ROLE OF GONADOTROPIN-RELEASING-HORMONE BASE-LINE CONCENTRATIONS IN THE CONTROL OF PITUITARY GONADOTROPIN AND OVARIAN-STEROID SECRETION IN THE PSEUDOPREGNANT RAT
Ga. Schuiling et al., ROLE OF GONADOTROPIN-RELEASING-HORMONE BASE-LINE CONCENTRATIONS IN THE CONTROL OF PITUITARY GONADOTROPIN AND OVARIAN-STEROID SECRETION IN THE PSEUDOPREGNANT RAT, Human reproduction, 11(1), 1996, pp. 13-18
To study the effect of moderately elevated gonadotrophin releasing hor
mone (GnRH) baseline concentrations during the luteal and the follicul
ar phase, pseudopregnant rats were infused s.c. with GnRH at several d
oses for 5 days, These rats were also treated with oestradiol or sham-
treated during the last 3 days of GnRH treatment, GnRH infusions start
ed on day 7 or day 3 of the luteal phase of the ovulatory cycle; in th
e rat, the luteal phase or pseudopregnancy lasts about 10 days, Lutein
izing hormone (LH) and follicle stimulating hormone (FSH) responses we
re induced by i.v. injection of GnRH on day 12 (after expected luteoly
sis) or on day 8 (before expected luteolysis). In normal rats the LH a
nd FSH responses induced by GnRH on day 12 were higher than on day 8 (
similar to 160 and similar to 50% respectively), In GnRH-infused rats
the LH and FSH responses were not increased, In these rats the luteal
phase was extended (the plasma progesterone concentrations remained hi
gh) and the onset of the follicular phase was postponed (plasma oestro
gen concentrations did not increase), Oestradiol increased the day 12
LH and FSH responses; this effect of oestradiol was suppressed by GnRH
infusion, On day 8, exogenous oestradiol also increased the LH and FS
H responses, but again the effect of oestradiol was suppressed when th
e animals were concomitantly infused with GnRH. These data may suggest
that in the rat, GnRH baseline concentrations participate in the neur
oendocrine system controlling gonadotrophin secretion and hence the ov
ulatory cycle.