Effect of Oxotremorine on Ornithine Decarboxylase Activity of the Adrenal Gland in Rat

Abstract: In this work we have studied the mechanism for the increase of adrenal ODC (ornithine decarboxylase, EC 4.1.1.17) activity provoked by oxotremorine, a muscarinic agonist. 1. Oxotremorine increased medullary ODC activity maximally at 2 h. Cortical enzyme responded much more slowly. 2. Blockade of peripheral muscarinic receptors with methylatropine partially reduced the response to oxotremorine in the medulla, but not cortex. 3. Hy-pophysectomy abolished the cortical, but not the medullary, responses to oxotremorine. Methylatropine reduced the effect of oxotremorine on medullary ODC in hypophysectomized rats. 4. In unilaterally splanchnicotomized rats oxotremorine caused an increase of ODC activity of the denervated adrenal gland relative to control value; activities in both medulla and cortex were significantly lower than those observed in the innervated gland. Evidence was obtained for a compensatory increase of ODC activity of the adrenal cortex (but not medulla) on the intact side of unilaterally operated rats. 5. Surgical intervention, in the form of a sham operation for transection of the spinal cord, leads to an increase of ODC activity in both parts of the adrenal gland. Transection of the cord attenuates these increases. 6. The additional increase of medullary ODC activity owing to the administration of oxotremorine to sham-operated rats is partially reduced in the adrenal medulla by muscarinic blockade, and completely in the cortex. This effect of methylatropine in regard to cortical ODC activity was not apparent in the other experiments with intact or unilaterally splanchnicotomized (unoperated side) rats. The results with unilaterally splanchnicotomized rats and those with transected spinal cord suggest that oxotremorine-induced modifications of adrenal ODC activity are centrally mediated, above the level of origin of the splanchnic nerves in the spinal cord (T_8–10). Experiments with hypophysectomized rats show that the response of the adrenal cortex to oxotremorine is entirely mediated by the hypophysis.