Pituitary LH Content During the Estrous Cycle in Female Hamsters: Comparisons with Males and Acyclic Females1

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Abstract
Pituitary LH (luteinizing hormone) content (by ovarian ascorbic acid depletion) has been measured during the 4 days of the hamster estrous cycle, in acyclic and pseudopregnant female hamsters and in the male hamster. Day 1 of the cycle corresponds to the day of "proestrus" in the rat and is marked superficially by heat which begins in the early evening; ovulation occurs at approximately 1 AM of Day 2. On Day 1, LH content=4.8 [mu]g; by the next morning ("postestrus" =Day 2) when fresh ova are seen in the oviduct, the content has dropped to 2.2 [mu]g. It remains at this low level on Day 3, but rises back to preovulatory levels (5.6 [mu]g) on Day 4. Uterine weight is maximal on Day 1, suggesting that secretion of estrogen takes place before that day. In acyclic female hamsters, uterine weights drop below the minimal cyclic values and the ovaries lack corpora lutea and growing follicles, but pituitary LH content is 4.1 [mu]g, suggesting a failure of LH release. In pseudopregnant hamsters on the 5th day (corresponding to Day 2 in a nonmated hamster) LH content is at preovulatory values (5.3 [mu]g) correlating with the blockade of ovulation. Thus, in the female hamster, as in the rat, pituitary LH content serves as an excellent indicator of release or nonrelease of the ovulatory surge of LH. Male hamsters show much higher pituitary LH contents than any of the females (>18 [mu]g).