Medroxyprogesterone acetate antagonizes inhibitory effects of conjugated equine estrogens on coronary artery atherosclerosis

Although estrogen replacement therapy is associated with reduced risk of coronary heart disease and reduced extent of coronary artery atherosclerosis, the effects of combined (estrogen plus progestin) hormone-replacement therapy are uncertain. Some observational data indicate that users of combined hormone replacement consisting of continuously administered oral conjugated equine estrogens (CEE) and oral sequentially administered (7 to 14 days per month) medroxyprogesterone acetate (MPA) experience a reduction in risk similar to that of users of CEE alone. However, the effects of combined, continuously administered CEE plus MPA (a prescribing pattern that has gained favor) on the risk of coronary heart disease or atherosclerosis are not known. We studied the effects of CEE (monkey equivalent of 0.625 mg/d) and MPA (monkey equivalent of 2.5 mg/d), administered separately or in combination, on the extent of coronary artery atherosclerosis (average plaque size) in surgically postmenopausal cynomolgus monkeys fed atherogenic diets and treated with these hormones for 30 months. Treatment with CEE alone resulted in atherosclerosis extent that was reduced 72% relative to untreated (estrogen-deficient) controls (P < .004). Atherosclerosis extent in animals treated with CEE plus MPA or MPA alone did not differ from that of untreated controls. Although treatment had marked effects on plasma lipoprotein patterns, statistical adjustment for variation in plasma lipoproteins did not alter the between-group relationships in atherosclerotic plaque size, suggesting that these factors do not explain substantially the atheroprotective effect of estrogen or the MPA-associated antagonism. Although the mechanism(s) remains unclear, we conclude that oral CEE inhibits the initiation and progression of coronary artery atherosclerosis and that continuously administered oral MPA antagonizes this atheroprotective effect.     

Randomized, double-blind, placebo-controlled study of the effects of raloxifene and conjugated equine estrogen on plasma homocysteine levels in healthy postmenopausal women

OBJECTIVE: To investigate the long-term effects of raloxifene on fasting plasma homocysteine levels in postmenopausal women compared with conjugated equine estrogen (CEE). DESIGN: Randomized, double-blind, placebo-controlled study. SETTING: Outpatient department of a university hospital. PATIENT(S): Fifty-two hysterectomized, healthy postmenopausal women. INTERVENTION(S): Oral raloxifene in two dosages (60 mg/d [n=13] and 150 mg/d [n=13]), oral CEE (0.625 mg/d [n=13], and placebo (n=13) were given for 24 months. MAIN OUTCOME MEASURE(S): Fasting plasma homocysteine concentrations. RESULT(S): Plasma homocysteine levels were not altered in the placebo group. After 12 months, a significant reduction versus baseline in the mean plasma homocysteine level (-16%) was found only in the raloxifene 150-mg group. The mean change in plasma homocysteine levels within this group also was significantly different from the changes versus baseline found in the placebo group (+2%) and the raloxifene 60-mg group (-2%), but not different from those found in the CEE group (-8%). After 24 months, plasma homocysteine levels were decreased significantly in the raloxifene 150-mg and CEE groups compared with both baseline (-13% and -10%, respectively) and placebo values (-15% and -11%, respectively). No significant change in plasma homocysteine levels was observed in the raloxifene 60-mg group. CONCLUSION(S): Raloxifene has a favorable, dose-related effect on plasma homocysteine levels in postmenopausal women.     

Acute myocardial infarction and residual impairment of coronary perfusion: unusual complications of mitral endocarditis in a paediatric patient

In children, acute myocardial infarction is a rare complication of infective endocarditis. Since it is usually fatal, few data on the patients who have survived are available. We report the case of a child with acute myocardial infarction and residual impairment of the coronary reserve, complicating a mitral endocarditis.     

Acute hemodynamic effects of estrogen administration in postmenopausal women

The hemodynamic effects of estrogens in replacement doses have not been fully clarified; therefore, we studied the acute hemodynamic changes after 0.625 and 1.25 mg of conjugated estrogens, administered intravenously, using a thermodilution catheter, in postmenopausal women without structural heart disease. Pulmonary and systemic pressures and resistances and stroke volume did not change compared with baseline, but heart rate and cardiac output decreased significantly, which may be associated with estrogen's previously described calcium-blocking effect or with a more recently contemplated beta-blocking action.     

The effects of Escherichia coli sepsis and short-term ischemia on coronary vascular reactivity and myocardial function

A moderately stable protein with typical folding kinetics unfolds and refolds many times during its cellular lifetime. In monomeric lambda repressor this process is extremely rapid, with an average folded state lifetime of only 30 milliseconds. A thermostable variant of this protein (G46A/G48A) unfolds with the wild-type rate, but it folds in approximately 20 microseconds making it the fastest-folding protein yet observed. The effects of alanine to glycine substitutions on the folding and unfolding rate constants of the G46A/G48A variant, measured by dynamic NMR spectroscopy, indicate that the transition state is an ensemble comprised of a disperse range of conformations. This structural diversity in the transition state is consistent with the idea that folding chains are directed towards the native state by a smooth funnel-like conformational energy landscape. The kinetic data for the folding of monomeric lambda repressor can be understood by merging the new energy landscape view of folding with traditional models. This hybrid model incorporates the conformational diversity of denatured and transition state ensembles, a transition state activation energy, and the importance of intrinsic helical stabilities.     

Therapeutic options for improvement of myocardial perfusion in coronary atherosclerosis]

The combination of morphological atherosclerotic alterations of coronary vessels and disturbance of coronary vasomotor control of epicardial and resistance vessels determines the amount of myocardial oxygen supply. The endothelium plays a crucial role for functional alterations of the coronary vessels in patients with early atherosclerosis or risk factors for coronary artery disease. A therapy which aims to ameliorate endothelium-dependent vasodilator capacity improves myocardial perfusion in patients with coronary artery disease. Thereby, even in patients with angiographically normal or minimally diseased coronary vessels who develop myocardial ischemia due to microvascular disease, symptomatic improvement might be achieved. Control of coronary vasomotor tone and proliferation processes within the vessel wall are both determined by the redox equilibrium of nitric oxide (NO) and superoxide radicals (O2-), induced by angiotensin II. Thus, vasomotor control and vessel wall proliferation is closely related to each other. Aim of a therapeutic intervention to enhance NO bioactivity is either to increase NO production in the endothelium or to decrease O2- production, which rapidly inactivates NO. NO bioactivity can be ameliorated by ACE-inhibitors, increase of shear stress on the endothelium by physical exercise, estrogens or L-arginine. For these therapies clinically an improvement of endothelial vasodilator function could be shown. In addition, improvement of endothelial vasodilator function can be achieved by a treatment which reduced oxidative stress in the vascular wall such as antioxidants and, especially, lipid lowering drugs. Endothelin-antagonists and angiotensin II receptor-blockers are promising to improve endothelial dysfunction. However, these therapies have to be validated. Most therapy strategies, which have shown to ameliorate endothelial dysfunction, are also able to improve prognosis of the patients. Whether endothelial dysfunction alone--without evidence of overt coronary atherosclerosis--is sufficient to justify a long-term therapy to improve prognosis, still has to be clarified.     

Acute effects of parathyroid hormone on proximal bicarbonate transport in the dog

Re-collection micropuncture and simultaneous clearance studies were performed in thyroparathyroidectomized (TPTX) dogs to evaluate the effects of the acute administration of parathyroid hormone (PTH) on bicarbonate reabsorption. The i.v. administration of PTH from 74 to 94 U/hr reduced proximal fractional reabsorption (FRHCO3) from 0.28 +/- 0.03 to 0.14 +/- 0.03 (P less than 0.005) and absolute bicarbonate reabsorption (THCO3) from 556 +/- 126 to 255 +/- 73 pmoles/min (P less than 0.05), whereas there were no changes in PCO2 (37.0 +/- 1.4 leads to 37.2 +/- 1.4 mm Hg, P greater than 0.90), plasma bicarbonate (PHCO3) (18.5 +/- 0.4 leads to 18.3 +/- 0.4, P less than 0.60), single nephron glomerular filtration rate (102.2 +/- 15;9 leads to 90.1 +/- 10.3 nl/min, P greater than 0.40), serum ultrafilterable phosphate concentration (SUFp) (1.71 +/- 0.13 leads to 1.83 +/- 0.12 mmoles/liter, P greater than 0.25), or serum ultrafilterable calcium (SUFCa) (1.85 +/- 0.05 leads to 1.88 +/- 0.05 mEq/liter, P greater than 0.60). PTH also reduced proximal fractional fluid (and sodium) reabsorption (0.40 +/- 0.04 leads to 0.28 +/- 0.08, P less than 0.05) while TFHCO3 did not change (20.5 +/- 0.4 leads to 20.8 +/- 0.4 mmoles/liter) indicating a rejection of bicarbonate proportional to the inhibition in tubular fluid transport. The invariable reduction in proximal bicarbonate reabsorption did not uniformly result in an increased urinary bicarbonate concentration.     

Antifibrillatory effects of BRL-32872 in anesthetized Yucatan minipigs with regional myocardial ischemia

The antifibrillatory potential of BRL-32872, a novel antiarrhythmic compound with K+ and Ca2+ channel blocking activities, was examined in a minipig model of ischemia-induced arrhythmia. The effects of intravenous (i.v.) BRL-32872 (0.3 and 1.0 mg/kg, n = 8), dofetilide (0.3 mg/kg, n = 8), and flecainide (2.0 mg/kg, n = 8), were investigated on the incidence of ventricular fibrillation (VF) during a 20-min occlusion of the left anterior descending coronary artery (LAD). Ischemia-induced VF occurred in 6 of 9 vehicle-treated pigs. BRL-32872 reduced the incidence of ischemic VF to 13% at 0.3 mg/kg (p < 0.05) and to 0% at 1.0 mg/kg (p < 0.01). Dofetilide also prevented the occurrence of VF (0%, p < 0.01) In contrast, flecainide did not reduce the incidence of VF (63%). Indeed, flecainide shortened the time to onset of VF from 17 +/- 1 min in the vehicle group to 10 +/- 1 min (p < 0.001). The antifibrillatory effects of BRL-32872 and dofetilide were associated with a prolongation of QT interval on ECG. Flecainide did not prolong repolarization, but slowed the ventricular conduction velocity, as shown by significant increases in PR and QRS intervals. During early reperfusion, 1 of 8 surviving pigs in each group treated with BRL-32872 and 4 of 8 in the dofetilide group developed VF. This study demonstrated an antifibrillatory effect of BRL-32872 associated with prolonged ventricular repolarization and showed enhanced efficacy over dofetilide on reperfusion arrhythmias which is most likely a consequence of its Ca2+ blocking activity.     

Alpha-adrenergic blockade improves recovery of myocardial perfusion and function after coronary stenting in patients with acute myocardial infarction

BACKGROUND: AMI reperfusion by thrombolysis does not improve TIMI flow and LV function. The role of infarct-related artery (IRA) stenosis and superimposed changes in coronary vasomotor tone in maintaining LV dysfunction must be elucidated. METHODS AND RESULTS: Forty patients underwent diagnostic angiography 24 hours after thrombolysis. Seventy-two hours after thrombolysis, the culprit lesion was dilated with coronary stenting. During angioplasty, LV function was monitored by transesophageal echocardiography. Percent regional systolic thickening was quantitatively assessed before PTCA, soon after stenting, 15 minutes after stenting, and after phentolamine 12 microg/kg IC (n=10), the alpha1-blocker urapidil 600 microg/kg IV (n=10), or saline (n=10). Ten patients pretreated with beta-blockers received urapidil 10 mg IC. Coronary stenting significantly improved thickening in IRA-dependent and in non-IRA-dependent myocardium (from 27+/-15% to 38+/-16% and from 40+/-15% to 45+/-15%, respectively). Simultaneously, TIMI frame count decreased from 39+/-11 and 40+/-11 in the IRA and non-IRA, respectively, to 23+/-10 and 25+/-7 (P<0.05). Fifteen minutes after stenting, thickening worsened in both IRA- and non-IRA-dependent myocardium (to 19+/-14% and 28+/-14%, P<0.05), and TIMI frame count returned, in both the IRA and non-IRA, to the values obtained before stenting. Phentolamine and urapidil increased thickening to 36+/-17% and 41+/-14% in IRA and to 48+/-11% and 49+/-17% in non-IRA myocardium respectively, and TIMI frame count decreased to 16+/-6 and to 17+/-5, respectively. Changes were attenuated with beta-blocker pretreatment. CONCLUSIONS: Our finding that alpha-adrenergic blockade attenuates vasoconstriction and postischemic LV dysfunction supports the hypothesis of an important role of neural mechanisms in this phenomenon.     

Assessing myocardial perfusion in coronary artery disease with magnetic resonance first-pass imaging

MRFP perfusion imaging can now be used clinically on most MR scanner systems (1.0 to 1.5 T). The current experimental data demonstrate that MRFP imaging allows the quantitative assessment of myocardial blood flow changes and accurate measurements of collateral flow, including changes in the collateral dependent zones. Certain protocols, however, as outlined here have to be followed to obtain all the possible diagnostic information. Based on the current data on MRFP imaging, it is realistic to anticipate that MRFP imaging in combination with cine or tagging MR imaging will provide clinicians with better methods to distinguish stunned and hibernating, from nonviable myocardium and obtain better outcome data. Dedicated MR scanners are now being designed to meet the needs for MR imaging of patients with coronary artery disease. These scanners, small in size and with better patient access, make placement near the coronary care unit or catheterization laboratory feasible. This is a major step toward enhancing the utility of this new technique by providing the necessary infrastructure for scanning large numbers of patients. The main obstacle to wider use of these new diagnostic tools to assess perfusion is the lack of a large clinical database because there have not yet been major multicenter trials. With the development of novel intravascular contrast agents, however, larger trials are planned that should provide the clinical data mandatory for full integration of MRFP imaging into clinical practice. In particular, the development of dedicated and user-friendly perfusion analysis software will create the means to evaluate MR perfusion data accurately in large patient populations. These studies need to be conducted in a collaborative fashion by cardiologists, heart surgeons, and radiologists to be fully accepted by health care providers in an increasingly cost-averse and competitive health care environment.     

Mechanisms of kinin B1-receptor-induced hypotension in the anesthetized dog

Our study was performed to investigate the mechanism underlying the phypotensive effect of kinin B1-receptor activation with des-Arg9-bradykinin (des-Arg9-BK), in comparison with B2-receptor activation with bradykinin (BK), in anesthetized dogs. Bolus intravenous and intraarterial injections of both kinins were compared. BK (0.6 microgram/kg) produced a transient hypotension of the same magnitude, regardless of the route of administration (from 110 +/- 6 mm Hg to 66 +/- 6 mm Hg, or -41 +/- 5%). In contrast, intraarterial injection of des-Arg9-BK (0.6 microgram/kg) induced a weaker hypotension compared with its intravenous injection (-27 +/- 2% vs. -39 +/- 3%, p < 0.05). The hypotension induced by both kinins was accompanied by increases in heart rate, maximum left ventricular dP/dt, and aortic blood flow, suggesting a reduction in peripheral resistance. The positive inotropic and chronotropic effects of BK and des-Arg9-BK were found to be mediated by the sympathetic nervous system, because they were abolished by propranolol. The hypotension induced by intravenous and intraarterial injections of BK and intravenous injections of des-Arg9-BK was only slightly reduced after nitric oxide (NO) synthase inhibition with NG-nitro-L-arginine (L-NNA). In contrast, the hypotensive effect of intraarterial injection of des-Arg9-BK was reduced by half after treatment with L-NNA (p < 0.05). Neither bilateral vagotomy nor ganglionic blockade with pentolinium reduced the hypotension induced by both kinins. In conclusion, the hypotensive effect of des-Arg9-BK and BK results from a peripheral vasodilation. The contribution of NO in this vasodilation is substantial for des-Arg9-BK when administered intraarterial but limited for BK and intravenous des-Arg9-BK.     

Changes in coronary and collateral flows and adequacy of perfusion in the dog following one and three months of circumflex occlusion

We investigated changes in circumflex, left anterior descending (LAD), and right coronary artery flows as well as changes in collateral flows to these vessels after long-term circumflex occlusion. Coronary and collateral flows of each vessel were determined simultaneously in an isolated heart preparation in which the vasculature was maximally dilated with dipyridamole. The resistances as related to total heart weight of the circumflex, LAD, and right coronary arteries of 16 control dogs were found to be 0.59 +/- 0.06, 0.93 +/- 0.09, and 2.37 +/- 0.17 (mean +/- SEM) mm Hg/[(ml/min)/100 g], respectively. Total minimal coronary resistance was 0.21 +/- 0.01. In 10 dogs subjected to occlusion for 1 month no significant change in circumflex coronary resistance was observed, but the resistance of the unimpaired vessels decreased significantly. The resistances of the LAD and right coronary arteries were 0.66 +/-0.04 and 1.72 +/- 0.13, respectively. Both values were considerably less (P less than 0.01) than control. In nine dogs subjected to occlusion for 3 months the resistance of the unimpaired LAD and right arteries, as well as the circumflex coronary resitance, were not significantly different from control. We also found that retrograde flows for all vessels increased 7-fold after 1 month and 10.5-fold (relative to control) after 3 months of occlusion. From these data we conclude that vascular adaptations, which occurred in response to an ischemic stimulus, are responsible for the long-term regulation of the metabolic needs of the myocardium.     

Salutary effects of myocardial ischemia in coronary artery disease

A novel fine wire bone transport system for use with Ilizarov frames has been used in Bristol. It uses parallel wires instead of crossed wires. Its stiffness has been tested and compared with a crossed wire construct. In its basic form it is not as stiff to bending and shear loading, however, by modification it can be made at least as stiff. A parallel wire construct does not transfix as much soft tissue as a crossed wire construct when used in the leg. This is advantageous, because soft tissue transfixion causes pain and limb swelling, which impair patient mobilization.     

Preglomerular resistance and glomerular perfusion in the rat and dog

Glomerular blood flow in the rat, measured with radioactive microspheres, averaged 233 +/- 59 nl/min per glomerulus, significantly less than the glomerular flow rate in the dog (568 +/- 115; P less than 0.005). The difference in glomerular blood flow rate could not be attributed to differences in mean or cortical flow rates, the fraction of acrdiac output received, cardiac output normalized to body weight, or the fractional distribution of blood flow or glomeruli from outer to inner cortex in the two species. The size of microspheres reaching the glomerulus, however, was significantly larger in the dog than in the rat (P less than 0.0005) suggesting that afferent arterioles were larger in the dog than rat. The difference in afferent resistance calculated from the size of microspheres delivered to the glomeruli was larger than the difference in glomerular blood flow. With a similar arterial pressure, a lower afferent resistance suggests a higher glomerular capillary pressure in the dog, consistent with a number of suggestions that filtration equilibrium is less likely in this species.     

Acute and chronic effects of dexfenfluramine on the porcine coronary artery

Experiments were designed to verify whether or not acute or chronic exposure to dexfenfluramine favors the occurrence of coronary vasospasm in vivo or in vitro. Rings of left anterior and left circumflex porcine coronary artery, with and without endothelium, were studied in conventional organ chambers for the measurement of isometric force. The donor pigs were divided into two groups: controls and animals fed for 4 weeks with dexfenfluramine. In each group, one-half of the animals underwent balloon denudation of the left anterior descending coronary artery at the beginning of the study. Coronary angiography was performed at the time of denudation and, in all animals, during the 3rd week of the study. Acutely, dexfenfluramine at concentrations higher than 10(-5) M caused contractions which were blunted by the presence of the endothelium and inhibited by indomethacin (an inhibitor of cyclooxygenase). Chronic treatment with dexfenfluramine did not affect coronary diameter and did not alter the response to intracoronary infusion of serotonin. Chronic treatment with dexfenfluramine reduced the contractions of rings without endothelium to serotonin, but not those to norepinephrine or endothelin. It did not affect endothelium-dependent relaxations in the absence or presence of pertussis toxin to serotonin, UK14304 (alpha-2 adrenergic agonist), adenosine diphosphate or aggregating platelets. Chronic treatment with dexfenfluramine did not modify relaxations of rings without endothelium to SIN-1 (nitric oxide donor; the active metabolite of molsidomine) or adenosine diphosphate. These findings do not support the hypothesis that acute or chronic exposure to dexfenfluramine favors the occurrence of coronary vasospasm.     

Differential effects of low- and high-dose estrogen treatments on vascular responses in female rats

In an attempt to study the mechanisms by which estrogens affect vascular responses, we utilized aortic preparations from intact and ovariectomized female rats receiving low- and high-dose subcutaneous estrogen treatments. Oil-treated, as well as male rats, served as controls. In ovariectomized females, low-dose 17-beta-estradiol injections (5 microg/kg daily for two days) affected the basal release of nitric oxide, as evaluated by concentration-related curves to superoxide dismutase and N(G)-Methyl-L-arginine acetate, which was found to be greater in 17-beta-estradiol-treated females compared to oil-treated females or males. Conversely, the nitric oxide-related vascular relaxation evoked by acetylcholine and sodium nitroprusside was unchanged. Prostacyclin production was also evaluated. Aortic rings from ovariectomized 17-beta-estradiol-treated females released significantly more prostacyclin than those from oil-treated females. These results point out a possible role for nitric oxide and prostacyclin in the vascular protection brought about by physiological levels of estrogens. When intact females were treated with high doses of ethynilestradiol (100 microg/Kg daily for one month), a component of contraceptive pills, either the basal release of nitric oxide, or acetylcholine-induced relaxation underwent a significant decrease. Likewise, the relaxant responses to sodium nitroprusside were impaired in the aortic rings obtained from ethynilestradiol-treated animals when compared to controls. Similarly, the amount of prostacyclin released from aortic tissues obtained from ethynilestradiol-treated animals was significantly reduced. These results may provide a possible explanation for the higher incidence of cardiovascular disease in women who take contraceptive preparations containing high doses of estrogens.     

Pharmacokinetics and pharmacodynamics of conjugated equine estrogens: chemistry and metabolism

Raf-1, A-Raf and B-Raf comprise a small family of highly conserved serine/threonine protein kinases, whose activities play a fundamental role in the control of proliferation and differentiation. The best studied family member, Raf-1, is expressed ubiquitously and constitutively, and its activity is regulated by post-translational mechanisms. Raf-1 can be activated by many signals that include growth factors, tumor promoters, inflammatory cytokines, calcium mobilization, DNA damaging agents, and oxygen radicals. Ras-mediated translocation of Raf-1 to the plasma membrane is a crucial step in its activation process, and is thought to facilitate phosphorylation by membrane-bound kinases. Raf-1 has also been reported to undergo intracellular redistribution following its activation: to the perinuclear space in murine NIH3T3 cells and rat hepatic Ito cells, and into the nucleus in gerbil hippocampal pyramidal cells and human MO7 leukemia cells. In contrast to the translocation to the plasma membrane, the perinuclear and/or nuclear translocation of Raf-1 has not been investigated in detail. In this paper, we report an examination of the subcellular localization of endogenous Raf-1 in a fibroblastic cell line (Rat-1) commonly used in transformation assays. Using the methods of cellular fractionation as well as in situ immunofluorescence, we show that no detectable movement of Raf-1 to the perinuclear or nuclear space can be observed. Tethering of activated Raf to the plasma membrane does not interfere with its transforming activity.