Response of seasonally anoestrous ewes to six-hour periods of GnRH infusion administered on six consecutive days

McLeod, B. J.; Haresign, W.

doi:10.1016/0093-691x(84)90023-2

Cited by 1 publication

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“…First, it may be that a small but constant background of GnRH is secreted during the follicular phase of the oestrous cycle and that this, in addition to pulsatile GnRH secretion, primes the pituitary gland for the ensuing positive-feedback event. Secondly, these data may explain the conundrum whereby anoestrous ewes may be induced to ovulate by a continuous low-dose infusion of GnRH (Domanski, Przekop, Skubiszewski et al 1977;McLeod, Haresign & Lamming, 1983;McLeod & Haresign, 1984); by superimposing a con¬ stant background of GnRH upon the endogenous pulsatile secretion, it may be possible to initiate the events that culminate in a preovulatory LH surge. The effects on the oestrogen-induced LH surge of a basal mode of GnRH input followed by pulses of GnRH has important implications, and should be the subject of further study.…”

Section: Discussionmentioning

confidence: 98%

Effects of modifying gonadotrophin-releasing hormone input before and after the oestrogen-induced LH surge in ovariectomized ewes with hypothalamo-pituitary disconnection

Phillips

Cummins²,

Clarke³

1990

Journal of Endocrinology

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The patterns of gonadotrophin-releasing hormone (GnRH) input to the pituitary gland that affect the expression of a positive-feedback event by oestrogen on LH secretion were investigated in ovariectomized ewes with hypothalamo-pituitary disconnection (HPD). In experiment 1, ovariectomized HPD ewes were given hourly i.v. pulses of 250 ng GnRH and an i.m. injection of 50 micrograms oestradiol benzoate (OB). The ewes were given a bolus pulse of 2.25 micrograms GnRH 16 h after injection of OB, followed by half-hourly pulses of 250 ng GnRH for 14 h (treatment A). The LH surge response was significantly (P less than 0.05) greater in these ewes compared with that in ewes given a continuous infusion of GnRH (250 ng/h) after the OB injection, followed by a continuous infusion of 500 ng GnRH/h after the bolus pulse of GnRH (treatment B). When no GnRH was administered after the OB injection, except for the bolus pulse of GnRH (treatment C), the surge response was significantly (P less than 0.05) reduced compared with that in treatment A, and was reduced compared with treatment B. These data suggest that GnRH pulses are important in the generation of the OB-induced LH surge, but that a baseline secretory component can prime the pituitary to some extent. In experiment 2, a doubling of the continuous infusion dose of GnRH used in treatment B to 500 ng/h before the bolus pulse of GnRH and to 1 micrograms/h afterwards (treatment D) gave a similar response compared with treatment A, suggesting that if the baseline input of GnRH is of sufficient magnitude, it can overcome the lack of pulsatile input. In experiment 3, halving the GnRH pulse amplitude used in treatment A from 250 to 125 ng (treatment E) did not reduce the LH surge response, implying that when the GnRH input is in a pulsatile mode, the amplitude of GnRH pulses is less important than the pulsatile nature per se. In experiment 4, removal of GnRH input after the bolus pulse of GnRH (treatment F) significantly (P less than 0.05) reduced the surge response compared with when pulses were maintained (treatment A), indicating that GnRH input is still required once the LH surge has been initiated. Collectively, these experiments show that several forms of GnRH delivery, both pulsatile and baseline, can result in the full expression of a positive-feedback response in ovariectomized ewes treated with oestrogen.

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Section: Discussionmentioning

confidence: 98%