Although cholera toxin induces a marked stimulation of adenylate cyclase activity in rat adipocyte plasma membranes, the holotoxin induces only a slight increase of cyclic AMP accumulation in intact cells. A similar apparent anomaly is seen with pertussis toxin, which has been shown to inhibit the Gi subunit of adenylate cyclase, and has a greater effect on cAMP accumulation and lipolysis than the activation by cholera toxin of the Gs subunit. To understand better the way in which these bacterial toxins are modifying the adipocyte cells, we prepared adipocyte plasma membranes and submitted them to ADP-ribosylation by cholera and pertussis toxins. During the incubation of control cells, we found endogenous ADP-ribosylation of Gs as a result of sustained stimulation of Gi by adenosine. Our results point to a possible homoeostatic system in which the autonomous adjustment of the basal activity of Gs as a function of that of Gi, under the control of feedback inhibitory ligands, ensures a steady production of cAMP within the cell.

Adenosine Deaminase↗

PubMedDate not supplied

DNA replication, repair, and repair tests.

The rate of inhibition and recovery of DNA synthesis can be used in a rapid assay system to detect genotoxic potentials of chemicals. Also, the observation that an agent stimulates DNA repair in a test system indicates its ability to cause damage in DNA. Different experimental approaches to the study of repair synthesis are discussed.

Animals↗

PubMedDate not supplied

Sister chromatid exchange and chromosome aberrations in lymphocytes of laboratory personnel.

The genotoxic risk caused by environmental chemicals may be detected by analyzing the frequency of sister chromatid exchanges in peripheral blood lymphocytes. Up to now the frequency of sister chromatid exchange has been correlated with smoking habits, and it is also observed to be significantly higher in lymphocytes of laboratory personnel.

Chromosome Aberrations↗

PubMedDate not supplied

[Hormonal control of prostaglandins biosynthesis during lipolysis in rat adipose tissue (author's transl)].

Lipolysis in rat fat pads was studied by determination of free fatty acid and glycerol production in various experimental conditions (absence or presence of glucose, adrenaline and insulin). These results were compared to the accumulation of endogenous prostaglandins E2 and F2 alpha during lipolysis. In the absence of glucose the prostaglandin production followed the adrenaline-ininduced fluctuations in released free fatty acids both in the presence or absence of insulin. In the presence of glucose and insulin, a drop in prostaglandin accumulation was observed whereas free fatty acid production was strongly stimulated. These results suggest either that free fatty acid composition is modified influencing the acitvity of prostaglandin synthetase, or that there exists a specific mechanism controlling prostaglandin synthesis.

Adipose Tissue↗

PubMedDate not supplied

Managing hot flashes after breast cancer.

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Breast Neoplasms↗