Effects of removing milk from the mammary ducts and alveoli, or of diluting stored milk, on the rate of milk secretion in the goat.

Goats were milked frequently (at 10.00, 11.30, 13.00 and 14.30 h) between normal morning and afternoon milking, using a catheter to drain the milk stored in the cistern and large ducts of the mammary gland; no increase in the rate of milk secretion occurred. When the same study was repeated but oxytocin was injected to elicit milk ejection and empty the alveoli, the rate of milk secretion increased significantly. The stimulatory effect of frequent catheter-milking plus exogenous oxytocin was evident at peak lactation as well as during declining lactation. When milk stored in the mammary gland was diluted with an isosmotic sucrose solution, the rate of milk secretion increased significantly. Again this effect was apparent at all stages of lactation. These results are discussed in relation to the local inhibitor hypothesis on the modulation of milk secretion.