Hormonal activation of ornithine decarboxylase in embryonic chick pelvic cartilage.
We assessed whether hormones and metabolic factors known to stimulate anabolic processes in the embryonic chick pelvic cartilage would stimulate ornithine decarboxylase (ODC) activity. In vitro organ culture of these pelvic cartilages in time-course experiments with N(6)-monobutyryl cyclic AMP (BtcAMP), insulin, and 5% rat serum demonstrated maximal stimulation of ODC activity between 4 and 6 h with each factor. However, at 2 h insulin and serum significantly stimulated ODC activity (P less than 0.05) and BtcAMP did not. ODC was stimulated above control (100%) with the following factors: parathyroid hormone (PTH) (555 +/- 15%), BtcAMP (324 +/- 34%), 1-methyl-3-isobutylxanthine (MIX) (223 +/- 6%), prostaglandin E1 (PGE1) (227 +/- 15%), 3,3',5-triiodothyronine (T3) (184 +/- 22%), insulin (182 +/- 14%), multiplication-stimulating activity (MSA) (178 +/- 6%), 5% rat serum (253 +/- 57%). THe increase in ODC activity seen with BtcAMP and insulin was not due to a change in Km or a decreased rate of degradation of the enzyme. Actinomycin D (1 microgram/ml) inhibited stimulation of ODC activity by T3 and the cyclic AMP-mediated factors (PTH, BtcAMP, MIX, PGE1), but had only minimal effects on ODC stimulation by insulin, MSA, or serum. Amanitin inhibited both BtcAMP and T3 stimulation of ODC, but had no effect on insulin stimulation of ODC. Thus, hormones and metabolic factors known to stimulate anabolic processes in chick embryonic pelvic cartilage also increase ODC activity through at least two mechanisms: transcriptional (cyclic AMP-mediated and T3) and posttranscriptional (insulin, serum, MSA).
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