Pulsatile GnRH administration stimulates the number of pituitary GnRH receptors in seasonally anoestrous ewes.
Twenty seasonally anoestrous ewes were pretreated with progesterone for 4 days and divided into four equal groups. Ewes in Group 1 received no GnRH treatment and were slaughtered immediately after progesterone removal. Ewes in Groups 2, 3 and 4 received i.v. injections of 250 ng GnRH every 2 h for 36 h starting at the time of progesterone removal. Ewes in Group 2 were slaughtered immediately after the 36 h GnRH pulsing, while ewes in Groups 3 and 4 were given a bolus injection of 125 micrograms GnRH at this time and were slaughtered 2 and 10 h after the bolus injection, respectively. Blood samples were collected every 30 min from ewes in Group 4 only, from 4 h before the start of GnRH treatment until 10 h after the bolus injection. Pulsing with GnRH resulted in episodic release of LH, and the bolus injection of GnRH was immediately followed by a preovulatory type LH surge in those ewes in which an endogenous surge had no already begun. The pituitary GnRH receptor numbers were significantly higher for the ewes in Group 2 than for any of the other treatment groups, while there was no significant difference in the receptor numbers between Groups 1, 3 and 4. The results suggest an up-regulation of GnRH receptors resulting from pulsatile GnRH therapy.
D000780:Anestrus; D000818:Animals; D004971:Estrus; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D011979:Receptors, Pituitary Hormone / Q000187:drug effects / Q000378:metabolism*; D012621:Seasons; D012756:Sheep
D010906:Pituitary Hormone-Releasing Hormones; D011979:Receptors, Pituitary Hormone; D007986:Luteinizing Hormone