The effects of ACTH and growth hormone on rat adrenal ornithine decarboxylase activity (ODA) were studied in hypophysectomized rats. Administered independently, each hormone produced an increase in ODA as compared to saline—injected hypophysectomized controls. ACTH caused a rise in ODA between 6 and 10 hr after stimulation with a peak at 8 hr. Increasing doses of ACTH from 2.5 IU to 10 IU produced progressive increases in ODA. The steroidogenic 1–24 portion of the ACTH molecule had full ODA—stimulating activity. There was a progressive fall in ODA responsiveness to a standard pulse of ACTH with increasing time after hypophysectomy. Growth hormone also produced a peak ODA response 8 hr after administration. Progressively increasing ODA responses were obtained by increasing doses of growth hormone from 1 to 5 mg. When ACTH and growth hormone were injected at the same time, a marked synergistic stimulation of ODA was observed. (Endocrinology92: 1089, 1973)
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Levine et al. (1973) studied this question.