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Biomedical subjects

D H Russell

Publications and source records attributed to D H Russell.

At least 253 records · Page 14Linked to original sources
PubMed1972

Polyamine biogenesis in the rat mammary gland during pregnancy and lactation.

Polyamines and RNA accumulate in the rat mammary gland during pregnancy, but the major increases occur after parturition. Therefore the major increases occur after the gland has obtained its maximal complement of epithelial cells. During lactation, the spermidine concentration rises above 5mm and RNA content in the lactating mammary gland reaches a value 16 times that of the unstimulated mammary gland. The ratio of spermidine/spermine, an increase of which initially signals an elevation in biosynthetic activity, is near 1 in the normal mammary gland and is greater than 10 in the lactating mammary gland. Putrescine concentration is very low during the entire course of mammary-gland development, with the exception of early pregnancy. The low putrescine concentration probably reflects the very rapid conversion of putrescine into spermidine. Both ornithine decarboxylase, the enzyme that synthesizes putrescine, and putrescine-stimulated S-adenosyl-l-methionine decarboxylase, the enzyme that synthesizes spermidine, increase in activity during middle and late pregnancy; during lactation, both enzyme activities are elevated until the 21st day of lactation, and then decline. These declines are concomitant with involution. Also, it was found that the amount of ribonuclease activity in the mammary gland was very high during lactation, almost double that in the gland during pregnancy.

Animals↗
PubMed1971

Putrescine and spermidine biosynthesis in the development of normal and anucleolate mutants of Xenopus laevis.

Ornithine decarboxylase (EC 4.1.1.17), the enzyme that catalyzes the synthesis of putrescine from ornithine, increases dramatically in developing Xenopus embryos. Between the 2-cell stage and early blastula stage, activity increases 10-fold, and in swimming tadpoles, the enzyme activity is 100-fold higher than that present in either unfertilized eggs or 2-cell embryos. S-adenosyl-L-methionine decarboxylase, an enzyme that catalyzes spermidine synthesis from putrescine and S-adenosyl-L-methionine, increases 40-fold in activity during the development of Xenopus, but does not increase in activity prior to gastrulation. Concomitant with these enzyme changes, putrescine and spermidine concentrations are elevated during the development of Xenopus embryos. Maximal accumulations are present in the swimming tadpole and correspond to maximal enzyme activities. Anucleolate-mutant embryos of Xenopus, which do not synthesize new ribosomes, have no detectable S-adenosyl-L-methionine decarboxylase activity and do not accumulate spermidine after gastrulation. Ornithine decarboxylase activity is depressed in these mutants and putrescine accumulation is decreased also. The activity of some dehydrogenases that increase in Xenopus embryos after gastrulation show normal increases in the anucleolate mutants. Thus, the synthesis of putrescine and spermidine in embryos correlates with the onset of ribosomal-RNA synthesis and the formation of a viable nucleolus in the embryonic cell.

Amines↗