Corpus Luteum Function in the Rat: A Critical Period for Luteal Activation and the Control of Luteal Maintenance12

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Abstract
The ability of LH or prolactin to initiate and maintain progestin secretion by the corpus luteum was tested in pseudopregnant rats using anti-LH (A/LH) and anti-prolactin (A/Pro) sera. Progestin secretion was evaluated by the decidual reaction test (12 groups of 6 animals/ group) and by competitive protein-binding assay. A/Pro or anti-LH given immediately after electrical stimulation of the cervix (1800 hr of proestrus) completely abolished the expected pseudopregnancy and decidual reaction. A/Pro given at 2000, 2200, 2400 of proestrus or at 0200 hr of estrus also completely blocked the decidual reaction, but resulted only in a depressed response when given later during estrus at 0400, 0600 or 0800 hr. When A/Pro treatment was delayed until 1000 hr of the morning of estrus, pseudopregnancy proceeded and the decidual reaction was maximal. A/LH given at the time of cervical stimulation completely abolished the expected reaction and also depressed deciduomata when given at 1000 hr on days 1, 2 or 3. In general, progestin levels were not substantially altered by A/Pro injections. However, since only total progestin levels were measured it is possible that progesterone concentration was affected by A/Pro without this becoming apparent within the unchanged total progestins. By contrast, A/LH administered at the time of cervical stimulation or on days 1, 2 or 3 of pseudopregnancy resulted in a significant (P <.001) and sustained decrease in serum progestins determined on days 1, 2, 3 and 4. These data indicate that the stimulation by prolactin is indispensable for corpus luteum activation during a “critical” period of the first 8-16 hr after the onset of pseudopregnancy but not for luteal maintenance following this time interval. On the other hand, LH appears to play an important role in both luteal activation and maintenance. (Endocrinology93: 316, 1973)

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