Antiserum to the milk fat globule membrane. Preparation and capacity to suppress milk secretion

Presence and genetic polymorphism of an epithelial mucin in milk of the goat (Capra hircus)

1. Analysis of individual samples of goat's milk by SDS-PAGE confirmed that they contain a polymorphic, high molecular weight (M(r) greater than 205 kDa) glycoprotein. 2. On SDS-gels, the polymorphism takes the form of two bands of variable mobility which usually stain with equal intensity. This polymorphism resembles that detected in milk mucins of other species and is best explained by an expression of codominant genes containing variable numbers of a tandemly repeated 60-base segment. 3. Analysis of milk fractions provided evidence that the goat mucin is exclusively a membrane protein, and that it can be purified from other fat globule proteins by gel filtration and peanut lectin affinity chromatography. 4. Among proteins in the goat milk fat globule, the mucin appears to be a strong immunogen but the resulting antibodies applied to Western blots only stained the cow's milk mucin mildly and the guinea pig and human milk mucins not at all.

Ultrastructural changes in lactating tissue related to the suppression of milk secretion by concanavalin A

The plant lectin, concanavalin A (Con A) suppresses milk secretion when infused into the mammary gland or when incubated with lactating tissue in vitro. Toward defining its mode of action, we infused Con A into rat and goat mammary glands via the teats and observed effects on lactating cells. Lectin dosages were 2 and 25 mg per gland for rats and goat, respectively. Tissue samples were taken 1 and 3 h post infusion for rats and at 24 h for the goat. Control and Con A-treated tissues were observed by light microscopy and by both thin section and freeze fracture electron microscopy. In comparison to controls, Con A-treated tissues of both species exhibited alveoli with enlarged cells and relatively empty lumina; cells were distended with secretory vesicles and fat droplets. Apical plasma membranes of lectin-affected cells of the rat displayed a marked reduction in the number of microvilli, and exhibited an atypical branching and folded structure. Morphometry was employed to quantitate changes in cell and secretory product parameters in both rat and goat tissue. Microtubule numbers and distribution did not appear to be altered by Con A but considerable changes were noted in the arrangement of microfilaments associated with the secretory surface of lectin-treated epithelial cells. Various related ultrastructural changes and the role of Con A in perturbing the microfilament system are discussed.

Suppression of milk secretion (exocytosis) by concanavalin a in vitro

The observation that concanavalin A can inhibit milk secretion was evaluated in an in vitro system employing minced mammary gland or isolated alveoli from lactating rats. Release of milk constituents (casein, lactose and fat globules) into the medium in the presence and absence of concanavalin A was measured during 1 or 2 h incubations. The effect of concanavalin A on glucose uptake and CO2 production of the minced tissue was also studied. Concanavalin A suppressed release of milk components at a concentration as low as 80 micrograms/ml of medium. Respiration of minced mammary tissue in the presence of concanavalin A (100 micrograms/ml of medium) was essentially the same as that of the control. The data are evidence that concanavalin A acts directly on the mammary cell in suppressing milk secretion and that the effect is not due to cytotoxicity.