NO EVIDENCE FOR BASOLATERAL SECRETION OF MILK PROTEIN IN THE MAMMARY-GLAND OF LACTATING GOATS

Recent research suggests that a small percentage of milk proteins may be secreted basolaterally, which would have implications for our work on the permeability of tight junctions in the mammary epithelium. In o ur work, the presence of alpha-lactalbumin (LA) or lactose in plasma i s used as an indicator of permeability. The aim of this study was to e xamine basolateral secretion by determining the presence of milk prote ins in efferent mammary lymph. Five Saanen goats were fitted with mamm ary lymph catheters and were administered intramammary isosmotic bolus infusions of sucrose control solutions or ethylene glycol-bis(8-amino ethyl ether)-N,N,N',N'-tetraacetic acid to induce leaky tight junction s. Lymph samples were collected before and approximate to 5 h after in fusion. Lymph was analyzed by Western blotting for the presence of alp ha-casein (CN), beta-CN, and alpha-LA. No alpha-CN or beta-CN was dete cted in lymph, but alpha-LA was detected in all lymph samples. Moreove r, the signal was much stronger in samples from goats that were treate d with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraaceti c acid, and concentrations of alpha-LA in lymph were significantly inc reased with this treatment. These changes and the absence of casein in lymph suggest increased permeability of tight junctions rather than b asolateral secretion. In summary, these data do not support basolatera l secretion.