Abstract
Eighteen corpora lutea were obtained from 10 lactating dairy cows of three breeds at three stages of the estrual cycle. Synthesis of progesterone in vitro in the presence of cholesterol-7 a -H3 and in the presence or absence of ICSH was studied in these glands. The response to ICSH in vitro was influenced by the age of the corpus luteum. Two criteria of ICSH activity, namely: (1) an increase in progesterone synthesis during incubation with ICSH, and (2) increased conversion of cholesterol-7 a -H3 to progesterone-H3 produced by ICSH, were greater at days 11 to 13 than with younger or older glands. Corpora lutea obtained at days 19 and 20 did not respond to ICSH. Breed of cow appeared to influence corpus luteum weight and concentration of progesterone following incubation and, perhaps, also the conversion of exogenous tritiated cholesterol to progesterone.
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