74
M.Ü. Wiegand
_1,jÏ
2226(n—3)
derivative
in
their
liver
triglycerides but do store
acid°
One
may
speculate that, when depot lipid is mobilized to supmnt
gonadal
recrudescence,
one
process
enhanced
would
be
the
production
22:6(n—3)
by
elongation
and
desaturation
of
appropriate
Selective
mobilization
of
stored
22:6(n—3)
and
its
precursors
to
supmü
gonadal recrudescence has recently been reported in other fish (Henderamïw
et
al., 1984; Takama et al», 1985)°
TRIGLYCERIDE LIPASE
'
Lipases
are
enzymes
which
hydrolyse
complex
lipids
such
as
acylglycerides,
ph08phOlipidS and wax esterse
A
triglyceride lipase has
been
partially purified from trout visceral adipose tissue (Sheridan æ
Allen, 1984)°
The
action
of
similar
enzymes
in mammals
permits release of
free
fatty
acids
(FFA)
into
the
bloodstream.
from.
adipose
tissue
The
isolation of
trout
adipose tissue triglyceride lipase invites not
only
comparative
work
in
other
fish
but
also
investigations
on
the
mechanism of
its
controle
In vivo
and in_vitro investigations with various
fish,
including
cyprinids,
have
shown
that,
unlike
the
case
in
plasma.
FFA.
levels
and
mobilization.
of
FFA
from
adipose
tissue
are
not
enhanced
by catecholamines (Farkas, 1967; 1969; Minick and Chavin,
Farkas
(1969) proposed a model in which release of FFA from adipose tissue
is
controlled by glucose availabilityn
In his model, low levels of glucose
permit release of FFA while higher glucose levels inhibit FFA release due
to
an
enhancement
of
esterification
of
adipose
tissue
FFA=
One
complicating factor in the study of abdominal adipose tissue is the diffuse
nature
of
the
exocrine
pancreas°
This
can.
pose
3
probleux due
to
the
presence of pancreatic lipase in extracts of mesenteric fat (Patton et
1978).
HORMONAL CONTROL OF LIPID METABOLISM.
Hormonal
control
of
lipid
deposition
has
been
studied
in
a
Wide
variety of teleost species, although a detailed hormonal strategy for this
process
has
not
emerged.
Mammalian
prolactin has been found to stimulate
either
'deposition
or
depletion
of
lipid
reserves
depending
0n
acclimation conditions and time of
injection (for review, see Peter, 1979)°
Pardo
and
de
Vlaming
(1976)
found
that
ovine
prolactin
stimulated
lipogensis
in
vitro
in
livers
removed
from
the
cyprinid
Notemigonus
crysoleucas held under short photoperiod at
The
lipogenic action of
prolactin was manifested both early and late in the photophase.
In
the
case
with fish acclimated to long photoperiods at 15°, prolactin effects on
_liver lipid concentrations varied with stage of the photophase although a
consistent
stimulation
of
triglyceride release was observed°
It
would be
of
interest
to
extend
this
work
to
the
colder
conditions
encountered in
w1nter
using h0m01080u5 Prolactin.
In the
same
species, insulin stimulated
liver
lipogenesis 'in
vitro
(de
Vlaming
and
Pardo,
1975)
and
estradiol
generally increased total liver lipid levels but had variable effects on
total body lipid levels (de Vlaming et al., 1977).,
the
liver
is
not
only a repository for lipid but is also active
in
lipid synthesis
and
export
of
lipoproteins,
perhaps
a
more
promising
avenue
of
research
into
overall
metabolic
strategies
would
be
an
examination of hormonal effects on the activities of those enzymes
that
syntheSize
the NADFH required for lipogenesis.
Unfortunately, such work is
in
its
infancy with regards to fish reproductionc
Significantly, however,
M.Ü. Wiegand
_1,jÏ
2226(n—3)
derivative
in
their
liver
triglycerides but do store
acid°
One
may
speculate that, when depot lipid is mobilized to supmnt
gonadal
recrudescence,
one
process
enhanced
would
be
the
production
22:6(n—3)
by
elongation
and
desaturation
of
appropriate
Selective
mobilization
of
stored
22:6(n—3)
and
its
precursors
to
supmü
gonadal recrudescence has recently been reported in other fish (Henderamïw
et
al., 1984; Takama et al», 1985)°
TRIGLYCERIDE LIPASE
'
Lipases
are
enzymes
which
hydrolyse
complex
lipids
such
as
acylglycerides,
ph08phOlipidS and wax esterse
A
triglyceride lipase has
been
partially purified from trout visceral adipose tissue (Sheridan æ
Allen, 1984)°
The
action
of
similar
enzymes
in mammals
permits release of
free
fatty
acids
(FFA)
into
the
bloodstream.
from.
adipose
tissue
The
isolation of
trout
adipose tissue triglyceride lipase invites not
only
comparative
work
in
other
fish
but
also
investigations
on
the
mechanism of
its
controle
In vivo
and in_vitro investigations with various
fish,
including
cyprinids,
have
shown
that,
unlike
the
case
in
plasma.
FFA.
levels
and
mobilization.
of
FFA
from
adipose
tissue
are
not
enhanced
by catecholamines (Farkas, 1967; 1969; Minick and Chavin,
Farkas
(1969) proposed a model in which release of FFA from adipose tissue
is
controlled by glucose availabilityn
In his model, low levels of glucose
permit release of FFA while higher glucose levels inhibit FFA release due
to
an
enhancement
of
esterification
of
adipose
tissue
FFA=
One
complicating factor in the study of abdominal adipose tissue is the diffuse
nature
of
the
exocrine
pancreas°
This
can.
pose
3
probleux due
to
the
presence of pancreatic lipase in extracts of mesenteric fat (Patton et
1978).
HORMONAL CONTROL OF LIPID METABOLISM.
Hormonal
control
of
lipid
deposition
has
been
studied
in
a
Wide
variety of teleost species, although a detailed hormonal strategy for this
process
has
not
emerged.
Mammalian
prolactin has been found to stimulate
either
'deposition
or
depletion
of
lipid
reserves
depending
0n
acclimation conditions and time of
injection (for review, see Peter, 1979)°
Pardo
and
de
Vlaming
(1976)
found
that
ovine
prolactin
stimulated
lipogensis
in
vitro
in
livers
removed
from
the
cyprinid
Notemigonus
crysoleucas held under short photoperiod at
The
lipogenic action of
prolactin was manifested both early and late in the photophase.
In
the
case
with fish acclimated to long photoperiods at 15°, prolactin effects on
_liver lipid concentrations varied with stage of the photophase although a
consistent
stimulation
of
triglyceride release was observed°
It
would be
of
interest
to
extend
this
work
to
the
colder
conditions
encountered in
w1nter
using h0m01080u5 Prolactin.
In the
same
species, insulin stimulated
liver
lipogenesis 'in
vitro
(de
Vlaming
and
Pardo,
1975)
and
estradiol
generally increased total liver lipid levels but had variable effects on
total body lipid levels (de Vlaming et al., 1977).,
the
liver
is
not
only a repository for lipid but is also active
in
lipid synthesis
and
export
of
lipoproteins,
perhaps
a
more
promising
avenue
of
research
into
overall
metabolic
strategies
would
be
an
examination of hormonal effects on the activities of those enzymes
that
syntheSize
the NADFH required for lipogenesis.
Unfortunately, such work is
in
its
infancy with regards to fish reproductionc
Significantly, however,