Transfer of prolactin from plasma into milk and associated physiological benefits to mammary cells.
The pituitary hormone prolactin (PRL) exists in milk in concentrations which usually approximate those in blood plasma. During the period immediately prior to parturition, PRL accumulates in cows' milk in concentrations far greater than those in blood plasma. Regular removal of this prepartum milk, and the PRL it contains, does not decrease intra-alveolar concentrations of PRL but rather stimulates the transfer of more PRL into milk to replace the quantity removed by milking. Furthermore, in cows from which prepartum milk was being removed regularly, pharmacologic inhibition of plasma PRL did not interfere with the intra-alveolar accumulation of PRL. Lactogenic benefits are hypothesized to result from the transfer of PRL into prepartum milk contained within the alveolar lumen. Preliminary results indicate a long-lasting lactogenic benefit only when prepartum removal of milk stimulated the transfer of PRL into alveoli of cows that were also rendered deficient in plasma PRL. If these results can be confirmed, it would show that the transfer of PRL into milk benefits lactogenesis when the quantities of blood-borne PRL are inadequate. In addition, immunoreactive PRL has been detected in several intracellular compartments (i.e., rough endoplasmic reticulum, Golgi apparatus, secretory vesicles) of bovine mammary cells. These results are consistent with a biological action of PRL molecules as they are transferred intracellularly from plasma into milk.
D000818:Animals; D001692:Biological Transport; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004873:Ergolines / Q000494:pharmacology; D005260:Female; D007743:Labor, Obstetric; D007774:Lactation / Q000187:drug effects; D008321:Mammary Glands, Animal / Q000502:physiology* / Q000648:ultrastructure; D008892:Milk / Q000378:metabolism*; D011247:Pregnancy; D011388:Prolactin / Q000097:blood* / Q000502:physiology; D012313:RNA / Q000378:metabolism
D004873:Ergolines; D012313:RNA; D011388:Prolactin