Ultrastructural alterations in mammary glands of pregnant rats after ovariectomy and hysterectomy: Effect of adrenal steroids and prolactin

Abstract

Pregnant rats were subjected to oophorectomy and hysterectomy (O–H) on the seventeenth day of pregnancy, a time when serum levels of prolactin, estrogen, and corticosterone are not substantially greater than the respective levels in nonpregnant rats. At 32 hours after O–;H, serum prolactin and corticosterone both rose more than threefold, and lactose appeared in the mammary glands. Biopsies of mammary tissue obtained at 8 hour intervals after O–H showed a progressive secretory response over 16 hours, similar to that previously shown to occur within a period of about 4 hours on the last day of pregnancy. Suppression of serum prolactin by ergocriptine administration and adrenalectomy 24 hours before O–H each prevented the secretory response. However, some differences in the effects of deprivation of the two types of hormones were evident. After cortisol acetate administration at O–H, mammary tissue responded rapidly despite adrenalectomy 24 hours earlier. It is concluded that simple withdrawal of progesterone is not sufficient to initiate lactation in the pregnant rat; glucocorticoids must be present continuously during progesterone withdrawal, and prolactin elevation and other factors present at parturition may be required as well.