Biology Reference
In-Depth Information
In most species studied, the plasma concentration and tissue content of
CORT and ALDO increase during late prometamorphosis/metamorphic
climax, more or less in parallel with the rise in TH production (
Carr &
Norris, 1988; Denver, 1998a; Glennemeier & Denver, 2002a; Jaffe, 1981;
Jolivet-Jaudet & Leloup-Hatey, 1984; Kikuyama, Suzuki, & Iwamuro,
1986; Kloas, Reinecke, & Hanke, 1997; Krain & Denver, 2004; Krug,
Honn, Battista, &Nicoll, 1983; Niinuma et al., 1989
). The majority of these
studies showed low to nondetectable CS during premetamorphosis and a
marked increase at metamorphic climax. The only exception is in
X. laevis
where whole-body CS content may be highest during premetamorphosis
(
Kloas et al., 1997
); although, there is a secondary, lower peak at metamor-
phic climax (
Glennemeier & Denver, 2002a
). CSs, being lipophilic, are
transported in blood bound to plasma proteins. Recently, binding properties
of a putative corticosteroid-binding globulin (CBG) were described in the
serum of an amphibian (
Ambystoma tigrinum
)(
Orchinik, Matthews, &
Gasser, 2000
). However, to my knowledge, the expression of CBG has
not been studied in amphibians.
1.2.2 CS actions during metamorphosis
CSs exert complex effects on tadpole growth and development. Depending
on the animal's developmental stage and TH status, CS can accelerate or
decelerate metamorphosis. If elevated during premetamorphosis, CS typi-
cally inhibit tadpole growth and slow development (
Belden, Moore,
Wingfield, & Blaustein, 2005; Darras et al., 2002; Frieden & Naile, 1955;
Glennemeier & Denver, 2002b; Gray & Janssens, 1990; Hayes, 1995;
Hayes, Chan, & Licht, 1993; Hu, Crespi, & Denver, 2008; Kobayashi,
1958; Wright et al., 1994
).
However, CS have been found to accelerate TH-induced and spontane-
ous metamorphosis (
Darras et al., 2002; Frieden & Naile, 1955; Gray &
Janssens, 1990; Hayes, 1995; Kikuyama et al., 1993, 1983; Kuhn, De
Groef, Grommen, Van der Geyten, & Darras, 2004; Kuhn, De Groef,
Van der Geyten, & Darras, 2005; Wright et al., 1994
). Taken together,
the findings suggest that elevated CS (e.g., in response to environmental
stressors) during premetamorphosis retard growth and slow development,
while increased CS during prometamorphosis accelerate metamorphosis.
The mechanisms of CS inhibition of growth in tadpoles have not been in-
vestigated, but based on studies in mammals, these actions could manifest at
multiple levels that
likely include diverse catabolic actions (
Sapolsky,
