After adrenalectomy and removal of the pups from rats on the 4th day of lactation, administration of oxytocin for 9 days had little or no effect in inhibiting mammary gland involution. However, simultaneous treatment with 9α-fluorocortisol (FC) resulted in a significant maintenance of mammary gland tissue. Prolactin had an appreciable effect in retarding mammary involution, in the absence of the adrenals, but this effect was not enhanced by concomitant administration of FC, which, given alone, had only a slight effect in adrenalectomized animals. Prolactin and growth hormone (GH) together had a marked synergistic effect.
In intact rats only comparatively slight effects on maintenance of the mammary gland were observed following treatment for 9 days with either FC or adrenocorticotrophic hormone (ACTH), and ACTH failed to enhance the action of prolactin and GH.
The apparent failure of oxytocin to induce release of prolactin in adrenalectomized rats cannot be explained solely on a metabolic or nutritional basis. It is suggested that either the release of stored prolactin is inhibited in the absence of the adrenals, or that the production of prolactin is adversely affected.