Jj. Bonavera et al., EVIDENCE IN SUPPORT OF NITRIC-OXIDE (NO) INVOLVEMENT IN THE CYCLIC RELEASE OF PROLACTIN AND LH SURGES, Brain research, 660(1), 1994, pp. 175-179
Studies were undertaken to determine whether nitric oxide (NO) is invo
lved in induction of the prolactin surge on proestrus and in that indu
ced by ovarian steroids in ovariectomized (ovx) rats, by using inhibit
ors of NO synthase, the enzyme that generates NO. Two week-ovariectomi
zed rats were treated either with estradiol benzoate (EB, 30 mu g/rat,
s.c.) alone, or with EB and 2 days later with progesterone (P, 2 mg/r
at, s.c.) to evoke a prolactin surge in the afternoon. Injections of t
he NO synthase inhibitor NW-nitro-L-arginine methyl ester (40 mg/kg, s
.c.) at 10.00, 12.00, and 14.00 h completely suppressed the steroid-in
duced prolactin surge in the afternoon. Similarly, another NO synthase
inhibitor, N-W-nitro-L-arginine (100 mg/kg, s.c.), injected at 1000,
1200, and 1400 h on proestrus suppressed prolactin and luteinizing hor
mone (LH) surges, but failed to alter the daily increase of corticoste
rone. These studies confirm our earlier report and show that NO is inv
olved in the complex processes that initiate the afternoon prolactin a
nd LH surges of proestrus.