Central administration of antiserum to vasoactive intestinal peptide delays and reduces luteinizing hormone and prolactin surges in ovariectomized, estrogen-treated rats
Em. Van Der Beek et al., Central administration of antiserum to vasoactive intestinal peptide delays and reduces luteinizing hormone and prolactin surges in ovariectomized, estrogen-treated rats, NEUROENDOCR, 69(4), 1999, pp. 227-237
The present study investigated the role of hypothalamic VIP in the regulati
on of the LH and PRL surge using immunoneutralization of endogenous VIP in
mature ovariectomized (OVX), estradiol benzoate (EB)-treated female Wistar
rats. We compared the effect of intracerebroventricular (i.c.v.) injections
of a VIP antiserum (VIP-Ab) with that of saline (Ctr) on LH and PRL profil
es in two separate groups of rats following two subcutaneous EB injections
on days 8 and 9 after OVX. VIP-Ab or Ctr injections were given during the s
econd half of the dark period, i.e. at 22:00 h (day 9), and, in addition, t
he following morning, i.e. at 08:00 h (day 10), just before the expected on
set of the LH surge. Hourly blood samples were collected between 09:00 and
18:00 h on day 10. In addition, we studied the reproducibility of EB-induce
d LH and PRL surges and compared the effect of Ctr and VIP-Ab treatment on
sequential surges in individual OVX females, i.e. 10 and 23 days after OVX,
using each animal as its own control. Although we observeda large variatio
n in the height and timing of LH and PRL peak levels between EB-treated fem
ales, the characteristics of successive surges of individual rats were high
ly reproducible. This reproducibility suggests that differences in function
ing of the suprachiasmatic nucleus as well as in the response of the hypoth
alamus to steroid feedback largely explain the normal variation in hormone
responses between rats. The VIP-Ab treatment resulted in a significant dela
y in the time course and a strong reduction of the magnitude of the afterno
on LH and PRL surge. When analyzed within individual females, the effect of
VIP-Ab treatment was even more pronounced due to a reduction in variabilit
y when each animal was used as its own control. These results suggest that
hypothalamic VIP is an important regulator of both the timing and the magni
tude of the EB-induced LH and PRL surge in the OVX rat, and suggest that it
s ro le may be stimulatory in this respect.