The structure of Pt particles on γ-Al2O3 support

Samples of the catalyst Pt/γ-Al2O3 have been examined by high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and microdiffraction techniques. An epitaxic relationship of metallic Pt crystals on the γ-Al2O3 has been established. In both calcined and reduced samples, the crystalline oxide α-PtO2 was found along with metallic Pt. The oxide has a hexagonal lattice with unit-cell dimensions about 6% smaller than those previously reported. Microdiffraction from areas less than 20 Å in diameter, combined with HRTEM, STEM and secondary electron microscopy (SEM), has proved to be a very powerful technique for the study of the structures of particles less than 50 Å in size.

Assessment of Björk-Shiley and porcine mitral valve dysfunction by m-mode echocardiographic left ventricular dimension

In this study of 46 patients with mitral valve prostheses, we report on the accuracy of the left ventricular maximum filling velocity (LVMFV) index as a diagnostic tool for valve dysfunction. Echocardiographic left ventricular internal dimensions were measured every 0.05 seconds, and every measure was transferred to an axis system. The tangent to this curve was traced at the point of maximum rate of increase of dimension, and the slope in mm/sec represents the LVMFV index. Six patients, each with an obstructed mitral valve prosthesis, had a reduced LVMFV index (p < 0.001). On the other hand, eight patients with a paravalvular leak showed a LVMFV index significantly higher (p < 0.05) than patients with a normally functioning mitral valve prosthesis. The results of this study suggest that analysis of the LVMFV index can be a useful and reliable substitute for other noninvasive diagnostic techniques in evaluating certain patients with suspected prosthetic mitral valve malfunction.

Human fetal pancreas--a potential source for transplantation

Human fetal pancreas (HFP) represents an ideal tissue source for transplantation into diabetic patients. Transplantation of HFP lacks many of the technical problems associated with whole organ transplantation and HFP is readily available. In order to proceed with clinical HFP transplantation it must be demonstrated that HFP can reverse experimentally induced diabetes, that HFP can respond to glucose challenge in a manner similar to adult tissue, and that the immunogenicity of HFP can be reduced. We transplanted HFP (13-17 weeks gestational age) beneath the kidney capsule of streptozotocin-induced diabetic BALB/c nu/nu mice. Within 6 to 8 weeks following transplantation, 6 out of 7 (88%) animals became normoglycemic. Oral glucose tolerance tests were performed to determine in vivo graft function. Results in cured animals were identical to those of normal BALB/c nu/nu mice. In vitro insulin response to glucose challenge demonstrated that grafted HFP was capable of insulin secretion in the presence of high glucose while fresh fetal tissue was not. Human passenger leukocytes, identified immunohistologically at various times after transplantation with monoclonal antibodies to HLA-DR and Leu 10, were greatly reduced by 32 weeks posttransplant. Our data demonstrate that HFP will differentiate and mature in the diabetic nude mouse and that human passenger leukocyte content can be reduced. These findings suggest that HFP is functionally suitable for transplantation into diabetic patients.

Percutaneous transluminal balloon dilatation for discrete subaortic stenosis

Seven patients, mean age 8 +/- 3.6 years, with clinical and hemodynamic diagnoses of discrete subaortic stenosis were treated by percutaneous transluminal balloon dilatation (PTBD) of the membrane during cardiac catheterization. One patient had an associated aortic coarctation that was first dilated. After PTBD left ventricular (LV) systolic pressure decreased significantly, from 181 +/- 25 to 139 +/- 11 mm Hg (p less than 0.005); peak gradient diminished from 65 +/- 18 to 12 +/- 9 mm Hg (p less than 0.001). Mild aortic regurgitation was present in 6 patients during basal conditions. After PTBD, the same degree of regurgitation was observed in all but 1 patient, in whom it disappeared. There were no major complications. Clinical observations after PTBD were consistent with hemodynamic findings. Precordial thrill always disappeared and the peak murmur became earlier in systole. In 2 patients the discrete subaortic stenosis was clearly visualized at 2-dimensional echocardiography as a fixed subvalvular structure throughout the cardiac cycle. After dilatation this was only identifiable at its implantation base; during contraction there was no fixed structure at the LV outflow tract. Four patients were hemodynamically reevaluated 6.7 +/- 1.7 months later and were found to have LV pressure relief and a degree of aortic regurgitation similar to those observed immediately after PTBD.

Percutaneous transluminal angioplasty of stenotic ductus arteriosus

This article describes our in vitro experience of balloon angioplasty of the ductus arteriosus (DA) in three post mortem human specimens, as well as an in vivo dilatation of a stenotic DA. The in vitro histologic observations revealed disruption of the intima and areas of pathologically fragmented and disorganized fibers at the media, with integrity of the ductal wall in all three DA. These findings led us to attempt percutaneous transluminal angioplasty (PTA) of a stenotic DA in a 2.3-kg newborn infant with hypoplastic left heart syndrome in a very deteriorated clinical condition. A Rashkind septostomy was associated with PTA of the stenotic DA. Following this, the gradients across the DA and across the atrial septum disappeared and the ductal angiographic diameter increased. Although an improved clinical condition was observed during the following hours, he died 1 day after. At necropsy, we found integrity of the ductal wall with histological changes similar to that observed in vitro. We conclude that PTA of stenotic DA could represent an alternative for palliative treatment of DA-dependent congenital heart disease.

Stimulation of Na+,K+-ATPase of isolated smooth muscle membranes by the Ca2+ channel inhibitors, nimodipine and nitrendipine

Nimodipine (0.015 to 1.5 microM) increased Na+, K+-ATPase activity by 70-120% in isolated smooth muscle membranes. At 0.015 microM, nitrendipine, but not nifedipine, verapamil or diltiazem, also activated this enzyme. Nimodipine stimulated this Na+, K+ATPase three times more than nitrendipine at 15 nM. Marked stimulation of Na+,K+-ATPase by nimodipine was seen in membranes from rat and guinea pig aorta and rat vas deferens, but not in membranes from guinea pig heart or brain. Although it is not known whether these results are applicable to intact cells, the results are consistent with the hypothesis that vasodilation produced by nimodipine and nitrendipine may be due not only to inhibition of Ca2+ entry but also to the stimulation of the Na+ pump.

Radioreceptor and high-performance liquid chromatographic assays for the calcium channel antagonist nitrendipine in serum

Radioreceptor and high-performance liquid chromatographic (HPLC) assays for nitrendipine were developed and applied to the analysis of serum samples. The HPLC assay required both extraction and concentration of the serum samples, whereas the radioreceptor assay involved only direct dilution of the serum. The HPLC assay, in contrast to the radioreceptor assay, can be used for detection and quantitative analysis of biologically inactive metabolites. The radioreceptor assay is based on the competition between nitrendipine in serum and [3H]nitrendipine for high-affinity binding sites on cardiac membranes. Forty-two serum samples were obtained from five volunteers, and the HPLC and radioreceptor assay results were compared. A correlation coefficient of 0.98 was found between the results of the two assays within the nitrendipine serum concentration range of 1 to 20 ng/ml. No significant levels of active metabolites or any other interferences were found. The radioreceptor assay provides a specific and sensitive alternative to HPLC; it is rapid and inexpensive and with minor modifications may be applicable to most presently available Ca2+ channel antagonists.

Psoralen-DNA cross-linking photoadducts in dyskeratosis congenita: delay in excision and promotion of sister chromatid exchange

Dyskeratosis congenita is a rare X-linked recessive disease, characterized by mucosal leukokeratosis, nail dystrophy, telangiectasia, reticulated hyperpigmentation, pancytopenia, and a heightened susceptibility to infection and malignancy. We exposed cultured fibroblasts and peripheral leukocytes from normal persons and from 2 unrelated young adult men with dyskeratosis congenita to 4,5',8-trimethylpsoralen and ultraviolet light. We than compared certain of their responses. Labeled DNA from fibroblasts exposed to 4,5',8-trimethylpsoralen and ultraviolet light showed fast-sedimenting DNA, a pattern we interpreted as evidence that cross-linking, psoralen-DNA photoadducts had been formed by the treatment. Fast-sedimenting DNA persisted for 24 hr in dyskeratosis congenita cells but disappeared from normal cells during a 24-hr repair period. Cultured peripheral blood leukocytes from persons with this syndrome similarly exposed to 4,5',8-trimethylpsoralen and ultraviolet light developed more sister chromatid exchanges than did cells from normal persons. These data suggest that a heightened susceptibility in DNA cross-links may be of fundamental importance in the etiology of dyskeratosis congenita.