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Biomedical subjects

B R Walker

Publications and source records attributed to B R Walker.

At least 55 records · Page 3Linked to original sources
PubMed2001

Tissue-specific dysregulation of cortisol metabolism in human obesity.

Cortisol has been implicated as a pathophysiological mediator in idiopathic obesity, but circulating cortisol concentrations are not consistently elevated. The tissue-specific responses to cortisol may be influenced as much by local prereceptor metabolism as by circulating concentrations. For example, in liver and adipose tissue cortisol is regenerated from inactive cortisone by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). In obese Zucker rats 11beta-HSD1 activity is reduced in liver but enhanced in adipose tissue. This study addressed whether the same tissue-specific disruption of cortisol metabolism occurs in human obesity. 34 men were recruited from the MONICA population study in Northern Sweden to represent a wide range of body composition and insulin insensitivity. Plasma cortisol was measured at 0830h and 1230h, after overnight low-dose dexamethasone suppression, after intravenous corticotropin releasing hormone (CRH), and after oral cortisone administration. Urinary cortisol metabolites were measured in a 24 h sample. A subcutaneous fat biopsy was obtained from 16 participants to measure cortisol metabolism in vitro. Higher body mass index was associated with increased total cortisol metabolite excretion (r = 0.47, p < 0.01), but lower plasma cortisol at 1230 h and after dexamethasone, and no difference in response to CRH. Obese men excreted a greater proportion of glucocorticoid as metabolites of cortisone rather than cortisol (r = 0.43, p < 0.02), and converted less cortisone to cortisol after oral administration (r = 0.49, p < 0.01), suggesting impaired hepatic 11beta-HSD1 activity. By contrast, in vitro 11beta-HSD1 activity in subcutaneous adipose tissue was markedly enhanced in obese men (r = 0.66, p < 0.01). We conclude that in obesity, reactivation of cortisone to cortisol by 11beta-HSD1 in liver is impaired, so that plasma cortisol levels tend to fall, and there may be a compensatory increase in cortisol secretion mediated by a normally functioning hypothalamic-pituitary-adrenal axis. However, changes in 11beta-HSD1 are tissue-specific: strikingly enhanced reactivation of cortisone to cortisol in subcutaneous adipose tissue may exacerbate obesity; and it may be beneficial to inhibit this enzyme in adipose tissue in obese patients.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2001

Glucocorticoid metabolism and adrenocortical reactivity to ACTH in myotonic dystrophy.

Dysfunction of the hypothalamic-pituitary-adrenal axis might contribute to metabolic disturbances frequently encountered in myotonic dystrophy. We hypothesized that abnormal adrenocortical sensitivity to ACTH and/or glucocorticoid metabolism could be important in myotonic dystrophy. We assessed diurnal rhythmicity of saliva cortisol, adrenocortical reactivity by a low-dose (1 microg) Synacthen test, and glucocorticoid metabolism in blood and urine in 42 myotonic dystrophy patients (22 males) and 50 controls (27 males). CTG triplet repeat expansions were quantified by Southern blot. Diurnal rhythmicity of saliva cortisol was flattened in both men and women with myotonic dystrophy, with significantly increased afternoon/evening levels (P < 0.013). The cortisol response to ACTH was associated with increased (CTG)(n) expansions in myotonic dystrophy men and women (P < 0.01). Male myotonic dystrophy patients also had increased activation of cortisol from cortisone by 11beta-hydroxysteroid dehydrogenase type 1. Both men and women with myotonic dystrophy had an increased 5alpha/5beta-reductase ratio (P < 0.05 and P < 0.01, respectively). Cortisol metabolites were related to the genetic defect in myotonic dystrophy men (P < 0.05), whereas ratios reflecting 11beta-hydroxysteroid dehydrogenase type 1 activity in myotonic dystrophy women were positively associated with obesity (P < 0.05). Increased 11beta-hydroxysteroid dehydrogenase type 1 activity and adrenocortical reactivity to ACTH are related to the genetic defect in myotonic dystrophy men, whereas abnormal glucocorticoid metabolism is associated with alterations in body composition in female myotonic dystrophy patients. These disturbances may explain altered circulating cortisol levels and contribute to features of the metabolic syndrome in myotonic dystrophy.

Adrenal Cortex↗
PubMed2001

The natural history of idiopathic urethrorrhagia in boys.

PURPOSE: We describe the presenting symptoms, evaluation and natural history of urethrorrhagia in boys. MATERIALS AND METHODS: The records of 27 consecutive toilet trained boys with idiopathic urethrorrhagia were retrospectively reviewed for information regarding age, symptoms, symptom duration, physical examination, and radiographic, endoscopic and laboratory data. Patient interviews were performed, and the resolution rate, symptom duration and associated urological abnormalities were evaluated. RESULTS: Mean age at presentation was 10.1 years. Symptoms included urethrorrhagia in 100% and dysuria in 29.6% of cases. Radiographic and laboratory evaluations were normal in all patients except for microscopic hematuria in 57%. Cystourethroscopy in 4 patients revealed bulbar urethral inflammation without stricture in 2. A total of 24 patients (89%) were followed an average of 37 months (range 10 to 106). Complete resolution developed in 46% of cases at 6 months, in 71% at 1 year and in 91.7% overall. The average duration of symptoms was 9.9 months (range 2 weeks to 38 months). In 2 boys (8.3%) urethrorrhagia persisted for 22 and 28 months, and in 1 cystoscopy revealed urethral stricture. Self-limiting urethrorrhagia recurred in 2 patients (8.3%) after initial resolution. Treatment consisted of watchful waiting in all patients except 1 with urethral stricture, who underwent urethral dilation. After urethrorrhagia resolved epididymo-orchitis recurred in 1 case. CONCLUSIONS: Routine radiographic, laboratory and endoscopic evaluation is unnecessary for evaluating urethrorrhagia. Watchful waiting is indicated because the condition resolves in 71% and 91.7% of patients at 1 and 2 years, respectively. Evaluation should be considered in patients with prolonged urethrorrhagia because urethral stricture may be identified.

Adolescent↗
PubMed2000

Invasive group A streptococcus infection of the scrotum and streptococcal toxic shock syndrome.

We report a case of invasive group A streptococcus infection of the scrotum that presented as epididymoorchitis and rapidly progressed to streptococcal toxic shock syndrome. The presentation, pathophysiology, and management of invasive group A streptococcus and streptococcal toxic shock syndrome are reviewed. Rapid recognition is necessary to avoid the significant morbidity and mortality associated with these invasive infections.

Adolescent↗
PubMed2000

Adult cardiovascular risk factors in premature babies.

Among babies born at term, low birthweight predicts cardiovascular risk factors and disease in adulthood. This study shows that babies born prematurely, whether or not they have intrauterine growth retardation, are predisposed to similar risks as adults.

Adult↗
PubMed2000

Cortisol inhibits cholinergic vasodilation in the human forearm.

Exogenous cortisol raises blood pressure (BP) in humans and there is accumulating evidence of abnormalities of glucocorticoid activity in essential hypertension. In this study we tested the hypothesis that exogenous cortisol attenuates the cholinergic dilator response in the forearm circulation. Fourteen healthy normotensive men were studied. Using bilateral forearm venous plethysmography, we examined forearm blood flow responses to intra-arterial acetylcholine (ACh) and sodium nitroprusside (SNP) pre- and post-NG-monomethyl-L-arginine (LNMMA) after 2 or 5 days of oral cortisol or placebo in a randomized, double-blind crossover study. Exogenous cortisol increased supine systolic (P < .05) and standing systolic (P < .05) BP and produced expected metabolic changes and suppressed serum cortisol concentration (P < .001). Baseline forearm blood flow did not differ between placebo and cortisol treatments at 2 or 5 days. Cholinergic vasodilatation was impaired after cortisol administration, reaching statistical significance at 5 days (P < .05). Cortisol did not affect responses to SNP. NG-monomethyl-L-arginine inhibited cholinergic vasodilatation in placebo-treated groups but had no additional effect in the presence of cortisol. These results support our hypothesis and suggest that the mechanism of impaired cholinergic dilatation in glucocorticoid-treated subjects involves abnormalities of the endothelial nitric oxide system.

Adrenocorticotropic Hormone↗
PubMed2000

Endogenous inhibitors of 11beta-hydroxysteroid dehydrogenase type 1 do not explain abnormal cortisol metabolism in polycystic ovary syndrome.

OBJECTIVE: The aetiology of enhanced adrenal androgen secretion in polycystic ovary syndrome is poorly understood. Previous reports suggest that enhanced peripheral metabolism of cortisol results in decreased negative feedback suppression of ACTH secretion, either by enhanced inactivation of cortisol by 5alpha-reductase or impaired reactivation of cortisol by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). Endogenous inhibitors of hepatic 11beta-HSD1 can be extracted from urine. We have tested the hypothesis that these are increased in patients with polycystic ovary syndrome. DESIGN: A case-control study. PATIENTS: 57 patients with polycystic ovary syndrome and 27 healthy control women. MEASUREMENTS: Aliquots from 24 h urine samples were extracted with Sep-Paks and incubated with rat liver microsomes in which 11beta-HSD1 activity was quantified by conversion of 3H-corticosterone to 3H-11-dehydrocorticosterone. RESULTS: Inhibition of 11beta-HSD1 activity was not different in extracts from patients compared with controls (40.8 +/- 18.9 arbitrary units in patients vs. 42.7 +/- 16.6 in controls, mean (+/- SEM, P > 0.60) and did not correlate with ratios of cortisol metabolites in urine or with body mass index. CONCLUSIONS: The altered cortisol metabolism in polycystic ovarian syndrome, which is consistent with impaired 11beta-HSD1 activity, cannot be accounted for by increased production of measurable endogenous inhibitors of this enzyme.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed2000

Independent effects of obesity and cortisol in predicting cardiovascular risk factors in men and women.

OBJECTIVES: Recent data suggest that higher plasma cortisol may be associated with hypertension and insulin resistance in otherwise healthy men, as it is in Cushing's syndrome. However, obesity in women is associated with lower plasma cortisol concentrations. This study sought to establish whether plasma cortisol is associated with cardiovascular risk factors in women as it is in men, and whether these relationships in either sex are confounded by obesity. DESIGN: A population-based cross-sectional study. SETTING: The MONICA study in northern Sweden. SUBJECTS: From a target cohort of 2500, 1921 subjects took part and 226 were randomly selected because they attended between 07.00 and 09.00 h after an overnight fast. A 75 g oral glucose tolerance test was performed and blood sampled at baseline and 2 h after glucose. RESULTS: Plasma cortisol was lower in relatively obese subjects: in men, this was observed only in the 2 h sample (r = -0.23, P = 0.02) and in women only in the fasting sample (r = -0.26, P < 0.01). Simple regression analysis did not identify relationships between plasma cortisol and blood pressure, serum lipids, fasting insulin or glucose tolerance. However, after adjusting for the effect of obesity by multiple regression, higher plasma cortisol was independently associated with higher diastolic blood pressure in men (r = 0.21, P = 0.04) but not in women, and higher fasting serum triglyceride levels in women (r = 0.28, P < 0. 001) but not in men. CONCLUSIONS: Increasing obesity and plasma cortisol concentrations make independent and sex-specific contributions to variations in blood pressure and aspects of the insulin resistance syndrome. Adverse cardiovascular risk is greatest in those with the combination of obesity and failure to downregulate plasma cortisol levels.

Aged↗
PubMed2000

Nitric oxide-dependent pulmonary vasodilation in polycythemic rats.

Polycythemia causes increased vascular production of nitric oxide (NO), most likely secondary to an effect of elevated vascular shear stress to enhance expression of endothelial nitric oxide synthase (eNOS). Because both polycythemia and increased eNOS expression are associated with chronic hypoxia-induced pulmonary hypertension, experiments were performed to test the hypothesis that increased hematocrit leads to upregulation of pulmonary eNOS and enhanced vascular production of NO independent of hypoxia. Rats were administered human recombinant erythropoietin (rEpo; 48 U/day) or vehicle for 2 wk. At the time of study, hematocrit was significantly greater in the rEpo-treated group than in the vehicle group (65.8 +/- 0.7% vs. 45.1 +/- 0.5%), although mean pulmonary artery pressure did not differ between treatments. Experiments on isolated, saline-perfused lungs demonstrated similar vasodilatory responses to the endothelium-derived NO-dependent agonist ionomycin in each group. Additional experiments showed that the vasoconstrictor response to the thromboxane mimetic U-46619 was diminished at lower doses in lungs from the rEpo group compared with the vehicle group. However, perfusate nitrite/nitrate concentration after 90 min of perfusion in isolated lungs was not different between groups. Additionally, no difference was detected between groups in lung eNOS levels by Western blot. We conclude that the predicted increase in shear stress associated with polycythemia does not result in altered pulmonary eNOS expression.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2000

Renal vasodilatory influence of endogenous carbon monoxide in chronically hypoxic rats.

Chronic hypoxia (CH) attenuates systemic vasoconstriction to a variety of agonists in conscious rats. Recent evidence suggests that similarly diminished responses to vasoconstrictors in aortic rings from CH rats may be due to increased endothelial heme oxygenase (HO) activity and enhanced production of the vasodilator carbon monoxide (CO). Thus we hypothesized that a hypoxia-induced increase in HO activity is responsible for decreased vasoconstrictor responsiveness observed in conscious CH rats. CH (4 wk at 0.5 atm) and control rats were renal denervated and instrumented for the measurement of renal blood flow (RBF) and blood pressure. First, renal vasoconstrictor responses to graded intravenous infusion of phenylephrine (PE) were assessed in conscious rats. CH rats demonstrated significantly diminished renal vasoconstrictor responses to PE compared with control responses that persisted even with acute restoration of normoxia. In additional experiments, CH rats exhibited increased renal vascular resistance and decreased RBF in response to the HO inhibitor zinc protoporphyrin IX (11 micromol/kg iv), whereas renal hemodynamics were unaffected by the inhibitor in control animals. Furthermore, we demonstrated greater HO enzyme activity in renal tissue from CH rats compared with controls. These data suggest that enhanced HO activity contributes a tonic vasodilatory influence in the renal vasculature of CH rats that may be responsible for the diminished sensitivity to vasoconstrictor agonists observed under these conditions.

Animals↗
PubMed2000

Low birth weight predicts elevated plasma cortisol concentrations in adults from 3 populations.

Low birth weight is linked with raised blood pressure in adult life. Recent evidence has suggested that a neuroendocrine disturbance involving the hypothalamic-pituitary-adrenal axis could mediate this link. We therefore investigated the relation between birth weight and fasting plasma cortisol concentrations and the association of cortisol with current blood pressure in population samples of 165 men and women born in Adelaide, South Australia, from 1975 to 1976, 199 men and women born in Preston, UK, from 1935 to 1943, and 306 women born in East Hertfordshire, UK, from 1923 to 1930. Fasting plasma cortisol was measured in plasma samples obtained between 8 and 10 AM. Blood pressure was measured with an automated sphygmomanometer. Low birth weight was associated with raised fasting plasma cortisol concentrations in all 3 populations. A combined analysis that allowed for differences in the gender composition, age, and body mass index between the studies showed that cortisol concentrations fell by 23.9 nmol/L per kilogram increase in birth weight (95% CI 9.6 to 38.2, P<0.001). Fasting plasma cortisol concentrations also correlated positively with the subjects' current blood pressure. However, the association between cortisol and blood pressure was most marked in subjects who were obese (P=0.038 for interaction between body mass index and cortisol, P=0.01 for interaction between waist-to-hip ratio and cortisol). These results show that low birth weight is associated with raised fasting plasma cortisol concentrations. Increased activity of the hypothalamic-pituitary-adrenal axis may link low birth weight with raised blood pressure in adult life.

Adult↗
PubMed2000

Increased cortisol: cortisone ratio in acute pulmonary tuberculosis.

To evaluate a possible role for altered cortisol metabolism in mediating the immunoparesis associated with progressive tuberculosis (TB), we have studied the hypothalamic-pituitary-adrenal axis, and the activities of the 11beta-hydroxysteroid dehydrogenases (11-HSDs) that interconvert active cortisol and inactive cortisone. In active pulmonary tuberculosis (PTB), the ratio of cortisol/cortisone metabolites in 24-h urine showed a shift towards active cortisol (ratio, 1.19 +/- 0.1, n = 16 versus 0. 89 +/- 0.05 in cured pulmonary tuberculosis (CTB), n = 13, p < 0. 01; and 0.78 +/- 0.04 healthy volunteers (HV), n = 11, p < 0.005). Conversion of cortisone (administered as 25 mg orally) to cortisol in peripheral plasma was higher in PTB (peak 1,157 +/- 55 nM, n = 14 versus 862 +/- 50 nM in CTB, n = 10, p < 0.005, and 882 +/- 73 nM in HV, n = 10; p < 0.005). Cortisol/cortisone ratio was increased in bronchoalveolar lavage fluid in PTB (7.73 +/- 1.48, mean +/- SE, n = 13) compared with HV (4.05 +/- 0.38, n = 11, p < 0.05) but was not different in plasma (PTB, 3.25 +/- 0.68; HV, 4.01 +/- 0.92). Responses of plasma cortisol to dexamethasone, CRH stimulation, and multidose ACTH stimulation were not different. These data suggest that in pulmonary tuberculosis, central control of glucocorticoid production is normal but that peripheral metabolism, in particular in the lung, is deviated in favor of the active metabolite cortisol. This offers a possible mechanism to explain the immunoparesis observed in progressive pulmonary tuberculosis.

Adolescent↗
PubMed2000

Understanding the role of glucocorticoids in obesity: tissue-specific alterations of corticosterone metabolism in obese Zucker rats.

The role of glucocorticoids in obesity is poorly understood. Observations in obese men suggest enhanced inactivation of cortisol by 5alpha-reductase and altered reactivation of cortisone to cortisol by 11betahydroxysteroid dehydrogenase type 1 (11betaHSD1). These changes in glucocorticoid metabolism may influence corticosteroid receptor activation and feedback regulation of the hypothalamic-pituitary-adrenal axis (HPA). We have compared corticosterone metabolism in vivo and in vitro in male obese and lean Zucker rats, aged 9 weeks (n = 8/group). Steroids were measured in 72-h urine and 0900 h trunk blood samples. 5alpha-Reductase type 1 and 11betaHSD activities were assessed in dissected tissues. Obese animals were hypercorticosteronemic and excreted more total corticosterone metabolites (2264+/-623 vs. 388+/-144 ng/72 h; P = 0.003), with a greater proportion being 5alpha-reduced or 11-oxidized. 11-Dehydrocorticosterone was also elevated in plasma (73+/-9 vs. 18+/-2 nM; P = 0.001) and urine (408+/-111 vs. <28 ng/72 h; P = 0.01). In liver of obese rats, 5alpha-reductase type 1 activity was greater (20.6+/-2.7% vs. 14.1+/-1.5%; P<0.04), but 11betaHSD1 activity (maximum velocity, 3.43+/-0.56 vs. 6.57+/-1.13 nmol/min/mg protein; P = 0.01) and messenger RNA levels (0.56+/-0.08 vs. 1.03+/-0.15; P = 0.02) were lower. In contrast, in obese rats, 11betaHSD1 activity was not different in skeletal muscle and sc fat and was higher in omental fat(36.4+/-6.2 vs. 19.2+/-6.6; P = 0.01), whereas 11betaHSD2 activity was higher in kidney (16.7+/-0.6% vs. 11.3+/-1.5%; p = 0.01). We conclude that greater inactivation of glucocorticoids by 5alpha-reductase in liver and 11betaHSD2 in kidney combined with impaired reactivation of glucocorticoids by 11betaHSD1 in liver may increase the MCR of glucocorticoids and decrease local glucocorticoid concentrations at these sites. By contrast, enhanced 11betaHSD1 in omental adipose tissue may increase local glucocorticoid receptor activation and promote obesity.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗
PubMed2000

Development-related increase in cortisol biosynthesis by human granulosa cells.

Antiinflammatory mechanisms are important in ovulation and may be regulated by cortisol (F). We previously showed that after administration of human (h)CG for ovulation induction, luteinized granulosa cells (LGC) abundantly express 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) messenger RNA but not 11betaHSD type 2 (11betaHSD2) messenger RNA. 11ssHSD1 is responsible for the reversible formation of antiinflammatory F from its inactive precursor cortisone (E), whereas 11betaHSD2 unidirectionally converts F to E through 11-oxidation. This pattern of gene expression predicts that LGC from periovulatory follicles would show increased activation of E to F, compared with granulosa cells from immature follicles (IGC), and that follicular fluid concentrations of E and F would alter accordingly. To test this hypothesis, we isolated IGC, thecal cells (TC), and follicular fluid, from ovaries of cyclic women, removed during surgery for benign gynecological disease. LGC and follicular fluid were aspirated from periovulatory follicles, 35 h after hCG injection, in patients undergoing in vitro fertilization treatment. In an 11betaHSD assay based on interconversion of tritiated E and F by cell suspensions in vitro, IGC (% conversion, 0.6 +/- 0.4, mean +/- SEM) and collagenase-dispersed TC (0.2 +/- 0.1%) were unable to convert E to F, whereas LGC (36.3 +/- 3.7%) were highly efficient at this reaction. Immature granulosa cells, LGC, and (to a lesser extent) TC were all able to convert F to E. Correspondingly, follicular fluid concentrations of total F and F:E ratios were significantly higher in periovulatory follicles, compared with immature follicles. Culturing IGC for 48 h in the presence of hFSH resulted in increased 11betaHSD1 reductase activity, paralleling stimulation of estrogen (aromatase activity) and progesterone biosynthesis. Similar treatment with hLH did not influence 11betaHSD1 reductase activity, except in a patient with more mature IGC, which also showed a significant increase in E-to-F conversion, as well as progesterone synthesis in response to hLH. These data confirm that 11betaHSD activity in the human ovary is developmentally regulated and gonadotropin responsive, favoring metabolism of F to E in immature follicles and E to F in periovulatory follicles. Increased formation of F by LGC in periovulatory follicles is consistent with an antiinflammatory function for this glucocorticoid at ovulation.

11-beta-Hydroxysteroid Dehydrogenases↗