Synthesis, mechanical properties and corrosion behavior of powder metallurgy processed Fe/Mg2Si composites for biodegradable implant applications.

Recently, Fe and Fe-based alloys have shown their potential as degradable materials for biomedical applications. Nevertheless, the slow corrosion rate limits their performance in certain situations. The shift to iron matrix composites represents a possible approach, not only to improve the mechanical properties, but also to accelerate and tune the corrosion rate in a physiological environment. In this work, Fe-based composites reinforced by Mg2Si particles were proposed. The initial powders were prepared by different combinations of mixing and milling processes, and finally consolidated by hot rolling. The influence of the microstructure on mechanical properties and corrosion behavior of Fe/Mg2Si was investigated. Scanning electron microscopy and X-ray diffraction were used for the assessment of the composite structure. Tensile and hardness tests were performed to characterize the mechanical properties. Potentiodynamic and static corrosion tests were carried out to investigate the corrosion behavior in a pseudo-physiological environment. Samples with smaller Mg2Si particles showed a more homogenous distribution of the reinforcement. Yield and ultimate tensile strength increased when compared to those of pure Fe (from 400MPa and 416MPa to 523MPa and 630MPa, respectively). Electrochemical measurements and immersion tests indicated that the addition of Mg2Si could increase the corrosion rate of Fe even twice (from 0.14 to 0.28mm·year-1). It was found that the preparation method of the initial composite powders played a major role in the corrosion process as well as in the corrosion mechanism of the final composite.

Effects of propranolol on the impulse activity of cardiovascular sympathetic afferent fibers.

The influence of beta-adrenergic receptor blockade on the impulse activity of 21 cardiovascular sympathetic afferent nerve fibers (11 from the thoracic aorta, 10 from the pulmonary veins), isolated from the left sympathetic rami communicantes T-3 and T-4 was studied in anesthetized, vagotomized cats. Aortic pressure, heart rate, and neural discharge were recorded during control conditions and during brief aortic occlusions of comparable amplitude and duration. Administration of dl-propranolol (0.2-0-4 mg/kg) did not modify aortic pressure or neural discharge of the fibers during control conditions, although, as expected, heart rate was diminished. dl-Propranolol administration did change the response of cardiovascular sympathetic afferents to similar aortic pressure increases. Before drug administration, aortic occlusion caused a significant increase in neural discharge of both aortic and pulmonary vein sympathetic afferent fibers, from 0.52 +/- 0.12 to 1.64 +/- 0.31 and from 0.67 +/- 0.10 to 2.08 +/- 0.25 impulses/sec, respectively (p less than 0.05). After dl-propranolol administration, comparable increases in aortic pressure resulted in slight but not significant increases in neural discharge of aortic and pulmonary vein fibers. Administration of d-propranolol (0.4-0.6 mg/kg), which possesses only membrane-stabilizing properties, did not modify the firing rate of four pulmonary sympathetic afferents, which subsequently decreased their response to pressure rises after administration of dl-propranolol. These results indicate that beta-adrenergic receptor blockade reduces the responsiveness to hemodynamic stimuli of sympathetic cardiovascular afferent fibers that are capable of mediating excitatory pressor reflexes.

Systemic and cerebral kinetics of 16 alpha [18F]fluoro-17 beta-estradiol: a ligand for the in vivo assessment of estrogen receptor binding parameters.

Estrogen receptors are expressed in several brain areas of various animal species, and steroid hormones exert physiologic and biochemical effects on the central nervous system. The aim of the present study was to evaluate in female adult rats, the suitability of 16 alpha [18F]fluoro-17 beta-estradiol ([18F]FES), a selective estrogen receptor ligand, for the in vivo assessment of brain estrogen receptors. This was considered to be a preliminary step in evaluating the potential usefulness of [18F]FES for studies of cerebral estrogen receptors with positron emission tomography (PET) in nonhuman primates and human subjects. We evaluated (a) the time course of the metabolic degradation of [18F]FES in blood; (b) the time course of distribution of the tracer in discrete cerebral areas; (c) the inhibitory effect of increasing doses of cold estradiol on cerebral [18F]FES uptake; and (d) the possibility of in vivo quantification of estrogen receptor binding parameters using both equilibrium and dynamic kinetic analyses. We quantified [18F]FES binding to estrogen receptors using both equilibrium and dynamic kinetic analyses. The results of this study indicate that [18F]FES is a suitable tracer for the measurement of estrogen receptors in the pituitary and hypothalamus, using either the equilibrium or the kinetic analysis. However, [18F]FES is inadequate for the in vivo investigation of estrogen binding sites in brain areas with low receptor density, such as the hippocampus.

Sympathetic predominance in essential hypertension: a study employing spectral analysis of heart rate variability.

In this study on 91 subjects we tested the hypothesis of an enhanced sympathetic activity in uncomplicated essential hypertension employing spectral analysis of heart rate variability. With this technique the tonic sympathetic and vagal activities and their changes are respectively assessed by the power of approximately 0.1 Hz (low frequency, LF) and approximately 0.25 Hz (respiratory linked, high frequency, HF) components of the spectrum of the beat by beat variability of RR interval. When comparing the 40 subjects with diastolic blood pressure consistently greater than 95 mmHg (hypertensives, Ht), with 35 age-matched controls (diastolic arterial pressure less than 90 mmHg, Nt), we observed that LF was greater and HF smaller in Ht as compared to Nt, thus suggesting an enhanced sympathetic activity and a reduce vagal activity in Ht. Additionally, passive tilt, which in Nt enhances LF [delta = 26 +/- 2 normalized units (nu)] and reduces HF (delta = -22 +/- 2, nu), produced smaller (P less than 0.05) changes in Ht (delta LF = 6.3 +/- 2.7 and delta HF = -7.5 +/- 2.3 nu). Furthermore, the values of LF at rest and the altered effects of tilt on LF and HF were significantly correlated with the degree of the hypertensive state. Chronic beta-adrenergic blockade (atenolol 100 mg once daily for 2 weeks, n = 13) reduced heart rate and blood pressure (from 162/103 to 136/88 mmHg) together with a significant diminution of LF and an increase of HF. Thus, spectral analysis of RR variability appears to be a convenient non-invasive technique to follow the progressive alterations in sympatho-vagal balance present in essential hypertension.

Altered pattern of circadian neural control of heart period in mild hypertension.

We addressed the problem of the circadian changes in neural control of heart period in ambulant hypertensive subjects. A running spectral analysis of R-R variability from Holter tapes provided markers of sympathetic, i.e. low-frequency component (LF) almost equal to 0.10 Hz, and vagal, i.e. high-frequency component (HF) almost equal to 0.25 Hz, controlling activities for the 24-h period of the recording. Significant circadian differences were observed in LF between the two groups of subjects: during night-time rest (0300-0400 h), LF was greater in hypertensives than in normotensives (56 +/- 2 and 48 +/- 2 nu, respectively; P less than 0.05). Furthermore, the difference between daytime and night-time LF values was progressively reduced with increasing severity of the hypertensive state, as assessed by resting arterial pressure levels. Spectral analysis of R-R variability suggests that essential hypertension may be characterized by a reduced day-night oscillation in sympathetic activity than can be quantified non-invasively using this approach.

Human biodistribution, dosimetry and clinical use of technetium(III)-99m-Q12.

UNLABELLED: Technetium(III)-99m-Q12, trans-(1,2-bis(dihydro-2,2,5,5-tetramethyl- 3(2H)furanone-4-methyleneimino)ethane)bis(tris(3-methoxy-1-propyl) - phosphine)technetium(III)-99m, is a nonreducible complex of Tc(III) which is herein evaluated as a myocardial perfusion imaging agent. METHODS: The biodistribution and dosimetry of 99mTc-Q12 were assessed in 10 normal volunteers, while its potential clinical use was evaluated in 70 patients. RESULTS: Safety parameters measured up to 24 hr postinjection demonstrate no clinically significant drug-related adverse reactions. Technetium(III)-99m-Q12 exhibits good heart uptake (2.2% injected dose at 1 hr postinjection under resting conditions) and no detectable myocardial washout or redistribution up to 5 hr postinjection. The biodistribution is characterized by very rapid hepatobiliary clearance which allows effective myocardial imaging at times as short as 15 min postinjection. Blood and plasma clearances and myocardial uptake are rapid, while lung uptake is minimal. The heart-to-lung and heart-to-liver ratios are higher at stress than at rest, independent of the time elapsed between injection and image acquisition, and independent of whether the patient is fasted or fed after tracer administration. A preliminary correlation shows that 46/47 patients with angiographically demonstrated CAD also have perfusion defects demonstrated by 99mTc-Q12. CONCLUSIONS: On the basis of the studies reported herein, 99mTc-Q12 appears to be a promising myocardial perfusion imaging agent.

Extracorporeal circulation as a new experimental pathway for myoblast implantation in mdx mice.

The deficiency of dystrophin, a sarcolemmal associated protein, is responsible for Duchenne muscular dystrophy (DMD). Gene replacement is attractive as a potential therapy. In this article, we describe a new method for myoblast transplantation and expression of dystrophin in skeletal muscle tissue of dystrophin-deficient mdx mouse through iliac vessels extracorporeal circulation. We evaluated the extracorporeal circulation as an alternative route of delivering myoblasts to the target tissue. Two series of experiments were performed with the extracorporeal circulation. In a first series, L6 rat myoblasts, transfected with LacZ reporter gene, were perfused in limbs of 15 rats. In the second series, the muscle limbs of three 6-8-week-old mdx were perfused with myoblasts of donor C57BL10J mice. Before these perfusions, the right tibialis anterior (TA) muscle of the rats and mdx was injected three times at several sites with bupivacaine (BPVC) and hyaluronidase. The ability of injected cells to migrate in the host tissue was assessed in rats by technetium-99m cell labeling. No radioactivity was detected in the lungs, bowels, and liver of animals treated with extracorporeal circulation. The tissue integration and viability of the myoblasts were ultimately confirmed by genetic and histochemical analysis of LacZ reporter gene. Following a single extracorporeal perfusion of myoblasts from donor C57BL10J, sarcolemmal expression of dystrophin was observed in clusters of myofibers in tibialis anterior muscles previously treated with BPVC and hyaluronidase. Furthermore, large clusters of dystrophin-positive fibers were observed in muscles up to 21 days after repeated treatments. These clusters represented an average of 4.2% of the total muscle fibers. These results demonstrate that the extracorporeal circulation allows selective myoblast-mediated gene transfer to muscles, opening new perspectives in muscular dystrophy gene therapy.

Biodistribution studies of 99mTc-labeled myoblasts in a murine model of muscular dystrophy.

The purpose of this study was twofold: first, to evaluate the myoblast labeling of various 99mTc complexes and to select the complex that best accomplishes this labeling, and second to evaluate the biodistribution of myoblasts labeled with this complex using mice with MDX muscular dystrophy (the murine homologue of Duchenne's muscular dystrophy). The following ligands were used to prepare the corresponding 99mTc complexes: hexakis-methoxy-isobutyl-isonitrile (MIBI), bis(2-ethoxyethyl)diphosphinoethane (Tf), (RR,SS)-4,8-diaza-3,6,6,9-tetramethyl-undecane-2,10-dione-bisoxime (HM-PAO), bis(N-ethyl)dithiocarbamate (NEt), and bis(N-ethoxy, N-ethyl)dithiocarbamate (NOEt). One million murine myoblasts were incubated for 30-60 minutes with 5 mCi of each of the 99mTc complexes prepared from the above ligands. Viability was assessed by microscopic counting after trypan blue staining, and the radioactivity absorbed in the cells was measured after centrifugation. The compound with the highest uptake in cellular pellets was [99mTc]N-NOEt. The biodistribution of myoblasts labeled with this complex was evaluated after intraaortic injection in dystrophic mice. Such an approach has the potential of effecting widespread gene transfer through the bloodstream to muscles lacking dystrophin.

Oestrogen receptors in meningiomas: a correlative PET and immunohistochemical study.

There have been a number of indications that sex hormones can affect the rate of growth of meningiomas during pregnancy. The presence of oestrogen or progesterone receptors in meningiomas and the influence of sex hormones upon cell cultures derived from human meningiomas have been extensively investigated. The results have been controversial, with most of the discussion centring upon the presence and possible role of oestrogen receptors. The aim of the present study was to assess oestrogen receptors in human meningiomas with 16alpha[l8F]fluoro-17beta-oestradiol ([18F]FES) and positron emission tomography (PET). With this purpose in mind, we measured the regional brain uptake of [18F]FES in six patients with a neuroradiological and histological diagnosis of meningioma, comparing the in vivo PET data with the immunohistological analysis of oestrogen receptors performed on formalin-fixed, paraffin-embedded tissue obtained at surgery. Two analyses were used for the in vivo measurement of [18F]FES binding to oestrogen receptors: the ratio of tumour activity to that of normal tissue (T/NT), calculated 90 min after tracer injection, and the ratio between the equilibrium distribution volume (DV) in normal and pathological tissues, calculated by means of a graphical kinetic analysis. PET studies demonstrated a marked uptake of [18F]FES by the tumour in four of the six patients. Immunohistochemical assay using a manual staining method capable of detecting oestrogen receptors at a level of > 10 pmol mg(-1) of protein detected only sparse immunostaining in one of the six meningiomas. Distinct albeit weak immunostaining was demonstrated in five of the six meningiomas when the sensitivity of the immunohistochemical assay was increased to < 10 pmol mg(-1) of protein by use of an automated staining method (Bioteck 1000). Comparison of the in vivo and immunohistochemical results showed a correlation in five of the six patients, thus indicating the high sensitivity of [18F]FES for the in vivo evaluation of oestrogen receptor expression.

Quality control of 99Mo/99Tcm generators: results of a survey of the Radiopharmacy Working Group of the Italian Association of Nuclear Medicine (AIMN).

A multicentre survey of the quality control of 99Tcm generators has been completed: 245 generators from seven different commercial sources were tested over a period of 2 years. The results indicate that the mean pH of the eluates was 5.8 +/- 0.6; the aluminium contents were typically < 10 ppm; the radiochemical purity was 99.8 +/- 0.4% and the median 99Mo content was 3.8 x 10(-4) percent. The elution profiles gave a volume of 1.9 ml to obtain 50% of the total eluted activity and of 4.9 ml to obtain 95%. Other radionuclide impurities and heavy metal breakthrough were evaluated by graphite furnace absorption spectrometry and inductively coupled plasma mass spectrometry. National guidelines for the standardization of radiopharmacy procedures are currently being compiled.

[Platelet aggregation in whole blood with the impedance method in subjects with non-complicated essential arterial hypertension]. / L'aggregazione piastrinica su sangue intero con metodo impedenzometrico nei soggetti portatori di ipertensione arteriosa essenziale non complicata.

Arterial hypertension is considered a major risk factor in atherosclerosis in the pathogenesis of which platelet activity plays a fundamental role. However the data in the literature on platelet function in arterial hypertension do not always agree. The present study was conducted on whole blood, using the impedance metering technique to assess platelet aggregation induced by ADP (10 pg) and collagen (2 mg/ml) in 15 patients with uncomplicated essential hypertension and 25 healthy controls. Analysis of the data shows a statistically significant difference between the aggregation curves of the hypertensive and the healthy subjects with excessive platelet aggregation in those suffering from uncomplicated arterial hypertension.

Afferent sympathetic unmyelinated fibres with left ventricular endings in cats.

1. We recorded the electrical impulse activity of thirty-three single afferent fibres with left ventricular endings from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocity ranged from 0.23 to 0.98 m/sec (group C). 2. The endings of each fibre were localized to the left ventricle by mechanical probing performed at the end of the experiment on the non-beating heart. No fibre had multiple sensory fields. 3. The impulse activity (0.95 +/- 0.2 impulses/sec) was spontaneous but most often a fixed temporal correlation between impulses and ventricular dynamics was not detectable. It was increased during occlusion of the thoracic aorta, I.V. administration of isoprenaline or infusion of saline. It was unaffected by asphyxia, haemorrhage and I.V. administration of acetylcholine. It was decreased during occlusion of inferior vena cava. Therefore these ventricular receptors appeared to be mainly sensitive to mechanical events. 4. The fibres were excited during the occlusion of the left main coronary artery, after a latency of 14.5 +/- 1.3 sec. They were also excited during ventricular fibrillation, exhibiting the highest values of impulse activity (2.51 +/- 0.4 impulses/sec). The increase in impulse activity during ventricular fibrillation was sometimes immediate and extreme, with peak frequencies of about 50 impulses/sec. 5. These spontaneously active ventricular receptors with unmyelinated nerve fibres participate in the transmission of the continuous impulse activity which from the cardiovascular system reaches the spinal cord through the sympathetic nerves and which is likely to contribute to the neural control of circulation. Thus the unmyelinated cardiac sympathetic afferents should not be considered as purely nociceptive in function.

Effects of intracoronary administration of bradykinin on the impulse activity of afferent sympathetic unmyelinated fibers with left ventricular endings in the cat.

In anesthetized and artificially ventilated cats, we recorded the impulse activity of 23 afferent sympathetic unmyelinated fibers with left ventricular endings, dissected from the left sympathetic rami T3 and T4. All fibers displayed a spontaneous discharge at a rate of 0.79 +/- 0.2 (mean +/- SE) impulses/sec. During constriction of the thoracic aorta, the discharge increased to 1.92 +/- 0.2 impulses/sec. During myocardial ischemia, produced by interruption of left main coronary artery perfusion, supplied through an extracorporeal pump, the impulse activity increased to 1.73 +/- 0.3 impulses/sec. The mean latency for this excitation was 16.5 +/- 1.5 sec. The intracoronary administration of bradykinin (5 and 10 ng/kg) elicited a marked increase in impulse activity that, following 5 ng/kg, reached 2.06 +/- 0.2 impulses/sec, after a latency of 18 +/- 2 sec and in absence of significant hemodynamic changes. Myocardial ischemia and bradykinin never revealed the existence of silent afferent fibers included in the split nerve strand. The results obtained with this experimental model indicate that the ventricular endings of these afferent sympathetic unmyelinated fibers act as "polymodal" receptors. We hypothesize that the peripheral mechanism for cardiac nociception involves intensive excitation of fibers discharging spontaneously and not recruitment of silent fibers which are purely nociceptive in function.

Spectral analysis of heart rate variability in the assessment of autonomic diabetic neuropathy.

We studied heart rate variability in 49 uncomplicated diabetics (27 with insulin therapy; 22 with oral hypoglycemic agents) and in 40 age-matched controls. An automatic autoregressive algorithm was used to compute the power spectral density (PSD) of beat by beat RR variability derived from the surface ECG. The PSD contains two major components (a low frequency approximately 0.1 Hz (LF) and a high frequency, respiratory linked, approximately 0.25 Hz (HF] that provide, respectively, quantitative markers of sympathetic and vagal modulatory activities and of their balance. As compared to controls, in diabetics, besides a reduced RR variance at rest (2722 +/- 300 and 1436 +/- 241 ms2, respectively), we observed during passive tilt an altered response of spectral indices of sympathetic activation and vagal withdrawal, suggestive of a complex modification in the neural control activities. In addition, we compared this approach to the commonly used clinical tests score, and observed that the latter provides overall results similar to those obtained with spectral changes induced by tilt (r = 0.42; P less than 0.01). Of potential clinical importance is that the data obtained with spectral analysis appear more thoroughly quantifiable and do not require the active collaboration of the patients.

Ion chromatographic analysis of high specific activity 18FDG preparations and detection of the chemical impurity 2-deoxy-2-chloro-D-glucose.

Because of the widespread use of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) prepared by the "Julich" method or its variants it was decided necessary to determine the major chemical impurities present in the final product. An analytical system for quantifying FDG was developed using pulsed amperometry after separation by high-performance anion exchange chromatography. With this system a heretofore unidentified impurity, 2-deoxy-2-chloro-D-glucose (C1DG, ca 20-2000 micrograms; typically < 100 micrograms), was found in our preparation and in those from other laboratories using the "Julich" method. C1DG arises from Cl- ion displacement during the labeling procedure where Cl- ion comes from several sources, and Cl- ion displacement from the HCl used in the hydrolysis step. FDG mass was present in the same preparations at a level of ca 1-40 micrograms. Other major chemical constituents were glucose (ca 1-6 mg) and mannose (ca 10-18 micrograms). Glycerol, arising from sterilizing filters, was also detected in most preparations. Although C1DG is a chemical impurity which has not been detected previously in nca FDG preparations, its biochemical and pharmacological properties are similar to FDG and 2-deoxy-D-glucose. Thus it is unlikely that the presence of small quantities of C1DG found in typical FDG preparations (ca 100 micrograms) would have adverse pharmacological or toxicological consequences that would limit continued application of this radiopharmaceutical in basic and clinical studies.

Antihypertensive efficacy of manidipine and enalapril in hypertensive diabetic patients.

Recent studies showed that in diabetic hypertensive patients, administration of angiotensin-converting enzyme (ACE)-inhibitors or calcium antagonists can effectively lower blood pressure (BP) and prevent diabetes-related cardiovascular complications with no adverse metabolic effects. We sought to assess the antihypertensive and metabolic effects of the new dihydropyridine calcium antagonist manidipine (M) in patients with diabetes mellitus and essential hypertension as compared with the ACE inhibitor enalapril (E). After 3 weeks of placebo, 101 (62 men; age range, 34-72 years) hypertensives with type II diabetes mellitus were randomized to M 10-20 mg or E 10-20 mg, od, for 24 weeks. At the end of the placebo period and the active-treatment phase, BP was measured with a mercury sphygmomanometer (office, O) and over the 24 h by ambulatory (A) monitoring. ABP recordings were analyzed to obtain 24-h, day (6 a.m. to midnight), and night (midnight to 6 a.m.) average systolic (S) and diastolic (D) BP and heart rate (HR) values. Homogeneity of the antihypertensive effect over the 24 h was assessed by the smoothness index [SI: i.e., the ratio between the average of the 24 hourly BP changes after treatment and the corresponding standard deviation (the higher the SI, the more uniform is the BP control by treatment over the 24 h]. The O SBP and DBP were significantly (p < 0.01) and similarly reduced by M (16 +/- 10 and 13 +/- 6 mm Hg, n = 49) and E (15 +/- 10 and 13 +/- 6 mm Hg, n = 45). The percentage of patients whose O DBP was reduced < or = 85 mm Hg (i.e., the value indicated to be the optimal DBP goal in diabetic hypertensives) was similar for M (37%) and E (40%). The reduction of 24-h BP also was similar between M (n = 38) and E (n = 38) for both drugs (systolic, 6 +/- 11 and 8 +/- 10 mm Hg; diastolic, 5 +/- 8 and 5 +/- 7; NS, M vs. E). The antihypertensive effect was distributed in a similar homogeneous fashion throughout the dosing interval, as shown by the similar SI values (M, 0.6 +/- 1.2 for SBP and 0.6 +/- 0.9 for DBP; E, 0.6 +/- 0.8 for SBP and 0.5 +/- 0.7 for DBP; NS, M vs. E). O and A HR were unchanged by either treatment. Markers of glucose and lipid metabolism and renal function were not significantly modified by treatment both with M and with E. In the diabetic hypertensives, M was as effective and metabolically neutral as the ACE-inhibitor E.