Compensatory adrenal growth in immature and mature male rats.

We measured adrenal weights 3 days after left- or sham-adrenalectomy in male Sprague-Dawley rats at 10 ages between 10 and 155 days. Compared to sham-operated rats, the magnitude of the increase in right adrenal weight ranged between 19 and 32% after unilateral adrenalectomy and was significant at 10, 20, 40, 50, and 60 days (p less than 0.01). Comparing left with right adrenals in unilaterally adrenalectomized rats, the right was heavier at all ages (p less than 0.01); in animals 40 days and younger, this is due to normal adrenal growth rate (0.3 mg/day) as well as compensatory adrenal growth, while in older animals normal growth rate is slow (0.04 mg/day) and this difference in left and right adrenal weights is due primarily to compensatory growth. We conclude from this study that compensatory adrenal growth occurs 3 days after left adrenalectomy at all ages except 15 and 30 days. Resting levels of plasma ACTH and corticosterone did not differ between left- and sham-adrenalectomized rats at any age. The ACTH response to 1 min exposure to ether vapors was markedly reduced in 7- and 12-day-old rats (p less than 0.01). We conclude that compensatory adrenal growth is a consistent response 3 days after unilateral adrenalectomy that depends neither on the age at which surgery is performed nor on the capacity of the rat to secrete markedly elevated levels of ACTH.