Adenohypophysial corticotrophin and plasma free corticosteroids during regeneration of the enucleated rat adrenal gland.

From planimetric measurements of the total gland and its components, at progressively later intervals following unilateral adrenalectomy and contralateral enucleation in the rat, full regeneration of the cortex was observed to occur within 6–8 weeks. Free corticosteroids disappeared from the plasma within 6–8 hours of the enucleation procedure. Their subsequent rise, already detectable on the 4th day, culminated in a transient and slightly supernormal peak on the 16th day. From a correlation of the plasma free corticosteroid levels to the corresponding amounts of cortex, the secretory activity of the regenerating gland per unit of cortical tissue was estimated at 570% of the paired-weight control base line after 16 days, and at slightly above 200% after 7 weeks, when it leveled off. The pituitary ACTH response to the procedure was characterized by a transient rise within the first 15 minutes, followed by a fall to 35% of the control level after 4 hours, and to 22% after 12, subsequent rise to a crest of 330% on the 16th day, and regression thereafter to near-normal values, recorded on the 184th day. The concomitant rises and falls of pituitary ACTH, cortical secretory index and plasma free corticosteroids, observed in association with cortical deficiency and regeneration, reinforce the conclusion, reached from previous studies, that both release and synthesis of ACTH are accelerated by hypo- and depressed by hypercorticoidism, and that, furthermore, the regulatory effect of steroids is predominantly exerted on synthesis.