The effects of estradiol (E(2)) on growth hormone (GH) production was
investigated in gonad-intact female goldfish. It was first necessary t
o generate a specific antibody for use in immunocytochemistry, Western
, and dot-blot analyses of GH production. To accomplish this, grass ca
rp GH (gcGH) cDNA was cloned by the reverse transcription polymerase c
hain reaction (RT-PCR) and expressed in Echerichia coli and a specific
polyclonal antibody to recombinant gcGH was generated in the rabbit.
In Western blot, the anti-gcGH antibody specifically immunoreacted wit
h recombinant gcGH, purified natural common carp GH, and with a single
21.5-kDa GH form from pituitary extracts of grass carp, common carp,
goldfish, and zebrafish but not salmon, trout, or tilapia. Intraperito
neal injection of the recombinant gcGH enhanced the growth rates of ju
venile common carp demonstrating biological activity of this GH prepar
ation. Electron microscopic studies showed that the anti-gcGH-I antibo
dy specifically reacted with GH localized in the secretory granules of
the goldfish somatotroph. Using anti-gcGH-I in a dot-blot assay, it w
as found that in vivo implantation of solid silastic pellets containin
g E(2) (100 mu g/g body weight for 5 days) increased pituitary GH cont
ent by 150% in female goldfish. In a second, independent study employi
ng a previously characterized anticommon carp GH antibody for radioimm
unoassay, it was found that E(2) increased pituitary GH content by 170
% and serum GH levels by approximately 350%. The E(2)-induced hypersec
retion of GH and increase in pituitary GH levels was not associated wi
th changes in steady-state pituitary GH mRNA levels, suggesting that t
his sex steroid may enhance GH synthesis at the posttranscriptional or
translational level. Previous observations indicate that GH can stimu
late ovarian E(2) production. The present results show that E(2) can i
n turn stimulate GH production, indicating the existence of a novel pi
tuitary GH-ovarian feedback system in goldfish. (C) 1997 Academic Pres
s.