Previous work indicating that luteinizing hormone (LH) is the bovine luteotropin suggested that LH should prolong the life span of the corpus luteum. Single subcutaneous injections of pituitary extract (three glands), bovine LH (30 units of NIIt-LH-B2) or bovine LIt incubated in 6 ~ urea at 40 C for 24 hr were given on Day 16 of the cycle. The hormones were homogenized with Freund's complete adjuvant to give a total volume of approximately 20 nil. Maintenance of the corpora was followed by rectal examinations and ]aparotomies. The length of the diestrous intervals (days) following treatments were (five heifers per group) : untreated controls, 20.0 --+ 0.7; pituitary extract, 31.0 2.9; bovine LH, 36.4 2.5; urea incubated LIt, 21.6 0.2 (P < 0.001). Pituitary extracts and bovine LH extended the life span of the corpus luteum, but the effect was lost after destruction of LH with urea.
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Donaldson et al. (1965) studied this question.
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