The supression of milk fat globule secretion by clochicine: an effect coupled to inhibition of exocytosis.

The effects of colchicine on release of milk lipids from mammary tissue were evaluated by biochemical analysis of milk and morphological study of the tissue following intramammary infusions of the alkaloid into lactating goats. Colchicine produces a reversible drop in milk yield. As the flow of milk resumes, 36--48 h after infusion, the fat content of the milk increases, phospholipid per g of total globule lipid falls, mean size of milk fat globules increases and diameters of fat droplets (presecretory milk fat globules) within lactating cells approximately double. These observations are consistent with the conclusion that colchicine suppresses milk fat globule secretion but that globules continue to grow in size wihtin cells during the suppression period. These findings indicate that secretion of milk fat globules and the skim milk phase are coupled.