POSSIBLE MODE OF ACTION OF PROSTAGIY~NDINS: V - DIFFE~IENTIAL EFFECTS OF PROSTAGLANDIN F2~ BEFORE AND AFTER THE ESTABLISHMENT OF PIACENTAL PHYSIOLOGY IN PREGNANT P~ATS,

Amar ChatterJee

Department of Physiology RaJa Peary Mohan College Uttarpara, Rooghly, West Bengal, INDIA.

ABSTIIACT

Prostaglandin F2~ (PGF2~) at a dose level of 2.00 mg/kg body weight could cause complete resorption of the implanted blastocysts when injected either on day 10 or day 11 of pregnancy in rats. The same injection apparent- ly failed to induce abortion oi resorption in rats having functional placentae on day 12 or day 13 of pregnancy. It was moreover observed that a concomitant exogenous adminis- tration of either prolactln or progesterone alongwith PGF~ could successfully reverse the abortifacient property of PGF2~ and keep the status of the ovaries, embryos, placen- tae etc. identical to that obtained in the control. It was suggested from the experimental evidences that the abortlfacient effects of PGF2~ in the rat might possibly be mediated through the pituitary or hypothalamo-pituitary complex.

ACKNO,iLEDGT'!ENTS

This research wor~ was financed by the Indian Council of Medical nesearch. The co-cperation of Mrs. A. Chatter- Jec in statlstic~l analysls is highly apFreciated.

Accepted December 4, 1972

F E B R U A R Y 1973 VOL. 3 NO. 2 189

PROSTAGLANDINS

INTRODUCTION

Earlier report from our laboratory has shown that a single injection of Prostaglandin F2~ (PGF2~) causes luteolysis and lysis of the deciduoma in pseudopregnant rats. Moreover, a concomitant treatment of the exogenous prolactin could successfully reverse the detrimental effects of PGF 2~ in luteolysis (i). Removal of the pi- tuitary at different stages of pregnancy shows that the pituitary gland is indispensible upto the mid-pregnancy in the rat, While after mid-pregnancy the placentae could exclusively replace the contributory role of the pituitary in terms of prolactin production for an appro- priate stimulation of gestagens secretion by the corpus luteum of pregnancy.

Using an intact pregnant animal model we have attempted to examine whether the antifertility effect of PGF2~ in the pregnant rats is mediated through the pituitary prolactin inhibition or does it directly affect the prolactin action at the ovarian level ?

MATF~IALS AND METHODS

Laboratory albino rats weighing 180-200 g were used. The animals were maintained under controlled lighting schedule (12 h light/12 h darkness) and had free access to food and drinking water, Daily vaginal smears were taken and three completed cycles were re- corded before the animals were subjected to any experi- ments. The animals were caged in the evening of the day of vaginal proestrus with fertile males, Insemination was confirmed the next morning by finding either sperma- tozoa in the vaginal smears or a vaginal plug. The day on which spermatozoa or vaginal plugs were found was designated Day 1 of pregnancy. Inseminated rats were distributed into several groups. The treatment schedules of the different groups of animals are shown in Table 1 and 7. PGF2~ was kindly donated by the UpJohn Company through the courtsey of Dr. J. E. Pike. PGF2~ solution was prepared in the usual manner (solution of i mg ~GF2~ in 0.1 ml of 95% ethanol dissolved in exactly 0.9 ml of 20.0 mg% Na2CO 3, the pH adjusted to 7.2) and injected sc as a slngle injection, The dose used was 2.0 mg per kg body weight. The hormone prolactin (Ovine prolactin, NIH $9) donated by the National Institute of Health, U.S.A., was prepared in 0.9% saline and injected sc as single daily injection (0.2 ml). Progesterone (Hydroxyprogesterone caproate, Delatu~in) was diluted with corn oil and admi- nistered sc as single daily injection in a volume of 0.2 ml

190 FEBRUARY 1973 VOL. 3 NO. 2

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Table

1

Effects of PGF2~ (2.0 mg/kg) on the weight

of foetus, placenta, ovary and corpus lu-

teum in rats

Day

of

Mean faetal wt.

Mean placental

Mean Ovarian wt.

treatment

(gin + SE)

wt.(mg_+SE)

(rag + SE)

Control (6)

S.2

_+ 0.65

428.7 _+ 8.7

75.16 +

S.O

i0 (8)

Resorbed

Resorbed

61.6

+ 1.2 *

ii (8)

Resorbed

54.11 +

7.4 *

65.75 _+ 2.3

12 (I0)

~oi +

0.8

3~.0 +

84.0

78.58 ++ ~.i

13 (lO)

2.2 +_ 0.9

4~7.5 +

1~.8

81.~5 _+ 2.0

* Significant compared to that of control.

Figure~in the parenthesis indicate the number of animals studied. Mean luteal wt.

(rag +_ SE

)

5.0 _+ 0,3

2.6 _+ 0.2 *

2.6 _+ O.1 *

4.7 _+ 0,5

4,8 +

O,1

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b~

Day of treatment

T able

2

Effect of PGF2< (2.0 mg/kg)

on faetal survival

rate until day 20 of pregnancy in rats,

i

No.of implantation

site at laparot~y

No. of faetuses

at sacrifice

Survival rate

Control (6)

4~

46

95,8

i0 (8)

65

0

0

11 (8)

6o

0 0

12

(io

) 8o

,5

0 6

2.5

13 (i0)

86

79

91.8

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OD

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~n

PROSTAGLANDINS

of the vehicle. The examination for the presence of implan- tation sites in the uterus was made through a midventral inclsslon on Day 8 of pregnancy.

~ESULTS

Effects of a single injectlon of PGF2~

A single injection of PGF2~ (2.0 mg/kg body weight) on Day 10 of pregnancy was found to cause complete resorp- tion of both the faetuses and placentae in all the animals when examined on Day 20 of pregnancy. The occurance of complete luteolysis in these animals was Judged on the basis of the status of ovaries and corpus luteum (Table i).

When the injection schedule was shifted .to Day ii instead of Day 10 of pregnancy, apparently an identical consequences were evident as found in the previous group, but the resorbing placentae in this group of rats were recovered at autopsy which had the mean weight of 54.11 + 7.4 against the mean control value of 428.7 ~ 8.7 (Table-l).

PGF2~ injection on Day 12 of pregnancy caused a partial 18ss of the implanted faetuses. The faetal survi- val rate in this group of animals when assessed on Day 20 of pregnancy was 62.5% against the control survlval rate of 95.8% (Table 2). Excepting an apparent lowering of the placental weight, the mean weight of the faetuses, ovaries and corpora lutea in these animals was almost identical to controls (Table 1). But when the injection schedule was delayed until Day 13 of pregnancy, no significant diffe- rences in the faetal survival rate, mean weight of the faetuses, placentae, ovaries and corpora lutea were evident from that of the controls (Table 1 and 2). Some of the treated rats were left for studying the duration of ~esta- tion and the percentage recovery of the viable youngs. It was observed that the post-implantation loss of embryos in the respective groups of animals having a single PGF2~ injection on Day 11, Day 12 and Day 13 was 100.0, 45.5 and 8.0%, respectively. It was also examined that all the experimental animals having PGF2~ injection either on Day 12 or Day 13 of pregnancy delivered viable pups between Days 22 and 23, coinciding with the time of Darturition of control animals (Table 3).

FEBRUARY 1973 VOL. 3 NO. 2 193

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Day of

treatment

C ontr ol (6)

ll (S)

12

(5

)

13

(6

)

ii +

Pro-

gesterone

(5)

ll +

LtH

(6)

T abl •

B

PGF2~

on the parturition of viable

pups and the effects of prolactin

(LtH) or ~rogesterone

D urat ion of

ges t at ion(days)

22 -

23

Terminated

22 -

23

22

-

23

22

-

23

-23

No. of implantation

No. delivered Survival

Mean wt.of

sites at laparotomy

(Viable)

rate (%)

pups(gm_+SE)

52

4

8

9~

,3

5.9

+

0

.7

60

n

il

all

-

35

2

0

55

,5

5.6

+

0

.8

50

4

6

99

,0

5.8

+_

0.5

41

35

85.3

6.0 +

0.i

54

47

87.~

5.9 __+ 0.3

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P R O S T A G L A N D I N S

~gversal of the abortifaolent effect of PGF2~ by exoge- nous Drolaotin o r p r o g e s t e r o n e .

It was evident from the present experiments that the detrimental effects of PGF2~ when injected on Day 11 of pregnancy could be successfully prevented by the exo- genous injections of either prolactin (5 mg per animal per day) or progesterone (5 mg per rat per day) from Day i0 through Day 12 of pregnancy. The survival rate of the embryos on Day 20 of pregnancy and the rate of recovery of the viable youngs at parturition in the prolactin- treated group were 87.8 and 87.2%, respectively and in the progesterone-treated group the respective values were 88.5 and 85.3%, When compared with the controls the mean weight of the embryos, placentae, ova- ries, corpora lutea and the viable pups of the prolactin or progesterone-treated animals was statistically insig- nificant (Tables 3 - 5).

DISCUSSION

Present experiments show that a single injection of PGF 2~ at a dose level of 2.0 mg/kg body weight on Day i0 or Day ii of pregnancy has a consistent effect in the resorption of implanted embryos in the uteri of rats. While the same injection could only exert a partial dele- terious effect when given on Day 12 of pregnancy, but the drug is absolutely ineffective when the injection is delayed to Day 13 of pregnancy. Moreover, a concomitant exogenous injection of prolactin or progesterone concu- rrently with PGF2~ could consistently prevent the detri- mental effect of PGF2~ in the interruption of gestation in rats.

The dramatic influence of PGF 2 ~ in the interruption of pregnancy in rats, mice, hamsters, rabbits, monkeys (2) and also in women (3) has been reported during years of search for suitable antifertility drugs. Regarding the mode of antifertility action of PGF2~ , several postula- tions have been put forward by the competent investiga- tors. In the rodents the luteolytic action of PGF2~ as does originally propose by Pharriss (4) due to restriction of blood flow through the ovaries has been recently contra- dicted by Berhman et al (5), ChatterJee (6) and McCracken et al (7). However, an exessive release of pituitary LH (8), interference with the action of prolactin on the cor- pus luteum (9) or inhibition of prolactln release by the pituitary in Situ (i) have been proposed as alternative mechanisms of luteolysis caused by PGF2~.

FEBRI~ARY 1973 VOL. 3 NO. 2 195

O~

T_able

4

Effects of Prolactln (L

tH)

or Progesterone

in the prevention of detrimental effect of

PGF2M

C > ©

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t-O

Hormone used

Mean faetal wt.

(gm Z

SE)

Unt r eat ed

control (6)

PGF~

Day ii

(control)

2.2

_+

0.6

5

Res orbed

PGF 2 ~ (day ll

) +

LtH(day lO-12)

2.28 _+ 0.9

PGF2~ (day ii

)

+ progesterone

(day 10-12)

Mean placental

wt. (rag +_ SE)

428.7

+

8.7

m

54.11 +

7°4 *

406,0

+ 13,2

Mean ovarian wt.

(rag + SE)

75.16 +

2.0

65

.75

__

+ 2',

3

70.8

_+ 2°8

2.1

0

+

0.2

4

05

.4

+ 1

5.5

6

8.8

+

2.3

* Statistically significant from the control.

Mean luteal wt.

Crag

+_ SE

)

5.0

+

0.3

2.6 +_ 0

.i

*

4.6

+

0

.8

5°0

+

0.7

C > < © ©

Hormone used

Untreated

control

PGF?~(day ll)

control

PC

~2~

(day

11

) +

L

tH

PGF2K(da%

ll)

+ progesterone

Table

5

Effects of Prolactin (LtH) on Progesterone

in the prevention of deleterious effect of

PGF~

Day of treatment

No.of implantation

sites at laparotcmy

No.of faetuses

at sacrifice

S urv iv al

rate(%)

48

46

95.8

60

0

0

IC-12

58

51

87.8

i0-12

70

62

8

8,5

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PROSTAGLANDINS

The failure of PGF2~ in the induction of luteolysis in our experimental rats after mid-pregnancy and the rever- sal of the luteolytic effects of PGF2~ before the esta- blishment of placental source of luteotrophin b~ the con- comitant treatment with exogenous prolactin or progesterone tempt to suggest that the deleterious effect of PGF2~ in the development of luteolysis in pregnant rats is possibly mediated either through the hypothalamus and/or the pitui- tary. Since in our preliminary experiments we have observed that PGF2~ almost fails to induce luteolysis when given on Day 10 or Day 11 of pregnancy in rats having pituitary graft under the kidney capsul~ (Chatterjee, unpublished).

198 FEBRUARY 1973 VOL. 3 NO. 2

P R O S T A G L A N D I N S

~EFERENCES

1.

2.

.

.

.

.

.

.

.

ChatterJee,A. The possible mode of action of prosta- glandins. I. Interruption of decidual reaction by PGF2~ and its prevention by using prolactin or progesterone, Acta endocrinol (kbh). 70 , 781-785 (1972).

Pharris,B.B. Prostaglandin induction of luteolysis, A~n.N.Y.Acad.Soi. 180 , 436-444 (1971).

Karim,S.M.M. Once-a-month vaginal administration of prostaglandins E 2 and F~M for fertility control, Contraception. 3 , 173-Y83 (1971).

Pharriss,B.B. The possible vascular regulation of luteal function, Perspect.Biol.Med. 13 , 434-444(1970).

Behrman,H., Yoshinaga,K., Wyman,H. and Greep,H.O. Effects of prostaglandins on ovarian steroid secretion and biosynthesis during pregnancy, Amer.J.Physiol. 221 , 189-193 (1971).

ChatterJee,A. The possible mode of action of prosta- glandins. II. Failure of prostaglandin F2~ in the pre- vention of compensatory ovulation and ovarian hyper- trophy following unilateral ovariectomy in rats, Acta endocrinol (kbh). 70 , 786-790 (1972).

McCrac~(en,J.A., Balrd,D.T. and Goding,J.~. Factors affecting the secretion of steroids by the transplanted ovary in the sheep, Rec.Progr.Rormone Res. 27 t 537-582 (1971).

Labhsetwar,A.P. Prostaglandins in reproduction, In Natural compound and Biological Regulators, Vol.II. (M.Gato, editor) Georg Thieme Verlag, Stuttgart (1972, Press).

Behrman,H.~., MacDonald,G.J. and Greep,R.O. Regulation of ovarian cholesterol esters t Evidence for enz#matic sites of prostaglandln-induced loss of corpus luteum function, Lipids. 6 , 791-796 (1971).

F E B R U A R Y 1973 VOL. 3 NO. 2 199