Positron emission tomography. The technique and its applications to the study of the cardiovascular system

The technical features of positron computed tomography are reviewed, and the positron-emitting tracers of flow and metabolism and their relation to physiologic processes are described. The authors report some of their clinical experience with this new modality and emphasize areas of pediatric disorders of the heart that are likely to benefit from positron computed tomography.

Regulation of the uptake and degradation of beta-very low density lipoprotein in human monocyte macrophages

In normal human monocyte macrophages 125I-labeled beta-migrating very low density lipoproteins (125I-beta-VLDL), isolated from the plasma of cholesterol-fed rabbits, and 125I-human low density lipoprotein (LDL) were degraded at similar rates at protein concentrations up to 50 micrograms/ml. The high affinity degradation of 125I-labeled human LDL saturated at approximately 50 micrograms/ml; however, 125I-labeled rabbit beta-VLDL high affinity degradation saturated at 100-120 micrograms/ml. The activity of the beta-VLDL receptor was 3-fold higher than LDL receptor activity on freshly isolated normal monocyte macrophages, but with time-in-culture both receptor activities decreased and were similar after several days. The degradations of both beta-VLDL and LDL were Ca2+ sensitive, were markedly down regulated by sterols, and were up regulated by preincubation of the cells in a lipoprotein-free medium. The beta-VLDL receptor is genetically distinct from the LDL receptor as indicated by its presence on monocyte macrophages from a familial hypercholesterolemic homozygote. Human thoracic duct lymph chylomicrons as well as lipoproteins of Sf 20-5000 from fat-fed normal subjects inhibited the degradation of 125I-labeled rabbit beta-VLDL as effectively as nonradioactive rabbit beta-VLDL. We conclude: 1) the beta-VLDL receptor is genetically distinct from the LDL receptor, and 2) intestinally derived human lipoproteins are recognized by the beta-VLDL receptor on macrophages.

Comparison of serum theophylline levels in asthmatic children receiving sustained-release and rapid-release theophylline tablets

Serum theophylline levels were compared after the administration of a sustained-release (Theo-Dur, Key Pharmaceuticals, USA) vs. a rapid-release (Glyphyllin, Ikapharm, Israel) theophylline preparation to 24 children suffering from chronic bronchial asthma. They received each of the two drugs for a 5-d period, and serum theophylline levels were determined on the 6th d. Therapeutic serum levels were achieved in 66.6 and 75% of the patients receiving sustained-release and rapid-release theophylline preparations, respectively. The peak-trough difference for the rapid-release drug was higher than that of the sustained-release preparations (5.5 +/- 2.6 micrograms/ml vs. 2.6 +/- 2.3 micrograms/ml). Both drugs caused nearly the same low percentage of side effects (15 and 16.6%). A noncompliance rate of 16.6% was found with the rapid-release drug, and all the parents preferred the sustained-release drug is preferable for chronic treatment of children with bronchial asthma, as it maintains more stable serum theophylline levels and has a higher compliance rate.

Stressful life events and marital dysfunction

The relationship between stress and marital dysfunction was examined in 1979-80 through a study of two demographically matched groups of married couples. The study group consisted of couples who had been referred for therapy for marital problems while the control group had never been referred for psychiatric treatment of any kind. The authors compared the incidence, magnitude, and source of stressful life events. The two groups of couples differed in their reports of the incidence and sources of stress, but not in the magnitude of stress. Study couples reported almost twice the frequency of stressful events over the three-year period before referral and a significant increase in stress in the year immediatly before referral. Changes in family structure, family interaction, or both were the major sources of stress for both groups but especially so far the referred couples. The authors concluded that a significant association exists between stressful life events and marital dysfunction, and that the clincal assessment of life events can play a meaningful role in evaluation and treatment planning.

Peak left ventricular pressure/volume (Emax) during exercise in control subjects and children with left-sided cardiac disease

The peak ratio of left ventricular systolic pressure/systolic volume (PV) has been shown to be a close approximation to Emax, an index of contractility independent of both preload and afterload. We studied 17 children with left-sided cardiac disease during catheterization by a combined high-fidelity catheter and m-mode echocardiographic technique. Emax, indexed for body surface area, was calculated at rest and during supine exercise at 25% and 50% of maximal upright workload. In addition, we studied 15 control subjects with a noninvasive approximation of peak P/V, the peak systolic LV pressure/smallest systolic LV volume. Patients with left ventricular pressure overload showed an increased Emax value at rest and a further increase with exercise. Patients with left ventricular volume overload or cardiomyopathy had a normal value of Emax at rest and had only small increases with exercise. Patients with both volume and pressure overload had a resting Emax value that was increased, but no further increase occurred with exercise. Emax in children seems to be a sensitive index of contractility during physiologic stress and can be used to assess left ventricular functional reserve capacity both pre- and post-operatively.

Role of substrains in persistent lymphocytic choriomeningitis virus infection

Two plaque-type mutants, a wild strain MB(1), and a slow-growing non-plaque-forming variant of LCM virus were compared in L cell cultures. The cultures were monitored at biweekly intervals following infection for plaque-forming virus titre and cytoplasmic and membrane specific immunofluorescence of the cells. Different patterns were obtained in each case and the relevance of these results to LCM persistence is discussed. While the LM variant continually produced virus for 35 transfers, with a cycling titre, the SC variant stopped producing detectable virus after 30 transfers. Thereafter this culture remained fluorescent and resembled the one infected with the slow-growing variant. The degree of specific immunofluorescence of both continued to cycle. The MB(1) strain stopped producing virus after the 18th transfer.

Lytic and turbid plaque-type mutants of lymphocytic choriomeningitis virus as a cause of neurological disease or persistent infection

Mouse-passaged lymphocytic choriomeningitis (LCM) virus was found to contain a mixture of two different plaque-type mutants when plated on BHK-21/13S cells in agarose suspension. One mutant gave rise to clear plaques, with death of the cells, whereas the other produced turbid plaques which were sometimes very difficult to see. The clear-plaque variant caused a pronounced cytopathic effect on BHK-21 cells, but the turbid variant caused none; it also interfered with the cytopathic effect due to the clear variant. Brain-passed LCM virus was found to consist mainly of the clear-plaque-type, whereas liver-passed virus was mainly turbid-plaque-type. The clear type induced convulsions and early death after intracerebral inoculation of adult mice; the turbid variant caused no convulsions and late deaths. In newborn mice, the clear-plaque-type was uniformly fatal, whereas the turbid variant caused no deaths but instead induced persistent tolerant infection.