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S S Eng

Publications and source records attributed to S S Eng.

3 recordsLinked to original sources

Comparison of dye dilution method to radionuclide techniques for cardiac output determination in dogs.

A study was undertaken to identify the most accurate 99mTc-labeled radiopharmaceutical and to determine the accuracy of a noninvasive radionuclide technique (antecubital injection and precordial detection) for cardiac output determinations. Phase I employed sodium pertechnetate, stannous pyrophosphate with sodium pertechnetate, technetium-99m red blood cells, and technetium-99m human serum albumin as radionuclide tracers. Cardiac output was determined by the dye dilution method and then by the invasive radionuclide technique. The radiopharmaceutical was injected into the same intracardiac catheter used in the dye dilution method. Seven to 10 mongrel dogs were used to test the accuracy of each radiopharmaceutical. A paired t test and regression analysis indicated that technetium-99m human serum albumin was the most accurate radiopharmaceutical for cardiac output determinations, and the results compared favorably to those obtained by the dye dilution method. In Phase II, technetium-99m human serum albumin was used as the radionuclide tracer for cardiac output determinations with the noninvasive technique. The results compared favorably to those obtained by the dye dilution method. Regression analysis indicated a correlation coefficient of 0.91. A paired t test demonstrated that the difference between the two methods was not statistically significant (p greater than 0.05). The data suggest that a noninvasive radionuclide technique using cardiac output determinations in humans.

Animals↗

Active-site-directed inactivation of aromatase from human placental microsomes by brominated androgen derivatives.

Several brominated androgen derivatives were tested for their ability to inactivate microsomal aromatase from term human placenta. In the experimental protocol, the microsomal homogenate was incubated either with androstenedione or a brominated derivative of androstenedione (16alpha-bromo-6-ketoandrostenedione, 16alpha-bromoandrostenedione, 7alpha-(3'-bromoacetoxypropyl)androstenedione, 6alpha-bromoandrostenedione, or 6beta-bromoandrostenedione) and reduced nicotinamide adenine dinucleotide phosphate in a nitrogen saturated buffer composed of glycerol, ethylenediaminetetraacetic acid, and dithiothreitol in tris(hydroxymethyl)aminomethane hydrochloride (pH 7.4) under nitrogen at 4 degrees C with shaking. After the incubation period, the microsomes were recovered by centrifugation and washed once before determining aromatase specific activity. The brominated androgen derivatives which inactivated aromatase were 7alpha-(3'-bromoacetoxypropyl)androstenedione and 6alpha-bromoandrostenedione. The structures of 6alpha- and 6beta-bromoandrostenedione were unequivocally established by single crystal x-ray diffraction techniques. The extent of the enzyme inactivation by 6alpha-bromoandrostenedione was linearly proportional to the logarithm of its concentration. The evidence that this inactivation occurs at the aromatase active site is that androstenedione, when coincubated with 6alpha-bromoandrostenedione, protected aromatase from this inactivation. Progesterone provided much less protection than androstenedione. Furthermore, both 6alpha- and 6beta-bromoandrostenedione are competitive inhibitors of androstenedione aromatization, as determined by a Lineweaver-Burk plot, and 6alpha-bromoandrostenedione gives the same type I cytochrome P-450 binding spectrum with placental microsomes as androstenedione. These data suggest that 6alpha-bromandrostenedione is effective as an active-site-directed inhibitor of placental microsomal aromatase.

Androstenedione↗