title: Pulsatile gonadotropin secretion determined by frequent sampling from the intercavernous sinus of the mare: possible modulatory role of progesterone during luteolysis.
abstract: Twelve horse mares were used in a repeated-measures design consisting of 3 replicates of 4 mares each. On Day 6 following ovulation, luteolysis was initiated with an i.m. injection of prostaglandin F2 alpha (PGF2 alpha; Lutalyse, 10 mg). Either 12 (-12) or 36 (-36) h before PGF2 alpha (PRE), blood samples were collected simultaneously from the intercavernous sinus (ICS) and jugular (JUG) vein at 10-min intervals for an 8-h period. Pituitary capacity to exogenous GnRH (2 micrograms/kg BW, i.v.) was evaluated at the alternate time point within this period. Frequent sampling and GnRH challenge were repeated 36 (+36) or 60 (+60) h after PGF2 alpha (POST). Progesterone reached a nadir 48 h after PGF2 alpha, while the first significant elevation in estradiol (p < 0.05) was not detected until 156 h. PRE LH and FSH pulse frequencies in ICS samples were 0.6 +/- 0.3 and 1.8 +/- 0.8 pulses/8 h, respectively. Three high-amplitude, concurrent ICS pulses of LH and FSH were observed during this period. These were associated with elevated gonadotropin levels in the corresponding JUG samples. In contrast, low-amplitude ICS pulses at this time were predominately releases of FSH alone that were not detectable in the JUG. Following luteolysis, POST gonadotropin pulse frequencies in the ICS increased (p < 0.001) to 7.4 +/- 0.4 and 6.8 +/- 0.5 pulses/8 h for LH and FSH, respectively. Concurrent LH and FSH releases of relatively low amplitude characterized 87.7% of the POST ICS pulses, none of which were measurable in corresponding JUG samples.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001800:Blood Specimen Collection / Q000379:methods; D002426:Cavernous Sinus; D003338:Corpus Luteum / Q000187:drug effects / Q000502:physiology*; D015237:Dinoprost / Q000494:pharmacology; D004958:Estradiol / Q000097:blood; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D006736:Horses / Q000502:physiology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D003341:Luteolysis; D010507:Periodicity; D011374:Progesterone / Q000502:physiology*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D015237:Dinoprost