A simple and reproducible method for the estimation of triiodothyronine uptake (thyroxine binding index) using a new adsorbent.

A simple, rapid and reproducible method for the determination of triiodothyronine uptake using heat-treated wheat flour (TWF) as adsorbent is described. Three ml of TWF suspension in barbital buffer containing 125I triiodothyronine is added to 0.1 ml of serum sample in a plastic tube. The mixture is shaken for 30 seconds and is left to settle for 12 minutes or alternatively is centrifuged for one minute at 600 X g. The 1.0 ml of supernatant is transferred to another tube for counting. This method is virtually time and temperature independent. The effects of altering the concentration of 125I triiodothyronine and TWF are reported. Within-run precision has been estimated for normal (C.V. 1.2), high (C.V. 1.2) and low (C.V. 1.8) ranges. Estimation of between -run precision gave similar results. Comparison of results obtained by this method and by Thyopac-3 reagent kit (Radiochemical Centre, Amersham, England) shows good correlation for Thyopac-3 values about 105, while for values below 105 the present method gives lower values than Thyopac-3.

The effect of ionizing irradiation on the oxidation of palmitate-1-14C by thymus and liver.

New Zealand rabbits, fasted for 12 hours, were subjected to 500 rads of whole-body irradiation. K+-palmitate-1-14C oxidation was assayed with the 600 X g supernatant of thymus and liver homogenates, in the presence of ATP, at various time intervals from irradiation. For a period of 24 hours following irradiation, oxidation by liver preparations was not significantly affected. The rate of oxidation by thymus was decreased to less than one-third of the control value within 12 hours from irradiation and, at 24 hours, was almost completely abolished. Increased ATP concentration could increase only to a small extent the oxidation by thymus preparations of irradiated animals. Oxidation by isolated thymus mitochondria was also inhibited by irradiation. Counting of the water-soluble oxidation products of palmitate-1-14C suggests that the inhibition is not due to the impairment of the reactions of the citric acid cycle. The non-esterified fatty acid concentration of thymus was not altered at 12 hours following irradiation. Esterification of K+-palmitate-l-14C into the thymus lipids was not affected 12 hours after irradiation.

The effect of ionizing irradiation on the lipid biosynthesis by thymus and liver.

New Zealand rabbits, fasted for 12 hours, were subjected to 500 rads of whole-body irradiation. Analysis of thymus lipids, at various time intervals following irradiation, showed a threefold increase of triglycerides at 24 hours. Fatty acid composition of the 600 X g supernatant was not affected at 24 hours after irradiation. Lipid biosynthesis from acetate-1-14C by the thymus homogenates was increased to a small extent at 4 hours following irradiation, while the radioactivity distribution into fatty acids was not considerably affected. Contrary to the above findings, fatty acid synthesis from acetate-l-14C by the liver preparations showed a decreased incorporation between the fourth and twelfth hour following irradiation. Counting of the radioactivity of the separated fatty acids suggested that the system for synthesis of short-chain fatty acids was impaired as early as 4 hours following irradiation.

The isolation and partial characterization of glycolipids of normal human leucocytes.

1. The lipids of purified human leucocytes were extracted with chloroform-methanol and the extract was washed with water. Glycolipids, isolated by Florisil chromatography, were subjected to mild alkaline hydrolysis and the alkali-resistant fraction was fractionated on a silicic acid column. 2. Three classes of glycolipid were separated. The less polar, containing 3.6% of the total glycolipid hexose as galactose, was tentatively identified as ceramide monohexoside. The major glycolipid fraction was characterized as ceramide dihexosides. The more polar glycolipids comprised 1.6% of the total glycolipid hexose as galactose and glucose (in the molar ratio 2:1) and were non-acidic. This class was separated as a mixture containing ninhydrin-positive glycolipids. 3. The ceramide dihexosides taken from two leucocyte preparations accounted for 15.2% and 16.4% by weight of the total lipids. 4. The carbohydrate moiety of the ceramide dihexosides contained galactose and glucose in the molar ratio 2:1. Partial acid hydrolysis and paper chromatography indicated that the hexoses are present as disaccharides, lactose being identified as one of them. 5. Palmitic acid (C(16:0)) and nervonic acid (C(24:1)) were the major fatty acids of this glycolipid. Hydroxy fatty acids were not detected.