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Biomedical subjects

D K Liu

Publications and source records attributed to D K Liu.

At least 37 records · Page 2Linked to original sources
PubMed1984

Phenobarbital enhances 2',5'-oligoadenylate synthesis in rat liver nuclei.

Treatment of rats with phenobarbital for three days greatly increases the activity of 2,5 oligoadenylate synthetase in liver nuclei. Analysis of 2',5'-oligoadenylates synthesized in vitro showed that nuclei from both phenobarbital-treated and control rats synthesized 2',5'-oligoadenylates ranging from di- to hexamers. However, nuclei from drug treated rats showed a two fold increase in trimer and tetramer synthesis and a three-four fold increase in longer chained oligoadenylates. There was no change in the nuclear 2'-phosphodiesterase activity as the result of phenobarbital treatment, This activity remained low in nuclei from either the treated or the control rats. To our knowledge, this is the first report on phenobarbital affecting the liver 2',5'-oligoadenylate system.

2',5'-Oligoadenylate Synthetase↗
PubMed1983

Mammary origin of rat milk ribonuclease.

When assayed under a variety of ionic conditions rat milk RNAase activity was highest under added Ca2+, while the serum enzyme was highest in no added ion, suggesting that milk was higher in the mammary-specific, Ca2+-stimulated, RNAase than was the serum of lactating rats. The acrylamide gel electrophoresis results demonstrated that milk RNAase differed from serum RNAase both in distribution and ionic preference; all milk RNAase species strongly preferred Ca2+ while serum RNAase species had no ionic preference. The Sephacryl S200 separation accentuated these differences by showing that 98% of the total milk RNAase activity was Ca2+-stimulated and clustered in a region of higher molecular weight than the serum enzyme which again had no ionic preference. From these results, we conclude that the vast majority of milk RNAase molecules are not transported by the serum, but must originate in the alveolar cells.

Animals↗
PubMed1982

Pregnancy stimulates DNA synthesis in R3230AC mammary adenocarcinoma.

The transplantable R3230AC mammary adenocarcinoma was grown in virgin, pregnant and lactating rats and in vivo rates of [3H]-thymidine incorporation into DNA and acid-soluble dTTP were compared between tumor and host mammary glands. The tumor differed from the host gland in that the rates of uptake and phosphorylation of the injected thymidine remained unchanged throughout the lactation cycle, but the dTTP pool increased greatly during pregnancy and declined during lactation. In both tumor and host gland, DNA labeling rates were higher during pregnancy than during lactation. Tumor DNA synthesis rates, in terms of incorporated dTMP, increased markedly during pregnancy and returned to pre-pregnant rates following parturition and during lactation. This pattern was similar to host mammary glands, but the change was of a greater magnitude. The data illustrate the usefulness of growing a transplantable mammary tumor in rats of varying physiological states. This way, similarities and differences between a mammary tumor and the host mammary gland regarding their responses to the hormonal milieu of pregnancy and lactation can be assessed.

Adenocarcinoma↗
PubMed1982

Species differences in ribonuclease activity of milk and mammary gland.

1. Ribonuclease (RNAase) activity in milk of mouse, rat, rabbit, dog, goat, cow and human and in mammary tissue of mouse and rat has been determined at pH 7.4 under various ionic conditions. 2. RNAase in milk of rabbit, cow, goat, human, dog and mouse exhibited no strong ionic preference while activity of rat milk RNAase was greatly enhanced by Ca2+. Enzyme from every source preferred pyrimidine over purine homopolymers as substrate. 3. Comparing the maximal activity per ml found for each species, milk of rabbit, rat and cow had the highest activity, that of human and goat was intermediate and that of dog and mouse was the lowest. Differences between strains were smaller than interspecific differences. 4. In rat and mouse, milk RNAase activity is a function of mammary RNAase activity in the gland.

Animals↗
PubMed1980

Ribonuclease H activity in rat mammary gland during the lactation cycle and in R3230AC mammary adenocarcinoma.

RNAase H, which catalyzes the hydrolysis of the RNA moiety of an RNA-DNA hybrid, was measured in the mammary gland of virgin, pregnant, lactating, and weaning Fischer rats and in the R3230AC mammary tumor grown in the same animals. In the normal mammary gland when DNA levels were low, as in the virgin state or during involution, RNAase H activity was also low. During pregnancy and lactogenesis when DNA levels increased, RNAase H activity, either on the basis of mammary gland weight or DNA content, also increased. During lactation when cellular proliferation ceases but rates of RNA and protein synthesis continue to reach peak values, RNAase H activity decreased. Compared to the corresponding enzyme from host glands, RNAase H from the R3230AC mammary tumor grown in pregnant and lactating hosts changes similarly, but to a lesser extent. The RNAase H activity which, ona tissue weight basis, was higher than in normal tissue also increased during pregnancy and directly after parturition, but decreased during lactation. During pregnancy these changes were accompanied by an increase in tumor DNA values. During lactation the tumor DNA values returned to the level seen in virgin hosts. These results are consistent with a role for RNAase H in DNA replication in rat mammary gland and in R3230Ac mammary tumor.

Adenocarcinoma↗