Paracellular Leakage of Lipoprotein Lipase Across the Mammary Epithelium of the Goat

Abstract

The ability of lipoprotein lipase to move across the mammary epithelium by a paracellular route was investigated. Five goats were milked hourly to activate the paracellular pathway. Three goats responded to hourly milking with a fivefold increase in milk lipoprotein lipase activity as compared with nonresponding goats. Massage of the mammary gland was necessary in the two nonresponding goats too cause increased lipoprotein lipase activity in milk. Oxytocin treatment during hourly milking also increased enzyme activity in milk from a nonresponding goat. Activation of the paracellular pathway by hourly milking increased milk sodium and protein and decreased potassium and lactose concentrations. After a 12-h milking interval, lipoprotein lipase activity was distributed primarily in the serum (48%) and cream (40%) fractions and, to a lesser extent, in the casein (12%) fraction. Hourly milking increased enzyme activity distributed in the serum fraction (62%), whereas enzyme activity associated with the cream (32%) and casein (6%) fractions decreased. Possible mechanisms for the origin of lipoprotein lipase in milk are discussed.

Combined effects of once-daily milking and feeding level in the first three weeks of lactation on milk production and enzyme activities, and nutritional status, in Holstein cows

“…The latter hypothesis would be consistent with a negative effect of increased intramammary pressure (or the accumulation of a Feedback Inhibitor of Lactation [43]) on mammary LPL synthesis and/or passage into milk since the milking frequency is decreased. Our findings are also consistent with the results of Azzara and Dimick [2] who showed that changing from two to 24 milkings a day induced a 5-fold increase in milk LPL activity in three of five experimental goats. These authors considered their results consistent with those of Linzell and Peaker ( [29]; cited by Azzara & Dimick [2]) who observed that hourly milkings through the physiological administration of ocytocin activated paracellular passage of blood components through the mammary epithelium.…”

“…Our findings are also consistent with the results of Azzara and Dimick [2] who showed that changing from two to 24 milkings a day induced a 5-fold increase in milk LPL activity in three of five experimental goats. These authors considered their results consistent with those of Linzell and Peaker ( [29]; cited by Azzara & Dimick [2]) who observed that hourly milkings through the physiological administration of ocytocin activated paracellular passage of blood components through the mammary epithelium. These latest observations would be compatible with the former hypothesis, although it would need to be confirmed in cows because goat's milk LPL is secreted through different mechanisms than cow's milk LPL [6,9].…”

Once-daily milking of dairy cows: a review of recent French experiments

“…To date, the impact of ODM on LPL activity has never been measured. Azzara and Dimick [2] observed an increase in LPL activity in the milk of goats milked hourly after oxytocin administration, an observation they attributed to the increased permeability of tight junctions. In the case of ODM -which also augments tight junction permeability -the decreases in LPL activity and FFA content in milk could both result from the large supply of precursors of short-chain fatty acids to the udder (acetate and 3-hydroxy-butyrate) relative to the reduced capacity of fat secretion of the udder.…”

Indigenous enzymatic activities in ovine and caprine milks

“…Finally, the increase of milking frequency increases LPL activity in the serum of caprine milk due to paracellular leakage of blood LPL across the mammary epithelium of the goat (Azzara and Dimick 1989).…”