Delay of estradiol-induced surge secretion of LH in gilts by intracerebroventricular injection of morphine.
In Experiment 1, ovariectomized (OVX) gilts, 143 d old and 58.5 +/- 1.8 kg BW, received 10 micrograms estradiol benzoate (EB)/kg BW i.m. and either 500 micrograms of the endogenous opioid peptide (EOP) agonist, morphine (MOR), in saline (SAL; n = 5), or SAL (n = 4) intracerebro-ventricularly at 40 and 48 hr after EB. With the exception of one MOR-treated gilt, which was deleted from Experiment 1, LH secretion was suppressed for at least 50 hr in all gilts. Timing of the LH surge was similar among gilts. However, total LH secreted was greater (P < 0.05) after SAL than MOR. The experiment was repeated at 179 d of age and 78.6 +/- 1.2 kg BW, except that treatments were reversed among gilts. Emergence of the LH surge was delayed (P < 0.005) by 10.8 hr and time to maximum LH concentration (P < 0.05) by 6.8 hr after MOR than after SAL. Magnitude and total LH secreted were not different among gilts. In Experiment 2, gilts which had displayed estrous cycles of 18-22 d were OVX and treated as in Experiment 1, except MOR (n = 3) or SAL (n = 4) were injected 10 hr later than in Experiment 1, i.e., at 50 and 58 hr after EB. Secretion of LH was suppressed for at least 60 hr in both groups. Time to emergence of the LH surge was delayed by 27 hr (P < 0.05) after MOR compared to after SAL. However, other parameters of the surge were not different among gilts. Thus, EOP modulate LH surge secretion negatively in the pig.
Asanovich
K M
KM
Animal and Dairy Science Department, University of Georgia, Athens 30602, USA.
Johnson
B
B
Chang
W J
WJ
Barb
C R
CR
Rampacek
G B
GB
Kraeling
R R
RR
D000818:Animals; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D007276:Injections, Intraventricular; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism*; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D010052:Ovariectomy; D013552:Swine / Q000502:physiology*
D009294:Narcotics; D004958:Estradiol; D009020:Morphine; D007986:Luteinizing Hormone