The effect of lactation on the transport of serum-derived IgA into bile of sheep.

The effect of lactation on the selective transport of IgA from serum into bile and the relationship between volume of milk production and IgA recovery in bile was examined in sheep following intravenous injection of radiolabelled dimeric IgA. Bile: plasma radioactivity ratios for lactating and non-lactating sheep were 6.20 +/- 1.50 and 1.97 +/- 0.35, respectively, and in lactating sheep the milk : plasma ratio was 8.20 +/- 0.81. When biliary flow rates and milk yield were taken into account, 7.3% and 42.0% of the radiolabelled IgA present in plasma at 1 min after injection was recovered in bile and milk, respectively, of low milk yielding ewes, whereas in high milk yielding ewes, recoveries were 4.0% and 66.0%, respectively. The data suggest that during lactation there is an overall increase in transport of IgA into bile, possibly due to the effect of lactogenic hormones on secretory epithelia, but that there may be competition between hepatocytes and mammary epithelial cells for available serum-derived IgA, depending on the secretory activity of the gland.