Ck. Murthy et Re. Peter, FUNCTIONAL EVIDENCE REGARDING RECEPTOR SUBTYPES MEDIATING THE ACTIONSOF NATIVE GONADOTROPIN-RELEASING HORMONES (GNRH) IN GOLDFISH, CARASSIUS-AURATUS, General and comparative endocrinology, 94(1), 1994, pp. 78-91
In goldfish, two native gonadotropin-releasing hormone (GnRH) peptides
, salmon GnRH (sGnRH) and chicken-II GnRH (cGnRH-II), stimulate gonado
tropin (GTH-II) and growth hormone (GH) secretion. In the present stud
y we tested whether sGnRH and cGnRH-II act through different or the sa
me population of GnRH receptors on GTH and GH cells, using various app
roaches. A GnRH antagonist [Ac-Delta(3)-Pro(1),4FD-Phe(2),D-Trp(3,6)]s
GnRH (analog C) equally inhibited GTH-II release by sGnRH and cGnRH-II
. Similarly, c-D(2)Nal(1),4Cl-D-Phe(2),D-(3)Pal(3),(6)]cGnRH-II (analo
g N) suppressed GTH-II stimulation by the two GnRH peptides equally. F
urther, in the continued presence of 100 nM sGnRH, a 100 nM pulse of c
GnRH-II failed to cause additional GTH-II release and vice versa. Prol
onged exposure of pituitary fragments to 100 nM sGnRH or cGnRH-II resu
lted in desensitization and reduced the GTH-II response to a subsequen
t pulse of either sGnRH or cGnRH-II equally. All these results indicat
e that both sGnRH and cGnRH-II act through the same population of GnRH
receptors on gonadotrophs. Similarly, the GH responses obtained with
(i) analog N treatment, (ii) pulse challenge to cGnRH-II during prolon
ged sGnRH treatment and vice versa, and (iii) desensitization studies
suggest that both sGnRH and cGnRH-II act through the same population o
f GnRH receptors on somatotrophs. However, the properties of GnRH rece
ptors on GTH-II and GH cells are different. Analog C stimulated GH rel
ease but not GTH-II release. In contrast, Delta(3)-Pro(1),4FD-Phe(2),D
-Trp(3),D-Arg(6)]mGnRH stimulated GTH-II release but weakly suppressed
GH release. These results indicate that sGnRH and cGnRH-II act on the
same population of receptors on GTH cells and on a functionally disti
nct population of receptors on GH cells. (C) 1994 Academic Press, Inc.