Cardiac MRI for assessment of myocardial perfusion: current status and future perspectives.

Cardiac magnetic resonance imaging (MRI) has recently been applied successfully to the assessment of myocardial perfusion. Cardiac MRI offers potential advantages over radioisotopic techniques because it provides superior spatial resolution, does not use ionizing radiation, and has no imaging orientation constraints. Current MRI perfusion approaches measure the alteration of regional myocardial magnetic properties after the intravenous injection of contrast agents. Several studies have validated the ability of perfusion MRI to detect the presence of significant coronary artery stenoses by detecting decreased signal intensity upslope or reduced maximal enhancement in the ischemic territories. Perfusion MRI has also been shown to assess accurately the extent of injury after a myocardial infarction and the presence of myocardial viability. With the introduction of newer contrast media, technologic improvements on MRI hardware and software, and the enhancement of quantitative analysis, MRI is likely to become a clinical tool for assessment of myocardial perfusion imaging in the near future.

Miliary tuberculosis in a patient with Epstein-Barr virus-associated angioimmunoblastic lymphadenopathy.

A 74-year-old woman developed angioimmunoblastic lymphadenopathy (AILD) with involvement of intra-abdominal and retroperitoneal lymph nodes. Southern blot analysis showed germline configuration of the JH genes and an oligoclonal pattern of the TcR beta genes. The immunoblasts were of B-cell phenotype and often expressed the CD30 antigen and the latent membrane protein 1 (LMP1) oncogene. Six nonsilent point mutations were identified near the 3' end of the LMP1 gene, leading to a cluster of six amino acid changes within a protein domain needed for maximal NF-kappa B stimulation. After a clinical remission of 8 months the patient relapsed with generalized lymphadenopathy and died secondary to tuberculosis. The oligoclonal rearrangements of the TcR beta genes may reflect an unsuccessful cellular immune response to Mycobacterium tuberculosis or an HLA-restricted T-cell response to B-immunoblasts expressing mutated viral antigens. A positive percutaneous tuberculin test observed 6 months prior to the onset of AILD is in favor of the first possibility.

Translational status of proenkephalin mRNA in the rat reproductive system.

The mRNA for the opioid peptide precursor proenkephalin is widely distributed throughout the male and female reproductive systems of rodents. In the present studies, the concentrations of proenkephalin-derived peptides in selected reproductive tissues of the rat have been determined. When compared with previously characterized tissues such as brain, the peptide contents in reproductive tissues were unexpectedly low relative to the abundance of proenkephalin mRNA. This suggested that either translation of proenkephalin mRNA is relatively inefficient in reproductive tissues or that the turnover of proenkephalin products occurs at a higher rate, or both. To distinguish between these possible mechanisms, the polysomal distributions of proenkephalin mRNA in different rat reproductive tissues and in rat brain were determined. In adult rat testis, in which the predominant proenkephalin RNA is the 1700-nucleotide form present in spermatogenic cells, the transcript was found to be mainly associated with translationally inactive ribonucleoprotein fractions. In contrast, the 1450-nucleotide form of proenkephalin mRNA appeared to be translated to a similar extent in rat brain, epididymis, ovary, and somatic cells of the immature rat testis. It therefore appears that inefficient translation of proenkephalin mRNA in spermatogenic cells is a major determinant of the low ratio of proenkephalin peptides to RNA in the adult rat testis, while posttranslational mechanisms (most likely peptide turnover) are involved in the rat epididymis, ovary, and presumably other reproductive tissues. These findings also indicate that mRNA and/or translation product concentrations within a given tissue are not always accurate indicators of the level of peptide or protein production.