Progesterone levels were measured at proestrus in intact, phenobarbital (sodium phenobarbital)-treated, hypophysectomized (ℏ) and irradiated hamsters by the competitive protein binding technique. Progesterone content and concentration in the ovary increased dramatically between 2:30 and 3:00 PM and the highest levels were reached at 8 PM. The concentration of follicular progesterone paralleled but was only one half of the total ovarian value. Plasma progestei-one was highest at 6 PM and did not decrease significantly until 12 midnight. Phenobarbital (phen) or ℏ at 1 PM completely blocked ovarian progesterone synthesis at 4 PM. LH but not FSH restored progesterone secretion in ℏ or phen-treated animals. LH significantly increased ovarian progesterone within 15 min in ℏ animals. Hamsters ℏ at 4 PM (after the initial rise in progesterone) continued to show progesterone at control levels for at least 4 hr. Therefore, the continued presence of LH does not appear to be necessary for sustained progesterone secretion. Several lines of evidence indicated that the interstitium is the major source of preovulatory progesterone. Chronic ℏ did not impair the ability of the ovary to produce progesterone in response to LH. Selective destruction of follicles or corpora lutea by X-irradiation did not decrease progesterone concentration in ovaries from proestrous hamsters. Furthermore, in intact hamsters the content of follicular progesterone represents less than 15 % of the total ovarian progesterone during most of the preovulatory period. (Endocrinology89: 598, 1971)
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Norman et al. (1971) studied this question.