A. Lo et Jp. Chang, IN-VITRO APPLICATION OF TESTOSTERONE POTENTIATES GONADOTROPIN-RELEASING HORMONE-STIMULATED GONADOTROPIN-II SECRETION FROM CULTURED GOLDFISHPITUITARY-CELLS, General and comparative endocrinology (Print), 111(3), 1998, pp. 334-346
The in vitro effects of overnight treatment with testosterone (T) on g
onadotropin (GTH)-II secretion from primary cultures of dispersed fema
le goldfish pituitary cells were examined. T (100 nM) did not affect b
asal GTH-II release, but increased GTH-II responses to initial applica
tions of 0.5-h pulses of sGnRH or cGnRH-II in cells from females at se
xually regressed, recrudescing, or mature (prespawning) stages. Pretre
atment with 10 nM T was also effective, except in experiments with cel
ls from sexually regressed females. Analysis of GTH-II response profil
es to the first GnRH pulse revealed that T increased the size of the i
nitial (first 15 min) and sustained (rest of response) release phases,
and the duration of the total response to both GnRHs. These results i
ndicate that direct positive influence of T on GnRH-stimulated GTH-II
release is demonstrable in cells from female goldfish at all ovarian m
aturational stages; in addition, T affects both the initial and the su
stained response phases. Howe-c er, compared to the initial GnRH chall
enge, responses to a second 0.5-h GnRH pulse were decreased in T-treat
ed but not in control cells, suggesting that T also enhanced desensiti
zation. Ovarian maturational conditions modulated the effects of T on
the GTH-II response kinetics. In cells prepared from sexually regresse
d females, T treatment changed the ''monophasic'' (initial phase only)
GTH-II response to sGnRH to a ''biphasic'' one characteristic of cell
s prepared from fish at later stages of gonadal recrudescence. Advanci
ng gonadal maturity increased the magnitude of both initial and sustai
ned phases of the T-enhanced GTH-IZ response to sGnRH, but only elevat
ed the initial phase of T-potentiated cGnRH-II-induced release. Direct
actions of T on pituitary cells may play a role in ovarian steroid fe
edback regulation of GTH-II secretion during the seasonal reproductive
cycle in goldfish. (C) 1998 Academic Press.