Evidence that lamprey GnRH-III does not release FSH selectively in cattle.
Experiments were performed to test the hypothesis that lamprey GnRH-III (lGnRH-III) selectively releases FSH. Primary cultures of bovine adenohypophyseal cells were treated with mammalian GnRH (mGnRH) and lGnRH-III (10(-9), 10(-8), 10(-7) and 10(-6) M) or control media in Experiment 1. All doses of mGnRH and the two highest doses of lGnRH-III stimulated (P < 0.001) a non-selective release of LH and FSH. In Experiments 2-4, Latin Square designs were utilized in vivo to examine whether physiological and hormonal milieu regulate putative selective effects of lGnRH-III. In Experiments 2 and 3, ovariectomized cows with basal levels of estradiol only (Experiment 2) or in combination with luteal phase levels of progester-one (Experiment 3) were injected with mGnRH and lGnRH-III (0.055, 0.11, 0.165 and 1.1 microg/kg body weight (BW) and saline. All doses of mGnRH released (P < 0.001) LH and FSH, but only the highest dose of lGnRH-III stimulated (P < 0.001) a non-selective release of both LH and FSH (Experiment 3). For Experiments 4A and 4B, intact, mid-luteal phase cows were injected with mGnRH and lGnRH-III (1.1 microg/kg BW; Experiment 4A), lGnRH-III (1.1 and 4.4 microg/kg BW; Experiment 4B) and saline. As before, mGnRH released (P < 0.001) both LH and FSH at all doses. In contrast, lGnRH-III at the highest dose released (P < 0.001) LH but not FSH. These findings suggest that lGnRH-III may act as a weak competitor for the mGnRH receptor and do not support the hypothesis that it selectively releases FSH in cattle.
Amstalden
M
M
Animal Reproduction Laboratory, Texas A&M University Agricultural Research Station, Beeville, Texas 78102, USA.
Zieba
D A
DA
Garcia
M R
MR
Stanko
R L
RL
Welsh
T H
TH
Hansel
W H
WH
Williams
G L
GL
D000818:Animals; D002417:Cattle / Q000502:physiology*; D002478:Cells, Cultured; D004958:Estradiol / Q000494:pharmacology; D004971:Estrus / Q000502:physiology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology*; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D013268:Stimulation, Chemical
D009842:Oligopeptides; C448022:gonadotropin-releasing hormone-III; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D005640:Follicle Stimulating Hormone; D011761:Pyrrolidonecarboxylic Acid