A possible Involvement of Prostaglandin E_2 in the Reproduction of Female Crested Newt, Triturus carnifex(Endocrinology)

10 Pages·1992·6.6 MB·English

by  Anna Gobbetti

ZOOLOGICAL SCIENCE 9: 639-648 (1992) © 1992Zoological SocietyofJapan
A possible Involvement of Prostaglandin E in the Reproduction
2
of Female Crested Newt, Triturus carnifex
Anna Gobbetti, Massimo Zerani and Virgilio Botte1
Department ofMolecular, Cellular andAnimal Biology, University ofCamerino,
via F. Camerini 1, 62032 Camerino MC, Italy, and lDepartment ofZoology,
University ofNaples, via Mezzocannone 8, 80134 Naples, Italy
—
ABSTRACT Plasmaprostaglandin E2 (PGE2), prostaglandin F2o(PGF2a), and sex steroid hormones
(progesterone, androgens, and 17/?-estradiol) were determined in the female crested newt, Triturus
carnifex, duringtheannualreproductivecycle. Invivoexperimentswerecarriedouttostudytheeffects
of PGE2 and PGF2a on plasma sex steroid hormones during prereproduction, reproduction, and
postreproduction;simultaneously, in vitroexperimentswereperformedtostudytheeffectsofthesetwo
PprGoFst2aagalnanddsienxssotnersoeixdshtoerromiodnehsorwmeorneesalsoovaerviaalnuarteelde.aseT.heThPeGEef2fepcltassomfaolneevewleweaks'slocwapftirvoimtyOocntoPbeGrEt2o,
December, then it rapidly increased to peak in March, after which it soon fell to reach its minimum
valueinMay. PlasmaPGF2aandsexsteroidhormonesshowedsimilartrendstothosefoundinprevious
studies. FromDecembertoApril,thePGE2plasmavalueswerenegativelycorrelatedtothoseofPGF2a
and positively to those of androgens; PGF2a plasma values were positively correlated to those of
estradiol. PGE2in vivotreatmentincreasedplasmaprogesteroneanddecreased 17/?-estradiolinApril,
while PGF2oinducedtheoppositeeffectsinthesame month; PGE2increasedandrogensinJanuaryand
March, and PGF2aincreased androgens in April. The in vitro experimentswere in agreement. These
results suggest that PGE2 and PGF2aplay opposite role(s) in the reproductive processes ofthe female
Triturus carnifex. PGE2 could be involved in the reproduction processes through androgen secretion,
while PGF2a in the ending ofreproduction through estradiol increase.
Triturus carnifex abdominal gland, suggested for
INTRODUCTION
PGE2 a role in inducing pheromonal activity [15];
In mammals, prostaglandins (PGs) of both F these data indicated an involvement of this pro-
and E series intervene in the regulation of the staglandin in reproductive processes.
ovary functions, including steroidogenesis [1-4]. It seemed, therefore, of interest to determine
PGs are involved in ovulation of the chicken the annual profile of PGE2, in relation to that of
follicle [5] and in inducing the relaxation of the PGF2a and of sex steroid hormones in the female
avian oviduct [6]. PGs are also implied in the crestednewt, Trituruscarnifex, and,inaddition, to
regulation of reproduction in reptiles [7-10]. evaluate the PGE2 and PGF2a effects on plasma
There is little information, however, on the role of levels andovarian output ofsexsteroid hormones.
PGs in amphibian reproductive processes. In the
anuran, Rana esculenta [11, 12], and in the MATERIALS AND METHODS
urodele, Triturus carnifex [13, 14], plasma prosta-
glandin F2a (PGF2a) levels change in relation to
Animals
the various periods of the annual reproductive
cycle, and in both species PGF2a could be implied The reproductive cycle of the Triturus carnifex
in breeding period termination. population comprises two major phases: during
A recent in vitro study, carried out on the male the summer period the animals disappear under-
ground (August-September), during the other
Accepted March 17, 1992 months the newts are in the pond and undertake
Received January 22, 1992 reproduction during the cold months (January to
640 A. GOBBETTI, M. ZERANI AND V. BOTTE
March). animals of each of the groups were bled, as de-
Adult female newts, Triturus carnifex (Laur.), scribed above, 6, 24, and 48hr after treatment.
were collected (15 each month) in a small moun- After centrifugation, plasma samples were kept at
tain pond (Colfiorito, Umbria, Italy; 870 m above —20°C until use. A further batch of seven un-
sea level), from October to July during 1990/91. treated animals were bled at the beginning of the
In that place, newts hide on land during August experiments (controls, time 0). The times of
and September and therefore, in these two treatment and the minimum effective doses of
months, it was not possible to obtain enough PGE2 and PGF2a were chosen after preliminary
animals for our study. At once, after capture, tests (data not shown).
newts were anesthetized in the field with 3-
aminobenzoic acid ethyl ester (Tricaine, Sigma, In vitro experiment
USA) and bled through a heparinized microtube The method used for the in vitro experiment
inserted in the heart. Individual blood samples followed Gobbetti and Zerani [15, 16]. In Decem-
were collected into chilled tubes containing acetyl- ber, January, March, and April, 7 female newts
salicylic acid (Aspirin, Sigma) and EDTA (5 fig (for each month) were captured, transferred to
and 1figlmX of blood, respectively) [11]. After laboratory aquaria, and maintained as reported
centrifugation, plasma samples were kept at above. One week later, the animals were decapi-
-20°C until use. tated, the ovaries rapidly removed and placed in
cold Dulbecco's modified Eagle medium (DME;
Captivity Sigma) containing 10mM Hepes, 1 mg Penicillin
In December (prereproduction), January (be- G/ml, and 2 mg streptomycin/ml. For each
ginning ofreproduction), March (ending ofrepro- month, theovaryfromoneanimalwasdividedinto
duction), and April (postreproduction), 15 female equally sized fragments, pooled and equally distri-
newts were captured and bled in the field as buted over 12 incubation wells. Multiwell tissue
reported above (control I), while simultaneously culture plates (Becton Dickinson, USA) were util-
15 other animals were transferred to our labora- ized. Each incubation set ofwellswasdividedinto
tory aquaria, kept under natural photothermal 3 experimental groups (each consistingof4wells).
conditions and fed on larvae of Chironomidae, The experimental groups were: a) ovarian tissue
DME
Tubifex and Daphnia, ad libitum to study the incubated with alone; b) ovarian tissue
effects of captivity on plasma hormone levels. A incubated with DME plus PGE2 (50ng); c) ova-
week later, the animals in captivitywere bled, and rian tissue incubated with DME plus PGF2a (50
simultaneously yet another 15 were sacrificed in ng). The final volume of each well was 1 ml.
the field (control II). Culture plates were wrapped with aluminium foil
and incubated in a shaking water bath (19°C), set
In vivo experiment at 30 revolutions/min. One well of each ex-
In December, January, March, and April, 84 perimental group was removed, respectively, after
female newts (for each month) were captured, 30, 60, 120and240minofincubation. Theincuba-
transferred to our laboratory and kept under nat- tion medium samples were immediately stored at
uralphotothermalconditions. Oneweeklater, the —20°C for later hormone determination; ovarian
animals were divided into 4 groups: a) 21 newts tissues were soon homogenized in amphibian
received a single s.c. injection of 350ng PGE2 saline, and protein content was determined by the
(Sigma; ca 35 ng/g body weight) dissolved in 100 Protein Assay method (Bio-Rad, USA). In addi-
ju\amphibiansaline (0.64% w/vNaClsolution);b) tion, the whole experiment was repeated with
21 newts received a single s.c. injection of 300ng incubation setswithoutovariantissue. The experi-
PGF (Sigma; ca 30ng/g body weight) dissolved ment was replicated 7 times for each month.
2«
in 100[A amphibian saline; c) 21 newts received a Preliminary evidence led to our choice for the
single s.c. injection of 100jA amphibian saline incubation conditions and the minimum effective
only; d) 21 newts were untreated. Seven ofthe 21 doses ofPGE2 and PGF2outilizedin the present in
PGE2 and Reproduction in T. carnifex 641
vitro study (data not shown).
Statistics
PGE2, PGF2a, progesterone, androgens, and 17(3- Data relative to each hormone were submitted
estradiol determination to analysis of variance (ANOVA) followed by
PGE2was determinedfollowingthe radioimmu- Duncan's multiple range test [18, 19]. Correlation
nological method (RIA) for plasma [13, 14] and coefficents followed Scossiroli and Palenzona [20].
incubation media [15], PGF2odeterminations used
for this species are here briefly described. PGE2 RESULTS
determinations were carried out on duplicate plas-
masamples (100ju\) andincubation media (500/A)
that were extracted with 10volumes of diethyl Hormone annual reproductive cycles
ether for 5 min. The mixtures were briefly centri- The PGE2plasmalevelwaslowfrom Octoberto
fuged, organicfractionswere transferredintoglass December, then it rapidly increased to peak in
tubes and evaporated to dryness under a nitrogen March (P<0.01 vs all months) and soon fell to
stream. Theextractswereresuspendedwith 100ju\ reach its minimum value in May (P<0.01 vs
of assay buffer and assayed. The recovery of January, February, March, April, June, andJuly),
added labelled PGE2was 85.9±0.84%. The para- then PGE2 level increased during the summer and
llelism among the standard curve in buffer, a peaked in July (P<0.01 vs all months except
standard curve in incubation medium (then ex- February) (Fig. 1). The PGF2a plasma level in-
tracted), andaserialdilutionofasingleincubation
medium sample (extracted) were constant. 4000 PGE
The progesterone, androgens, and 17/?-estradiol 3000
content of the plasma and incubation media was 2000
determined by RIA according to the previously 1000-1
reported methods [13, 15, 17].
5000
The following sensitivities were recorded:
3750
PGE2, 18pg (intra-assay variability: 6.5%; inter- 2500
assay variability: 12%); PGF2a, 17pg (intra-assay 1250
variability: 5%; inter-assay variability: 11.5%);
progesterone, 7.0pg (intra-assay variability: 5%; 3000 PROGESTERONE
inter-assay variability: 11.5%); androgens, 9.0pg 2250
(intra-assayvariability: 6%; inter-assayvariability: 1500
9%); 17/?-estradiol, 8.5 pg (intra-assay variability: 750
4%; inter-assay variability: 9%). The PGF2a,
progesterone, testosterone, and 17/?-estradiol anti- 5000 ANDROGENS
3750
serawere providedbyDr. G. F. Bolelli andDr. F.
2500
Franceschetti (CNR-Physiopathology of Repro-
1250
duction Service, University ofBologna, Italy), the
PGE antiserum was purchased from Cayman
2 12000 17J3-ESTRADI0L
Chemical (USA). Testosterone was not separated 9000
from 5a-dihydrotestosterone and therefore, since 6000
the antiserum used is not specific, the data are 3000
expressed as androgens. Tritiated PGE2, PGF2o, Oct Nov Dec iiJan Feb liar iiApr May Jun Jul
progesterone,testosterone, and 17/?-estradiolwere
PREREPR0DUCTI0N REPRODUCTION P0STREPR0DUCTI0N
plaunrdc)h,asneodn-rfardoimoacAtmieversPhGaEm2,Inptreorgneasttieornaolne,(Etnegs-- Fig.h1.ormPolnaessmadulrevienlgstohfePaGnEnu2a,lPGreFp2r«o,duacntdivseexcysctleeroiidn
tosterone, and 17/3-estradiol from Sigma. female crested newt, Triturus carnifex. Each mean
refers to 15 determinations+S.D..
642 A. GOBBETTI, M. ZERANI AND V. BOTTE
creased in autumn to peak in December (P<0.01 estradiol plasma level peaked in December (P<
vs all months except April), decreased from Janu- 0.01 vs all months except April, May, and July)
ary to March and peaked again in April (P<0.01 and in April (P<0.01 vs all months) (Fig. 1).
vs all monthsexcept December), andwaslowfrom From December to April the following correla-
May to July (Fig. 1). The progesterone plasma tions were found: PGE2 plasma values were nega-
level exhibited minor changes, reaching the mini- tively correlated to those ofPGF2a (r=-0.523; df
mum value in April (P<0.01 vs all months) (Fig. =73; P<0.001) and estradiol (r=-0.469; df=73;
1). The plasma androgensincreased from October P<0.001), and positively correlated to those of
to December and more from January to March (P androgens (r=0.501; df=73; P<0.001), PGF
2a
<0.01 vs October, November, December, April, plasma values were negatively correlated to those
May, June, andJuly), theystartedtodropinApril of androgens (r=-0.545; df=73; P<0.001), and
and reached the minimum value in July (P<0.01 positivelytothoseofestradiol (r=0.434; df=73; P
vs all months except June) (Fig. 1). The 17/?- <0.001), androgensplasmavalueswerenegatively
correlated to those of estradiol (r=—0.408; df=
4400 73; P<0.001).
3300-
Captivity
One week's captivity in laboratory aquaria de-
creased PGE2 plasma levels inJanuary and March
(P<0.01),PGF2oinApril(P<0.01)andandrogens
in January, March and April (P<0.01) (Fig. 2).
2000-ipR0GESTER0NE
1500-
1000
o>
Q.
^-" 500
CO
_l
LU
>
LU
_l
< 20000 17J3-ESTRADI0L
21
C<O 15000
ioooo-
5000
December January March April oJ
Fig. 2. Effectsofoneweek'scaptivityonPGE2,PGF2a, HOURS
andandrogensplasmalevelsinfemalecrestednewt,
Triturus carnifex, during December (prereproduc- Fig 3. In vivo effects of350ng PGE2 or300ng PGF2a
tion),January (reproduction beginning), March (re- injection on progesterone and 17/?-estradiol plasma
production ending), and April (postreproduction). levels in female crested newt, Triturus carnifex,
Experimental groups: (): newts captured in the during April (postreproduction). Experimental
field and bled at once (control I); (): newts bled groups: (): untreated newts; (): amphibian-
after one week's captivity in laboratory; (M): newts saline-only injected newts; (m): PGE2 injected
captured and bled at once in the field, one week newts;(m): PGF2oinjectednewts. Eachmeanrefers
after control I (control II). Each mean refers to 15 to 7 determinations+S.D.. * P<0.01 vs untreated
determinations+S.D.. * P<0.01 vscontrolI andII andamphibian-saline-onlyinjectednewts(Duncan's
(Duncan's multiple range test). multiple range test).
PGE2 and Reproduction in T. camifex 643
In vivo experiment In vitro experiment
PGE2 treatment increased progesterone level in PGE2 basal release was higher in January and
April at 6 and 24hr (P<0.01) (Fig. 3), androgens March (P<0.01) compared with December and
in January and March at 6, 24 and 48 hr (P<0.01) April; March values were higher (P<0.01) than
(Fig. 4), and decreased 17/?-estradiol in April at24 those ofJanuary (Fig. 5). PGF2obasal release was
and48hr (P<0.01) (Fig. 3). higherin April (P<0.01) comparedwith the other
PGF2a treatment decreased progesterone level months (Fig. 5). Progesterone basal release was
in April at 6, 24 and 48hr (P<0.01) (Fig. 3), lower in April (P<0.01) compared with the other
increased androgens in April at 24 and 48hr (P< months (Fig. 6). Basal release of androgens was
0.01) (Fig. 4), and 17/?-estradiol in April at 24 and higher in January and March (P<0.01) compared
48hr(P<0.01) (Fig. 3). with the other months (Fig. 7). Estradiol basal
levelwashigherin DecemberandApril (P<0.01);
April values were higher (P<0.01) than those of
December (Fig. 8). At all incubation times, the
3000- DECEMBER
2250-
1500-
c 750-
o-
o
£_ 3000- JANUARY
Q-
2250-
C^
b 1500-
750-
Q.
a
oJ
S
Li_ 3000n MARCH
CL 2250-
-J^3
Fig. 4. In vivo effects of350ng PGE2 or 300ng PGF2o 30INCUBAT60ION TIM12E0 (mm)240
injection on androgens plasma levels in female
crested newt, Triturus camifex, during December Fig. 5. In vitro basal release of PGE2 () and PGF2a
(prereproduction), January (reproduction begin- () from ovary of female crested newt, Triturus
ning), March (reproduction ending), and April camifex, incubatedin December(prereproduction),
(postreproduction). Experimental groups: (): un- January (reproduction beginning), March (repro-
treated newts; (): amphibian-saline-only injected duction ending), and April (postreproduction).
newts; (M): PGE2 injected newts; (m)\ PGF2a in- Eachmeanrefersto7determinations+S.D. a, P<
jectednewts. Eachmeanrefersto7determinations 0.01 vs same time December and April; b, P<0.01
+S.D.. * P<0.01 vs untreated and amphibian- vs same time January; c, P<0.01 vs same time
saline-only injected newts (Duncan's multiple range December, January, and March (Duncan's multiple
test). renge test).
'
644 A. GOBBETTI, M. ZERANI AND V. BOTTE
1200-i DECEMBER '0001 DECEMBER
900 750
600 500
250 H^
J •zzzczfea Wffll
° 1200 JANUARY 7 iooo JANUARY
L. 900 o 7501
Q. !_
600 Q. 500
E 300 u£> 250 i\
Cl "av.> J
—o.
1200i MARCH 1000 MARCH
900 £ 750
LU
600 O 5001
O
ik
300 CQL 250
ZL
O <
? 1200i ApR|L 1000 APRIL
900 750
600 n ifta 500
300 m m m H 250
30 60 120 240 30 60 120 240
INCUBATION TIME (min) INCUBATION TIME (min)
Fig. 6. In vitroeffectsof50ngPGE2or50ngPGE2qon Fig 7. In vitroeffectsof50ngPGE2or50ngPGF2aon
progesterone release from ovary of female crested androgens release from ovary of female crested
newt, Triturus carnifex, incubated in December newt, Triturus carnifex, incubated in December
(prereproduction), January (reproduction begin- (prereproduction), January (reproduction begin-
ning), March (reproduction ending), and April ning), March (reproduction ending), and April
(postreproduction). Experimentalgroups: (): ova- (postreproduction). Experimentalgroups: (): ova-
ry incubated with medium alone; (): ovary incu- ry incubated with medium alone; (): ovary incu-
bEaatcehdmweiathnPreGfEer2s;t(oH7):deotvearrmyiniantciuobnaste+dSw.iDt.h.PaG,FP2<q. EbaatcehdmweiathnPreGfeEr2s;t(oD7):deotvearrmyiniantciuobnaste+dSw.iDt.h.PaG,FP2<o.
0.01vssametimeDecember,January, andMarch; * 0.01vssametimeDecemberandApril; *P<0.01vs
P<0.01 vssametimemedium-alone(Duncan'smul- same time medium-alone (Duncan's multiple range
tiple range test). test).
Table 1. CorrelationcoefficientsamongPGE2, PGF2q,androgens(A),and 17/?-estradiol(E)
levels released by female Triturus carnifex ovary incubated at various times during
December, January, March, and April
Incubation times
30min 60min 120min 240min
PGE2 vs PGF2( 0.768 -0.657 -0.743 -0.757
PGF2 vs A 0.724 0.745 0.774 0.761
PGE2 vs E 0.650 -0.637 -0.672 -0.621
PGF2o vs A 0.733 -0.759 -0.731 -0.749
PGF2o vs E 0.715 0.748 0.686 0.668
A vs E 0.620 -0.670 -0.646 -0.645
All correlations show the same level of significance (P<0.001). df=26.
PGE2 and Reproduction in T. carnifex 645
2400- DECEMBER April at 60, 120 and 240min (P<0.01) (Fig. 8).
1800- PGF2a treatment decreased progesterone levels in
1200- April at 30, 60 and 120min (P<0.01) (Fig. 6),
increased androgens in April at 60 and 120min (P
600- W ^
^r~ <0.01) (Fig. 7), and estradiol in April at 60, 120
—c ^ ' I ' I and 240min (P<0.01) (Fig. 8).
o 2400nJANUARY
o
1800-
£_
Q_ DISCUSSION
1200-
O*
E 600- The mountain population of female Triturus
OQ*. J tM ' I I i carnifex, utilized in this study, shows a discon-
tinuous reproductive cycle similar to those de-
o_l 2400-i MARCH scribed in several other newts living in temperate
1800-
Q zones [21-23]. In thisfemale newt, ovulations and
< 1200-
egg depositions occur from January to the end of
q:
h- 600- March, the oogenetic cycle in spring and summer,
co
LU o- and vitellogenesis in autumn and winter [24],
2400- APRIL This is the first work to evidence in vivo and in
1800 vitro the presence of PGE2 in female Triturus
1200- carnifex. The PGE2 plasma titers showedpeculiar
changes during the newt annual reproductive cy-
600 a,b
iTl^ cle; during the reproductive period (January-
30 60 120 240 March), this prostaglandin had high values which
INCUBATION TIME (min) rapidly fell during postreproduction (April). The
Fig 8. Invitroeffectsof50ngPGE2or50ngPGF2qon high plasma levels of PGE2 during reproduction
17/?-estradiol release from ovary of female crested suggest the involvement of this prostaglandin in
n(eprwetr,eprToridtuucrtuison)c,arniJfaenxu,ariyncu(braetperdoduicntiDonecebmegbienr- the breeding processes. PGF2a, progesterone,
androgens and estradiol plasma levels showed
ning), March (reproduction ending), and April
(postreproduction). Experimentalgrousp: (): ova- similar annual trends to those reported in previous
ry incubated with medium alone; (): ovary incu- studies [14, 24]. Briefly, the April increase of
bEaatcehdmweiathnPreGfEer2s;t(om7):deotvearrmyiniantciuobnaste+dSw.iDt.h.PaG,FP2<q. prilsaesamnadPaGpFr2oagewsatsersoinmeuldtraonpe.ouHsigwihtphlaansmeastvraalduieosl
0.01vssametimeJanuaryandMarch;b, F<0.01 vs
of androgens characterized the reproductive
same time December; * P<0.01 vs same time
medium-alone (Duncan's multiple range test). period in female Triturus carnifex, confirming pre-
vious studies carried out in the same species [25,
26] and in the same population [24], which estab-
PGE2valueswere negativelycorrelatedtothoseof lished the role ofandrogens in inducing the repro-
PGF2« (P<0.01) and estradiol (P<0.001), and ductive processes was addressed in the female
positively correlated to those of androgens (P< crested newt. In this context we recall that, in
0.001); PGF2avalueswere negativelycorrelated to another amphibian species, Rana esculenta, the
those of androgens (P<0.001), and positively to highest values of male and female brain androgen
those of estradiol (P<0.001); androgens values receptors were found during the reproductive
were negatively correlated to those ofestradiol (P period [27]. As regards estradiol plasma pattern,
<0.001) (Tab. 1). low levels were found in autumn andwinter, when
PGE2 treatment increased progesterone release vitellogenesis occurs. It was well estrablished in
in April at 30, 60 and 120min (P<0.01) (Fig. 6), amphibians that estradiol induces vitellogenin
androgensinJanuaryandMarchat60, 120and240 synthesis [28], therefore the low estradiol plasma
min (P<0.01) (Fig. 7), and decreased estradiol in values found during vitellogenesis are difficult to
646 A. GOBBETTI, M. ZERANI AND V. BOTTE
explain, but, in this context, we recall that similar Taken together, these results suggest that PGE
2
data were obtained in other amphibian species and PGF2a play opposite role(s) in the reproduc-
[29]. In accordance with the plasma values, the in tive processes of the female Triturus carnifex.
vitro studies demonstrated that ovarian tissue re- Summarizing, PGE2 is involved in the reproduc-
leased high amounts of PGE2 and androgens dur- tion through androgens secretion, while PGF2a in
ing reproduction and high levels of PGF2a and the ending of reproduction through estradiol in-
estradiol during postreproduction, while in this crease. This possible antagonistic role between
latter period progesterone was low. PGE2 and PGF2a is supported by their negative
The in vivo and in vitro PGE2 treatment in- correlationfoundin the plasma. Thishypothesisis
creased androgens levels during reproduction sug- in agreementwith previous studieswhichassign an
gesting a causal relationship between these two inhibitory role to PGF2a in sexual behavior in the
hormones. This hypothesis is also supported by reptiles, Anolis carolinensis and Thamnophissirta-
the positive correlation between PGE2 and lis parietalis [36, 37] and in the amphibian, Bufo
androgens found in the plasma of the animals americanus [38], but a stimulatory role to PGE2 in
sacrificed in the field. The same positive correla- receptivity behavior in another amphibian, Xeno-
tion was also found between the basal values of pus laevis [30].
PGE2 and androgens obtained in the in vitro The antagonistic effect of PGE2 and PGF2a in
experiment. These resultsseemfurtherto indicate the regulation ofin vivo and in vitro progesterone
that PGE2 is involved in the reproductive proces- release found during postreproduction is still un-
ses, by the regulation of the androgens synthesis, known. We recall that a positive 3/?-hydroxy-
evenifothermechanismscannotbeexcluded. The steroid dehydrogenase response was reported in
involvement of this prostaglandin in reproduction the postovulatory structures of Triturus carnifex
is also suggested by previous studies which attri- [39], Rana esculenta [40] and Rana cyanophlyctis
bute to PGE2 a role in inducing pheromonal [41], but evidence of ultrastructural analysis is
activitybythe abdominalglandof Trituruscarnifex lacking [22]. Nevertheless, in mammals, PGE2
[15]. Also in another amphibian species, Xenopus counteracts the luteolytic effect of PGF2a and
laevis, PGE2 was found to be involved in the might be one ofseveral factors prolonging the life
breeding processes, since this prostaglandin in- span of the corpus luteum [42, 43].
duced the sexual behavior [30]. Finally, this work confirms that captivity caused
The in vivo and in vitro results indicated that a decrease of circulating PGs and androgens.
PGE2 treatment in animals captured in April in- These resultsare in agreementwith those reported
duced opposite effects to those determined by for this [14] and other amphibian species [44-47].
PGF2a administered in the same month. In fact,
PGE2 in vivo and in vitro increased progesterone ACKNOWLEDGMENTS
and decreased estradiol, while PGF2a decreased
progesterone and increased estradiol during this The authors would like to thank James Burge, ofthe
period, in agreement with the plasmatic trends Camerino University Institute of Linguistics, for help
with English, and Elio Marchegiani for his assistance.
here and previously reported [14, 24]. The causal This work was supported by a grant to Prof. Alberta
relationship which binds the PGF2ft and estradiol Polzonetti from Italian Ministry ofEducation and C. N.
plasma patterns supported the hypothesis that R.
PGF2ocontributedto reproductive periodtermina-
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