Advanced glycation end products alter steroidogenic gene expression by granulosa cells: an effect partially reversible by vitamin D.

STUDY QUESTION: Does vitamin D attenuate the adverse effects of advanced glycation end products (AGEs) on steroidogenesis by human granulosa cells (GCs)? SUMMARY ANSWER: AGEs alter the expression of genes important in steroidogenesis while 1,25-dihydroxyvitamin D3 (vit D3) in vitro attenuates some of the actions of AGEs on steroidogenic gene expression, possibly by downregulating the expression of the pro-inflammatory cell membrane receptor for AGEs (RAGE). WHAT IS KNOWN ALREADY: Vitamin D attenuates the pro-inflammatory effects of AGEs in non-ovarian tissues. STUDY DESIGN, SIZE, DURATION: Women who were undergoing IVF were enrolled. Follicular fluid samples (n = 71) were collected and cumulus GCs (n = 12) were treated in culture. PARTICIPANTS/MATERIALS, SETTING, METHODS: Follicular fluid levels of the anti-inflammatory soluble RAGE (sRAGE), AGEs and 25-hydroxyvitamin D (25-OHD) were quantified for possible correlations. GCs of each participant were split equally and treated with either media alone (control) or with human glycated albumin (HGA as a precursor for AGEs) with or without vit D3 after which RT-PCR and immunofluorescence were performed and cell culture media estradiol (E2) levels were compared. MAIN RESULTS AND THE ROLE OF CHANCE: In follicular fluid, sRAGE levels were positively correlated with 25-OHD levels. HGA treatment (i) increased CYP11A1 (by 48%), 3ß-HSD (by 38%), StAR (by 42%), CYP17A1 (by 30%) and LHR (by 37%) mRNA expression levels (P < 0.05 for all) but did not alter CYP19A1 or FSHR mRNA expression levels; and (ii) increased E2 release in cell culture media (P = 0.02). Vit D3 treatment (i) downregulated RAGE mRNA expression by 33% and RAGE protein levels by 44% (P < 0.05); (ii) inhibited the HGA-induced increase in CYP11A1, StAR, CYP17A1 and LHR mRNA levels, but not the increase in 3ß-HSD mRNA levels; and (iii) did not inhibit the HGA-induced E2 release in cell culture media. LIMITATIONS REASONS FOR CAUTION: This study used luteinized GCs that were collected from women who received gonadotropins thus the results obtained may not fully extrapolate to non-luteinized GCs in vivo. WIDER IMPLICATIONS OF THE FINDINGS: This study suggests that there is a relationship between AGEs and their receptors (RAGE and sRAGE) with vitamin D. Understanding the interaction between AGEs and vitamin D in ovarian physiology could lead to a more targeted therapy for the treatment of ovarian dysfunction. STUDY FUNDING/COMPETING INTEREST(S): Funding was received from NIH (R01 NS045940), American Society for Reproductive Medicine, Ferring Pharmaceuticals Inc., and University of Vermont College of Medicine Bridge Funds. All authors have nothing to disclose.

Formerly eclamptic women have lower nonpregnant blood pressure compared with formerly pre-eclamptic women: a retrospective cohort study.

OBJECTIVE: To compare nonpregnant blood pressure and circulating metabolic factors between formerly pre-eclamptic women who did and did not deteriorate to eclampsia. DESIGN: Retrospective observational cohort study. SETTING: Tertiary referral centre. POPULATION: Formerly pre-eclamptic women with (n = 88) and without (n = 698) superimposed eclampsia. METHODS: Women who experienced pre-eclampsia with or without superimposed eclampsia during their pregnancy or puerperium were tested for possible underlying cardiovascular risk factors at least 6 months postpartum. We measured blood pressure and determined cardiovascular and metabolic risk markers in a fasting blood sample. Groups were compared using Mann-Whitney U test, Spearman's Rho test or Fisher's Exact test (odds ratios). MAIN OUTCOME MEASURES: Differences in postpartum blood pressures and features of the metabolic syndrome between formerly pre-eclamptic and formerly eclamptic women. RESULTS: Formerly pre-eclamptic women who developed eclampsia differed from their counterparts without eclampsia by a lower blood pressure (P < 0.01) with blood pressure correlating inversely with the likelihood of having experienced eclampsia (P < 0.001). In addition, formerly eclamptic women had higher circulating C-reactive protein levels than formerly pre-eclamptic women (P < 0.05). All other circulating metabolic factors were comparable. Finally, 40% of all eclamptic cases occurred in the puerperium. CONCLUSIONS: Formerly pre-eclamptic women with superimposed eclampsia have lower nonpregnant blood pressure compared with their counterparts without neurological sequelae with blood pressure negatively correlated to the occurrence of eclampsia. As about 40% of all eclamptic cases occur postpartum, routine blood pressure monitoring postpartum should be intensified.

Maturation is associated with changes in rat cerebral artery structure, biomechanical properties and tone.

AIM: This study evaluated the hypothesis that physiological maturation affects cerebral artery smooth muscle-endothelial interactions involved in pressure-induced tone and alters the dimensional and biomechanical properties of small posterior cerebral arteries (PCA). METHODS: Secondary branches of PCA from young (4-5 weeks old, n=11), adult (14-16 weeks old, n=11) and mature (44-47 weeks old, n=11) male Sprague-Dawley rats were isolated, cannulated, pressurized and subjected to a range of intraluminal pressures (10-110 mmHg) to determine tone with and without pharmacologic nitric oxide synthase (NOS) inhibition. Measurements of passive lumen diameter and wall thickness as a function of pressure were used to determine changes in structure, distensibility and wall stress; histological analysis was performed on vessel cross-sections to assess collagen and elastin contents. RESULTS: Although pressure-dependent tone decreased significantly during ageing, differences between groups were abolished by NOS inhibition. Vessel diameters increased in adult vs. young rats (at 90 mmHg, 233 ± 6.0 µm vs. 192 ± 4.5 µm; P<0.05), possibly secondary to somatic growth. Further ageing was associated with reductions in lumen diameter (207 ± 6.5 µm; P<0.05), increased wall and media thickness (and wall/lumen ratio) and cross-sectional area. Distensibility and wall collagen were unchanged, although elastin content was significantly reduced. CONCLUSIONS: Maturation is associated with differences in PCA dimensional properties that indicate a pattern of initial outward eutrophic, followed by inward hypertrophic remodelling. Functionally, the contribution of basal NO increases with age in a way that reduces pressure-dependent tone and diminishes vasodilator reserve.

Mechanical signaling through connective tissue: a mechanism for the therapeutic effect of acupuncture.

The mechanism of action of acupuncture remains largely unknown. The reaction to acupuncture needling known as 'de qi', widely viewed as essential to the therapeutic effect of acupuncture, may be a key to understanding its mechanism of action. De qi includes a characteristic needling sensation, perceived by the patient, and 'needle grasp' perceived by the acupuncturist. During needle grasp, the acupuncturist feels pulling and increased resistance to further movement of the inserted needle. We hypothesize that 1) needle grasp is due to mechanical coupling between the needle and connective tissue with winding of tissue around the needle during needle rotation and 2) needle manipulation transmits a mechanical signal to connective tissue cells via mechanotransduction. Such a mechanism may explain local and remote, as well as long-term effects of acupuncture.

Threshold duration of ischemia for myogenic tone in middle cerebral arteries: effect on vascular smooth muscle actin.

BACKGROUND AND PURPOSE: We investigated the effect of different periods of ischemia on the myogenic tone of middle cerebral arteries (MCAs) and tested the hypothesis that ischemia disrupts the actin cytoskeleton in vascular smooth muscle. METHODS: The MCA occlusion model was used in male Wistar rats (n=27) to induce different periods of ischemia (15, 30, and 120 minutes) with 24 hours of reperfusion. Successful occlusion was determined by laser-Doppler flowmetry. MCAs were then studied in vitro with a specialized arteriograph system that allowed control of transmural pressure and measurement of lumen diameter. After equilibration for 1 hour at transmural pressure of 75 mm Hg, lumen diameter was measured, and the amount of spontaneous myogenic tone was determined. Arteries were then fixed with 10% formalin while still pressurized in the arteriograph bath and stained for filamentous (F-) actin with fluorescently labeled phalloidin, a specific probe for F-actin. The amount of F-actin was quantified by confocal microscopy. RESULTS: The amount of tone was similar between control and 15 minutes of ischemia (27.0+/-2.0% and 25.3+/-1.7%, respectively; P>0.05) but was significantly diminished after 30 and 120 minutes (11.7+/-2.0% and 8.5+/-2.0%, respectively; P<0.01 versus control). F-actin content also decreased at the longer ischemic periods and correlated significantly with vascular tone (P=0.04) such that the lesser the tone, the lesser was the F-actin content. Fluorescence intensity for control and 15, 30, and 120 minutes of ischemia was (x10(7)) 3.21+/-0.25, 2.54+/-0.32 (P>0.05), 2.32+/-0.15 (P<0.01), and 2.22+/-0.16 (P<0.01), respectively. CONCLUSIONS: These results demonstrate that ischemia disrupts the actin cytoskeleton in smooth muscle and diminishes vascular tone of MCAs in a threshold-dependent manner. This effect likely exacerbates brain tissue damage during stroke, including infarction and edema formation.

Efficacy of antioxidant therapies in transient focal ischemia in mice.

BACKGROUND AND PURPOSE: Ginkgo biloba extract (EGb) and alpha-lipoic acid (LA) are commercially available "antioxidant supplements" with a variety of actions that may be beneficial during acute stroke. These actions include inhibiting platelet and leukocyte activation and adhesion, reducing free radical generation, and increasing cerebral blood flow. Both EGb and LA have been shown to be neuroprotective in cell culture and global central nervous system ischemia models. In this study we investigated the neuroprotective efficacy of EGb and LA in a clinically relevant, transient focal central nervous system ischemic model. METHODS: In the EGb study, 60 adult C57blk mice were randomized to treatment with EGb given orally (via gavage) for 7 days: low dose, 50 EGb mg/kg daily; high dose, 100 mg/kg daily; matched placebo. On day 7, reversible middle cerebral artery occlusion was produced by advancing a silicone-coated 8-0 filament into the internal carotid artery for 45 minutes followed by reperfusion. At 24 hours, the animals were evaluated on a 28-point clinical scale, and infarct volume was determined with the use of triphenyltetrazolium chloride. In the LA study, 24 C57blk mice were treated with 100 mg/kg SC of LA or placebo 1.5 hours before transient MCAO, as in the EGb study. RESULTS: In the EGb study, values for infarct volume at 24 hours were as follows (mean+/-SD): low dose (n=18), 13+/-5 mm(3); high dose (n=22), 22+/-12 mm(3); placebo (n=20), 20+/-10 mm(3) (P:=0.03 overall; P=0.02, low dose versus placebo). Infarct percentage of hemisphere values were as follows: low dose, 14+/-5%; high dose, 21+/-11%; placebo, 20+/-9% (P=0.03 overall; P=0.02, low dose versus placebo). Ten percent of the high-dose group showed significant intracerebral hemorrhage (ICH) within the infarct, while no ICH was seen in the other groups. Neurological function scores were as follows: low dose, 11.8+/-1.5; high dose, 11.4+/-1.7; placebo, 11.3+/-1.8 (P=NS). In the LA study, infarct volume was as follows: 100 mg/kg LA (n=12), 16.8+/-8.3 mm(3); placebo (n=12), 27.2+/-14.6 mm(3) (P<0.05). LA also produced a significant improvement in neurological function at 24 hours: LA, 9.5+/-1.2; placebo, 11.2+/-1.8 (P=0.02). There was no evidence of ICH in any of the animals. CONCLUSIONS: Both oral EGb and LA therapies produced significant reductions in stroke infarct volume. However, for EGb this beneficial effect appears to be dose related, with higher doses potentially increasing the risk of ICH.

High resolution imaged laser speckle strain gauge for vascular applications.

An imaged laser speckle strain gauge that yields strain rates directly is described for vascular applications. The strain gauge does not rely upon cross correlations between a reference image and subsequent strain-modulated images as most current speckle interferometric methods do. Instead, it relies upon a two-dimensional frequency transform of "stacked speckle histories" which are time series of one-dimensional views of the speckle patterns arranged into a spatio-temporal array such that space is along the abscissa and time is along the ordinate. The tilt of the stacked speckle histories is related to the time rate of speckle pattern shift. The strain gauge is sensitive only to in-plane strains. Strain rates of 30.1 +/- 3.2 and 24.83 +/- 2.1 mu epsilon/s were evaluated in vitro on a fresh human tibial artery and rat inferior vena cava, respectively. The total strains measured were 21.6 and 19.86 mu epsilon, respectively. This is at least one order of magnitude more sensitive than other current soft-tissue strain measurement techniques.

The effect of elevated homocysteine levels on adrenergic vasoconstriction of human resistance arteries: the role of the endothelium and reactive oxygen species.

PURPOSE: This study investigated the effect of elevated homocysteine levels on adrenergic contraction of human resistance arteries and tested the hypothesis that homocysteine-induced generation of reactive oxygen species contributes to vascular reactivity changes. METHODS: Small (<200 microm) subcutaneous arteries were cannulated and pressurized in an arteriograph chamber that allowed the measurement of lumen diameter. Two arteries from the same patient were obtained; one was perfused and superfused (intraluminal pressure = 50 mm Hg) with physiologic saline solution (control, n = 6), and the other was perfused and superfused with physiologic saline solution plus 200 micromol/L homocysteine (HC, n = 6); the reactivity to adrenergic stimulation was assessed. Another group of arteries was incubated in 200 micromol/L homocysteine plus 1200 U/mL superoxide dismutase and 120 U/mL catalase (HC + SC, n = 6), and the reactivity to norepinephrine was determined. The vasoreactivity of homocysteine was further assessed in intact (n = 6) and denuded (n = 6) arteries that were precontracted with an intermediate concentration of norepinephrine and homocysteine (20-200 micromol/L) added to the bath while the lumen diameter was continuously recorded. RESULTS: Sensitivity to norepinephrine was diminished in HC arteries, which increased the median effective concentration (EC(50)) from 0.24 +/- 0.06 micromol/L in control arteries to 0.65 +/- 0.10 micromol/L in HC arteries (P <.01). Homocysteine also caused concentration-dependent vasodilation of arteries contracted with an intermediate concentration of norepinephrine that was greater in intact than denuded arteries, with the half-maximum responses occurring at 61 +/- 6 micromol/L (intact) and 90 +/- 11 micromol/L (denuded; P <.05). There was no significant difference in sodium nitroprusside sensitivity between control and homocysteine arteries (EC(50) = 61 +/- 3 nmol/L vs 50 +/- 19 nmol/L; P >.05) or in sensitivity to acetylcholine (EC(50) = 19 +/- 7 nmol/L vs 12 +/- 3 nmol/L; P >.05). Arteries in the presence of superoxide dismutase and catalase had similarly impaired reactivity to norepinephrine as did homocysteine arteries (EC(50), 0.58 +/- 0.15 micromol/L; P >.05 vs HC, P <.01 vs control). CONCLUSION: An elevated homocysteine level in vitro diminishes adrenergic contraction, with a differential endothelial versus smooth muscle influence that appears unrelated to the generation of reactive oxygen species.

Postischemic attenuation of cerebral artery reactivity is increased in the presence of tissue plasminogen activator.

BACKGROUND AND PURPOSE: We investigated the combined effect of tissue plasminogen activator and ischemia on middle cerebral artery (MCA) reactivity to determine whether abnormal MCA function after 2 hours of ischemia was worse in arteries perfused with recombinant tissue plasminogen activator (rtPA). METHODS: The intraluminal suture model of focal cerebral ischemia was used to induce 2 hours of ischemia in rats, after which occluded MCAs were removed and studied in vitro with an arteriograph system that allowed control of transmural pressure (TMP) and measurement of lumen diameter. Arteries were either nonischemic (control; n=8), nonischemic and perfused with 400 microg/mL rtPA (rtPA; n=5), ischemic (ISC; n=6), or ischemic and perfused with 400 microg/mL rtPA (ISC-rtPA; n=6). After a 1-hour equilibration at 75 mm Hg, TMP was increased to 125 mm Hg and lumen diameter was recorded at each pressure. Reactivity to acetylcholine (ACh, 0.1 to 10.0 micromol/L) and serotonin (0.01 to 10 micromol/L) was then determined. RESULTS: Control arteries responded myogenically to pressure and increased the amount of tone from 18.5+/-3.8% at 75 mm Hg to 24.8+/-3.0% at 125 mm Hg (P<0.05), which decreased diameter from 241+/-7 to 232+/-6 microm. In contrast, all other groups decreased tone at 125 mm Hg, which demonstrated a loss of myogenicity. The percent tone in each group at 75 versus 125 mm Hg was rtPA, 16.0+/-4.5% versus 11.8+/-3.8%; ISC, 23.5+/-4.5% versus 13. 5+/-3.1%; and ISC-rtPA, 23.5+/-4.2% versus 12.3+/-3.2% (P<0.05 for all). The percent increase in lumen diameter at each concentration of ACh was diminished in all groups compared with control; ISC-rtPA arteries responded the least, which suggests an additive effect of rtPA in ischemic arteries. The percent increase in lumen diameter at 10(-5)mol/L ACh was 23+/-4% for control versus 15+/-2% for rtPA; 17+/-3% for ISC arteries (P<0.05), and 8+/-2% for ISC-rtPA arteries (P<0.01). Sensitivity to serotonin was equally diminished in all groups compared with control: EC(50) (micromol/L) was 0.06+/-0.01 for control, 0.17+/-0.02 for rtPA, 0.22+/-0.07 for ISC, and 0.16+/-0. 04 for ISC-rtPA (P<0.05). CONCLUSIONS: These results demonstrate that both ischemia and rtPA perfusion diminish cerebral artery reactivity and that the combination may produce an additive effect. This impaired reactivity may contribute to reperfusion-induced injury during or after thrombolysis by altering upstream cerebrovascular resistance.

Elevated glucose potentiates contraction of isolated rat resistance arteries and augments protein kinase C-induced intracellular calcium release.

The effect of elevated glucose on arterial contractions and intracellular calcium ([Ca++]i) release induced by protein kinase C (PKC) activation and potassium depolarization (KCl) was investigated. Mesenteric resistance arteries (phi < 200 microm) isolated from male Wistar rats were studied using an arteriograph system that allowed control of transmural pressure (TMP) and measurement of lumen diameter. Arteries were incubated in either 11 or 44 mmol/L glucose and the concentration-response to Indolactam V (ILV; a specific PKC activator; LC Laboratories, Woburn, MA) and KCl was determined, as well as the sensitivity to Ca++ in the presence of either agonist. An additional group of arteries were incubated in 5.5 mmol/L glucose and the concentration-response to ILV was compared versus 11 and 44 mmol/L glucose. Arteries in 44 mmol/L glucose were more sensitive to both ILV and KCl, contracting to 10.0 micromol/L ILV, 53.9 +/- 10.1% in 11 mmol/L versus 85.1 +/- 2.0% in 44 mmol/L glucose (P < .01); arteries in 5.5 mmol/L glucose responded the least to ILV, contracting only 36.0 +/- 4% to 10.0 micromol/L ILV (P < .01 v 11 and 44 mmol/L glucose). The KCl EC50 (ie, the value at which the agonist produced 50% maximal contraction) for 11 versus 44 mmol/L glucose was 41.3 +/- 4.8 versus 31.1 +/- 1.2 mmol/L (P < .05). There was no change in Ca++ sensitivity in elevated glucose for either agonist; however, Ca++ sensitivity was augmented threefold for ILV versus KCl, demonstrating an agonist-dependent modulation of Ca++ sensitivity. The Ca++ EC50 for ILV and KCl in 11 versus 44 mmol/L was 0.18 +/- 0.05 versus 0.21 +/- 0.05 and 0.59 +/- 0.09 versus 0.60 +/- 0.10 micromol/L (P < .01 v ILV). The effect of elevated glucose on [Ca++]i release from the sarcoplasmic reticulum (SR) was investigated in arteries incubated in zero Ca++ buffer containing either 11 or 44 mmol/L glucose by measuring the contraction produced by 50 mmol/L caffeine, 3.0 micromol/L ILV, or 60 mmol/L KCl. Contraction to caffeine in 11 versus 44 mmol/L glucose was comparable, constricting 42.0 +/- 6.0% in 11 mmol/L and 36.0 +/- 4.4% in 44 mmol/L glucose (P > .05), and contraction to KCl was almost undetectable in both glucose concentrations. However, contraction to ILV increased from 5.6 +/- 0.9% in 11 mmol/L to 18.7% +/- 2.2% in 44 mmol/L glucose (P < .01), indicating that although the amount of Ca++ in the SR (caffeine-sensitive stores) was not increased in elevated glucose, PKC-induced release of [Ca++]i was enhanced, a consequence that may explain the noted glucose-induced increase in contraction to PKC activation.

Propionyl-L-carnitine dilates human subcutaneous arteries through an endothelium-dependent mechanism.

PURPOSE: The vasoactive effects of propionyl-L-carnitine (PLC) on human arteries, including endothelial and smooth muscle cell influences, were studied. METHODS: Small (less than 200 microm) subcutaneous fat arteries (n = 19), obtained from human patients undergoing vascular surgery, were dissected and mounted in an arteriograph system that allowed measurement of lumen diameter and control of transmural pressure. To investigate the role of the endothelium, arteries were compared intact, intact and in the presence of either 0.3 mmol/L nitro-L-arginine (an inhibitor of nitric oxide synthesis) or 10 micromol/L indomethacin (an inhibitor of prostaglandin synthesis), or denuded of endothelium. After a 1-hour equilibration at a pressure of 50 mm Hg, arteries were precontracted 50% with an intermediate concentration of norepinephrine, and clinically relevant concentrations of PLC (0.1 to 100 micromol/L) were cumulatively added to the bath while the lumen diameter was continually measured. RESULTS: Intact arteries dose-dependently dilated to PLC, with the half maximal dilation occurring at 2.9 +/- 1.2 micromol/L, increasing diameter 91% +/- 5% at 100 micromol/L. In contrast, PLC had significantly less effect on deendothelialized arteries, increasing diameter only 24% +/- 11% at 100 micromol/L (P <.01 vs. intact). This indicates the endothelial dependency of this compound. Blockade of nitric oxide did not inhibit this vasodilation, with the half-maximal response occurring at 8.6 +/- 7 micromol/L, increasing diameter 85% +/- 8% at 100 micromol/L ( P >.05 vs. intact). However, this vasodilation was significantly diminished in the presence of indomethacin, which dilated arteries only 53% +/- 18% at 100 micromol/L (P <.01 vs. intact; P >.05 vs. denuded). CONCLUSION: PLC is an endothelium-dependent vasodilator, the mechanism of which is partially mediated by prostaglandin synthesis, not nitric oxide. The beneficial effects of this compound may, in part, be related to vasodilation and enhanced blood flow.

Vascular smooth muscle actin cytoskeleton in cerebral artery forced dilatation.

BACKGROUND AND PURPOSE: We investigated the role of actin polymerization in regulating arterial diameter in response to increasing pressure and modulating forced dilatation of cerebral arteries at pressures above the upper limit of autoregulation. METHODS: Posterior cerebral arteries (n = 12) were isolated and pressurized in a special arteriograph that allowed control of intravascular pressure and measurement of lumen diameter. Intact arteries in the absence (control) or presence of 3.0 mumol/L cytochalasin B (CB), an inhibitor of actin polymerization, were subjected to stepwise increases in pressure from 75 to 200 mm Hg. Lumen diameter was continuously recorded, as was the pressure at which forced dilatation (loss of tone) occurred. After a period of time at 200 mm Hg, pressure was returned to 75 mm Hg and the extent of tone recovery was evaluated. RESULTS: Arteries with and without CB developed a similar amount of tone during equilibration at 75 mm Hg: percent tone = 27 +/- 3% for control versus 29 +/- 4% for CB arteries (P > 0.05). However, arteries in the presence of CB could not withstand pressure as well and underwent FD at significantly lower pressures: 168 +/- 5 mm Hg for control versus 142 +/- 5 mm Hg for CB arteries (P < 0.01). The amount of tone that arteries regained after FD when pressure was returned to 75 mm Hg was also less in CB arteries: percent tone = 34 +/- 3% for control versus 11 +/- 2% for CB arteries (P < 0.01). CONCLUSIONS: Cytoskeletal integrity appears important for maintaining cerebral arterial diameter during changing intravascular pressure. In addition, the process of actin polymerization may be a significant contributor to development of myogenic tone after forced dilatation.

Myoendometrial versus placental uterine arteries: structural, mechanical, and functional differences in late-pregnant rabbits.

OBJECTIVE: This study compared late-pregnant radial uterine arteries that supplied the placenta versus the myoendometrium to evaluate differences in active and passive mechanical properties. STUDY DESIGN: Pressurized segments of placental versus myoendometrial radial uterine arteries from late-pregnant (day 28 to 30) New Zealand White rabbits (n = 12) were compared in vitro for differences in luminal diameter, wall thickness, distensibility, and intrinsic tone as a function of transmural pressure. RESULTS: Both types of arteries responded to increased transmural pressure with active vasoconstriction; however, the amount of tone present in myoendometrial arteries was significantly greater than in placental arteries (percent tone at 75 mm Hg = 39% +/- 3% for myoendometrial versus 31% +/- 2% for placental arteries, p < 0.01). Measurements of unpressurized, fully relaxed arteries revealed that placental arteries were 38% larger in diameter and had thicker walls than myoendometrial arteries did. However, myoendometrial arteries were significantly more distensible at transmural pressures >5 mm Hg. CONCLUSIONS: The increased size and diminished tone of placental compared with adjacent myoendometrial arteries would favor increased blood flow to the placenta; differences in size and passive mechanical properties suggest that a localized factor(s) originating from the fetus or placenta contributes to the gestational enlargement of those arteries that perfuse the placenta.

High glucose concentrations dilate cerebral arteries and diminish myogenic tone through an endothelial mechanism.

BACKGROUND AND PURPOSE: Diabetes is associated with cerebrovascular disease and impaired autoregulation of cerebral blood flow. The purpose of this study was to determine the effect of acute glucose exposure on basal tone and myogenic reactivity of isolated rat cerebral arteries. METHODS: Posterior cerebral arteries (PCAs, n = 38) were dissected from male Wistar rats and mounted on glass cannulas in a system that allowed control of transmural pressure (TMP) and measurement of lumen diameter. Arteries were exposed to various concentrations of glucose, and the amount of basal tone and reactivity to TMP was measured. The effect of elevated glucose on cerebral endothelial modulation of basal tone was determined by mechanical denudation and the use of inhibitors of both nitric oxide and prostaglandin synthesis. RESULTS: Arteries exposed to 44 versus 5.5 mmol/L glucose developed significantly less intrinsic tone (percent tone, 2 +/- 1% versus 28 +/- 2%; P < .01) and responded passively to increases in TMP. Preexisting tone present in 5.5 mmol/L glucose was eliminated on exposure to 44 mmol/L glucose, which decreased tone from 30 +/- 5% to 5 +/- 4% (P < .01). Glucose-induced dilations were concentration dependent such that half-maximal responses were obtained at 25 +/- 2 mmol/L. Endothelial removal abolished this effect, and the amount of tone was similar in 5.5 versus 44 mmol/L glucose (percent tone, 46 +/- 6% versus 49 +/- 5%; P > .05), as did inhibition of nitric oxide production with 0.3 mmol/L nitro-L-arginine (percent tone, 52 +/- 4% versus 46 +/- 3%; P > .05); however, blockade of the cyclooxygenase pathway with indomethacin (10(-5) mmol/L) only partially inhibited the dilation to glucose (percent tone, 32 +/- 3% in 5.5 mmol/L versus 12.4 +/- 3% in 44 mmol/L; P < .01). CONCLUSIONS: Acute glucose exposure dilates arteries with intrinsic tone and impairs cerebrovascular reactivity to TMP via an endothelium-mediated mechanism that involves nitric oxide and prostaglandins.

Reperfusion decreases myogenic reactivity and alters middle cerebral artery function after focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: After focal cerebral ischemia, the function of cerebral arteries is critical to maintain cerebrovascular resistance and minimize damage to ischemic brain regions during reperfusion. In this study we examined the contractile function of isolated and pressurized middle cerebral arteries (MCAs) after 2 hours of occlusion with either 1 to 2 minutes or 24 hours of reperfusion using the intraluminal suture model of transient focal ischemia in rats. METHODS: MCAs were dissected after 2 hours of occlusion with either 1 to 2 minutes (OCC, n = 8) or 24 hours (RPF, n = 5) of reperfusion and compared with those of controls that did not have surgery (n = 5). Isolated MCAs were mounted on two glass cannulas in an arteriograph chamber that allowed control over transmural pressure (TMP) and measurement of lumen diameter. Responses to changes in TMP (including myogenic reactivity, basal tone, and passive distensibility) and sensitivity to serotonin and acetylcholine were compared. RESULTS: Increasing TMP from 25 to 75 mm Hg caused vasoconstriction and development of tone that was similar in control and OCC arteries: percent tone was 33 +/- 5% versus 25 +/- 7% (P > .05). In contrast, tone was severely diminished in RPF MCAs after 24 hours of reperfusion: percent tone = 8 +/- 4% (P < .01). Sensitivity to serotonin was reduced in OCC arteries, increasing the EC50 value from 0.04 +/- 0.1 to 0.11 +/- 0.02 mumol/L (P < .05); after 24 hours of reperfusion, sensitivity of RPF MCAs was similar to control. Vasodilation to 10.0 mumol/L acetylcholine was significantly impaired only in RPF arteries: percent increased lumen diameter was 19 +/- 3% (control) and 13 +/- 4% (OCC, P > .05) versus 9 +/- 2% (RPF, P < .01). Passively, OCC MCAs were more distensible, which was reversed after 24 hours of reperfusion; RPF vessels had distensibility similar to that of control arteries but thicker arterial walls. CONCLUSIONS: Abnormal structure and function of MCAs occur after 2 hours of ischemia, with diminished myogenic reactivity and tone associated with longer reperfusion.

Endothelial function and adrenergic reactivity in human type-II diabetic resistance arteries.

PURPOSE: This study was performed to examine the role of the vascular endothelium in modulating arterial reactivity to adrenergic vasoconstriction in subcutaneous arteries from patients with type II diabetes. METHODS: Small subcutaneous arteries (inner diameter = 90 to 180 microns) from control subjects (n = 22) and patients with diabetes (n = 18) were dissected from skin biopsies obtained at surgery and mounted on a specialized arteriograph that allowed for continuous measurement of lumen diameter under controlled pressure. The sensitivity to norepinephrine was compared in arteries that were either intact, denuded of endothelium, or intact and exposed to N omega-nitro-L-arginine (L-NNA), an inhibitor of nitric oxide synthesis. Stimulated release of nitric oxide by acetylcholine and smooth muscle cell responses to sodium nitroprusside were also evaluated in diabetic and control arteries. RESULTS: Sensitivity to norepinephrine was augmented in diabetic arteries and the amount of agonist necessary to contract the vessels 50% of maximum (EC50) decreased from 0.35 +/- 0.05 mumol/L in the control arteries to 0.16 +/- 0.06 mumol/L in the diabetic arteries (p < 0.05). Both endothelial removal and blockade of nitric oxide synthesis increased sensitivity to norepinephrine in control arteries (EC50 denuded = 0.14 +/- 0.03 mumol/L and EC50 L-NNA = 0.14 +/- 0.04 mumol/L; p < 0.01) but failed to augment sensitivity in diabetic arteries (EC50 denuded = 0.17 +/- 0.05 mumol/L and EC50 L-NNA = 0.15 +/- 0.04 mumol/L; p > 0.05). Stimulated release of nitric oxide by acetylcholine was increased in the diabetic arteries: EC50 control = 0.04 +/- 0.01 mumol/L versus EC50 diabetic = 0.009 +/- 0.001 mumol/L (p < 0.05). Sensitivity of vascular smooth muscle to sodium nitroprusside was similar in both nondiabetic and diabetic arteries. CONCLUSIONS: The endothelium mitigates adrenergic reactivity in control arteries, which is lacking in diabetic arteries and results in enhanced reactivity to norepinephrine; increased sensitivity of diabetic arteries to acetylcholine, however, indicates a possible alteration at the receptor level.

Mevalonate availability affects human and rat resistance vessel function.

Previous data in rat conductance vessels indicated that cellular mevalonate contributes to vascular tone and systemic blood pressure control. Using exogenous mevalonate (M) or lovastatin, a 3-hydroxy-3-methyl-glutaryl CoA (HMG-CoA) reductase inhibitor (L), we characterized the role of mevalonate availability in resistance artery function, both in experimental animals and humans. Rat mesenteric artery resistance vessels (MARV, n = 9) were incubated for 48 h with either L, M, L + M, or vehicle (V) and tested for reactivity to NE, serotonin, acetylcholine, atrial natriuretic peptide, and sodium nitroprusside (SNP). Lovastatin increased sensitivity to NE (P < 0.03) and serotonin (P < 0.003), and significantly impaired the response to all three vasodilators. These effects were reversed by co-incubation with mevalonate. Mevalonate alone had no effect. In separate experiments, intravascular free Ca2+ concentration (ivfCa2+) was determined in fura-2AM loaded MARV. Basal ivfCa2+ was increased after a 48-h exposure to L (52.7 +/- 4.6 nM, L, vs. 29.7 +/- 2.4 nM, V, n = 12, P < 0.003), as were ivfCa2+ levels following stimulation with low (100 nM) NE concentrations. Similar ivfCa2+ concentrations were achieved during maximum contraction with NE (10 mM) in both groups. Human resistance arteries of human adipose tissue were also studied. Lovastatin increased the sensitivity to NE (ED50 = 372 +/- 56 nM, V, and 99 +/- 33 nM, L, P < 0.001) and significantly decreased the relaxation to acetylcholine and SNP of human vessels. We conclude that mevalonate availability directly contribute to resistance vessel function and vascular signal transduction systems in both experimental animals and humans. The study calls for the identification of non-sterol, mevalonate-derived vasoactive metabolites, and suggests that disorders of the mevalonate pathway can alter vascular tone and cause hypertension.