M. Seidelin et al., Effects of insulin-like growth factor-I and cortisol on Na+,K+-ATPase expression in osmoregulatory tissues of brown trout (Salmo trutta), GEN C ENDOC, 113(3), 1999, pp. 331-342
The effect of recombinant bovine IGF-I (rbIGF-I) on hypo-osmoregulatory abi
lity and the effect of rbIGF-I and cortisol (F) alone and in combination on
Na+,K+-ATPase expression in fresh water (FW) acclimated brown trout (Salmo
trutta) were examined in two experiments. In Experiment 1, fish were given
three injections of saline or 0.01 or 0.1 mu g rbIGF-I/g, respectively, an
d subjected to a 24-h 25 ppt seawater (SW) challenge test 24 h after the la
st injection. Fish treated with 0.01 and 0.1 mu g rbIGF-I/g had better hypo
-osmoregulatory ability than control fish as judged by their higher level o
f muscle water content and lower plasma osmolality after 24 h exposure to 2
5 ppt SW. Compared with control fish, gill Na+,K+-ATPase activity was uncha
nged 24 h after the first injection at either dose but significantly stimul
ated after three injections of either dose of rbIGF-I. In Experiment 2, fis
h were given three injections of saline, 0.1 mu g rbIGF-I/g, 4 mu g F/g, or
0.1 mu g rbIGF-I + 4 mu g F/g and sampled in FW 24 h after the last inject
ion. IGF-I and F had additive stimulatory effects on Na+,K+-ATPase activity
and alpha-subunit Na+,K+-ATPase mRNA levels in the gill. Injections of IGF
-I and F alone and in combination increased Na+,K+-ATPase-immunoreactive (N
KIR) cell number in the primary gill filament but had no effect on secondar
y lamellar NKIR cell number. NKIR cells were abundant in kidney tubules, py
loric ceca, and posterior intestine, but Na+,Kf-ATPase enzyme activity war
unaffected by treatment with F and/or IGF-I in these tissues. F but not rbI
GF-I increased in vitro fluid transport capacity in the posterior intestine
. In addition to confirming an overall SW-adaptive effect of rbIGF-I and F
in FW-acclimated S. trutta, the study suggests the effect to be associated
with stimulation of chloride cell development and Na+,K+-ATPase expression
in the gill. The study indicates that the stimulatory effects of the two ho
rmones on Na+,K+-ATPase expression are additive, highly organ specific, and
restricted to the primary filament epithelium of the gill. (C) 1999 Academ
ic Press.