A. Gobbetti et M. Zerani, NITRIC-OXIDE MEDIATES GONADOTROPIN-RELEASING-HORMONE EFFECTS ON FROG PITUITARY, Journal of neuroendocrinology, 10(6), 1998, pp. 407-416
We studied the possible role of nitric oxide (NO) in GnRH-induced gona
dotropin secretion in the female water frog, Rana esculenta. During pr
e-reproduction, pre-ovulation, ovulation, post-ovulation, refractory,
recovery and hibernation, pituitaries were incubated with medium-alone
, GnRH, NO donor (NOd), NO synthase inhibitor (NOSI), cyclic GMP analo
gue (cGMPa), soluble guanylate cyclase inhibitor (sGCi), GnRH plus NOS
I, GnRH plus sGCi, and NOd plus sGCi. Because antisera raised against
gonadotropins are not available for this species, we measured these ho
rmones indirectly through their effects on ovarian progesterone secret
ion. The ovaries were superfused with the pituitaries pre-incubated as
reported above, In addition, NOS activity and cGMP levels were determ
ined in the pre-incubated pituitaries. Those pre-incubated with medium
-alone and with GnRH increased progesterone secretion during pre-repro
duction, pre-ovulation, ovulation and recovery; the increase induced b
y GnRH was higher than that induced by medium-alone during pre-reprodu
ction, pre-ovulation and recovery. NOd and cGMPa increased progesteron
e in all considered reproductive phases except ovulation; the increase
induced by NOd and cGMP was higher than that induced by medium-alone
during pre-reproduction, pre-ovulation and recovery, NOS activity was
highest during ovulation and lowest during post-ovulation, refractory
and hibernation, GnRH increased NOS activity during pre-reproduction,
pre-ovulation and recovery. Cyclic GMP levels were highest during ovul
ation and lowest during post-ovulation, refractory and hibernation. Gn
RH increased cGMP levels during pre-reproduction, pre-ovulation and re
covery, NOd during all considered reproductive phases. These results s
uggest that NO mediates basal and GnRH-induced gonadotropin secretion
in female Rana esculenta.