Alterations in plasma gonadotrophin patterns caused by sodium pentobarbitone in ewes at oestrus and in anoestrous ewes after infusion of oestradiol.

A radioimmunoassay system for the measurement of ovine follicle-stimulating hormone (FSH) was established. After the onset of normal oestrus, there were simultaneous surges of luteinizing hormone (LH) and FSH, and 24 h later, a surge of FSH alone. Administration of sodium pentobarbitone when the dual surge of LH and FSH was expected inhibited the release of LH, but prolonged that of FSH. Development of corpora lutea that took place immediately was normal in ewes treated with sodium pentobarbitone, but after the subsequent oestrus, the life-time of corpora lutea was abnormally short. When sodium pentobarbitone was administered at the time when the second surge of FSH was expected, no effect was observed on the level of LH or FSH. Subsequent development of corpora lutea was similar to that in the non-treated group. Administration of sodium pentobarbitone at the expected time of the dual surges of LH and FSH after infusion of oestradiol to anoestrous ewes blocked the release of both LH and FSH. Administration of sodium pentobarbitone at the expected time of the second surge of FSH after infusion of oestradiol delayed the increase in the level of FSH. In a pilot experiment after combined infusion of androstenedione and oestradiol, sodium pentobarbitone did not completely inhibit the release of FSH, but the release of LH was totally prevented.