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 < 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 E 1 (PGE 1 ) (227 ± 15%), 3,3',5-triiodothyronine (T 3 ) (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 K(m) or a decreased rate of degradation of the enzyme. Actinomycin D (1 μg/ml) inhibited stimulation of ODC activity by T 3 and the cyclic AMP-mediated factors (PTH, BtcAMP, MIX, PGE 1 ), but had only minimal effects on ODC stimulation by insulin, MSA, or serum. Amanitin inhibited both BtcAMP and T 3 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 T 3 ) and posttranscriptional (insulin, serum, MSA).
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