Pituitary LH Content in Rats Exposed to Continuous Illumination

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Abstract
Adult female rats were exposed to constant light (LL). Initially they ran "normal" estrous cycles; later the vaginal smear pattern became increasingly irregular, and finally a persistent-estrous (PE), anovulatory state developed. Pituitary LH content was measured by the OAAD method on proestrus and estrus of cycles 1-5 in LL, and after 5-30 days of PE. During the early period of LL exposure, while the rats were still cycling, pituitary LH values resembled those obtained in control cyclic rats in an alternating light-dark environment[long dash]i.e., high (8.3 [mu]g) on proestrus, and low (4.7 [mu]g) on estrus when fresh oviductal ova were found[long dash]and did not vary significantly from cycles 1-5. LH content of pituitaries from 10-day PE rats was dependent upon the length of time these rats were in LL before PE developed. It was high (11.4 [mu]g) when the PE state evolved during the first 2 months in LL, and low (3.8 [mu]g) when PE occurred following a more prolonged exposure to LL. Pituitary LH in rats showing 5, 15, 20 and 30 days of PE also appeared to be dependent upon the total duration of LL exposure.