CYP 450 enzyme induction by chronic oral musk xylene in adult and developing rats.

Developmental and adult toxicity of musk xylene was studied in Long Evans (LE) rats fed with chow containing musk xylene (MX) in food pellets in concentrations of 1 mg, 10 mg, 33 mg, 100 mg and 1000 mg MX per 1 kg chow corresponding to a daily intake of 0.07-0.08 mg MX/kg up to 70-80 mg MX/kg body weight. Adult male and female rats were MX exposed for a minimum of 10 weeks before mating. Exposure continued throughout pregnancy, birth and lactation. The effects of MX on CYP1A1/1A2 were studied in liver microsomes by EROD (7-ethoxyresorufin-rosomes deethylase) for CYP1A1 and by MROD (methoxyresorufin-o-demethylase) for CYP1A2 activity and by Western blotting. MX induced these enzymes dose dependently in adult and developing rats at PN (postnatal day) 1 and 14. The lowest effective maternal dose was 2-3 mg MX/kg/day. Western blot data of CYP2B and CYP3A indicated the induction of both P450 enzyme proteins in developing rats at PN 14 at the higher dose of 70-80 mg MX/kg/day. In contrast, upon high MX exposure CYP2B but not CYP3A was found to be induced in adult first generation male and female rats, indicating differential sensitivity to MX in development.

CYP 450 enzyme induction by chronic oral musk xylene in adult and developing rats.

Developmental and adult toxicity of musk xylene was studied in Long Evans (LE) rats fed with chow containing musk xylene (MX) in food pellets in concentrations of 1 mg, 10 mg, 33 mg, 100 mg and 1000 mg MX per 1 kg chow corresponding to a daily intake of 0.07-0.08 mg MX/kg up to 70-80 mg MX/kg body weight. Adult male and female rats were MX exposed for a minimum of 10 weeks before mating. Exposure continued throughout pregnancy, birth and lactation. The effects of MX on CYP1A1/1A2 were studied in liver microsomes by EROD (7-ethoxyresorufin-o-deethylase) for CYP1A1 and by MROD (methoxyresorufin-o-demethylase) for CYP1A2 activity and by Western blotting. MX induced these enzymes dose dependently in adult and developing rats at PN (postnatal day) 1 and 14. The lowest effective maternal dose was 2-3 mg MX/kg/day. Western blot data of CYP2B and CYP3A indicated the induction of both P450 enzyme proteins in developing rats at PN 14 at the higher dose of 70-80 mg MX/kg/day. In contrast, upon high MX exposure CYP2B but not CYP3A was found to be induced in adult first generation male and female rats, indicating differential sensitivity to MX in development.

Autocrine or paracrine transforming growth factor-beta modulates the phenotype of chick embryo sternal chondrocytes in serum-free agarose culture.

Sternal chondrocytes of 17-day-old chick embryos in serum-free agarose culture secrete transforming growth factor-beta. Media conditioned by such cells prevent serum-induced chondrocyte hypertrophy and cause a phenotypic modulation in serum-free culture which is similar to that observed for chondrocytes in monolayer culture. The modulated cells lose the round shape of differentiated chondrocytes and increasingly with time resemble tendon fibroblasts embedded into agarose. In addition, they produce less matrix macromolecules which include collagen I rather than cartilage collagens II, IX, X, and XI. All of these effects are abolished upon addition to the conditioned media of a monoclonal antibody against recombinant human transforming growth factor-beta 2. The same factor caused effects closely similar to those elicited by conditioned media. Therefore, the phenotypic modulation in adhesion-dependent cultures of chondrocytes in vitro does not directly result from cell-matrix interactions but can be produced also in suspension culture under the direction of appropriate diffusible stimuli that include transforming growth factor-beta. In addition, the results support the concept of transforming growth factor-beta as a multifunctional cytokine acting differently on cells of the same developmental origin depending on their stage of differentiation.

Induction of proliferation or hypertrophy of chondrocytes in serum-free culture: the role of insulin-like growth factor-I, insulin, or thyroxine.

In bone forming cartilage in vivo, cells undergo terminal differentiation, whereas most of the cells in normal articular cartilage do not. Chondrocyte hypertrophy can be induced also in vitro by diffusible signals. We have identified growth factors or hormones acting individually on 17-d chick embryo sternal chondrocytes cultured in agarose gels under strictly serum-free conditions. Insulin-like growth factor I or insulin triggered the first steps of chondrocyte maturation, i.e., cell proliferation and increased matrix deposition while the chondrocytic phenotype was maintained. However, cells did not progress to the hypertrophic stage. Proliferation and stimulated collagen production was preceded by a lag period, indicating that synthesis of other components was required before cells became responsive to insulin-like growth factor I or insulin. Very small amounts of FBS exerted effects similar to those of insulin-like growth factor I or insulin. However, FBS could act directly and elicited hypertrophy when constituting greater than 1% of the culture media. Basic FGF has been claimed to be the most potent chondrocyte mitogen, but had negligible effects under serum-free conditions. The same is true for PDGF, a major serum-mitogen. Under the direction of thyroxine, cells did not proliferate but became typical hypertrophic chondrocytes, extensively synthesizing collagen X and alkaline phosphatase.

Origin of leg musculature during Drosophila metamorphosis.

Pro- and mesothoracic leg imaginal disks of late third-instar larvae of genotypes affecting the electrophoretic mobilities of alpha-glycerolphosphate dehydrogenase (EC 1.1.1.8) and arginine kinase (EC 2.7.3.3) were transplanted into host larvae of different genotypes. The metamorphosed implants were analyzed microscopically for the presence of musculature, histochemically for the distribution of enzyme activity, and electrophoretically for determination of the phenotypes of the two muscle-marker enzymes. The results permit the conclusion that leg imaginal disks contain muscle stem-cells.