Biomedical subjects
Publications and source records attributed to S O Byers.
The cholesterol-7alpha-hydroxylase activity of hepatic microsomal preparations of hypothalamic hypercholesterolemic rats and normal rats was assayed in rats fed diets high and low in cholesterol, and in rats killed at the supposed height and at the nadir of the diurnal cycle of enzyme activity. The activity of this enzyme system appeared to be unimpaired in the hypothalamic hypercholesterolemic rat.
The administration of phenobarbital was observed to inhibit the rise in serum cholesterol that occurred in rats after thyroidectomy or hypophysectomy and in rabbits after inclusion of cholesterol in their diet. This hypocholesterolemic effect of phenobarbital was found to be due to its capacity to inhibit the intestinal absorption of cholesterol in both these species. We found no evidence to suggest that phenobarbital altered the endogenous process of cholesterol metabolism in either of these two species of animals.
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Plasma norepinephrine (NE) and epinephrine (E) were assayed in 15 men prone to develop coronary heart disease (type-A behavior pattern) and in 15 coronary-disease-resistant men (type-B behavior pattern) under resting, noncompetitive conditions and also immediately before, during, and after participation in a nonphysical competitive struggle. The average concentration of catecholamines was virtually the same in both groups under resting conditions. Under competitive conditions the NE concentration of the coronary-susceptible group rose an average of 30%, while that of the resistant group remained essentially unchanged. E concentration remained unchanged in both groups.
Some of the possible mechanisms responsible for the hypocholesterolemic effect of glucagon were investigated. Glucagon was found to inhibit the intestinal absorption of cholesterol. In addition, it was found to either hasten the rate of egress of lipoprotein cholesterol from the blood into the liver or to retard the rate of re-entry of cholesterol from the liver into the blood. The data do not distinguish between these two possibilities, which indeed may occur simultaneously.
The time, temperature, and pH of the trihydroxyindole reaction were controlled to minimize interference between norepinephrine (NE) and epinephrine (E) so that, in plasma catecholamine assay within normal human physiologic range, NE contributes less than 1 per cent to the fluorescence produced from E, and E contributes only 0.5 to 10 per cent to NE fluorescence; assay and blank measurements show superior stability. Elution from alumina and instrumental factors, such as optical filters, were optimized so that a single 5 ml. plasma sample sufficed for triplicate analyses of both NE and E, with duplicate blanks for each. This triplicate fluorescence assay was combined with duplicate recovery measurements of radioactive catecholamines added in tracer quantities to the plasma so as to make possible reliable estimates of the precision of measurement of each individual sample. The mean levels found for men aged 40 to 60 years from antecubital vein blood drawn during the subject's working hours (but after a brief rest) were, for NE 0.38 ng. per milliliter, range 0.15 to 0.54 ng. per millilter, and for E 0.09 ng./ml, range 0.01 to 0.27 ng. per millilter. The high precision and small amounts of blood required by this method made possible the measurement of basal plasma levels of E and NE in rats under two-stage phenobarbital anesthesia. The mean levels for 13 male and 4 female Long-Evans-stain rats weighing 250 to 350 grams were, for NE 0.26 ng. per millilter, range 0.16 to 0.37 ng. per millilter, and for E 0.36 ng. per millilter, range 0.14 to ng. per millilter. These rat values are called basal because they are only 1/5 to 1/10 as large as values obtained on plasma secured by single-stage pentobarbital anesthesia or from unanesthetized rats. Eight to 11 ml. of whole blood obtained from each rat were sufficient for individual analyses, an improvement over most other reported methods which require blood from a number of animals to be pooled. The average precision of an individual determination of NE was plus or minus 10 per cent in the range of 0.20 to 0.40 ng. per millilter. The average recovery for NE was 65 per cent and for E it was 55 per cent. Major factors influencing recovery were quantitatively investigated and discussed.
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