Role of luteinizing hormone in regulating luteal function in ruminants.

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The technique of hypothalamic-pituitary stalk-disconnection was used to reinvestigate the roles of luteinizing hormone (LH) and prolactin in the regulation of luteal function in ewes. Stalk-disconnection was performed on d 5 of the estrous cycle and ewes were administered either saline (control), LH at 40 micrograms at 4-h intervals, 2 mg of alpha-ergocryptine at 12-h intervals or both LH and ergocryptine. The treatment regimen for LH was designed to mimic luteal phase concentrations of this hormone. Blood samples were collected from all stalk-disconnected and 6 sham-disconnected ewes at 4-h intervals beginning at 0600 h on the day of surgery for determination of serum concentrations of prolactin, cortisol and progesterone. Corpora lutea were collected from control ewes on d 5 of the estrous cycle and from the stalk-disconnected and sham-disconnected ewes on d 12 of the cycle. The luteal tissue was weighed, a slice taken for morphometric analysis of cell numbers, sizes and types and luteal progesterone content was determined. The weight and progesterone content of corpora lutea collected from stalk-disconnected ewes were similar to those observed in control ewes on d 5 of the cycle but less (P less than .05) than those in control ewes on d 12 of the cycle. However, serum concentrations of progesterone were unaffected by stalk-disconnection. Luteinizing hormone replacement therapy increased both the weight and progesterone content of corpora lutea in stalk-disconnected ewes to values similar to those observed in control ewes on d 12. Treatment of stalk-disconnected ewes with alpha-ergocryptine reduced serum concentrations of prolactin by greater than 95% but was without effect on the parameters of luteal function measured. The number of small steroidogenic luteal cells in any of the stalk-disconnected ewes was not different from that observed in control ewes. However, treatment of stalk-disconnected ewes with LH was followed by an increase (P less than .05) in the diameter of small luteal cells. The number of large luteal cells was greater (P less than .05) in LH-treated, stalk-disconnected ewes than in intact control ewes on d 12 of the estrous cycle. The mean diameter of large luteal cells was not affected by treatment with LH.(ABSTRACT TRUNCATED AT 400 WORDS)