Gonadotropin requirements for dominant follicle selection in GnRH agonist-treated cows.
A study was conducted to examine the effects of gonadotropins on ovarian follicular development and differentiation in GnRH agonist (GnRHa)-treated cattle. Holstein cows were allotted into two pre-treatment groups: controls (n = 5) and GnRHa-treated (n = 9). Ovaries were removed from control cows on day 5 following a synchronized estrus. Treatment with GnRHa resulted in follicular arrest at <5 mm. Following follicular arrest, GnRHa-treated cows received a constant infusion of FSH for 96 h (GnRHa/FSH), with a randomly selected subset receiving hourly pulses of LH in addition to FSH during the last 48 h of infusion (GnRHa/FSH + LH). At the end of infusion, ovaries were removed, follicles were counted and measured, and follicular fluid samples were collected from large follicles (>10 mm). Differences in expression of mRNA for LH receptor, FSH receptor, cytochrome P450 side-chain cleavage, 3beta-hydroxysteroid dehydrogenase, cytochrome P450 17alpha-hydroxylase (P450c17) and cytochrome P450 aromatase were determined in large follicles using in situ hybridization. The number of large follicles did not differ between GnRHa/FSH-treated and GnRHa/FSH + LH-treated cows (P = 0.64), but was greater than control animals (P < or = 0.004). Follicular fluid concentrations of estradiol-17beta and androstenedione were highest in GnRHa/FSH + LH-treated cows (P < or = 0.04), intermediate in control cows, and lowest in GnRHa/FSH-treated cows. Hybridization intensity of P450c17 was greater in GnRHa/FSH + LH-treated versus control or GnRHa/FSH-treated cows (P < or = 0.03). These results indicate that while FSH can support bovine follicular growth >10 mm, LH increases androgen production and expression of P450c17.
Hampton
J H
JH
Department of Animal Sciences,163 Animal Science Research Center, University of Missouri, Columbia, Missouri 65211, USA.
Bader
J F
JF
Lamberson
W R
WR
Smith
M F
MF
Youngquist
R S
RS
Garverick
H A
HA
D015096:3-Hydroxysteroid Dehydrogenases / Q000235:genetics; D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D001141:Aromatase / Q000235:genetics; D002417:Cattle; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000235:genetics; D004958:Estradiol / Q000378:metabolism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006062:Gonadotropins / Q000494:pharmacology*; D017403:In Situ Hybridization / Q000379:methods; D007986:Luteinizing Hormone / Q000494:pharmacology; D006080:Ovarian Follicle / Q000187:drug effects*; D012333:RNA, Messenger / Q000032:analysis; D011962:Receptors, FSH / Q000235:genetics; D011974:Receptors, LH / Q000235:genetics
D006062:Gonadotropins; D012333:RNA, Messenger; D011962:Receptors, FSH; D011974:Receptors, LH; D007987:Gonadotropin-Releasing Hormone; D000735:Androstenedione; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D015096:3-Hydroxysteroid Dehydrogenases; D001141:Aromatase; D002786:Cholesterol Side-Chain Cleavage Enzyme