The effect of hypothalamic hemi-islands on compensatory adrenal growth

Unilateral hypothalamic disconnections were made with a Halász knife in young male rats to determine the effects of these lesions on adrenal weight, and the response to unilateral adrenalectomy. Rats were unilaterally adrenalectomized or sham-adrenalectomized 5-7 days after the hypothalamic surgery. No lesion affected adrenal weight in sham-adrenalectomized rats. Compensatory adrenal growth 3 days after unilateral adrenalectomy is prevented by a unilateral hypothalamic hemi-island on the side ipsilateral, not contralateral, to the first removed adrenal (P less than 0.01). Portions of the ipsilateral hemi-island were examined to determine which interrupted the compensatory adrenal growth response. The anterior 90 degrees portion enhanced compensatory adrenal growth (P less than 0.01). The posterior 90 degrees portion only partially inhibited compensatory adrenal growth (P less than 0.05), while the posterolateral portion completely inhibited the response (P less than 0.01). Plasma ACTH and corticosterone levels at the time of sacrifice were unaffected by unilateral adrenalectomy, but were slightly elevated by the hypothalamic cuts. These studies provide further evidence that compensatory adrenal growth is mediated neurally.