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

The influence of sodium pentobarbitone (SPB) on the gonadotropin patterns at estrus and anestrus after infusion of estradiol-17beta (E2) were studied. Animals were treated as follows: 1) injected with SPB 14 hours before or 14 hours after estrus; 2) treated with E2 for 6 hours during anestrus and blood samples taken in animals anesthetized with SPB or untreated; and 3) animals infused with E2 alone or in combination with androstenedione (36 mcg/hour) for 6 hours and either left untreated or anesthetized with SPB. During estrus the administration of SPB inhibited the release of luteinizing hormone (LH) when the combined LH and follicle stimulating hormone (FSH) surges were expected and prolonged the release of FSH. The treated estrus showed normal development of corpora lutea. However the subsequent estrus had corpora lutea with abnormally short lifetimes. Administration of SPB during the 2nd surge of FSH was without effect. After administration of E2 during anestrus SPB blocked the release of both LH and FSH. Administratio of SPB at the expected time of the 2nd surge of FSH delayed the increase in the level of FSH. When combined E2/androstenedione treatment was used LH was completely blocked and FSH only partially inhibited.