Platelet angiotensin II binding in pregnant women with chronic hypertension Philip N. Baker, DM, and Fiona Broughton Pipkin, DPhil Nottingham, United Kingdom

Levels of platelet angiotensin 11 binding were significantly lower in pregnant women with chronic hypertension compared with those of women with gestational hypertension (p < 0.01) and approximated those of normotensive pregnant women. (Am J OBsTET GYNECOL 1994; 170: 1301-2. )

Key words: Angiotensin II, platelet membrane glycoproteins, pregnancy, hypertension, renin-angiotensin system

Specific angiotensin Il (All) binding sites with many of the characteristics of receptors have been demon- strated on the surface of human platelets. " ' In preg-

From the Department of Obstetrics and Gynaecoloo University Hospital. Supported by the British Heart Foundation. Received for publication September 7,1993; revised October 15, 1993; accepted November 1,1993. Reprint requests: F. Broughton Apkin, DPhil, Department of Ob- stetrics and Gyn4ecology, University Hospital, QMC, Nottingham NG7 2UH, United Kingdom. Copyright 0 1994 by Mosb)-Year Book, Inc. 0002-9378194 $3.00 +0 611152564

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nancy levels of platelet All binding have been found to mirror changes in AII pressor sensitivity, with decreased binding in normotensive pregnancy and increased binding in pregnancies complicated by gestational hy- pertension. ' Indeed, measurement of platelet All bind- ing has been suggested as a more acceptable screening test for gestational hypertension than is the invasive All

sensitivity test. ' In nonpregnant subjects essential hypertension is not

associated with altered levels of platelet All binding. ' There have been no previous studies of platelet All binding in pregnant women with chronic hypertension.

hypertensive

GROUPS Fig. 1. Platelet All binding in the eight pregnant women with chronic hypertension. Interquartile ranges of binding in normotensive pregnant women and women with gestational hypertension (PIH) are shown for comparison. Horizontal lines, Median values.

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Eight nulliparous pregnant women with elevated blood pressures at the initial antenatal clinic visit (me- dian 140/85 mm Hg, range 130/80 to 150/95 nun Hg) and in the third trimester of pregnancy (140/90 mra fig, range 140/90 to 160/100 mm Hg) were recruited. All eight women had elevated blood pressures when reviewed 3 months after delivery (135/90 mm Hg, range 130/85 to 155/100 mm Hg). No subject had clinically detectable proteinuria during or after pregnancy. Be- fore delivery 30 ml of venous blood was taken from each subject for measurement of platelet All binding and estimation of plasma All concentration, as previ- ously described. ', ' At the time of study no subject was taking any medication except iron and vitamin supple- ments.

At the time of investigation the maternal ages (25 years, range 17 to 42 years) and gestational ages (36 weeks, range 31 to 38 weeks) of the eight pregnant women with chronic hypertension did not differ signifi- cantly fro

,m either those of the previously studied nor-

motensive pregnant women or women with gestational hypertension' (P > 0.3, Z>-1.0, Mann-Whitney U test). As illustrated in Fig. 1, although there were no significant differences between the levels of platelet All binding in the pregnant women with chronic hyperten- sion (1-0 finol/10' cells, 0 to 2.7) and those of the

May 1994 Am j Obstet Gynecol

normotensive pregnant women' (P > 0.4), platelet All binding in the pregnant women with chronic hyperten- sion was significantly lower than had previously been found in women with gestational hypertension' (P < 0.0 1, Z=-2.7). There were no significant differ- ences between the levels of plasma All (29.4 pg/ml, range 10 to 250 pg/ml) in the pregnant women with chronic hypertension compared with the levels previ- ously found in normotensive pregnant women and in women with gestational hypertension (P > 0.1, Z>-1.6).

Only a small number of pregnant women with chronic hypertension are available for study. Neverthe- less, the finding that the values of platelet All binding in this group approximated those of normotensive pregnant women and were lower than those of subjects with gestational hypertension supports the concept that levels of platelet All binding are central to the devel- opment of gestational hypertension.

REFERENCES 1. Ding YA, Kenyon Cj, Semple PF. Regulation of platelet

receptors for angiotensin 11 in man. j Hypertens 1985; 3: 209-12.

2. Baker PN, Broughton Pipkin F, Symonds EM. Platelet angiotensin 11 binding sites in normotensive and hyperten- sive pregnancy. Br j Obstet Gynaecol 199 1; 98: 436-40.