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Biomedical subjects

J W Funder

Publications and source records attributed to J W Funder.

At least 55 records · Page 3Linked to original sources
PubMed1996

Substrate and inhibitor specificity of the cloned human 11 beta-hydroxysteroid dehydrogenase type 2 isoform.

The 11 beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) enzyme is thought to confer specificity on the mineralocorticoid receptor by inactivating glucocorticoids in mineralocorticoid target organs. The cloned 11 beta HSD2 displayed Michaelis constant values for corticosterone and cortisol of 5.1 and 61 nM, respectively. Linearity in the dose-response curve ranged between 1 and 200 nM for corticosterone and 25 and 2,000 nM for cortisol, with no evidence for complex kinetics. Inhibition of cortisol oxidation by other steroids was purely competitive in nature. Inhibition of 11 beta HSD2 activity by the end product or aldosterone occurred only at supraphysiological levels, whereas corticosterone and deoxycorticosterone displayed significant inhibition at physiological concentrations and progesterone at concentrations that occur during pregnancy. In intact transfected CHOP cells, dexamethasone was converted to 11-dehydrodexamethasone by 11 beta HSD2 but not type 1 11 beta-hydroxysteroid dehydrogenase, an aspect that may be useful in evaluating 11 beta HSD activity in intact cells.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1996

cAMP modulates glucocorticoid-induced protein accumulation and glucocorticoid receptor in cardiomyocytes.

Glucocorticoids have complex effects on cardiac muscle growth in vivo, and one possible reason may the regulatory cross talk between glucocorticoids and second messengers. In this study we investigated the effect of adenosine 3',5'-cyclic monophosphate (cAMP), shown to affect cardiomyocyte growth and glucocorticoid action in several systems, on glucocorticoid-induced protein accumulation and glucocorticoid receptor (GR) in neonatal rat cardiomyocytes. Dexamethasone (DEX) decreased the protein-to-DNA ratio, and 8-bromoadenosine 3',5'-cyclic monophosphate (BrcAMP) or forskolin increased this ratio. The inhibitory effect of DEX was potentiated by an elevated cAMP, despite the stimulatory effect of cAMP alone. Nuclear GR binding was increased by BrcAMP, with no change in GR mRNA or protein levels, via increased affinity of nuclear GR. H-89 blocked the effects of BrcAMP. In conclusion, glucocorticoids have an inhibitory effect on protein accumulation in cardiomyocytes via GR, an effect potentiated by elevated cAMP via increased nuclear GR binding. These results suggest that glucocorticoid effects on cardiomyocytes may be modulated by cAMP-mediated mechanisms, which may produce the complex effects of glucocorticoids on cardiomyocyte growth in vivo.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

Estrogen enhances basal nitric oxide release in the forearm vasculature in perimenopausal women.

The mechanisms of estrogen-induced cardiovascular protection are incompletely understood. Acute estrogen administration enhances acetylcholine-induced vasorelaxation, suggesting that endothelium-dependent factors may be important. The effect of long-term estrogen supplementation on endothelial function has not been well defined. In this double-blind, randomized study, we examined endothelial function in forearm resistance arteries in 11 perimenopausal women before and after 8 weeks of estrogen supplementation (estradiol valerate, 2 mg daily, n = 6) or placebo (n = 5). Forearm blood flow was measured by venous-occlusion plethysmography, and vasoactive agents were infused through a brachial artery cannula in doses that did not influence blood pressure or heart rate. Estrogen supplementation significantly reduced systolic and diastolic pressures but had no effect on plasma lipoproteins. Estrogen did not alter the vasodilator responses to acetylcholine at doses of 9.25, 18.5, and 37 micrograms/min (rise in forearm blood flow before estrogen: 263 +/- 72%, 288 +/- 66%, and 383 +/- 84%, respectively; after estrogen: 205 +/- 34%, 260 +/- 44%, and 359 +/- 54%, P > .05.). Vasodilator responses to the endothelium-independent agent sodium nitroprusside (1.6 micrograms/min) were also unchanged after estrogen supplementation. However, estrogen enhanced vasoconstrictor responses to the nitric oxide synthase inhibitor NG-mono-methyl-L-arginine at doses of 1, 2, and 4 mumol/min (fall in fore-arm blood flow before estrogen: 13 +/- 9%, 20 +/- 7%, and 26 +/- 8%, respectively; after estrogen: 18 +/- 9%, 36 +/- 7%, and 47 +/- 7%, P = .04). Responses to vasoactive agents were unchanged after administration of placebo. Thus, in perimenopausal women, estrogen supplementation reduces blood pressure and enhances basal but not acetylcholine-induced nitric oxide release in fore-arm resistance arteries.

Acetylcholine↗
PubMed1996

High glucose stimulates aldosterone-induced hypertrophy via type I mineralocorticoid receptors in neonatal rat cardiomyocytes.

Previous studies have shown that aldosterone plus salt loading cause cardiac hypertrophy in rats in vivo, and that in vitro, both aldosterone and glucose stimulate fibroblast growth. The present studies examined the effects of adrenal steroids via mineralocorticoid and glucocorticoid receptors (MR and GR) on [3H]leucine incorporation by neonatal rat cardiomyocytes in culture and the role of elevated glucose in modulating such effects. GR occupancy by corticosterone, the highly selective type II (glucocorticoid) receptor agonist RU28362, or high doses of aldosterone lowers incorporation; when this effect is blocked by coincubation with the glucocorticoid antagonist RU486, aldosterone, but not corticosterone, markedly elevates leucine incorporation, indicating a specific mineralocorticoid effect via MR. Incubation with high glucose alone does not increase incorporation, but markedly increases the hypertropic effect of aldosterone in terms of both threshold and maximum response. The glucose-aldosterone synergy is via MR and is completely blocked by spironolactone. The time course of increased incorporation is identical for aldosterone acting alone or with elevated glucose, consistent with widespread transcriptional effects and suggesting that the contribution of high glucose is not rate limiting. The glucose effect reflects neither induction of MR synthesis nor an increase in their affinity; it is specific, in that it is not mimicked by L-glucose or mannitol at equal concentrations, and is mediated via an increase in protein kinase C activity that can be measured in both soluble and particulate compartments. The role of this synergy in the cardiac sequelae of diabetes remains to be explored.

Aldosterone↗
PubMed1996

Localization of 11beta-hydroxysteroid dehydrogenase type 2 in rat tissues: in situ studies.

In the rat, the enzyme 11beta-hydroxysteroid dehydrogenase 2 (11betaHSD2) converts the glucocorticoid corticosterone into receptor-inactive 11-dehydrocorticosterone, thereby allowing preferential access of aldosterone to mineralocorticoid receptors (MR). The present study examines the distribution of this enzyme by in situ hybridization, using a homologous complementary RNA probe for 11betaHSD2. 11betaHSD2 messenger RNA was detected in classic epithelial aldosterone target tissues (kidney, salivary glands, and colon), the female reproductive system (ovary, oviduct, uterus, and placenta), and the adrenals; levels in heart, testis, and liver were below the limits of detection. We interpret the finding of 11betaHSD2 expression in both classical MR-containing aldosterone target tissues and a variety of other tissue as evidence that in the rat, the enzyme may play physiological roles in addition to that of excluding glucocorticoids from epithelial MR.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1996

Specific nuclear localization of 11-dehydrocorticosterone in rat colon: evidence for a novel corticosteroid receptor.

When colonic crypt cells isolated from intact rats are incubated with [3H]corticosterone specific nuclear binding is displaced by neither aldosterone nor the antiglucocorticoid RU38486, suggesting that [3H]corticosterone is binding to a site distinct from classical mineralocorticoid and glucocorticoid receptors. TLC revealed that the predominant nuclear [3H]steroid in the nucleus of [3H]corticosterone-incubated colonic crypt cells is [3H]11-dehydrocorticosterone. Where the enzyme 11 beta-hydroxysteroid dehydrogenase converting corticosterone to 11-dehydrocorticosterone is absent (cytosol preparations), [3H]corticosterone binds to classical glucocorticoid and mineralocorticoid receptors; in whole cells when 11 beta-hydroxysteroid dehydrogenase is blocked by carbenoxolone, cytoplasmic and nuclear binding of authentic [3H]corticosterone rises. Saturation and Scatchard analyses of nuclear [3H]11-dehydrocorticosterone binding demonstrate a single saturable binding site with a dissociation constant of < or = 10 nM at 22 C. We interpret these studies as evidence for a novel 11-dehydrocorticosterone-preferring receptor that may mediate glucocorticoid effects in tissues with high level of 11 beta-hydroxysteroid dehydrogenase activity.

Aldosterone↗
PubMed1996

Presence of pro-opiomelanocortin peptides and corticotropin-releasing factor in human placenta.

Immunoreactive adrenocorticotropin (ACTH), beta-endorphin (BEP) and corticotropin-releasing factor (CRF) were detected in human term placenta obtained from elective Caesarian surgery. The concentrations of ACTH, BEP and CRF in placenta detected by radioimmunoassay (RIA) were 2.83 +/- 0.36, 0.52 +/- 0.05 and 0.56 +/- 0.15 ng/g wet weight of tissue respectively. Pro-opiomelanocortin (POMC) peptides were also detected in the amnion and chorion membranes and in the decidua. The concentrations of ACTH were 1.72 +/- 0.20, 4.43 +/- 0.39 and 5.80 +/- 0.17 ng/g and the levels of BEP were 0.42 +/- 0.18, 0.65 +/- 0.20 and 3.66 +/- 1.10 ng/g in the amnion, chorion and decidua respectively. In contrast to placenta, immunoreactive CRF was not detected in the amnion, chorion and decidua. Immunoreactive N-acetylated BEP was also not detected in all the placental subfractions. Comparison of the amounts of both ACTH and BEP in the various placental components indicated the following distribution: decidua > chorion > placenta > amnion. In decidua, POMC peptides were present in an equi-molar ratio but in the other three placental fractions, ACTH levels were three to five-fold higher than BEP. In immunohistochemical studies, only a positive staining for ACTH was obtained for decidua. Our results confirm the presence of POMC peptides and CRF in placenta and their physiological roles in pregnancy and parturition.

Adrenocorticotropic Hormone↗
PubMed1995

Glucocorticoid receptor, mineralocorticoid receptors, 11 beta-hydroxysteroid dehydrogenase-1 and -2 expression in rat brain and kidney: in situ studies.

In mammals, 11 beta-hydroxysteroid dehydrogenase (11-HSD) activity allows aldosterone occupancy of mineralocorticoid receptors (MR) by inactivating endogenous glucocorticoids. The present study examined the distribution of 11-HSD2, 11-HSD1, glucocorticoid receptor (GR) and MR in kidney and brain. High levels of expression of 11-HSD2 were found in renal cortical distal tubules and more diffusely expressed in distal tubules of the medulla. No expression of 11-HSD2 was found on serial sectioning of the brain. 11-HSD1 was expressed in proximal tubules of the kidney and throughout the brain. GR mRNA was found predominantly in renal proximal tubules and diffusely in brain, while MR mRNA was located in the renal distal tubules and also in various brain nuclei. These anatomical findings support a functional relationship between 11-HSD1 and GR in both brain and kidney, but between 11-HSD2 and MR in kidney only.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

Glucocorticoid-induced hypertension in the elderly. Relation to serum calcium and family history of essential hypertension.

To explore the syndrome of glucocorticoid-induced hypertension in the elderly, we analyzed the clinical findings from 35 patients aged more than 65 years (12 men, 23 women) who received glucocorticoid therapy. Resting blood pressures (BP) were less than 140/90 mm Hg before glucocorticoid therapy, and patients were apparently disease-free apart from the condition for which glucocorticoid therapy was prescribed. Glucocorticoid-induced hypertension is defined as systolic BP more than 160 mm Hg and/or diastolic BP more than 95 mm Hg after glucocorticoid administration. Glucocorticoid-induced hypertension was seen in 13 patients (37.1%); all patients with hypertension [steroid (glucocorticoid)-induced hypertension (SH(+)) group] received more than 20 mg of prednisolone daily, and BP rose rapidly within a week of commencing glucocorticoid administration. The SH(+) group did not differ significantly in terms of age, heart rate, blood count, plasma biochemistry, plasma renin activity, plasma aldosterone, routine urinalysis, or urinary electrolytes from patients who did not show hypertension [SH(-) group]. However, serum total calcium concentrations were significantly lower in the SH(+) group both before and after 2 weeks of glucocorticoid therapy than in the SH(-) group. Furthermore, the SH(+) group showed a significantly higher percentage of patients with a positive family history of essential hypertension than the SH(-) group. In conclusion, although the detailed mechanisms are as yet uncertain, glucocorticoid-induced hypertension occurs often in elderly patients, and is more common in patients with total serum calcium concentrations lower than the normal range, and/or in those with positive family history of essential hypertension.

Aged↗
PubMed1995

Glucocorticoids but not mineralocorticoids modulate endothelin-1 and angiotensin II binding in SHR vascular smooth muscle cells.

Both glucocorticoids and mineralocorticoids are involved in circulatory homoeostasis and blood pressure control. In recent years direct effects of both steroid classes on vascular smooth muscle cells (VSMC) have been reported. We have thus examined the effects of RU 28362, a pure glucocorticoid agonist, and aldosterone, the physiologic mineralocorticoid, on the binding to VSMC from spontaneously hypertensive rats (SHR) of two key vasoactive peptides, endothelin-1 and angiotensin II. Binding of angiotensin II rose, and that of endothelin-1 declined, in a time- and dose-dependent fashion with maximal effects observed at 24 h and half-maximal effects for each at 2-3 nM RU 28362. Scatchard analysis showed that for both endothelin-1 and angiotensin II, RU 28362 alters receptor number but not affinity; competition studies with receptor-selective ligands (BQ123, S6C, DuP753 and PD123319) show that glucocorticoids specifically elevate (X2) AT-1 receptors and specifically lower (to approximately 30%) levels of ETA receptors. Treatment of VSMC with the antiglucocorticoid RU 38486 reversed the effect of glucocorticoids on endothelin-1 and angiotensin II binding, confirming the Type II (glucocorticoid) receptor mediated effect of the glucocorticoids. Aldosterone (100 nM) also lowers endothelin-1 binding and increases angiotensin II binding in VSMC; that this effect reflects aldosterone occupancy of classical glucocorticoid receptors is shown by the blockade of the aldosterone effect by an equal concentration (100 nM) of RU 38486--i.e. there is no evidence for an action of aldosterone via mineralocorticoid receptors. We interpret our results as evidence for a complex modulation of receptors for vasoactive peptides in VSMC by glucocorticoid but not mineralocorticoid hormones.

Aldosterone↗
PubMed1995

Mineralocorticoid receptors and hypertension.

Mineralocorticoid receptors (MR) have equal affinity for the mineralocorticoid aldosterone, and the physiological glucocorticoids cortisol and corticosterone. In epithelial tissues in vivo, MR are protected against glucocorticoid occupancy by the enzyme 11 beta-hydroxysteroid dehydrogenase, allowing access by the lower circulating levels of the physiological mineralocorticoid aldosterone. In non-epithelial tissues, including the heart and most areas of the central nervous system, MR are not so protected, and their physiological ligand is cortisol/corticosterone. Intracerebroventricular infusion studies have shown that aldosterone occupancy of such unprotected circumventricular MR is necessary for mineralocorticoid hypertension, and the hypertensinogenic effects of peripherally infused aldosterone can be blocked by intracerebroventricular infusion of the MR antagonist RU28318. Prolonged (8 weeks) administration of mineralocorticoids to salt-loaded rats has been shown to be followed by hypertension, cardiac hypertrophy and cardiac fibrosis. Whether the hypertrophy and fibrosis reflect primary effects of aldosterone via cardiac MR, or effects secondary to occupancy of protected, epithelial MR, remains to be determined, as does the mechanism of action of salt loading in this model of mineralocorticoid hypertension.

Aldosterone↗
PubMed1995

Corticosteroid hypertension.

Over the past year, the focus in corticosteroid hypertension has been on the cloning of the enzyme 11 beta-hydroxysteroid dehydrogenase, and the demonstration of a variety of mutations or deletions in the sequence coding for this enzyme in the syndrome of apparent mineralocorticoid excess. This syndrome is the third single-gene cause of human hypertension to be characterized, with glucocorticoid remediable aldosteronism (1992) and Liddle's syndrome (1994). The three conditions are characterized by inappropriate control of aldosterone secretion (glucocorticoid remediable aldosteronism), sodium retention (Liddle's syndrome) or aldosterone action (apparent mineralocorticoid excess), and underline a potential role of an aldosterone: salt imbalance in mineralocorticoid hypertension. No comparable mechanisms of hypertension following glucocorticoid receptor occupancy have been documented to date.

Adrenal Cortex Hormones↗
PubMed1995

Nongenomic effects of aldosterone on intracellular Ca2+ in vascular smooth muscle cells.

Genomic mechanisms of steroid action have been increasingly elucidated over the past four decades. In contrast, rapid steroid actions have been widely recognized only recently, and detailed analysis of the mechanisms involved are still lacking. The present article describes rapid effects of mineralocorticoid hormones on free intracellular calcium in vascular smooth muscle cells as determined by fura 2 spectrofluorometry in single cultured cells from rat aorta. These effects are almost immediate and reach a plateau after only 3 to 5 minutes and are characterized by high specificity for mineralocorticoids versus glucocorticoids. The potent mineralocorticoids aldosterone and fludrocortisone are agonists with estimated apparent EC50 values of approximately 0.1 to 0.5 nmol/L; deoxycorticosterone acetate is an agonist with an EC50 of approximately 5 nmol/L; and progesterone, cortisol, corticosterone, and estradiol have much lower potency (EC50 values of approximately 0.5 to 5 mumol/L). The effect of aldosterone is blocked by neomycin and short-term treatment with phorbol esters but augmented by staurosporine, indicating an involvement of phospholipase C and protein kinase C. The Ca2+ effect appears to involve the release of intracellular Ca2+, as shown by the inhibitory effect of thapsigargin; intriguingly, a relatively small maximum effect (approximately 40 nmol/L increase) is consistently seen. This mechanism operates at physiological subnanomolar aldosterone concentrations and appears to be a likely candidate for rapid fine tuning of cardiovascular responsivity. It may also contribute to known clinical features of mineralocorticoid action that are difficult to explain by the traditional genomic mechanism alone.

Aldosterone↗
PubMed1995

Hybridization histochemical localization of 11 beta-hydroxysteroid dehydrogenase type 2 in rat brain.

11 beta-hydroxysteroid dehydrogenase (11-HSD) activity allows aldosterone occupancy of mineralocorticoid receptors by inactivating endogenous glucocorticoids. The expression of the 11-HSD2 gene, a low Km, NAD+ dependent species of 11-HSD, was found in several discrete areas of the rat brain by in situ hybridization. Cells strongly positive for 11-HSD2 mRNA were found in the commissural portion of the nucleus tractus solitarius, subcommissural organ and ventrolateral ventromedial hypothalamus. Scattered labeled cells were also seen in the medial vestibular nucleus. The expression of 11-HSD2 mRNA in the brain is quite distinct from that of 11-HSD1 mRNA and allows for diverse roles in modulating corticosteroid receptor involvement in control of salt appetite, blood pressure and the hypothalamo-pituitary-adrenal axis.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1995

Glucocorticoid receptor expression is down-regulated by Lp(a) lipoprotein in vascular smooth muscle cells.

Glucocorticoids have been reported to protect against atherosclerosis and have been used clinically as protective therapy for restenosis after balloon angioplasty. Recently, Lp(a) lipoprotein [Lp(a)] levels have been suggested to be an independent risk factor for atherosclerosis, although its mechanisms of action are still uncertain. To clarify this atherogenic mechanism of Lp(a), we investigated the effects of Lp(a) on glucocorticoid receptor (GR) expression in human vascular smooth muscle cells (SMC). Levels of nuclear GR in SMC began to decrease after 12-h incubation with Lp(a), to 55 +/- 8% of the control value at 48 h; binding affinity did not change. Lp(a) had no effect on estrogen receptor binding in SMC. Moreover, low, very low, and high density lipoproteins had no effect on GR binding in SMC. The effects of Lp(a) on nuclear GR in rat SMC were very similar to those in human SMC; in contrast, Lp(a) did not alter GR or estrogen receptor levels in rat endothelial cells. GR messenger RNA levels in SMC decreased after 1-h treatment with Lp(a) to 23% of the control value after 12 h. Further, the antiproliferative effect of glucocorticoids on SMC was blunted by exposure to Lp(a). We conclude that Lp(a) down-regulates GR gene expression, resulting in a decreased number of GR in SMC. These findings suggest the possibility of a novel atherogenic mechanism of Lp(a) via inhibition of a protective action of glucocorticoids on SMC.

Aged↗