Serum Levels of Follicle-Stimulating Hormone during the Bovine Estrous Cycle

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Abstract
A specific radioimmunoassay for bovine follicle-stimulating hormone (bFSH) has been developed using rabbit antiserum to ovine FSH and radioiodinated human FSH. Employing this radioimmunoassay, as little as 3 ng of FSH can be quantified. Inhibition curves obtained with bovine serum, crude pituitary extract and other partially purified bovine pituitary preparations containing FSH were parallel to those obtained with the bFSH standard preparation. FSH estimates obtained by radioimmunoassay in preparations containing varying amounts of FSH, LH, TSH, GH and prolactin were in good agreement with the values obtained by bioassay. Exogenous bFSH could be quantitatively recovered from 200 ul of serum suggesting that serum components per se did not interfere with the radioimmunoassay. Mean serum concentrations of FSH (in equivalents of NIH-FSH-SI) were: normal males, 76 ± 5 ng/ml; castrated males 102 ± 2 ng/ml; females in follicular or luteal phase 66 ± 8 ng/ml and estrus females 78 ± 8 ng/ml. When serum samples were collected at daily intervals, there was a trend for FSH levels to be elevated on the day of estrus, however, this elevation was not significant. However, a significant increase in FSH concentrations was noted coincident to the LH peak when samples were collected at 2-hr. intervals around estrus. Following the injection of 250 jug of gonadotropin releasing hormone (Gn-RH) a highly significant release of FSH was observed with maximum levels occuring between 90 to 120 min. post-injection. Copyright © 1974. American Society of Animal Science . Copyright 1974 by American Society of Animal Science.

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