Changes in the Gonadotropin- Releasing Hormone Pulse Generator Activity during the Estrous Cycle in the Goat

Self Cite

Abstract. Male pheromones in ruminant species such as sheep and goats are known to reactivate quiescent ovarian function in seasonally anestrous females. We have previously shown that only a few minutes exposure to the male pheromone can accelerate the GnRH pulse generator activity immediately in the female goat. In this study the effect of 4 h continuous exposure to the male pheromone on the GnRH pulse generator activity was examined by recording the specific multiple unit acitivity (MUA) from the medial basal hypothalamus. Pooled buck hair was used as the source of male pheromone. Six ovariectomized estradiol-primed does were fitted with a nose-mask for 8 h, and during the latter 4 h period 2.0 g of pooled male hair was set in the chamber at the rostral end of the mask. As compared with the period when only an empty mask was put on, the exposure to the male hair resulted in a shortening (p<0.05) of the interval between the MUA volleys, namely the electrophysiological manifestation of the pulsatile GnRH neurosecretion. This stimulatory effect was observed throughout the time when animals were exposed to the male pheromone. This result demonstrates that the hypothalamic GnRH pulse generator of the recipient female is accelerated as long as the exposure to the male pheromone continues.

Section: Discussionsupporting

confidence: 73%

Stimulation of the GnRH Pulse Generator Activity by Continuous Exposure to the Male Pheromones in the Female Goat.

Ichimaru

Takeuchi

Mori

1999

Self Cite

“…These findings support the general concept that the P concentration depends on the luteal activity. Regarding the mechanism regulating E2 concentration, some reports have shown that a large amount of P secreted from CL and a small amount of E2 secreted from the follicles coexisting with CL jointly exert negative feedback on the hypothalamus and pituitary gland in the luteal phase, and suppress the pulsatile secretion of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) [23,24]. However, since the negative feedback action is not adequate to supress the GnRH and LH secretion in the bovine recipients with poor luteinization and the low blood P concentration, LH pulse frequency may be inadequately suppressed.…”

Section: Discussionmentioning

confidence: 99%

The Relationship of Blood Progesterone and Estrogen Concentrations on the Day Before and the Day of Frozen-Thawed Embryo Transfer to Pregnancy Rate in Japanese Black Beef Cattle

Nishigai

Kamomae

Tanaka

et al. 2000

Self Cite

Abstract. The relationship of blood progesterone (P) and estradiol-17β (E2) concentrations to the pregnancy rates in Japanese Black beef cattle recipients was investigated by determining blood P and E2 concentrations on the day before (day 6; day 0=onset of estrus) and the day of embryo transfer (day 7). Embryos were thawed by the stepwise method and transferred on day 7. The pregnancy rate showed a tendency toward increase with increasing P concentrations on both days 6 and 7 of embryo transfer. There was no significant correlation between the blood E2 concentration on day 6 and the pregnancy rate, wthereas pregnancy rate tended to rise when the blood E2 concentration on day 7 was low. The relationships of the blood E2/P ratio (× 10 3 ) on days 6 and 7 to the pregnancy rate were investigated. When the E2/P ratio was 1.0, the pregnancy rate tended to decrease. The bovine recipients, which showed poorly development CL, high blood E2/P ratio and coexistence of follicle 1.0 in diameter with CL, showed a tendency toward decrease in the pregnancy rate. From these observations, it is supposed to be important to select bovine recipient with the high bood P concentration and with the low blood E2 concentration on days 6 and 7 as bovine recipients for improvement of the pregnancy rate in bovine frozen-thawed embryo transfer.

“…Similar to observations made in cattle [9], the peak level of plasma estradiol during the first latent wave was smaller than that of the third wave immediately before ovulation. The frequency of pulsatile GnRH release from the hypothalamus in Shiba-goats is reduced by progesterone in combination with estrogen [10]. Significant increase in estradiol secretion does not occur from follicular development at the first latent wave because the frequency of gonadotropin pulses may not be sufficient due to high progesterone levels.…”

Section: Discussionmentioning

confidence: 99%

Induction of Short Ovulatory Cycle in Shiba-Goats by Repeated Treatments with Prostaglandin F2.ALPHA..

Sinozaki

Imakawa

et al. 2001

Abstract. Follicular growth of ruminant species occurs more than once during an estrous cycle either resulting in ovulation (ovulatory follicular wave) or not resulting in ovulation (latent follicular wave). Using Shiba-goats, we examined if ovulation could be induced from every latent follicular wave and if the resulting ova were fertile. Ovarian follicular development was monitored daily by transrectal ultrasonographic examination in 20 female goats for 2 consecutive estrous cycles. After the second spontaneous ovulation (day 0 = ovulation), all animals were each treated with a luteolytic dose of prostaglandin F2α (PGF2α) on days 3 and 4,which resulted in ovulation from the first latent wave. Fertile males goats (n=2) were immediately introduced to the first group of animals (n=5), resulting in 4 pregnancies. For the second group of goats (n=9), 4 consecutive short estrous cycles were induced by the PGF2α treatment at a mean interval of 6.5 ± 1.2 days with a range of 4-9 days. Five of 9 goats were allowed to mate following 4 consecutive short ovulatory cycles; normal behavioral estrus was observed at each estrus, and four of five animals became pregnant. The third group of goats (n=6), in addition to PGF2α treatment, received exogenous progesterone supplement which allowed latent follicular development to occur, but prevented ovulation until the effect of progesterone supplement subsided. These results suggest that female Shiba-goats possess physiological mechanisms for the final steps of follicular maturation and subsequent ovulation at short intervals when progesterone production from the newly developed corpus luteum is terminated.