S. Albert

The uptake of radioactive phosphorus by rat liver following partial hepatectomy

Summary o 1. Adult male Holtzman rats were given a single subcutaneous injection of radioactive phosphorus, as NaH 2 P 32 O 4 , at 16 hr., and 1, 3, 5, 7, or 14 days after partial hepatectomy. The animals were sacrificed 4 hr. after injection, and the radioactivity and total P content of the acid-soluble organic and inorganic, lipide, phosphoprotein, pentose nucleic acid (PNA), and desoxypentose nucleic acid (DNA) fractions were determined. 2. Following partial hepatectomy there was an increase in the concentration of P per unit of protein N in the acid-soluble inorganic, lipide, PNA, and DNA fractions of the “regenerating” livers. Maximum concentrations were observed at about 1 day in the first two fractions and at 3–5 days in the nucleic acids. Thereafter the concentrations decreased slowly. There were no significant changes in the acid-soluble organic and phosphoprotein P. 3. In the hypertrophying liver cell following partial hepatectomy there was a marked increase in the uptake of P 32 in the acid-soluble organic and inorganic, phosphoprotein, PNA, and DNA fractions over that seen in the controls. With the shift from hypertrophy to cell hyperplasia there was a decline in the P 32 uptake by these fractions. 4. The maximum uptake of P 32 by the phospholipide fraction coincided with maximum mitotic activity.

Phospholipide metabolism in cell fractions of regenerating liver.

Abstract The P 32 uptake in a number of phosphorus-containing fractions of the nuclei, mitochondria, microsomes, and supernatant of liver cells was investigated in normal rat liver and during the premitotic and mitotic phases of liver “regeneration” following partial hepatectomy. The cephalins of all the cell fractions of the normal livers incorporated P 32 much faster than the lecithins, while the sphingomyelins incorporated it relatively slowly. The increased P32 uptake of the phospholipides observed earlier to be associated with mitotic activity can be accounted for by an increased P 32 uptake by the cephalins of the nucleus, by the lecithins of the mitochondria, microsomes, supernatant, and possibly the nuclei, and by the sphingomyelins of the supernatant. The data, viewed in the light of observations made in earlier studies, suggest that P 32 turnover in lecithin occurs in all parts of the cell during interphase; that of nuclear cephalins and of supernatant sphingomyelins occurs following preprophase and prior to or during metaphase processes.

Metabolism of phospholipides associated with cell division

Abstract Male Holtzman rats 6–7 months old were partially hepatectomized and sacrificed 18 hr. or 3 days later. Five hours prior to sacrifice, acriflavine at a level of 2 mg./100 g. body weight was administered subcutaneously to the experimental (treated) animals, and 1 hr. prior to sacrifice both the treated and untreated rats received a subcutaneous injection containing 0.45 μc. P32/g. body weight. The uptake of P32 and total P in the acid-soluble, lecithin, cephalin, sphingomyelin, and DNA fractions, and the amounts of di-, tri-, tetra-, and pentaenoic acids were measured in the livers of all animals. The uptake of P32 in livers of unoperated control animals was much more rapid in the cephalin than in either the lecithin or sphingomyelin fractions. During “regeneration” following partial hepatectomy, the P32 uptake in the lecithin fraction increased markedly, reaching a maximum at 3 days when mitotic activity was highest. During this period, uptake in the sphingomyelin was increased to a smaller extent, while that in the cephalin fraction was not elevated prior to the onset of mitosis (18 hr.), but was elevated slightly and nonsignificantly at 3 days. Acriflavine, a preprophase inhibitor, caused a marked inhibition of P32 uptake in all of the phospholipides and in DNA in the animals 18 hr. following partial hepatectomy; 3 days afterward it markedly inhibited mitosis but had little or no effect on the incorporation of P32 into the phospholipides. This suggests that the increased phosphorylation of lecithin shown to be associated with mitosis occurs during preprophase processes. The data do not bear out a relationship between unsaturated fatty acid concentrations and mitosis.

Lipide metabolism during cell division.

Abstract 1. 1. Adult male Holtzman rats were each given a single injection of P32 as NaH2P32O4 at 1, 3, and 18 days after partial hepatectomy, and were sacrificed 1 hr. later. Six hours prior to sacrifice, unoperated controls and 3-day hepatectomized rats received 0.03 mg. colchicine/100 g. body weight by subcutaneous injection. Livers were removed and the radioactivity and P in the lecithin, cephalin, and sphingomyelin fractions, as well as di-, tri-, tetra-, and pentaenoic acids were determined. 2. 2. The high P32 uptake by the phospholipide fraction coincident with mitosis occurred in all three types of phospholipide isolated. It was not abolished by colchicine, a metaphase inhibitor, suggesting that it is associated with either interphase or prophase, but not with anaphase or telophase. 3. 3. There was an increase in the concentration of trienoic and a decrease in tetraenoic acid coincident with the period of hypertrophy (premitosis) in regenerating liver. There was an increase in dienoic acid coincident with the period of high mitotic activity. Blocking mitosis in metaphase with colchicine did not influence the level of dienoic acid.

In vitro activation of cysteine desulfhydrase by rat liver microsomes.

Summary The cysteine desulfhvdrase of rat liver was found in the cytoplasmic supernatant but was not associated with either nuclei, mitochondria, or microsomes. There was an increase in enzyme activity when the microsome fraction was added to the cytoplasmic supernatant. This increase was greater as larger amounts of microsomes were added. No enhancement was observed when microsomes were added to a whole homogenate from which microsomes only had been removed, suggesting a complex interdependence of the various cytoplasmic elements.

Phospholipide metabolism during hypertrophy and hyperplasia in rat prostates and seminal vesicles

Abstract Control, castrated, and testosterone-treated rats were given subcutaneous injections of 0.45 μc. of radioactive phosphorus, as NaH 2 P 32 O 4 , and were sacrificed 2 hr. later. The radioactivity and total P contents of the acid-soluble, phospholipide, cephalin, lecithin, sphingomyelin, and DNA fractions of prostates and seminal vesicles, and the mitotic incidence in these tissues, were determined. Testosterone administered to normal animals caused hypertrophy of the prostates and hyperplasia and hypertrophy of the seminal vesicles. These were accompanied, in both tissues, by an increased P 32 uptake in all the P fractions. Treating the castrated animals with testosterone produced hyperplasia and hypertrophy in both tissues. This was again accompanied by increases in P 32 uptake in the P fractions. However, the increase in the phospholipide fractions that was associated with the hyperplasia in the prostates was much greater than that associated with hypertrophy and was not dependent on the P 32 uptake activity of the acid-soluble fraction. These results are interpreted as demonstrating that in the prostate, as in regenerating liver (1), mitotic activity is associated with a maximum P 32 uptake in the phospholipides.

Biochemical Changes Occurring in Mouse Liver Cells with Ageing.

Summary Nitrogen and phosphorus contents of large and small granules and cytoplasmic supernatant from livers of mice 1 1/2-2, 6-7, 10-11, and 18-21 months of age were determined and expressed on a per nucleus basis. There were increased nitrogen contents, and relatively smaller increases in phosphorus contents in each of these fractions in older animals. The results, viewed in the light of observations of Weinbach and Garbus (7), suggest that as an animal ages, its liver cells lose metabolic capacity, and, also, that an attempt is made to restore at least some aspects of it by forming more of the active sites within the cell. Cell fractions examined in older animals differed chemically from those in younger animals, however, as indicated by decreased P/N ratios.

Lipid Metabolism in Kidney Undergoing Compensatory Hypertrophy.

Summary The increased P32 uptake of the various phosphorus-containing fractions during hypertrophy in liver and prostatic tissue is not exhibited during renal hypertrophy. It is suggested that the P32 increases seen in the liver and prostatic tissue during hypertrophy are associated with subsequent mitotic activity found in these tissues.

An evaluation of the heterogeneity of cytoplasmic particles obtained by differential centrifugation.

Abstract 1. 1. As a cell fractionation procedure of the differential fractionation type is continued in order to create new fractions, the degree of heterogeneity of each fraction will increase. Sufficient criteria must be employed to differentiate between fractions. However, on increasing the number of criteria, one tends also to increase the similarities between fractions. In the present study, when about 50% of the comparisons did not distinguish one fraction from another, further fractionation yielded no “new” fractions. 2. 2. It is unlikely that one can determine either the actual number of particles present in the cytoplasm of a cell, or their homogeneity, by the technique of differential centrifugation employing a single medium. The “concentration gradient” method may be more desirable from this standpoint. 3. 3. It is necessary that data describing the biochemical properties of subcellular particles be subjected to statistical analysis, in order that their value in determining the uniqueness of a fraction be properly assessed.