Thyroid Hormones Enhance the Synthesis and Secretion ofα-Lactalbumin by Mouse Mammary Tissuein Vitro*

Publisher Website
Google Scholar
Abstract
The synthesis and secretion of casein and .alpha.-lactalbumin were examined in organ culture of midpregnancy mouse mammary glands using serum-free medium supplemented with various combinations of insulin, hydrocortisone, prolactin [PRL] and L-triiodothyronine [L-T3]. Using highly specific antibodies raised against mouse caseins and .alpha.-lactalbumin, a selective enhancement of .alpha.-lactalbumin and lactose synthesis and secretion was demonstrated when all 4 hormones are present in the culture medium. Production of casein was not modified by the presence of L-T3. Hydrocortisone at concentrations of 10-9-10-6 M inhibited the secretion of both casein and .alpha.-lactalbumin into the culture medium. The addition of L-T3 to the medium selectively overcame the inhibition of .alpha.-lactalbumin secretion by hydrocortisone. Extracts of tissue cultured in the presence of L-T3 contained 2 distinct forms of .alpha.-lactalbumin, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the absence of L-T3, synthesis of a single form of .alpha.-lactalbumin prevailed. In the culture medium, predominantly one form of .alpha.-lactalbumin was detected regardless of the presence of L-T3 during culture. Thyroid hormones apparently play an important regulatory role in functional differentiation of the mouse mammary gland.