Incorporation of [3H]thymidine by isolated fetal myoblasts and fibroblasts in response to human placental lactogen (HPL): possible mediation of HPL action by release of immunoreactive SM-C.
We investigated the actions of human placental lactogen (HPL) and human growth hormone (HGH) on [3H]thymidine incorporation and the release of immunoassayable somatomedin-C (SM-C) by isolated myoblasts, dermal fibroblasts, and costal cartilage explants taken from human fetuses at 11-21 weeks of gestation. The incorporation of [3H]thymidine by myoblasts and fibroblasts was significantly increased after incubation for 20 hr or 44 hr, and cell number after incubation for 7 days, in the presence of 50-250 ng/ml HPL. Incubation with HPL did not increase [3H]thymidine incorporation into cartilage explants, whereas incubation with HGH failed to enhance the uptake of this isotope by any of the tissues. Following extraction with acid-ethanol, culture medium conditioned by exposure to myoblasts or fibroblasts for 44 hr, and to cartilage explants for 7 days, contained radioimmunoassayable SM-C. Myoblast-conditioned medium contained significantly more SM-C [1,609 +/- 953 mU/mg cell protein (mean +/- SD); n = 10] than did that conditioned by fibroblasts (637 +/- 323; n = 5; P less than 0.02). In 1 week of culture, cartilage explants released 4.1 +/- 1.1 mU/mg wet weight (n = 7). The release of immunoassayable SM-C from cultured cells was significantly increased in the presence of 250 ng/ml HPL in five of eight experiments with myoblasts and two of four experiments with fibroblasts. Neither fibroblasts or myoblasts showed increased SM-C release following exposure to HGH. The results suggest that HPL, but not HGH, is growth-promoting for some human fetal tissues in vitro and that this action is mediated, at least in part, by an increased release of somatomedins.
D002356:Cartilage / Q000166:cytology / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D005333:Fetus / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D007158:Immunologic Techniques; D007334:Insulin-Like Growth Factor I / Q000276:immunology / Q000378:metabolism*; D009132:Muscles / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D010928:Placental Lactogen / Q000494:pharmacology*; D012272:Ribs; D012867:Skin / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D013002:Somatomedins / Q000378:metabolism*; D013936:Thymidine / Q000378:metabolism*; D014316:Tritium
D013002:Somatomedins; D014316:Tritium; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D010928:Placental Lactogen; D013936:Thymidine