Search PubMed⌕ Search

Biomedical subjects

K G Stewart

Publications and source records attributed to K G Stewart.

13 recordsLinked to original sources
PubMed2001

Endogenous estrogen mediates vascular reactivity and distensibility in pregnant rat mesenteric arteries.

The role of estrogen in the maternal systemic cardiovascular adaptations during pregnancy is still controversial. Female Sprague-Dawley rats were implanted at day 14 of pregnancy with either a 50-mg tamoxifen pellet (estrogen receptor blocker, n = 10) or placebo pellet (n = 10). Virgin female rats were a nonpregnant control (n = 7). At days 20-22 of pregnancy, resistance-sized mesenteric arteries were mounted onto a dual-chamber arteriograph system. Pregnancy significantly blunted the pressor response to phenylephrine [measurement of the effective concentration that yielded 50% maximum response (EC(50)) values were 1.5 +/- 0.22 vs. 0.69 +/- 0.16 microM (P < 0.05)] and enhanced vasodilation to ACh [EC(50) = 1.13 +/- 2.53 vs. 3.13 +/- 6.04 nM (P < 0.05)] compared with nonpregnant rats. However, tamoxifen treatment during pregnancy reversed these effects. Inhibition of nitric oxide (NO) synthase with N(G)-monomethyl-L-arginine (250 microM) shifted only the responses of the placebo-treated pregnant group to both phenylephrine and ACh. Arterial distensibility in the placebo-treated pregnant group was also significantly increased (P < 0.05) compared with nonpregnant and tamoxifen-treated pregnant animals. In summary, endogenous estrogen during pregnancy increases NO-dependent modulation of vessel tone and arterial distensibility.

Adaptation, Physiological↗
PubMed2001

A comparison of ovariectomy models for estrogen studies.

Many estrogen-replacement studies use ovariectomized animals as controls. However, ovariectomy greatly increases body weight and can enhance the peripheral synthesis of estrogen. Tamoxifen is commonly used as an antiestrogen, but it may elicit mixed agonist or antagonist actions. The aim of our study was to compare vascular function in mesenteric arteries among groups of rats with low estradiol levels. The groups (n = 5, each) of Sprague-Dawley rats were cycling (diestrus), ovariectomized (OVX), OVX + tamoxifen (OVX-T), OVX + 4-hydroxyandrostene-3,17-dione, an aromatase inhibitor (OVX-A) to prevent peripheral synthesis of estrogen, and control-fed OVX to prevent excess weight gain. Body weight was significantly elevated in only the non-control-fed OVX group. Estrogen levels were significantly greater in the cycling rats compared with the other groups, whereas uterine weights were significantly reduced in only the OVX-A and control-fed OVX groups. Methacholine relaxation was blunted only in the OVX-A and control-fed OVX groups, suggesting a possible estrogenic influence in the non-control-fed OVX and OVX-T groups. These data indicate the potential for confounding factors to decrease the efficacy of OVX controls.

Animals↗
PubMed2000

Vascular matrix metalloproteinase-2-dependent cleavage of calcitonin gene-related peptide promotes vasoconstriction.

Matrix metalloproteinase (MMP)-2 has been historically associated with the process of vascular remodeling through the cleavage of extracellular matrix proteins. However, we recently found that MMP-2 also cleaves the endothelium-derived peptide big endothelin-1, ET-1[1-38] and yields the novel vasoconstrictor ET-1[1-32]. We therefore investigated the effects of MMP-2 inhibitors as potential vasodilators. MMP inhibition with ortho-phenanthroline (0.3 to 30 micromol/L) induced vasorelaxation of isolated rat mesenteric arteries (maximum of relaxation=74.5+/-27.6% at 30 micromol/L). However, phosphoramidon (0.3 to 30 micromol/L), which inhibits some metalloenzymes, but not MMP-2, did not dilate the arteries. Selective inhibition of endogenous MMP-2 with the novel tissue-permeable cyclic peptide CTTHWGFTLC (CTT, 10 micromol/L) also caused vasorelaxation (by 85+/-6%), whereas STTHWGFTLS (10 micromol/L), an inactive CTT analogue, did not dilate the arteries. Interestingly, the vasorelaxation that results from MMP-2 inhibition was endothelium-independent. Thus, we examined whether MMP-2 acted on peptides derived from the smooth muscle or the perivascular nerves. Recombinant human MMP-2 cleaved calcitonin gene-related peptide (CGRP) specifically at the Gly(14)-Leu(15) peptide bond and reduced the vasodilatory potency of CGRP by 20-fold. Inhibition of MMP-2 increased the amount of intact CGRP in arteries and enhanced vasorelaxation induced by anandamide, which stimulates CGRP release. Vasorelaxation in response to MMP-2 inhibition was abolished by CGRP[8-37], a selective CGRP receptor antagonist, and by capsaicin, which depletes arterial perivascular nerves of CGRP. We conclude that vascular MMP-2 cleaves endogenous CGRP and promotes vasoconstriction. These data suggest a novel mechanism of regulating the vasoactive and, possibly, the neurohormonal actions of CGRP and establish MMP-2 as a modulator of vascular function.

Animals↗
PubMed2000

Aging increases PGHS-2-dependent vasoconstriction in rat mesenteric arteries.

During aging, the vascular endothelium changes functionally and morphologically. Although previous studies have shown that endothelium-derived eicosanoids increase vessel tone in aging, the precise mechanism(s) has not been fully determined. We hypothesized that aging would increase prostaglandin H synthase (PGHS)-dependent vasoconstriction as well as decrease nitric oxide-dependent relaxation. Mesenteric arteries from 3-month-old (n=9) and 12-month-old (n=14) female Sprague-Dawley rats were studied in a myograph system. Aging significantly blunted the endothelium-dependent relaxation response to methacholine compared with young rats (EC(50)=7.77x10(-8) versus 2.68x10(-8) mol/L, P<0. 05). Nitric oxide synthase inhibition reduced methacholine-induced relaxation in the young (P<0.05) but had no effect in the aging group. Specific inhibition of the PGHS-1 isoform did not significantly affect methacholine-mediated relaxation in the young or aged groups. However, PGHS-2 inhibition greatly enhanced relaxation to methacholine (1.59x10(-8) versus 7.77x10(-8) mol/L, P<0.01) in the aged group only, restoring vessel function to that of the young. In the aged group, inhibition of the prostaglandin H(2)/thromboxane A(2) receptor enhanced methacholine-dependent relaxation similar to that of PGHS-2 inhibition. Moreover, arterial expression of PGHS-2 protein increased with age. In summary, nitric oxide-dependent modulation of vessel function decreased with age, PGHS-1 did not significantly affect vessel tone in either the young or aging group, and PGHS-2 greatly increased vasoconstriction in aging. Thus, we have identified enhanced PGHS-2-mediated vasoconstriction in aging and therefore suggest that inhibition of this isoform is potentially a new target for therapeutic intervention to improve vascular function.

Aging↗
PubMed2000

Estrogen replacement reduces age-associated remodeling in rat mesenteric arteries.

Estrogen replacement therapy significantly decreases the incidence of cardiovascular disease in postmenopausal women. In aging, there is an increase in vascular stiffness along with a decrease in matrix metalloproteinase (MMP) activity. Our hypothesis was that estrogen replacement would increase MMPs and therefore reduce the vascular stiffness that is associated with aging. Female Sprague-Dawley rats were implanted with a placebo or 17ss-estradiol-containing pellet (0.5 mg/pellet, 60-day release) at 10 months of age (n=6, each). Six young rats (3 months old) were also studied. After a 2-month exposure to the pellet, mesenteric arteries were studied on a pressurized arteriograph system. Distensibility and wall thickness were measured in response to stepwise increases in intraluminal pressure in Ca(2+)-free physiological saline solution buffer with papaverine (10(-4) mol/L). In response to increasing pressure, aged placebo rats exhibited a significant decrease in distensibility compared with young rats (P<0.05) that was accompanied by an increase in wall thickness (P<0.05). Conversely, estrogen replacement increased distensibility and decreased wall thickness in aged rats (old estrogen-replaced versus old placebo, P<0.05). Zymography data indicated that MMP-2 activity decreased in aging but was increased by estrogen replacement. In summary, estrogen replacement in aging female rats reduces age-associated vascular remodeling.

Aging↗
PubMed1991

Comparison of high and low doses of suxamethonium.

In a double-blind study, 67 young adult patients undergoing anaesthesia for dental extractions were allocated at random to receive either 0.5 mg/kg or 1.5 mg/kg suxamethonium. A greater increase in arterial pressure was seen following induction in the 1.5 mg/kg group, although overall intubating conditions were similar in the two groups. Suxamethonium-associated muscle pains were significantly more common in the group which received the larger dose (p less than 0.05).

Adult↗
PubMed1991

Inaccuracy of pulse oximetry in patients with severe tricuspid regurgitation.

The accuracy of pulse oximetry was studied in a group of patients with severe tricuspid regurgitation. Measurements of arterial oxygen saturation from a finger and an ear probe were compared with those from a radial arterial blood sample analysed in vitro. Lower values were obtained using the pulse oximeter; the difference ranged from +2% to -11%. The discrepancies between pulse oximeter and laboratory oximeter readings were greater in this group of patients than in a control group who did not have tricuspid regurgitation. There was, however, no correlation between the magnitude of this discrepancy and either the peak central venous pressure or the venous pulse pressure.

Ear↗
PubMed1991

Oral ketamine.

Explore the source record for details and available documents.

Administration, Oral↗
PubMed1990

Oral ketamine premedication for paediatric cardiac surgery--a comparison with intramuscular morphine (both after oral trimeprazine).

In a single-blind controlled study, forty children with congenital heart disease were premedicated with oral trimeprazine 3 mg/kg and either intramuscular morphine 0.1 mg/kg or oral ketamine 10 mg/kg. Cardiovascular and respiratory effects of premedication and degree of sedation induced were similar in the two groups of patients. Oral ketamine is a safe and effective premedicant in this group of patients.

Administration, Oral↗
PubMed1989

Clinical evaluation of pressure support ventilation.

A 5-year-old child required a prolonged period of ventilatory assistance, provided in the form of pressure support ventilation. There was a significant negative correlation between the level of pressure support and the PaCO2. Requirements for sedation were reduced with pressure support compared with conventional controlled ventilation. Changing the ventilator trigger level from -1 cm H2O to -3 cm H2O did not affect PaCO2. Satisfactory arterial blood-gas tensions were obtained only when the inspiratory pressure was increased to 10 cm H2O above positive end-expiratory pressure.

Child, Preschool↗
PubMed1988

Propofol reduces seizure duration in patients having anaesthesia for electroconvulsive therapy.

Twenty-five patients received either methohexitone 1.0 mg kg-1 or propofol 1.3 mg kg-1 to induce anaesthesia during two separate electroconvulsive therapy (ECT) treatments. A forearm was isolated before administration of suxamethonium 0.5 mg kg-1, so that unmodified seizure duration could be measured. Bifrontotemporal electrodes were applied to administer a standard 3-s ECT shock. Median (quartile deviation) duration of seizure was reduced significantly after propofol (19.0 (9.0) s), compared with after methohexitone (33.0 (7.8) s). Therefore propofol may not be an appropriate anaesthetic for ECT because of its adverse effect on seizure duration.

Anesthesia, Intravenous↗
PubMedDate not supplied

Estrogen decreases prostaglandin H synthase products from endothelial cells.

OBJECTIVE: Because we showed recently that estrogen replacement prevents prostaglandin H synthase (PGHS)-dependent vasoconstriction in rats, the aim of this study was to determine how estradiol affects production of PGHS-dependent eicosanoids. METHODS: Cultured bovine coronary microvascular endothelial cells were exposed to physiologic levels of 17 beta-estradiol (0.01 nM [about 2.7 pg/mL], 0.1 nM [about 27 pg/mL], or 1.0 nM [about 270 pg/mL]) for 4, 8, or 24 hours. Thromboxane (TXA2), prostacyclin (PGI2), and nitric oxide (NO) were measured as their stable metabolites, thromboxane B2 (TXB2), 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha), and nitrite (NO2), respectively. RESULTS: Estradiol had no effect on nitrite production. However, exposure to 0.1 nM and 1.0 nM estradiol for 24 hours reduced TXB2 production to 67 +/- 16% and 69 +/- 12% of control, respectively. Furthermore, 0.1 nM and 1.0 nM estradiol also reduced production of 6-keto PGF1 alpha to 35 +/- 19% and 17 +/- 11% of control, respectively. Prostaglandin H synthase expression was not altered by estradiol. However, the estrogen receptor inhibitor, tamoxifen, reversed the inhibitory effect of estradiol. CONCLUSION: Estradiol acts through a receptor-dependent process to decrease PGHS-dependent products, thus further elucidating this novel effect of estradiol on the vascular system.

6-Ketoprostaglandin F1 alpha↗