Time Interval Between Injection of Estradiol Benzoate and LH Release in the Rat and Effect of Actinomycin D or Cycloheximide

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Abstract
Ovariectomized rats were injected with 0.5 μg/day of estradiol benzoate (EB) for 5 days. Fifty ng of EB was given in a single injection at varying hours on day 6 or 7. All animals were killed at 1630 hr on day 7, and LH levels in the serum were determined by radioimmunoassay. EB given at 1100, 1200, or 1800 hr on day 6 induced release of LH, but EB given at 2400 hr on day 6 or at 0700 or 1200 hr on day 7 did not. Actinomycin D (AD) given either prior to, or 7 or 13 hr after the 50 μg of EB blocked LH release. AD given 20 hr after EB did not block LH release. Cycloheximide given either prior to, or 20 or 25 hr after EB blocked LH release. AD failed to block LH release induced in vivo with exogenous LRF. These results suggest (a) that the minimal latent period of EB, under the regimens used in this study, for inducing a significant release of LH was between 16.5 and 22.5 hr, and (b) that induction of LH release by EB may require de novo synthesis of RNA and protein over a period of several hours. (Endocrinology93: 887, 1973)

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