The effects of deprivation of carotene and anterior pituitary hormone on the partition of vitamin A in the blood and milk of the cow

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Abstract
Injections of an anterior pituitary preparation "Ambinon" (Organon Laboratories Ltd.) which contains thyrotrophin and gonadotrophins, were given to Ayrshire cows, both in the presence and in the absence of dietary carotene in the form of greenstuff, and carotene, vitamin A ester and vitamin A alchohol levels in blood and milk were compared with data from 2 control cows receiving exactly the same dietary treatment. The pituitary preparation increased vitamin A alcohol output in milk whether greenstuff was present in the diet or not. With no dietary green-stuff the output of vitamin A alcohol in milk increased and this increase was enhanced in the hormonally treated cows. In the absence of green food there was no vitamin A ester in blood and yet the output of vitamin A ester in milk was also increased by the hormone preparation so that the hormonal treatment increased the rate of esterification of vitamin A by the mammary gland. When greenstuff was present in the diet blood contained vitamin A ester in amounts which were increased by hormonal treatment. Hormonal treatment increased vitamin A alcohol in blood serum whether or not there was greenstuff in the diet. Like thyroxine, the hormone preparation appeared to accelerate the mobilization of hepatic reserves as vitamin A alcohol into the blood and hence into the milk as alcohol and ester. In addition the hormone preparation appeared to accelerate the transformation of dietary carotene into vitamin A in the gut. Thus vitamin A ester in the milk could, when the diet contained carotene, have either a hepatic or a dietary origin according as it came from the alcohol or the ester of vitamin A circulating in the blood.