Effect of neonatally injected ACTH and ACTH analogues on eye-opening of the rat.

Three-day old rats were injected subcutaneously either with natural purified pig ACTH (ACTH 1–39), ACTH 1–24, or ACTH analogues as long-acting zinc-phosphate preparations. ACTH 1–39, ACTH 1–24, ACTH 1–18, ACTH 1–16 accelerated the time of eye-opening, whereas an extract of corticosteroids produced $\text{in}$$\text{vitro}$ by excised adrenals of ACTH-treated three-day old rats was ineffective. Injections with ACTH on the twelfth day of life had no effect on eye-opening. It is concluded that a neonatal injection with ACTH or closely related analogues with markedly less corticotropic activity can accelerate the time of eye-opening. This effect is not mediated by the adrenal cortex. The sensitive period for it appears to be shortly after birth.