Mechanisms of Secretion: Effects of Colchicine and Vincristine on Composition and Flow of Milk in the Goat

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Abstract
Colchicine, the plant alkaloid, produced a dramatic decrease in milk flow when infused into the udder of the goat. The compound (1-5 mg) dissolved in 5 ml of water was inserted into 1 side of the udder via the teat canal. Such treatments consistently caused a depression in milk yield from the infused side with maximum at 36 h and substantial reversal by 72-96 h. Milks from both the infused and unifused sides of the udder were essentially normal in composition (fat, protein and lactose). Globulins and riboflavin were elevated in milks from the infused side. The plant alkaloid, vincristine, produced effects on milk secretion similar to those of colchicine but at dosages roughly 1/10 the latter. The 2 substances had no effect on the amount of milk from the uninfused side of the udder. Experiments employing 14C colchicine revealed that less than 20% of the infused colchicine is secreted in the milk. Both the secretion of fat globules and the emptying of secretory vesicles by the lacating cell are inhibited by colchicine, indicating that a portion of the cell population is turned off from secretion. Plant substances such as colchicine and vincristine may at times limit yields of milk, especially in grazing ruminants.