The effects of colchicine on milk secretion, mammary metabolism and blood flow in the goat

Mammary function in the conscious goat was studied during colchicine-induced depression of milk secretion in one mammary gland. Milk yield of the treated gland was reduced to approximately a quarter of previous, while there were significant increases in afternoon milk yield from the untreated glands on the 2nd and 3rd days after treatment in goats in late lactation. Milk composition in the untreated glands was not significantly affected. In the treated gland, milk Na+], Cl-], citrate] and protein] increased while K+] and lactose] decreased, although the time course of these changes differed; milk fat] was unaffected. Mammary extractions ((A-V)/A) of glucose, acetate and most amino acids were significantly decreased during the period of maximal inhibition of secretion. There were no significant changes in arterial plasma concentrations of glucose, acetate or any essential amino acids. In another series of experiments, mammary blood flow increased and then returned to normal after colchicine treatment even though milk yield and mammary glucose uptake decreased markedly; oxygen uptake was not significantly affected. The results are discussed in relation to the actions of colchicine on the mammary secretory cell, to the normal control of mammary blood flow and to the mechanism of compensation by the untreated gland.