PROSTAGLANDINS

POSSIBLE M.D.

ROLE

Mitchell,

FOR PROSTACYCLIN

IN HUMAN

J.G. Bibby,

Hicks

B.R.

PARTURITION

and A.C.

Turnbull

Nuffield Department of Obstetrics and Gynaecology, University of Oxford, John Radcliffe Hospital, Headington, Oxford, OX3 9DU, U.K. ABSTRACT Human amnion, chorion, decidua and placenta produced 6-oxo-PGFla when superfused -in vitro. Further more amnion, an avascular tissue, produced more 6-0x0PGFla after labour than all other tissues investigated and its production of 6-oxo-PGFla was significantly greater after labour than before the onset of labour. These findings suggest that prostacyclin production by foetal membranes may have a role in the mechanisms controlling human parturition. Moreover, this is the first evidence for the production of prostacyclin by an avascular tissue. INTRODUCTION Prostacyclin (PGI2) was first isolated and identified after its production from prostaglandin endoperoxides (PGG2 and PGH2) by aortic microsomes (1,2). Fresh arterial and venous tissues have also been shown to transform prostaglandin endoperoxides into prostacyclin (3,4) which is the most potent inhibitor of platelet aggregation so far described (1) and may also contract uterine muscle Prostacyclin is unstable (5). in aqueous media and is rapidly hydrolysed to 6-0x0PGFl The production of 6-oxo-PGFla hence reflects (2). pros & acyclin production and 6-oxo-PGFla production has now been demonstrated in several tissues (5-9). Little is known about prostacyclin production by human intrauterine tissues although recently placental tissue was shown to have prostacyclin-like activity (10). We the possible intra-uterine have, therefore, investigated sites of prostacyclin production during late human pregnancy and parturition by measuring production of 6 -0x0-PGFla by these tissues when superfused -in vitro.

DECEMBER 1978 VOL. 16 NO. 6

931

PROSTAGLANDINS

PATIENTS

AND METHODS

P l a c e n t a e w e r e o b t a i n e d f r o m two g r o u p s o f w o m e n w h o w e r e d e l i v e r e d at t e r m a f t e r u n c o m p l i c a t e d pregnancies. The f i r s t g r o u p c o m p r i s e d t e n w o m e n i n w h o m l a b o u r w a s of s p o n t a n e o u s o n s e t a n d d e l i v e r y w a s accomplished vaginally. In the s e c o n d g r o u p o f t e n women delivery was by eledtive caesarean section because of cephalo-pelvic disproportion, p r e s e n t a t i o n b y the b r e e c h o r a p r e v i o u s c a e s a r e a n section. The m e t h o d s o f tissue collection and superfusion have been fully desc r i b e d e l s e w h e r e (11-13). The time f r o m d e l i v e r y to the s t a r t o f s u p e r f u s i o n w a s a l w a y s l e s s t h a n 30 minutes. A r a c h i d o n i c a c i d w a s n o t a d d e d to the s u p e r f u s i o n m e d i u m f o r two r e a s o n s . F i r s t l y , we h a v e d e m o n s t r a t e d that s u f f i c i e n t e n d o g e n o u s s u b s t r a t e is available for prostaglandin p r o d u c t i o n to r e m a i n r e l a t i v e l y c o n s t a n t f o r at l e a s t t w i c e the e x p e r i m e n t a l p e r i o d (11,12). Secondly, recent findings have s u g g e s t e d t h a t the a d d i t i o n o f a r a c h i d o n i c a c i d to a n i n c u b a t i o n c a n a l t e r the n a t u r a l p r o p o r t i o n s of p r o d u c t s f o r m e d a n d in the c a s e c i t e d the p r o d u c t i o n o f 6 - o x o P G F I ~ w a s a d v e r s e l y a f f e c t e d (14). 6-oxo-PGFl~ was measured by radioimmunoassay as d e s c r i b e d p r e v i o u s l y (15), w i t h the o m i s s i o n o f c h r o m a t o g r a p h y since i n preliminary e x p e r i m e n t s m e a s u r e d l e v e l s in s u p e r f u s i o n medium were similar with or without chromatography (p > 0.1). S t a t i s t i c a l a n a l y s e s w e r e b y the M a n n W h i t n e y R a n k S u m T e s t a n d W i l c o x o n S i g n e d R a n k Test. RESULTS

The p r o d u c t i o n rates of 6-oxo-PGFl~ by the tissues studied a r e s u m m a r i z e d i n T a b l e 1. Only the production by amnion was significantly d i f f e r e n t b e t w e e n the two g r o u p s studied; there b e i n g g r e a t e r p r o d u c t i o n a f t e r labour. T h i s d i f f e r e n c e w a s e m p h a s i s e d b y the c o m p a r i son of rates of production between tissues. After s p o n t a n e o u s v a g i n a l d e l i v e r y the p r o d u c t i o n r a t e o f 6-oxo-PGFl~ by amnion significantly exceeded those of the o t h e r t i s s u e s s t u d i e d (p < 0.01) w i t h the r a t e o f production by chorion being significantly greater than t h o s e o f d e c i d u a (p < 0.02) a n d p l a c e n t a (p < O . O 1 ) . Decidual and placental rates of production were similar (p > 0.1). A f t e r e l e c t i v e c a e s a r e a n section, h o w e v e r , the r a t e o f p r o d u c t i o n of 6 - o x o - P G F 1 ~ b y a m u i o n w a s g r e a t e r t h a n t h a t of p l a c e n t a o n l y (p < 0.05); product i o n b y c h o r i o n e x c e e d e d t h a t o f p l a c e n t a (p < O . O 1 ) . O t h e r w i s e t h e r e w e r e no d i f f e r e n c e s i n the r a t e s of

932

DECEMBER 1978 VOL. 16 NO. 6

PROSTAGLANDINS

p r o d u c t i o n of 6 - o x o - P G F l ~ in this group. Comparison of the r a t e of p r o d u c t i o n of 6 - o x o - P G F _ with those of thromboxane B 2 (TXB 2) and p r o s t a g l a n d i ~ E and F (PGE, PGF) are i l l u s t r a t e d in Table 2. A r e l a t i v e l y consistent p a t t e r n of d i f f e r e n t i a l rates of p r o d u c t i o n emerged. Foetal membranes, p a r t i c u l a r l y anmion, p r o d u c e d p r e d o m i n a n t l y PGE and 6 - o x o - P G F l ~ whereas p l a c e n t a p r o d u c e d m a i n l y PGE and TXB 2. Decidual rates of p r o d u c t i o n were g e n e r a l l y similar.

TABLE

1

PRODUCTION

OF 6 - O X O - P G F I ~

BY P R E G N A N T

UTERINE

SUPERFUSED

TISSUES

Anmion Tissues

(NG P E R G DRY

W E I G H T P E R MIN)

obtained

spontaneous

after

vaginal

HUMAN

INTRA-

IN VITRO

Chorion

Decidua

Placenta

6.31

2.43

1.46

1.33

± 2.40

± 0.64

~ 0.43

± 0.39

delivery Tissues elective

obtained

at

caesarean

2.37

1.76

1.41

1.11

± 0.65

± 0.40

± 0.38

~ 0.21

section

Values are means ~ SEM of ten individual determinations. Each individual was o b t a i n e d from four i n d e p e n d e n t observations. *

p < 0.05 c o m p a r e d to p r o d u c t i o n elective c a e s a r e a n section.

DECEMBER 1978 VOL. 16 NO. 6

by tissue

taken at

933

PROSTAGLANDINS

A

t~ 40

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+I

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~J

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*-~

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~ tt~

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4"I

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+1

"l-I

+1

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~

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~ •1"1

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I

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~ o

o I

o I

o I

0

0

0

0

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~ 0 .H 40

~ 0 .d 40

0 .H 40

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o

gSS *

*

gSS

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DECEMBER

1978

oSS V

V

V

.

* *

* * *

VOL.

16 NO.

6

PROSTAGLANDINS

DISCUSSION These results d e m o n s t r a t e that h u m a n i n t r a - u t e r i n e tissues produce 6 - o x o - P G Y 1 ~ , and hence prostacyclin, w h e n s u p e r f u s e d in vitro. A l t h o u g h q u a n t i t a t i v e l y it was n e v e r the m a j o r p r o s t a g l a n d i n p r o d u c e d by any single tissue, the g r e a t e r p o t e n c y of p r o s t a c y c l i n in m a n y b i o l o g i c a l systems w o u l d suggest that it is the m a j o r p r o s t a g l a n d i n p r o d u c e d w h e n c o n s i d e r i n g overall b i o l o g i cal activity. The control of placental, and p e r h a p s foetal, h a e m o d y n a m i c s m a y provide both a l i k e l y and crucial role for p r o s t a c y c l i n p r o d u c e d w i t h i n the uterus. The f i n d i n g of measurable, i n d e e d high, rates of p r o d u c t i o n of 6 - o x o - P G Y l ~ by a m n i o n has at least two i n t e r e s t i n g aspects. Flrstly, a growing b o d y of evidence has led Liggins (16) to propose that the onset of l a b o u r in m a n m a y be i n i t i a t e d by a signal a r i s i n g in the foetal m e m b r a n e s i n v o l v i n g p r o s t a g l a n d i n s . The l a b o u r a s s o c i a t e d increase in the rate of p r o d u c t i o n of 6-oxo-PGY by a m n i o n is c o n s i s t e n t w i t h the e x t e n s i o n of such an h y p o t h e s i s to embrace p r o s t a c y c l i n . Secondly, to our knowledge, this is the first d e m o n s t r a t i o n of p r o s t a c y c l i n p r o d u c t i o n by an a v a s c u l a r tissue (17). It has b e e n shown that p r o s t a c y c l i n may be formed in the absence of p l a t e l e t s ( 1 8 , 1 9 ) , h o w e v e r our findings d e m o n s t r a t e that p r o s t a c y c l i n may be formed in the absence not o n l y of p l a t e l e t s but also of b l o o d vessels. The p h y s i o l o g i c a l s i g n i f i c a n c e of p r o s t a c y c l i n p r o d u c t i o n by a m n i o n remains to be elucidated. Although the s i g n i f i c a n t increase in the rate of p r o d u c t i o n w i t h l a b o u r suggests a role in the m e c h a n i s m of h u m a n p a r t u r i tion, o t h e r p o s s i b i l i t i e s such as the control of amniotic fluid volume and content r e m a i n to be explored. ACKNOWLEDGEMENTS We thank Dr. J.E. Pike (Upjohn Co., Kalamazoo, U.S.A.) and Drs. K. Gibson, S.R. Slater and B.J.A. Purr (I.C.I. Ltd., M a c c l e s f i e l d , U.K.) for gifts of a u t h e n t i c 6-oxo-PC~F1~. M.D.M. a c k n o w l e d g e s r e c e i p t of the Staines M e d i c a l R e s e a r c h F e l l o w s h i p at Exeter College, Oxford. This w o r k was s u p p o r t e d by an M.R.C. Programme Grant a w a r d e d to A.C.T.

DECEMBER 1978 VOL. 16 NO. 6

935

PROSTAGLANDINS

REFERENCES

I.

Moncada, S., Gryglewski, R., Bunting, S. and Vane, J.R. An enzyme isolated from arteries transforms p r o s t a g l a n d i n endoperoxides to an unstable substance that inhibits platelet aggregation. Nature 26~: 663, 1976.

2.

Johnson, R.A., Morton, D.R., Kiuner, J.H., Gorman, R.R., McGuire, J.C., Sun, F.F., Whittaker, N., Bunting, S., Salmon, J.A., Moncada, S. and Vane, J.R. The chemical structure of prostaglandin X (prostacyclin). Prostaglandins 12: 915, 1976. m

.

Gryglewski, R., Bunting, S., Moncada, S., Flower, R. and Vane, J.R. Arterial walls are protected against deposition of platelet thrombi by a s u b stance (prostaglandin X) which they make from p r o s t a g l a n d i n endoperoxides. Prostaglandins 12: 685, 1976. Moncada, S., Higgs, E.A. and Vane, J.R. Human arterial and venous tissues generate p r o s t a c y c l i n (prostaglandin X) a potent inhibitor of platelet aggregation. Lancet ~: 18, 1977.

.

Omini, C., Moncada, S. and Vane, J.R. The effects of p r o s t a c y c l i n (PGI 2) on tissues which detect prostaglandins (PG's). Prostaglandins I~4 : 625,

1977. .

936

Dawson, W., Boot, J.R., Cockerill, A.F., Mallen, D.N.B. and Osborne, D.J. Release of novel prostaglandins and thromboxanes after immunological challenge of guinea pig lung. Nature 262 : 699, 1976.

.

Pace-Asciak, C.R. Isolation, structure and b i o synthesis of 6 - k e t o - p r o s t a g l a n d i n FI~ in the rat stomach. Journal of the American Chemical Society 98: 2348, 1976.

.

Fenwick, L., Jones, R.L., Naylor( V., Poyser, N.L. and Wilson, N.H. P r o d u c t i o n of prostaglandins by the p s e u d o - p r e g n a n t rat uterus, in vitro, and the effect of tamoxifen with the ident---ification of 6k e t o - p r o s t a g l a n d i n FI~ as a major product. British Journal of P h a r m a c o l o g y 59: 191, 1977-

DECEMBER 1978 VOL. 16 NO. 6

PROSTAGLANDINS .

Pace-Asciak~ C.R. and Rangaraj, G. The 6-ketoprostaglandin FI~ pathway in the lamb ductus arteriosus. Biochimica et Biophysica Acta 486:

583, 1977. 10.

Myatt, L. and Elder, M.G. Inhibition of platelet aggregation by a placental substance with prostacyclin-like activity. N a t u r e 2 6 8 : 159, 1977.

11.

Mitchell, M.D. and Flint, A.P.F. Prostaglandin production by intra-uterine tissues from periparturient sheep: use of a superfusion technique. Journal of Endocrinology 76: 111, 1978.

12.

Mitchell, M.D., Bibby, J.G., Hicks, B.R. and Turnbull, A.C. Specific production of prostaglandin E by human amnion in vitro. Prostaglandins1~:

377, 1978. 13.

Mitchell, M.D., Bibby, J.G., Hicks, B.R., Redman, C.W.G., Anderson, A.B.M. and Turnbull, A.C. Thromboxane B 2 and human parturition: concentrations in plasma and production in vitro. Journal of Endocrinology. In press.

14.

Sun, F.F. and McGuire, J.C. In: Advances in ProstaElandin and Thromboxane Research Vol 4 ( F . Coceani and P.M. Olley, eds). Raven Press, New York, 1978, p. 75.

15.

Mitchell, M.D. A sensitive radioimmunoassay for 6-keto-prostaglandin FI~: preliminary observations on circulating concentrations. Prostaglandins and Medicine I: 13, 1978.

16.

Liggins, G.C., Forster, C.S., Grieves, S.A. and Schwarz, A.L. Control of parturition in man. BioloEy of Reproduction 16: 39, 1977.

17.

Bourne, G.L. The microscopic anatomy of the human antnion and chorion. American Journal of Obstetrics and Gynecology 79: 107 ° , 1960.

18.

De Deckere, E.A.M., Nugteren, D.H. and Ten Hoor, F. Prostacyclin is the major prostaglandin released from the isolated perfused rabbit and rat heart. Nature 268: 160, 1977.

19.

MacIntyre,

D.E., Pearson,

J.D. and Gordon,

J.L.

Localisation and stimulation of prostacyclin production in vascular cells. Received

8/1/78 - Approved

DECEMBER 1978 VOL. 16 NO. 6

Nature 271: 549,

1978.

10/8/78 937