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Biomedical subjects

O Greengard

Publications and source records attributed to O Greengard.

At least 73 records · Page 4Linked to original sources
PubMed1975

Biochemical changes in cultured foetal rat liver explants.

Liver explants from 20-day-old foetuses cultured for 48h in the absence of serum released 70% of their total soluble protein content into the medium. In the presence of serum this loss still amounted to 60%. The concentration of total particulate protein remained unchanged but there was some translocation of mitochondrial enzymes to the cytosol, and enzymes expected to increase during this stage of development failed to do so. The addition of cortisol plus glucagon (to serum-containing media) did not decrease the loss of total soluble protein from the explants but induced considerable tyrosine aminotransferase activity which was not released into the medium. The observations suggest that under the usual culture conditions a minority of the cells retain their functional integrity. The extent of deterioration, not reflected in histologically visible necrosis or cell damage, can be conveniently monitored by the malate dehydrogenase activity released to the medium.

Animals↗
PubMed1975

Cortisol treatment of neonatal rats: effects on enzymes in kidney, liver and heart.

Cortisol treatment of neonatal rats did not have permanent effects on the levels of 2-7 enzymes in heart, kidney, brain, and liver, even though some exhibited abnormally high concentrations during the first 1 or 2 weeks. An injection of cortisol at birth evoked premature rises of glucose-6-phosphatase (G6P-ase) in kidney, of soluble and particulate aspartate aminotransferase (AAT) in kidney and heart and of soluble AAT in liver. These enzymes (with the exception of soluble AAT in the female) did not respond to cortisol in adult rats. The significance of the varying effects of cortisol is discussed in relation to previously studied developmental enzyme formations.

Age Factors↗
PubMed1975

Peptidyl proline hydroxylase in adult, developing, and neoplastic rat tissues.

A sensitive assay system, optimally supplemented with tritiated protocollagen substrate and cofactors, is described which is suitable for determining the peptidyl proline hydroxylase (PPH) content of a wide spectrum of rat tissues. In most tissues, less than 50 percent of the total activity was soluble; the particulate portion of the activity (concentrated in the mitochondrial and microsomal fractions) was doubled by pretreatment with Triton X-100. Among normal adult tissues, lung had the highest total PPH activity (2.4 times that of liver) and small intestine had the lowest (25 percent that of liver). In brain and lactating mammary gland, the activity was similar to that in skin (60 percent of that in liver). Fetal tissues contained 3 to 8 times more PPH than the corresponding adult tissues, and a much lower portion of the total activity was soluble. In four tissues studied in detail (lung, liver, kidney, and brain), the total PPH declined rapidly during the last few days of gestation; brain attained its low adult value before term, whereas the other three tissues continued to decrease in the course of postnatal development. An injection of cortisol to fetal rats enhanced the decline of PPH in lung, liver, and skull. These experiments suggest that during normal differentiation the decline in collagen synthesis is initiated by fetal glucocorticoid secretion which is maximal on the 19th gestational day. PPH activity appears to be a sensitive indicator of neoplastic growth. In renal, mammary, muscle, and hepatic tumors, the PPH activities were 4 to 10 times higher than in the cognate adult tissue. Even in well-differentiated, slowgrowing tumors, the activity was considerably higher than in any normal, mature, or immature tissue, with the exception of the skull and lung of the 19-day-old fetus.

Animals↗
PubMed1973

Subcellular morphometric and biochemical analysis of developing rat hepatocytes.

Livers of rats between the 16th gestational and 100th postnatal day of age were subjected to quantitative biochemical and electron microscope, morphometric analyses. The amount of total mitochondrial protein per gram of liver remained at 34% of the adult level throughout the last 4 days of gestation but this was the period of rapid rise in the levels of cytochrome c oxidase, aspartate aminotransferase, and glutamate dehydrogenase in mitochondria; the nuclear fraction also acquired some glutamate dehydrogenase but lost most of it during postnatal development. During early postnatal life the amount of mitochondrial protein rose in parallel with the levels of cytochrome c oxidase and glutamate dehydrogenase but the upsurges of glutaminase and, later, of ornithine aminotransferase were accompanied by relatively little change in total mitochondrial protein. The surface area of rough endoplasmic reticulum per unit volume of hepatocyte cytoplasm (S(v) (RER)) did not change significantly throughout the period of development studied. From the 16th day of gestation to term the surface area of smooth ER (S(v) (SER)), the volume occupied by mitochondria (V(v) (MT)) and their number (N(v) (MT)) remained at 30, 66, and 45% of their adult values, respectively. V(v) (MT) and N(v) (MT) attained their maximal levels by the 2nd postnatal day and S(v) (SER) between days 2 and 12. Mitochondria of adult liver are thus smaller and contain more protein per unit volume than do those of fetal liver. After the 12th postnatal day, hepatocytes treble their size; they acquire more cytoplasm with additional enzymes but without further change in organelle concentration. The data reveal several distinct phases in the differentiation of hepatocytes. Each phase can be characterized by the extent to which the quantity and composition of various subcellular compartments evolve.

Animals↗
PubMed1972

The quantitative determination of phenylalanine hydroxylase in rat tissues. Its developmental formation in liver.

A sensitive method was developed for determining the phenylalanine hydroxylase activity of crude tissue preparations in the presence of optimum concentrations of the 6,7-dimethyl-5,6,7,8-tetrahydropterin cofactor (with ascorbate or dithiothreitol to maintain its reduced state) and substrate. Tissue distribution studies showed that, in addition to the liver, the kidney also contains significant phenylalanine hydroxylase activity, one-sixth (in rats) or half (in mice) as much per g as does the liver. The liver and the kidney enzyme have similar kinetic properties; both were located in the soluble phase and were inhibited by the nucleo-mitochondrial fraction. Phenylalanine hydroxylase, like most rat liver enzymes concerned with amino acid catabolism, develops late. On the 20th day of gestation, the liver (and the kidney) is devoid of phenylalanine hydroxylase and at birth contains 20% of the adult activity. During the second postnatal week of development, when the phenylalanine hydroxylase activity was about 40% of the adult value, an injection of cortisol doubled this value. Cortisol had no significant effect on phenylalanine hydroxylase in adult liver or on phenylalanine hydroxylase in kidney at any age.

Age Factors↗
PubMed1972

Liver phenylalanine hydroxylase activity in relation to blood concentrations of tyrosine and phenylalanine in the rat.

The plasma concentration of phenylalanine and tyrosine decreases in normal rats during the first few postnatal days; subsequently, the concentration of phenylalanine remains more or less constant, whereas that of tyrosine exhibits a high peak on day 13. The basal concentrations of the two amino acids were not altered by injections of thyroxine or cortisol, except in 13-day-old rats, when an injection of cortisol decreased the concentration of tyrosine. In young rats (13-15 days old), treatment with cortisol increased the activity of phenylalanine hydroxylase in the liver (measured in vitro) and accelerated the metabolism of administered phenylalanine: the rate constant of the disappearance of phenylalanine from plasma and the initial increase in tyrosine in plasma correlated quantitatively with the activity of phenylalanine hydroxylase in the liver. In adult rats, the inhibition of this enzyme (attested by assay in vitro) by p-chlorophenylalanine resulted in a proportionate decrease in tyrosine formation from an injection of phenylalanine. However, the quantitative relationship between liver phenylalanine hydroxylase activity and phenylalanine metabolism within the group of young rats was different from that observed among adult rats.

Animals↗
PubMed1972

Cytomorphometry of developing rat liver and its application to enzymic differentiation.

Quantitative stereological methods have been adapted for the measurement of the volume of liver attributable to parenchymal, hematopoietic, and Kupffer cells and for the measurement of the relative and absolute number (per unit volume) of these cell types and the mean volume of the parenchymal cell. These morphological parameters are the main ones for interpreting the biochemical differentiation of liver. Quantitative changes in these parameters, in rat liver between the 15th day of gestation and adult life, are presented. Despite the large number of hematopoietic cells, the parenchymal cells fill more than half of the liver volume between the 15th and 18th days of gestation and 0.85 of the liver volume at term. The fraction of liver volume occupied by Kupffer cells is never more than 0.02; the number of Kupffer cells per cubic centimeter increases less than twofold between fetal and adult life. The mean volume of individual parenchymal cells undergoes a threefold rise during late fetal life, declines in the neonatal period, and doubles between the 12th and 28th postnatal days. With the morphometric data obtained, it is impossible to convert enzyme concentrations (units per gram, determined in homogenates of whole liver) to enzyme amounts per unit volume of parenchymal or hematopoietic tissue or per individual cell of either type. In late fetal liver, only rises in enzyme concentration less than twofold may be attributed to the enrichment of parenchymal tissue at the expense of hematopoietic elements. The sudden upsurge, by more than twofold, of hepatic enzymes of the late fetal cluster (and also of the neonatal and late suckling cluster) reflects rises per parenchymal mass and per parenchymal cell. Thyroxine and glucagon, the administration of which to fetal rats promotes enzyme differentiation in liver, are without appreciable effect on the cytological parameters studied. Hydrocortisone accelerates the involution of hematopoietic tissue in fetal liver. Enzymes that are diminished by prenatal injection of hydrocortisone may be concentrated in hematopoietic cells.

Aging↗