Luteinizing hormone secretion in hypophysial stalk-transected pigs given progesterone and pulsatile gonadotropin-releasing hormone.
This study was conducted to determine whether progesterone inhibits luteinizing hormone (LH) secretion in female pigs by a direct action on the pituitary gland. Eight ovariectomized, hypophysial stalk-transected gilts were given 1-microgram pulses of gonadotropin-releasing hormone iv every 45 min from Day 0 to 12. On Days 5-12, each of four gilts received either progesterone or oil vehicle im at 12-hr intervals. Serum progesterone concentrations in steroid-treated gilts reached 70 +/- 6.8 ng/ml (mean +/- SE) by Day 8 and remained elevated thereafter, whereas serum progesterone concentrations in oil-treated controls were less than 1 ng/ml for the entire study. Daily serum LH concentrations were not different between gilts treated with progesterone or oil. The 1-microgram pulses of gonadotropin-releasing hormone reliably evoked pulses of LH in both treatment groups. The LH pulse frequency and amplitude, assessed from samples collected every 15 min for 6 hr on Day 12, were similar for progesterone- and oil-treated gilts. These results provide evidence that progesterone does not act at the pituitary gland to alter LH secretion in pigs.
Estienne
M J
MJ
Animal and Dairy Science Department, University of Georgia, Athens 30602.
Kesner
J S
JS
Kraeling
R R
RR
Rampacek
G B
GB
Barb
C R
CR
D000818:Animals; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000097:blood / Q000494:pharmacology*; D007016:Hypophysectomy; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010052:Ovariectomy; D011374:Progesterone / Q000494:pharmacology*; D012016:Reference Values; D013552:Swine / Q000502:physiology*
D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D007986:Luteinizing Hormone