GONADOTROPIN-RELEASING-HORMONE AND NOREPINEPHRINE RELEASE FROM THE RABBIT MEDIOBASAL AND ANTERIOR HYPOTHALAMUS DURING THE MATING-INDUCED LUTEINIZING-HORMONE SURGE

The release of hypothalamic GnRH in association with the mating-induced LH surge was studied in the rabbit. Push-pull perfusion (PPP) of the mediobasal (MBH) or anterior (AH) regions of the hypothalamus was performed on conscious, unrestrained does for 3 h before and 5 h after exposure to a vasectomized buck. In experiment 1, GnRH concentrations were measured by RIA in 20-min fractions of MBH-PPP. An -100- fold increase in GnRH release was observed within 1 h of coitus (pre, 1.15 ± 0.29 pg/ml; peak, 106.67 ± 37.42 pg/ml; n = 6; P < 0.05). Concomitant surges of LH and PRL in the peripheral circulation were observed. In experiment 2, GnRH and norepinephrine (NE) were measured (the latter by radioenzymatic assay) in 10-min fractions of MBH-PPP. A 218% postcoital rise in NE levels (n = 5; P < 0.05) in MBH-PPP accompanied an ~50-fold peak rise in GnRH in the same samples (pre, 1.57 ± 0.23 pg/ml; peak, 76.52 ± 50.14 pg/ml; P < 0.05). MBH-NE, MBH-GnRH, LH, and PRL release began rising within 10 min of coitus. In experiment 3, GnRH was measured in 20 min fractions of AH-PPP. Coitus induced a marked rise in AHGnRH release (precoitus, 0.31 ± 0.03 pg/ml; peak, 2.25 ± 0.80 pg/ml; n = 4; P < 0.05) which differed from coitus-induced MBH-GnRH release both quantitatively (i.e. ~7-fold increase for AH vs. ~50-100-fold increase for MBH; 50-min lag time for AH vs. <20 min for MBH) and qualitatively (i.e. AH-GnRH release was discontinuous, while MBH-GnRH release rose sharply, plateaued, and then declined slowly over the 2-5 h following coitus). No changes in MBH-NE, MBH-GnRH, AHGnRH, LH, FSH, or PRL were observed in sham-mated does (Exp 1, n = 7; Exp 2, n = 3; Exp 3, n = 4). These data support the hypotheses that: 1) hypothalamic GnRH release is a component of reflexive ovulation in the rabbit; 2) increased hypothalamic noradrenergic tone is related to the surge-release of GnRH; and 3) AH-GnRH release is enhanced following coitus. © 1990 by The Endocrine Society.