Ultrastructural alterations in mammary glands of pregnant rats after ovariectomy and hysterectomy: effect of adrenal steroids and prolactin.
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.
D000818:Animals; D002369:Castration; D003345:Corticosterone / Q000097:blood*; D004873:Ergolines / Q000494:pharmacology; D005260:Female; D006854:Hydrocortisone / Q000494:pharmacology; D007044:Hysterectomy; D007774:Lactation; D007785:Lactose / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000648:ultrastructure*; D008854:Microscopy, Electron; D011247:Pregnancy; D011374:Progesterone / Q000097:blood*; D011388:Prolactin / Q000037:antagonists & inhibitors / Q000097:blood*; D051381:Rats
D004873:Ergolines; D011374:Progesterone; D011388:Prolactin; D007785:Lactose; D003345:Corticosterone; D006854:Hydrocortisone