Patterns of Ovulation-Inducing LH Release Following Coitus, Electrical Stimulation and Exogenous LH-RH in the Rabbit¹

The effect of LH-RH administration on LH release in the female rabbit

“…Administration of LH-RH in the female rabbit readily stimulated LH release as reported previously by Kanematsu et al (1974) and Dufy-Barbe et al (1975). The amount of this gonadotrophin released during infusion resulted in peak concentrations similar to that caused by mating (Carlson et al, 1977) and was sufficient to induce ovulation.…”

“…Although recent studies in this species indicate that LH-RH administration can stimulate an ovulatory release of LH (Amoss, Blackwell & Guillemin, 1972;Kanematsu, Scaramuzzi, Hilliard & Sawyer, 1974;Dufy-Barbe, Franchimont, Dufy & Vincent, 1975), the effects that ovarian hormones have upon this response are unclear. The ability of LH-RH administration to cause LH release in the female rabbit during various reproductive conditions was therefore examined.…”

Immobilization Does not Inhibit the Post-Coital Ovulatory Surge of Luteinizing Hormone in the Rabbit

“…Moreover, estrogens are required for the initiation of the LH surge in the rat, whereas vaginal stimulation induces LH discharge in the rabbit [for review see Sawyer, 1975]. It is possible that immobilization can inhibit the LH surge, noted 8 h after a single dose of EB in rabbits [Kanematsu et al, 1974], However, this estrogeninduced LH elevation is far below that initiated by coitus. Also, it has been shown that immobilization can cause elevated proestrous LH levels to de crease in the rat [Euker et al, 1973].…”

“…LH-RH or coitus in the rabbit can initiate LH release in sufficient quan tities to cause ovulation [Kanematsu et al, 1974]. If it is postulated that immobilization inhibits castration-induced LH-RH release [Blake, 1975], then the same type of stress should inhibit copulation-induced LH release.…”

Effects of in-vivo administration of GnRH on the release of gonadotrophins in the female rabbit

“…The LH response of isolated and superfused pituitaries to GnRH was also greatest on Days 15 and 20 (Naish et al, 1986 (1986) to show a seasonal variation in the LH response to GnRH in the brown hare but much lower than the 0-5 pg/100 g dose used by Debeljuk et al (1972) to show a response in the rat. Kanematsu et al (1974) have previously demonstrated that 250 ng/kg was the minimal ovulating dose of GnRH required to induce an LH peak in rabbits. In the mature domestic rabbit there is a definite seasonal variation in the activity of the GnRH pulse generator (Ramirez et al, 1986) and progesterone can influence its activity if given in a pulsatile manner (Lin & Ramirez, 1988 Armstrong, 1981) or GnRH- (YoungLai, 1985) induced LH surges suggest that these high levels are probably not GnRH-mediated unless the high values are due to infrequent, randomly occurring synchronization of low-frequency GnRH pulses, as postulated by Ojeda & Urbanski (1988) for the rat.…”