Brain palmitate incorporation in awake and anesthetized rats

Uniformly labeled [14C]palmitate was injected intravenously in awake and barbiturate-anesthetized rats, and arterial plasma radioactivity due to unesterified [14C]palmitate was determined on plasma samples removed at timed intervals up to the time of death. Overall brain radioactivity was determined by liquid scintillation spectroscopy, and regional brain radioactivity was determined by quantitative autoradiography. The transfer constant, k, for the unidirectional uptake of radiotracer palmitate into the brain at 4 h was calculated from the brain radioactivity and the integrated plasma radioactivity from injection to 4 h. The unidirectional palmitate uptake was calculated as the product of k and the plasma concentration of unesterified palmitate. Barbiturate anesthesia reduced regional palmitate transfer constants and unidirectional palmitate uptakes into different brain regions by 40-60%. Palmitate incorporation into the brains of awake rats at 4 h represents uptake into structural brain components which contain lipids. The results indicate that pentobarbital anesthesia reduces this rate of incorporation by about half.     

Hormonal Stimulation of Eucaryotic Cell ADP-ribosylation: EFFECT OF THYROTROPIN ON THYROID CELLS

The effect of thyrotropin (TSH) on the ADP-ribosylation of endogenous thyroid cell acceptor proteins was examined. Cells were “permeabilized” at 4°C in hypotonic medium and then exposed to [³²P]- or [³H-adenine]NAD⁺. The net incorporation of labeled ADP-ribose was measured by trichloroacetic acid precipitation. TSH (100 mU/ml) enhanced ADP-ribosylation with a maximum effect after 30-60 min in the majority of experiments. TSH stimulation was observed even when the incubation contained 1,000-fold more exogenous NAD⁺ than the amount of NAD⁺ contributed by the permeabilized cells, indicating an effect on enzymatic activity rather than an alteration in NAD⁺ pool size or specific activity. No incorporation of radioactivity from labeled NAD⁺ was observed in cells not rendered permeable to NAD⁺ by hypotonic shock. TSH did not increase the rate of disappearance of trichloroacetic-precipitable radioactivity and did not contain intrinsic NAD⁺ glycohydrolase activity. Alkali and snake venom phosphodiesterase, but not ribonuclease or deoxyribonuclease digestion of trichloroacetic acid precipitable thyroid cell radioactivity, revealed primarily 5′-AMP, consistent with an effect of TSH on mono-ADP ribosylation. Nicotinamide and thymidine (50 mM) inhibited both basal and TSH-stimulated ADP-ribosylation of thyroid cell protein. Dibutyryl cyclic (c)AMP (0.1 mM) inhibited endogenous ADP-ribosylation by ~35% but had no effect at lower concentrations. 0.5 mM isobutylmethylxanthine inhibited this reaction by ~60%.     

Influence of posture on the serum concentration of calcium

Experiments were designed to study the effects of change in posture on the serum concentrations of total calcium, plasma ionic calcium, magnesium, protein-bound calcium, total protein, albumin, and globulin. Plasma ionic calcium and serum magnesium were not influenced by changes in posture. All the remaining constituents responded in a consistent manner, namely, on changing from the lying to the erect position, their concentrations rose significantly. On sitting or on lying down, their values fell reaching minimal levels after about $\text{1}\text{2}\text{hr}$ and showing little change thereafter. All the values attained on lying were significantly lower than those reached on sitting in the same time periods. Variations in the concentrations of calcium and protein due to alteration in posture could amount to as much as 47% and 71%, respectively, of their normal range spans. These variations were considerably reduced by the use of protein corrections developed by Dent and in particular by Parfitt. A sex difference was noted in the concentrations of both serum total calcium and total protein, more marked in the latter. The difference in calcium appears due to a difference in its protein-bound component. It is clear that the influence of posture must be considered when interpreting serum calcium concentrations. Failure to recognize this influence has undoubtedly contributed to the variations in the normal ranges of serum calcium proposed by different workers.     

Contrast media: quantitative criteria for designing compounds with low toxicity.

Toxicity of contrast media that are ionized iodobenzoic acids or their derivatives is highly correlated with lipid solubility, as measured by the octanol/water partition coefficient. New contrast media have been designed with lower lipid solubility than media in current use, taking into account the additive-constitutive nature of the partition coefficient of an organic compound. If these contrast media are chemically stable, they should also be less toxic. It remains to be tested whether the relation between clinical toxicity and lipid solubility applies to non-ionized contrast media as well.     

Regional myocardial dysfunction: evaluation of patients with prior myocardial infarction with fast CT

A prototype ultrafast cine computed tomographic (CT) scanner, designed specifically for cardiac imaging, was used to evaluate a preliminary series of patients with prior myocardial infarction (n = 21) and a control group without coronary artery disease (n = 5). Multilevel 50-msec CT scan exposures were obtained during peripheral intravenous bolus injections of contrast medium. A comparison was made between cine-CT scans and standard left ventriculographic images in assessing segmental left ventricular motion. Results indicate that cine CT, performed at sufficiently rapid speeds (20 scans per second) to allow useful analysis of regional ventricular wall motion, can provide adequate image quality. Analysis of 110 segments revealed a good correlation (90.9%) between the two techniques in characterizing normal from abnormal regional wall motion. Cine CT, based on this initial study, demonstrates considerable potential for evaluating not only cardiac chamber dimensions but also segmental wall dynamics.