PKC beta II-RACK1 interactions in PKC epsilon-induced heart failure: a role for RACK1.

Recent investigations have established a role for the beta II-isoform of protein kinase C (PKC beta II) in the induction of cardiac hypertrophy and failure. Although receptors for activated C kinase (RACKs) have been shown to direct PKC signal transduction, the mechanism through which RACK1, a selective PKC beta II RACK, participates in PKC beta II-mediated cardiac hypertrophy and failure remains undefined. We have previously reported that PKC epsilon activation modulates the expression of RACKs, and that altered epsilon-isoform of PKC (PKC epsilon)-RACK interactions may facilitate the genesis of cardiac phenotypes in mice. Here, we present evidence that high levels of PKC epsilon activity are commensurate with impaired left ventricular function (dP/dt = 6,074 +/- 248 mmHg/s in control vs. 3,784 +/- 269 mmHg/s in transgenic) and significant myocardial hypertrophy. More importantly, we demonstrate that high levels of PKC epsilon activation induce a significant colocalization of PKC beta II with RACK1 (154 +/- 7% of control) and a marked redistribution of PKC beta II to the particulate fraction (17 +/- 2% of total PKC beta II in control mice vs. 49 +/- 5% of total PKC beta II in hypertrophied mice), without compensatory changes of the other eight PKC isoforms present in the mouse heart. This enhanced PKC beta II activation is coupled with increased RACK1 expression and PKC beta II-RACK1 interactions, demonstrating PKC epsilon-induced PKC beta II signaling via a RACK1-dependent mechanism. Taken together with our previous findings regarding enhanced RACK1 expression and PKC epsilon-RACK1 interactions in the setting of cardiac hypertrophy and failure, these results suggest that RACK1 serves as a nexus for at least two isoforms of PKC, the epsilon-isoform and the beta II-isoform, thus coordinating PKC-mediated hypertrophic signaling.

Actins↗

PubMed2001

Altered vascular reactivity in arterioles of chronic intermittent hypoxic rats.

Recurrent episodic hypoxia (EH) is a feature of sleep apnea that may be responsible for some chronic cardiovascular sequelae such as systemic hypertension. Chronic EH (8 h/day for 35 days) causes elevation of diurnal resting (unstimulated) mean arterial blood pressure (MAP) in the rat. We used in vivo video microscopy to examine arteriolar reactivity in the cremaster muscle of male Sprague-Dawley rats subjected to 35 days of EH. Cremaster muscles of EH (n = 6) and control (n = 6) rats were exposed to varying doses of norepinephrine (NE) (10(-10) to 10(-5) M), ACh (10(-9) to 10(-5) M), and endothelin-1 (10(-12) to 10(-8) M). In a separate experiment, EH (n = 5) and control (n = 6) rats were given one dose of a nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 10(-5) M). We also examined endothelial NOS mRNA from the kidneys of EH-stimulated and control (unstimulated) rats. Telemetry-monitored EH rats showed a 16-mmHg increase in MAP over 35 days, whereas control rats showed no change. The response to NE and endothelin-1 were similar for EH and control rats. ACh vasodilatation of arterioles in EH rats was significantly attenuated compared with that of controls. The degree of vasoconstriction in response to blockade of the nitric oxide system by L-NAME was significantly less (83% of baseline diameter with L-NAME) for arterioles of EH rats compared with that for controls (61% of baseline diameter), implying lower basal resting nitric oxide release in the EH rats. Whole kidney mRNA endothelial NOS levels were not different between groups. These data support the hypothesis that chronic elevation of blood pressure associated with EH involves increased peripheral resistance from decreased basal release or production of nitric oxide after 35 days of EH.

Acetylcholine↗

PubMed2000

Microvascular responses to endothelin in deoxycorticosterone acetate-salt hypertensive rats.

The objective of the present study was to determine if endothelin-1 played a role in the elevated peripheral resistance in deoxycorticosterone-acetate (DOCA)-salt hypertension. Radioimmunoassay showed that the concentration of endothelin-1 was higher in thoracic aorta of the DOCA-salt group than that of the control normotensive (CN) group. Responses of arterioles in the rat cremaster to endothelin-1 were also observed using in vivo closed circuit television microscopy. Microvascular sensitivity to endothelin-1 was decreased in the DOCA-salt group. In the presence of an endothelin type A (ET-A) receptor antagonist, low concentrations of endothelin-1 induced a significant vasoconstriction in the DOCA-salt group. In the presence of endothelin type B (ET-B) receptor antagonist, microvascular responses to endothelin-1 were attenuated in the DOCA-salt group. These results indicated that the increased tissue level of endothelin-1 may decrease the ET-A receptor-mediated vascular response to endothelin-1. However, the ET-B receptor-mediated vasoconstriction is potentiated during DOCA-salt hypertension.

Animals↗

PubMed1999

Altered expression and activity of G-proteins, mitogen activated protein kinases, and tyrosine kinases in aging kidney cortex.

BACKGROUND: Renal function declines with age and this may be related to changes in the expression or activity of various signal transduction proteins in the kidney. METHODS: The present study compared the expression and activity of G alpha i(1-3) and G alpha s phosphorylation of mitogen activated protein kinases (MAP-K) (44 and 42 kd) and the activity of tyrosine kinase in renal cortical homogenates of young (4-month-old) and aging (14-month-old) rats. RESULTS: The GTP/(GTP + GDP) binding ratio of G alpha s was significantly decreased in the kidney cortex of aging rats compared to young rats, while the GTP/(GTP + GDP) binding ratio of G alpha i(1-3) increased significantly in kidney cortex of aging rats. Tyrosine kinase activity and phosphorylation of MAP-K (44 and 42 kd) were also reduced in the kidney cortex of aging rats compared to young rats. CONCLUSIONS: These results suggest that diminished phosphorylation of MAP-K and tyrosine kinase activity as well as changes in the binding of GTP/(GTP + GDP) to G alpha i(1-3) and G alpha s may contribute to the age-related decline in renal tubular and vascular function seen in aging animals.

Aging↗

PubMed1998

Increased erythrocyte aggregation in spontaneously hypertensive rats.

Alterations of red blood cell (RBC) aggregation and plasma viscosity are major contributors to the changes in blood rheologic properties that cause an increase in peripheral vascular resistance during the development of hypertension. Although basic research and clinical study have provided considerable understanding of the pathophysiology of hypertension, the objective of this study was to determine whether an increase in RBC aggregability and plasma viscosity precede or accompany the development of high arterial blood pressure. To address this question, RBC aggregation and plasma viscosity were studied in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) at 3 and 12 weeks of age. The plasma concentrations of fibrinogen and fibronectin (FN) were also analyzed in both age groups. RBC aggregability and plasma viscosity were increased in both young and mature SHR compared to age-matched normotensive WKY rats. Mean arterial blood pressure and diastolic pressures were increased in mature hypertensive rats, whereas in young SHR only diastolic pressure was elevated significantly. The concentration of fibrinogen was higher only in the mature hypertensive rats, whereas plasma FN content was greater in both 3- and 12-week-old SHR compared to age-matched WKY. These results show the existence of increased RBC aggregability and plasma hyperviscosity not only during the established phase of hypertension, but also during the early stage of hypertension development, when mean arterial blood pressure is not yet significantly elevated in the genetically hypertensive rat model. These changes may be related to significant increase in the plasma protein FN, which occurs at the same time as the RBC aggregability and plasma viscosity changes. These results may increase attention to changes in the rheologic properties and to the mechanisms involved in these processes in the early stages of hypertension development.

Animals↗

PubMed1998

Release of endogenous nitric oxide mediates arteriolar dilation to endothelin in rat striated muscle.

Previous studies demonstrated that endothelin-1 is a potent vasoconstrictor in the microcirculation. In this study, we assessed the ability of endothelin-1 to induced dilation of small arterioles in the rat cremaster muscle. Responses to topical application of endothelin-1 were assessed by using intravital microscopy. Exposure to increasing concentrations of endothelin-1 (10[-13]-10[-8] M) produced a dose-dependent constriction of third-order arterioles (20 +/- 1.4 microm). Pretreatment with hydroquinone (HQ) or N omega-nitro-L-arginine methyl ester (L-NAME), antagonists of nitric oxide production, caused a significant potentiation in the reactivity of third-order arterioles to endothelin-1. In addition, we observed a significant vasodilation to low levels of endothelin-1 (10[-14]-10[-12] M) in the presence of the endothelin type-A receptor (ET-A) antagonist, BQ123. This dilation was abolished in the presence of a 10(-4) M bath concentration of L-NAME. These results indicated that endothelin-1 caused arteriolar dilation by stimulating endogenous production of nitric oxide. This effect appeared to attenuate the constrictor effects of endothelin-1 on small resistance vessels in striated muscle.

Animals↗

PubMed1998

Platelet thrombus formation in microvessels of young spontaneously hypertensive rats.

We have previously shown an increase in platelet-to-endothelial cell adhesion in microvessels of spontaneously hypertensive rats (SHR) during the established stage of hypertension (12 weeks). The objective of the current study was to determine if the platelet-to-endothelial cell interaction would be altered in the early developmental phase of hypertension. Male weanling (3 weeks old) SHRs (n=6) and age matched normotensive Wistar-Kyoto (WKY) rats (n=6) were used to study platelet thrombus formation. Intravascular fluorescein isothiocyanate tagged to bovine serum albumin was activated with 450-490 nm light to induce thrombus formation in microvessels. Plasma concentrations of von Willebrand factor (vWF), fibrinogen and fibronectin (FN) were measured in rats during both early (3 week) and established stages of hypertension development. Thrombus initiation time in both arterioles (847+/-85 sec) and venules (222+/-40 sec) of young SHRs was significantly shorter (p<0.05) than in arterioles (1270+/-88 sec) and venules (630+/-72 sec) of age matched WKY rats respectively. After thrombus appearance, however, overall time for vessel occlusion in arterioles (2590+/-90 sec) and venules (935+/-131 sec) of SHRs was not different compared to that in arterioles (2650+/-191 sec) and venules (1240+/-93 sec) of age matched WKY rats. The plasma concentration of FN was increased (p<0.05) in both the young (0.9+/-0.1 mg/ml) and mature (1.1+/-0.2 mg/ml) hypertensive rats (n=5) compared to that in young (0.6+/-0.03 mg/ml) and mature (0.5+/-0.1 mg/ml) WKY rats (n=5), while fibrinogen content (3.6 +/-0.3 mg/ml) was elevated (p<0.05) only in mature SHRs (n=5) compared to that (2.7+/-0.02 mg/ml) in age matched WKY rats (n=5). The plasma concentration of vWF was similar to that of controls in either age group of hypertensive animals. These results suggest that changes in platelet-to-endothelial cell interactions occur in the early phase of genetic hypertension development in rats, and appears to result from alteration of plasma concentration of adhesion proteins.

Analysis of Variance↗

PubMed1998

Role of tumor necrosis factor-alpha in small intestinal microcirculation.

The systemic manifestations of sepsis are associated with increased cardiac output, peripheral vasodilatation, and mesenteric vasoconstriction. Our objective was to determine whether tumor necrosis factor (TNF)-alpha regulates small intestinal microcirculatory changes observed during sepsis. An intact loop of terminal ileum of an anesthetized rat was exteriorized into modified Krebs solution and then topically suffused with varying concentrations of TNF-alpha (10(-4) ng/ml to 10(2) ng/ml), norepinephrine (10(-4) M), and sodium nitroprusside (10(-5) M). Videomicroscopy was used to measure arteriolar (A1, A2, A3) and venular (V1, V2) diameter changes in response to topical TNF-alpha. First order vessel diameters did not change in response to TNF-alpha. However, second and third order arterioles dilated maximally by 35 +/- 16 and 52 +/- 12 per cent, respectively, in a dose dependent manner in response to TNF-alpha. Higher order vessels were more sensitive to TNF-alpha than lower order vessels. Norepinephrine (10(-4) M) produced vasoconstriction in all vessels tested (A2 18 +/- 3 per cent, p < 0.05; A3 6 +/- 6 per cent; V2 13 +/- 4 per cent, p < 0.05). Topical TNF-alpha caused dilation in preconstricted vessels as in the nonpreconstricted vessels. TNF-alpha induced vasodilation was prolonged and not reversed by removal of TNF-alpha. These data demonstrate statistically significant dilation in response to TNF-alpha in second and third order arterioles and venules of the small intestine. Persistent vasodilation suggests an induced mechanism of vasodilation in response to TNF-alpha that remains active even after removal of exogenous TNF-alpha. We, therefore, conclude that TNF-alpha causes persistent vasodilatation beyond the period of actual exposure to TNF-alpha in the small intestinal microcirculation. This effect is not altered by the presence of norepinephrine. These data suggest that small intestinal vasoconstriction observed during clinical conditions such as sepsis is unlikely to be mediated by TNF-alpha.

Animals↗

PubMed1998

Potentiation of pulmonary arteriolar vasoconstriction to endothelin-1 by inhibition of nitric oxide synthesis in the intact lung.

OBJECTIVE: To observe pulmonary arteriolar effects of endothelin-1 (ET-1) in the intact lung and determine if constriction to ET-1 is potentiated by inhibition of nitric oxide (NO) synthesis. METHODS: In anesthetized male Sprague-Dawley rats with open chest, the lungs were ventilated with air through the lower trachea and in vivo responses of pulmonary arterioles were examined by video microscopy. Observations were made when the lungs were statically inflated with oxygen to a pressure of approximately 10 cm H2O for brief periods. A lens with a dipping cone was held at the pleural surface. ET-1 (10(-7)-10(-5)M; approximately 0.1 ml) was applied topically to the fluid layer under the dipping cone. RESULTS: ET-1 (10(-6)M) constricted parent arterioles 60 +/- 5 microns in diameter by 52 +/- 12% (range: 20-100%) and branches 45 +/- 3 microns in diameter by 36 +/- 4% (19-48%). Constriction persisted and there was a dramatic long-lasting decrease in flow. Alveolar walls quickly became pale, indicating reduced capillary perfusion. A lower concentration of ET-1 (10(-7)M) constricted (p > 0.05) parent arterioles 61 +/- 4 microns in diameter by 7 +/- 3% initially, and by 13 +/- 8% after 14 +/- 2 minutes, while smaller branches did not respond. In separate experiments, infusion of the NO synthase inhibitor L-NAME (1 mg/kg per minute), modestly (10 +/- 3%) decreased (p < 0.05) baseline parent arteriolar diameter from 72 +/- 7 microns to 64 +/- 5 microns. Branch diameter changed insignificantly from 42 +/- 7 microns to 38 +/- 7 microns. After L-NAME, ET-1 (10(-7)M) constricted (p < 0.05) parent arterioles by 17 +/- 4% initially and 40 +/- 14% after 14 +/- 2 minutes. Concurrently, branches constricted (p < 0.05) by 14 +/- 4% and 26 +/- 15%. CONCLUSIONS: Arterioles less than 80 microns in diameter were very responsive to ET-1, which could be a factor in altering pulmonary microvascular resistance. Inhibition of NO synthesis appears to potentiate constriction to ET-1.

Animals↗

PubMed1997

Vasodilator effect of insulin on the microcirculation of the rat cremaster muscle.

We recently showed that, in conscious rats, acute infusions of insulin (10-15 fold increase in plasma insulin) produced decreases in hindquarter vascular resistance, but only if, changes in sympathetic outflow were prevented with a ganglionic blocker. The aim of the present investigation was to determine if similar effects of insulin could be observed in a preparation that allowed direct visualization of striated muscle (cremaster) microvessels. Initial studies with topical application of insulin showed that third-order arterioles (A3), but not first- or second-order arterioles vasodilated in response to 800 microU/ml and 8 mU/ml of insulin. Systemic (euglycemic) infusion of insulin (6 mU/ml, but not 2 mU/ml) also increased A3 arteriole diameter in animals treated with a ganglionic blocker, but not in control rats. These data show that insulin can have a direct vasodilator effect on striated muscle microvessels if concomitant increases in sympathetic outflow are absent. However, the response was only present with supraphysiological doses of the hormone.

Administration, Topical↗

PubMed1997

In vivo platelet thrombus formation in microvessels of spontaneously hypertensive rats.

Sustained high blood pressure causes functional changes in both vascular endothelial cells and platelets. Therefore, we hypothesized that in vivo platelet thrombus formation would be increased in the cremaster muscle microvessels of rats during genetic hypertension. Experiments were carried out on spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) at 12 weeks of age. Fluorescein isothiocyanate tagged to bovine serum albumin (FITC-BSA) was injected intraarterially and 450 to 490 nm light was used to activate the FITC-BSA and induce a thrombus within the vasculature. In vivo television microscopy was used to quantitate thrombus formation and microvascular diameter changes. The time of platelet thrombus initiation and subsequent time of thrombus growth were studied at wall shear rates of approximately 2000 sec(-1) and 270 sec(-1) in third-order arterioles and venules, respectively. In SHR, times for platelet thrombus initiation and vessel occlusion were significantly less in both arterioles and venules, whereas time for platelet thrombus growth following initiation was significantly prolonged. Greater shear rates in arterioles compared to venules decreased platelet adhesion and subsequently decreased the rate of thrombus formation in both WKY and SHR groups. However, the ratio of WKY to SHR platelet thrombus growth (platelet aggregation) time remained similar (0.83 +/- 0.06 in arterioles and 0.79 +/- 0.06 in venules). These results indicate that there is increased thrombus formation during hypertension and that the platelet adhesion processes may be of greater importance than platelet aggregation in producing this increase.

Animals↗

PubMed1997

Differing regulation of major histocompatibility class II and adhesion molecules on human umbilical vein endothelial cells by serotonin.

Major histocompatibility class II molecules (MHC class II), whose biosynthesis and expression by endothelial cells can be induced by gamma-interferon (IFN-gamma), play a major role in antigen recognition and subsequent cell-cell interactions involved in the initiation of immune responses. Adhesion molecules such as E-selectin and intercellular adhesion molecules (ICAM-1), whose biosynthesis and membrane expression by endothelial cells is regulated by proinflammatory cytokines (IL-1 and TNF), are necessary for the attachment and subsequent extravasation of leukocytes into the surrounding tissue. In the present study, the effects of preformed inflammatory mediators (histamine and serotonin) on the induction and expression of MHC class II, E-selectin, and ICAM-1 molecules by human umbilical vein endothelial cells were examined. Serotonin but not histamine was found to significantly inhibit in a dose-response fashion the induction and expression of MHC class II molecules. Inhibition occurred when it was added 24 h before, at the same time (most effective), or 24 h after IFN-gamma stimulation. No enhancement or stimulation of MHC class II biosynthesis could be detected using moderate or low concentration of either histamine or serotonin alone. In contrast to MHC class II molecules, neither serotonin nor histamine blocked the induction and biosynthesis of E-selectin and ICAM-1 molecules as detected by specific H18/7 and RR1/1 monoclonal antibodies, respectively, using flow cytometry. These findings suggest that serotonin but not histamine can assist in regulating the induction and expression of MHC class II molecules. Failure to block biosynthesis of E-selectin and ICAM-1 induced by TNF-alpha and IL-1 beta indicates the inhibitory effect exerted by serotonin was selective in nature.

Cell Adhesion Molecules↗

PubMed1996

Direct effects of meconium on rat tracheal smooth muscle tension in vitro.

Increased airway resistance is a component of the meconium aspiration syndrome. Experiments were done to determine whether meconium can have a direct affect on tracheal smooth muscle tension. Tracheal segments (4-5 mm long) were isolated from male Sprague-Dawley rats and suspended in organ baths with physiologic salt solution at 37 degrees C gassed with 95% O2-5% CO2. Each segment was attached to a fixed glass rod on one side and to a force displacement transducer on the other side to measure transverse tension. The segments were stretched to 1.5 g of tension and equilibrated for 2-5 h. Human meconium was diluted in physiologic salt solution (20 g/100 mL) and filtered through gauze. Tension was generated in the segments by adding acetylcholine (10(-6) M) to the tissue bath. Addition of meconium to the organ bath (0.1-5 mg/mL) caused tracheal smooth muscle relaxation in 44% of tracheal segments tested. Contraction occurred in 8% of tested segments, but only at the intermediate and low doses. The amount of relaxation increased significantly in a concentration-dependent manner. These responses were not affected by pretreating segments with indomethacin, removing the tracheal epithelium, using KCl to generate tone, or by heating meconium above 60 degrees C for 1 h. Addition of oleic acid to the organ bath (3.5 x 10(-6) to 3.5 x 10(-4) M) caused concentration-dependent tracheal smooth muscle responses (with relaxation predominating at 3.5 x 10(-4) M and contraction predominating at 3.5 x 10(-6) M). These results suggest that meconium can cause tracheal smooth muscle relaxation by a mechanism that does not appear to be mediated by cyclooxygenase products, by the tracheal epithelium, or a protein. The direct action of meconium on tracheal smooth muscle, which may in part be mediated by a fatty acid, does not appear to contribute significantly to the increased airway tone associated with the meconium aspiration syndrome.

Acetylcholine↗

PubMed1996

Alterations in skeletal muscle microcirculation of head-down tilted rats.

The head-down tilted whole body suspended (HDT/WBS) rat is recognized as a model that reproduces many of the responses seen during exposure to microgravity including an increase in systemic blood pressure. Functional alterations of microscopic blood vessels (arterioles) in skeletal muscle (cremaster muscle) were assessed for their role in the observed elevations of blood pressure associated with HDT/WBS. Arteriolar baseline diameters, vasoconstrictor responses to norepinephrine and vasodilation to nitroprusside were assessed in control rats, rats suspended for 7 or 14 days, and rats allowed to recover for 1 day after 7 days of HDT/WBS. Using in vivo videomicroscopy, neither baseline diameters nor ability to dilate were altered by HDT/WBS. Maximum vasoconstriction to norepinephrine was significantly greater in arterioles of hypertensive 14 day HDT/WBS rats. This study of the intact microvasculature of skeletal muscle reveals an elevated contractility of arterioles to norepinephrine in suspended rats, and suggests that an elevated peripheral resistance in skeletal muscle may contribute to the increase in blood pressures among animals subjected to HDT/WBS.

Animals↗

PubMed1995

Differences in the capsaicin-induced dilation of arterioles and venules in rat striated muscle.

We previously found that capsaicin can dilate third-order arterioles in striated muscle by a mechanism that appears to involve release of endogenous calcitonin gene-related peptide (CGRP). Experiments were done to determine 1) whether capsaicin has similar effects on larger arterioles and venules and 2) whether relaxation involves endogenous CGRP and synthesis of endothelium-derived relaxing factor. In male Sprague-Dawley rats anesthetized with pentobarbital (50 mg/kg, i.p.), we examined responses of first- and second-order microvessels in the cremaster muscle using video microscopy. Addition of capsaicin (0.1 microgram/ml) to vessels constricted by norepinephrine (10(-7) M) dilated 1A's by 91% +/- 28%, 2A's by 113% +/- 18% 1V's by 11% +/- 6% and 2V's by 42% +/- 18%. Capsaicin in the presence of the specific CGRP receptor antagonist CGRP (8-37) caused an attenuated arteriolar dilation but had no significant venodilatory effect (1A's 29% +/- 18%, 2A's 55% +/- 14%, 1V's 7% +/- 3%, 2V's 16% +/- 3%). Pretreatment with N-nitro-L-arginine methyl ester (10(-4) M) did not prevent capsaicin-induced arteriolar dilation (A1's 118% +/- 11%; A2's 129 +/- 24%) but blocked capsaicin-induced venodilation (V1's constricted by 5% +/- 5%; V2's constricted by 2% +/- 6%). N-nitro-L-arginine methyl ester also blocked CGRP-induced dilation of both orders of venules, but not arterioles. These data suggest that capsaicin-induced dilation may involve synthesis of endothelium-derived relaxing factor in the venules but not in the arterioles.

Animals↗

PubMed1994

A novel method to assess reactivities of retinal microcirculation.

This study introduces a novel method of bovine retinal microcirculation preparation to assess reactivities of retinal microvessels in ex vivo. This preparation is perfused intraluminally through the retinal artery. Effects of vasoactive hormones on these microvessels can be studied by perfusion or topical application to muscle bath. Effects of these compounds on the retinal microvessels of 1A (180- to 200-microns diameters), 2A (50- to 60-microns diameter), and 3A (20- to 30-microns diameter) can be assessed simultaneously using video microscopy. In this study, the water-soluble compound endothelin-1, when applied topically, caused dose-dependent vasoconstriction of all microvessels but had no effect when perfused intraluminally. On the other hand, lipid-soluble prostaglandin F2 alpha (PGF alpha) caused dose-dependent vasoconstriction when administered either intra- or extraluminally. Furthermore, preconstricted retinal arterioles (by PGF alpha) were dilated in a dose-dependent manner when acetylcholine was perfused through the retinal artery. This vasodilation was attenuated by atropine or N3-monomethyl arginine, a nitric oxide synthase inhibitor. Topical potassium chloride also caused dose-dependent vasoconstriction of all retinal microvessels. Fluorescein angiography showed no breakdown of the blood-retinal barrier. Thus, in this ex vivo perfused bovine retinal microcirculation preparation, the water-soluble compounds may not cross the blood-retinal barrier to affect microcirculation while lipid soluble can affect this circulation. Additionally this study shows that endothelial-derived compounds, endothelin and nitric oxide, caused vasoconstriction and dilation, respectively.

Acetylcholine↗