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Blood Lipids in Preeclampsia*
BLOOD LIPIDS IN PREECLAMPSIA'" ELDO~
M.
BOYD,
M.A., M.D., C.l\L,
KI~GRTON. C\!"ADA
(F1'om Quan's Uni'l'i'rsity)
T HAS been preyiously shown in this JOURNALl that the convulsive and preconvulsive stages of eclampsia are characterized by a signifieant increase in the ratio of phospholipid to total cholesterol values of blood plasma. At that time it was intimated that a further stndy of this relationship was being made in eases diagnosed as prl?eelampsia in an effort to determine if this ill-defined eoudition eould he ~mhdivided on the hasis of the plasma P ITC ratio. The TH'csent report is concerned with blood lipid findings in 49 eases of preedampsia. Previous literature on this subject has been covered in the former commnnication. 1 Professor H. Kurten of Munich has kindly informed the author that he had already suggested that lipid ratios were of significanee in the toxemias of pregnancy and eclampRia in a paper pnhlished in 1!l24.2 The pres('nt series of easeR were of sever(' or relatively severe }ll'Peclampsia. The patients exhihited hypcrtellRlon, albuminuria and ed('ma all of considerable extent. In addition many complained of headaehes, visual disturbances, and oliguria. Renal function tests (phenol· phthalein excretion, 11rea elearance, polyuria. etc.) occasionally indio cated some impairment of rena] activity but the results were not eonsistent. Likewise the usual blood chemistI)' finding'S were of a variable nature (urea, uric acid, creatinine, sugnr, carbon dioxide, cte.). All patients were at or near the termination of pregnancy. and there was no history OI' other evidence of chronic nephritis in the group hereill repm1(>d. ~md toxemias with slight h~'Iwrtellsioll or albumilluria hay!' not h('en included in this series, althongh ill incid('lH'c they comprised about all ('qnal number to the mOl'e seyere cases aUll most of them, 1'<11' tlw lack of (lata to the contrary, were diag-nosN! as preeelampsia. An oxalated specimen of blood WHS obtained in the morning usually under fasting conditionR. All pHtients wpre hospitalized at the time' blood was taken, and under these conditioIlR breakfast does not appreciably affect plasma lipid values of normHI persons,! hut there may be a slight difference in the values of the red blood eells.~ Potassium oxalate as ,Ill antieoagnlallt tend!; to dilute plasma l'esulting: ill ahout 10 per ('cnt lower values for the lipids 6 but oxalated hlood was uRed .in the previous studies of normal pregnall!'y and edampsill with whirh it was deRil'etl to
I
"Received for publication. May 7, 1936. '[his work was aided financially by the Alice F. Richardson Fund of the Kingston Uen",ral Hospital, and was begun While the authol" was associated with the University of Jt,,('hf~ster School of Medicine and Dentistry, Rochest
937
988
AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY
compare the present results. Extracts of plasma and of the red blood cells were prepared and each was analyzed by the author's modification of Bloor '8 oxidative microtechnic,7. 8 When the cases were considered collectively by means and standard deviations, there appeared to be no significant variations from the corresponding values for normal pregnancy,S Since the significant variation found in eclampsia was an increase in the plasma P fTC ratio, a frcquency distribution curve of this value in preeclampsia was prepared, This is sho'wn in Fig. 1. It is obvious that there are two peaks in the distribution and that it is possible to construct two frequency curves. This indicated that there were two types of cases in the prceclamptic
10
0.7
0.9
u
1.5 13 PLASMA P/TC RATIO
11
1.9
ji'ig, I.-The frequency distribution of values for the plasma P/TC ratio in 49 cases of preeclampsia,
group, one having a relatively normal plasma P JTC ratio and another smaller group in which the ratio was elevated as in eclampsia, An arbitrary ratio value of 1.5 was taken as the dividing line and the cases tabulated into two groups according to whether their ratio was above or below 1.5, It is recognized that a few cases of the lower ratio group might have values above 1.5 iu a Im'ge series and that a few eases of the higher ratio group might be below l,ri. To be on the safe side when a question of therapy is involved, the author advises the use of 1.4 as the lower limit for potential eclamptiCf; since values in the vfcLiss have been found in eclampsia. ' The value of 1.5 was selected now since it was desired to compare lipid values for plasma and the red blood
BOYD:
9:l9
BLOOD LIPIDS IN PREECLAMPSIA
cells in the two groups and 1.5 appeared to be the nearest delineation statistically. The value of the ratio depends, of course, upon the methods used for phospholipid and total cholesterol, but it would appear possible to employ methods other than those used by the author, providing the normal range and the range in the two groups of preeclampsia be first established. A comparison of plasma lipid values in the normal and high ratio groups of preeclampsia is giYen in Table I. The complete tabulation of all yaluefl would require the presentation of some one thousand figures. TABLE I. AN ANALYSIS OF THE LIPID VALUES FOUND IN BLOOD PLASMA IN PRE· ECLA:llPSJAi THE RESULTS ARE EXPRESSEll IN MG. PER 100 C.C'. OF PLASMA (o~{POSrrION
VALrE
LIPID
01" TOTAl, LIPID
i PHOS, _ _-,-_--;-_ _ PHO-
NEUTRAL FAT
LIPID RATIOS
Normal Ratio Group (38 Cases)
Total lipid 655 126 Maximum 'rotal lipid 1380 .553 Mean values 953 342 Htandard devia- 208 122 tion Rtandard devia- 22% 36% tion in per cent of mean
2HJ
1.04
3,48
1,48
::li4 2(\8
1.13 1.14 0.17
3.28 3.67 0.58
1.72
:n% 15%
]fl%
7 o/(~,
55
28%
21%
28%
22%
Vifi 0.12
High Ratio Group (11 Cases)
Total lipid 840 Maximum Total lipid 1350 Mean values 990 181 Standard tion Standard 18% tion in per cent of mean
97 382 352 183
482
213
2.t\2 2,4!J 2~73
0.7+ 27t}f,
and hence a statistical method has been employed. The formula used for calculating the standard deviation has been previously given in this JOURNAL. 1
It may be seen from Table I that there were no marked differences in the plasma lipid values between the two types of preeclampsia. The high ratio group tended to have higher values for all lipids except ester cholesterol which was low and consequently produced a low total cholesteroL Along with this tendency to a low ester cholesterol, plasma phospholipid was somewhat higher in the high ratio group. Comparing mean values, ester cholesterol was 28 per cent lower and phospholipid 37 per cent higher in the high than in the normal ratio group of preeclampsia. In no ease was the range of \'alues in one group beyond the
940
AMERICAN JOURNAL OF OBS'l'ETRICS AND GYNECOLOGY
range in the other as calculated from the means and standard deviations. Practically all the plasma lipid values in both groups of preeclampsia were higher than those previously found in normal pregnancy,3 but the differences were in no case sufficiently great to extend the expected range beyond that of normal gravidas. It may be concluded that this group of the toxemias of pregnancy tends to exhibit a slightly greater lipemia than normal pregnancy, but t.his is of academic interest only since cases even of eclampsia Inay show relatively low plasma lipid values. 1 From the practical point of view, one cannot distinguish preeclampsia from normal pregnane;;.' h;;.' comparing plasma lipid values in anyone given case. On the other hand there is evident a significant difference in the phospholipid to cholesterol ratios. In the normal ratio group of preeclampsia, the mean value of the plasma P ITO ratio was 1.14 with a standard deviation of 0.17. This mean plus the standard deviation in this group ( = 1.31) was t.hus lower than the mean minus the standard deviation 0.26 1.42). Statistic.ally, approxiof the high ratio group (1.68 mately 75 pel' cent of cases of the high ratio g-ronp ma:" lw t'xpected to have plasma P ITC' ratios ahove 75 per c.ent ('ases in the low or normal ratio group. Prac.tically, this would appear to he a ready means of distinguishing between these two types of preeelampsia. On reviewing the case histories in relation to the subdivision of preeclampsia hy means of the plasma P /TC ratios, it was found hnpossible to designate any further symptomatic difference between the types. In general the high ratio group showed more severe symptoms, hut this was far from an absolute rule. In view of the similarity in findings hetween the high ratio group of preeclampsia and eclampsia itself,l it is offered that the two conditions represent one and the flame disease. in the one case without and in the other rase with convulsions. On the other hand, the majority of eases now inc1uded under the diagnosis of preeclampsia do not appear to be literalJy preeclamptic. at all. Of the present series, 38 casefl out of 49 were of a normal ratio (~ noneelamptic) type or 78 per cent of the whole group. Since many milder cases diagnosed as preeclampsia were not included in this study, it. is likely that the incidence of high ratio cases (~ truly preeclamptic) would be not more than 10 per cent of the whole group. Plasma c.holesterol is composed of two fractions, a free or unbound type and cholesterol linked with fatty acids to form cholesterol esters. This latter fraction is usually designated ester cholesterol. In the plasma of normal persons, cholesterol estel'S constitute by weight the lipid of greatest bulk present. 'I'he question arose as to whether only the ratio of phospholipid to total cholesterol (P ITC) was the signifieant difference or if thel'e were also significance differences in the ratio of phospholipid to free (P /FC) and to ester cholesterol (P lEe) . Hence these latter
BOYD:
BLOOD LIPIDS IN PREECI,A}fPSTA
~l41
two ratios were also calculated and a statistical analysis OT the results included in Table 1. It may be seen that the P IFC ratio was higher in the high ratio group but that the ranges overlapped. However, Ii l'pal diffprerwe existed in the P IBC ratios: the IUelin pIns the shmdard devil!· lion of the l10rmal ratio group (1.65 ., 0.12 = ].77) was lower than the mean minus the standard deviation ot tlw high ratio group (2.73 - 0.7-1 1.99). In fact the differences were of the same order of magnitu(\(' as those of tlle P ITC ratio. There wonld thus appear to be some dis· tnrbance in the normal balance between plasma phospholipid and plasma cholesterol esters in this group of preeclampsia, and it may be notrd at this point that these two lipids constitute the bulk of all lipids normall~' present in human blood plasma. The, let us say, truly preeclamptie group may thus be distinguished from the remaining cases of' pel'· eclampsia by the plasma P lEe ratio as well as the plasma P ITC ratio. As a matter of fact it is easier to determine total cholesterol than ester cholesterol by the author's technic and by most other methods of lipid analysis. So that there is little to be gained and more work involved in determining the P lEe ratio rather than the P ITC ratio, The significanee of the phmrpholipid to cholesterol ratios is f111'th01' evidenced by a comparison of their relative variation wit.h that of the aetnal lipids, This has been shown in Tahle I under "standard dedation in perc'ent of mean." It lllay he seen that in practically all eases thel'p was less relative variation in the lipid ratios than in the aetna I lipid valnes. This would indicate that whereas the lipids themselves may ntry considerably in value, there is a tendency toward the maintenance of a relatively constant ratio between them. The lipid composition of the red blood cells in the two groups of PI'\'edampsia has been given in Table II. In general, it may be said that the red cells of the normal ratio group contained slightly more of almost all lipids than was found in the red cells of normal gravidas,3 while thosr of the high ratio group contained slightly less than healthy pregnant. women. This may be seen only in the means and is not apparent from individual eases, nor is the range of one group beyond the range of' the other. From the first few eases studied, it was calculated thai there was a significant increase in red cell neutral fat in the noncon,ulsive toxemias,9 but further studies indicated, as herein pointe(l out, that this difference was not as great as was at first thought. The relative yariations of the red cell lipids are well illustrated in Table II. Neutral fat and cholesterol esters were found to be extremely variable and usually present in small quantities only. These red cell extracts were prepared in the conventional manner by heating [or It !5hort time the alcohol-ether extract of the hemolyzed cells. This pro('edure introduced colored decomposit.ion products of hemoglobin, and fl'OllI work now in progress, it is apparent that this colored matter t.ends
942
AMERICAX JOURNAL OF OBSTETRICS AND GYNECOLOGY
to give false high values for all lipids and especially neutral fat. Rowever the same method of extraction was used in the eclamptic cases and a comparable one in normal pregnancy with (loth of which the present values have been compared. The lipids least variable in amount in the red cells were phospholipid and choleRterol, and these together constitute the bulk of red cell lipids. TABLE
II.
AN ANALYSIS OF LIPID VALUES FOUND IN THE RED BWOD CEr,LS IN PREMo. PER 100 C.C. OF RED CELLS
ECI~AMPSIA; THE RESULTS ARE EXPRESSED IN
COMPOSITION OF TOTAL LIPID TOTAL LIPID
VALUE
NEU· TRAL FAT
!
TOTAL FATTY
i.
ACIDS
.II
CHOLESTEROL TOTAl, lESTER
J
FREE
J.
PIIOS' PHOLIPID
N onnal Ratio Group Total lipid Maximum Total lipid Mean values Standard deviation Standard deviation in per cent of mean
I
418
169
289
60
1067 626 177 28%
377 103 142 138%
732
;162 142 39%
128 135 35 26%
69
0
60
191
0 20 31 155%
128 115 34 30%
562 374 95 26%
0
69
167
127 89
367 310 74 24%
High Ratio Group Minimllm
Total lipid Maximum Total lipid Mean values Standard deviation Standard deviation in per cent of mean
236 805 519 181 35%
0 311 77 118 153%
I 112 540 299 139 47%
I
127 118 37 31%
0 29 37 128%
26
29%
DISCUSSION
It has been shown that plotting the :frequency distribution o:f plasma p ITC ratios in preeclampsia reveals the presence of two types of cases, one with a normal range of ratio values and a smaller group with elevated ratios. The findings in the latter group were comparable to th{)se previously found in eclampsia. Renee, it is postulated that the high ratio group o:f preeclampsia represents cases of eclampsia without convulsions, while the normal ratio group may be an entirely separate condition. It cannot be gainsaid on present information that cases with a normal ratio may not go on to a high ratio if left untreated, and this point is being :further investigated. From the small amount of data now available, it does not appear that a normal ratio commonly, if at all, becomes an increased one. A statistical eomparison of plasma and red cell lipids revealed that no lipid value possessed a range, determined from the mean plus and minus the standard deviation, significantly different in one group from the range in the other. The high ratio group of preeclampsia tended to have a slightly greater plasma lipid content and slightly lower red cell lipid
-.<1
BOYD:
BLOOD LIPIDS IN PREECIJA){PSIA
943
f'ontent on the average. The high ratio in this group was due chiefly to relatively higher values for phospholipid and lower values for PElt!'r eholesterol. These several observations indicate some disturbance in lipid metabolism. It has been knOW"1l for many years that lipid metabolism is altered in pregnancy, and the present work has shown that there oecurs It further abnormal change in eclampsia and in a group which may be separated from what we now diagnose as preeclampsia. The nature of this disturbance in lipid metabolism has been, and still is, enveloped ill obscurity; its cause, its importance, its effect, even its nature are largely unknown. In the past few years the author has been interested in these problems, but in spite of a good deal of work barely more than the surface has been scratched. It has been shown that the lipemia of pregnaney in women is analogous chemically to lipemias in other conditions and is eharacterized by an orderly increase in plasma lipid values with no change in the lipids of the red blood ce11s.3 Following parturition, the lipemia gradually subsides, but if normal lactation be prevented. a further lipemia supervenes which may be taken to indicate that the drying up of the breasts, though frequently resorted to, is in reality pathologic. lO At the end of prt!gnancy, the leucocyte count is usually elevated, but the lipid content of the white cells is not significantly changed: after labor there is an increase in the phospholipid and free cholesterol of the blood leueocytes (indicative of increased activity) and an increase in neutral fat which latter probably represents a scavenger action on the part of the white cells in removing debris fat from the involuting uterusY Evidenee has been presented that the human placenta is "permeable" to lipids and that a good deal of fatty substances, especially phospholipids, is absorbed by the human fetus from the umbilical circulation, suggesting that one result of the lipemia in the mother may possibly be the nourishment of the infant in utero.12 The latter part of pregnancy in rabbits 13 and guinea pigs14 was found associated with evidence of increased lipid metabolism in the placenta, suggesting that the placental tissues may be actively engaged in the transfer of lipids from the mother to the offspring. In the rabbit it was found that a marked increase in the lipid content of the fetus does not occur until the latter third or so of gestation,t3 at which time the lipid metabolism of the placenta also increases. It does not appear that the lipemia of pregnancy in women is of toxic origin, since an even greater lipemia may occur in the lower animals, for example guinea pigs. is There is a certain amount of dil'ect evidence that the changes in endocrine balance during pregnancy may have something to do ",ith the changes in the concentration of blood lipids. By comparing blood lipid values in pregnant and pseudopregnant rabbits, it was possible to show that in early gestation certain
944
AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY
changes may be rlne to the direct or indirect effects of the products of conception and other changes to the direct or indirect effects of the presence of the corpus luteum.lfi In the rabbit, in which a lipopenia or decrease in blood lipid values occnrs rlnring' pregnancy (for the use of the term lipopenia see Boyd17 ), there is a marked rise and fall in the lipid composition of the ovary. 18 On the other hand a lipemia is found during pregnancy in guinea pigs as in women I !> and practically no change occurs in the lipid content of guinea pig ovaries throughout gestation. '9 The author has also found in unpublished experiments the phospholipid and free cholesterol content of the human ovary to he quite low at the end of pregnancy in one or two cases studied. This evidence points to the endocrine system as a factor in the disturbed lipid metabolism of pregnancy hut is far from sufficient to establish the exact relationship. SUM:\IARY
The lipid composition of blood plasma and of the red blood cells was determined by oxidative micromethods in 49 cases of preeclampsia. On the basis of the plasma P ITC ratio it was possible to show that these eases could be divided into two groups, one with a normal P ITC ratio and one in which the ratio was elevated As in eclampsia. Cases with a high plasma P ITC ratio tended to have slightly higher plasma lipid valnes and slightly lower red cell lipid values than cases of a normal ratio. The increase in the plasma P ITC ratio was due chiefly to relatively high plasma phospholipid and relatively low plasma ester cholesterol values. It is offered that cases of preeclampsia with a high ratio are in reality eclampsia without convulsions, while the remaining normal ratio cases are not literally preeclamptic at all. The significance of changes in lipid metabolism during gestation has been discussed. REFERENCES
(1) Boyd, E. M.: AM. J. OBST. & GY:>lEC. 30: ::23, 19:15. (2) Kurten, H.: Klin. \\,(·hn~ehr. 3: 1216, 1924. (3) Boyd, E. le.: J. Clin. Inve8tigation 13: 347, 1934. (4) Idem: J. BioI. Chern. 110: 61,1935. (5) Bayd, E. M., and 1'weddeU, H. J.: Trans. Royal Soc. Canada, Sect. V 29: 113, 1935. (6) Boyd, E. M.: .T. BioI. Chern. 114: 223, 1936. (7) Idem: J. BioI. Ohem. 91: 1, 1931. (8) Idem: J. BioI. Chern. 101: 323, 1933. (9) Idem: Unpublished data presented before the Royal Soc. Canada, Hamilton, Ontario, May, 1935. (10) Idem: AM. J. OnST. & GYNEC. 29: 797, 1935. (11) Idem: Surg. Gynec. Obst. 59: 744, 1934. (12) Boyd, E. M., and Wilson, K. M.: J. Clin. Investigation 14: 7,1935. (13) Boyd, E. M.: Biochern. J. 29: 985,1935. (14) Idem: Oamtd .•J. Researeh B. 14: 155, 193!5. (15) Boyd, E. M., and Fellows, M.: Am. J. Physiol. 114: 635, 1936. (16) Boyd, E. M.: J. Physiol. 86: 250, 1936. (17) Idem: Canad. M. A. J. 32: 500, Ill35. (18) Idl'tn: J. BioI. Chern. 108: 607, 193fi. (11) Idem: .T. BioI. Ohern. 112: 591,1935·1936.
M.
BOYD,
M.A., M.D., C.l\L,
KI~GRTON. C\!"ADA
(F1'om Quan's Uni'l'i'rsity)
T HAS been preyiously shown in this JOURNALl that the convulsive and preconvulsive stages of eclampsia are characterized by a signifieant increase in the ratio of phospholipid to total cholesterol values of blood plasma. At that time it was intimated that a further stndy of this relationship was being made in eases diagnosed as prl?eelampsia in an effort to determine if this ill-defined eoudition eould he ~mhdivided on the hasis of the plasma P ITC ratio. The TH'csent report is concerned with blood lipid findings in 49 eases of preedampsia. Previous literature on this subject has been covered in the former commnnication. 1 Professor H. Kurten of Munich has kindly informed the author that he had already suggested that lipid ratios were of significanee in the toxemias of pregnancy and eclampRia in a paper pnhlished in 1!l24.2 The pres('nt series of easeR were of sever(' or relatively severe }ll'Peclampsia. The patients exhihited hypcrtellRlon, albuminuria and ed('ma all of considerable extent. In addition many complained of headaehes, visual disturbances, and oliguria. Renal function tests (phenol· phthalein excretion, 11rea elearance, polyuria. etc.) occasionally indio cated some impairment of rena] activity but the results were not eonsistent. Likewise the usual blood chemistI)' finding'S were of a variable nature (urea, uric acid, creatinine, sugnr, carbon dioxide, cte.). All patients were at or near the termination of pregnancy. and there was no history OI' other evidence of chronic nephritis in the group hereill repm1(>d. ~md toxemias with slight h~'Iwrtellsioll or albumilluria hay!' not h('en included in this series, althongh ill incid('lH'c they comprised about all ('qnal number to the mOl'e seyere cases aUll most of them, 1'<11' tlw lack of (lata to the contrary, were diag-nosN! as preeelampsia. An oxalated specimen of blood WHS obtained in the morning usually under fasting conditionR. All pHtients wpre hospitalized at the time' blood was taken, and under these conditioIlR breakfast does not appreciably affect plasma lipid values of normHI persons,! hut there may be a slight difference in the values of the red blood eells.~ Potassium oxalate as ,Ill antieoagnlallt tend!; to dilute plasma l'esulting: ill ahout 10 per ('cnt lower values for the lipids 6 but oxalated hlood was uRed .in the previous studies of normal pregnall!'y and edampsill with whirh it was deRil'etl to
I
"Received for publication. May 7, 1936. '[his work was aided financially by the Alice F. Richardson Fund of the Kingston Uen",ral Hospital, and was begun While the authol" was associated with the University of Jt,,('hf~ster School of Medicine and Dentistry, Rochest
937
988
AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY
compare the present results. Extracts of plasma and of the red blood cells were prepared and each was analyzed by the author's modification of Bloor '8 oxidative microtechnic,7. 8 When the cases were considered collectively by means and standard deviations, there appeared to be no significant variations from the corresponding values for normal pregnancy,S Since the significant variation found in eclampsia was an increase in the plasma P fTC ratio, a frcquency distribution curve of this value in preeclampsia was prepared, This is sho'wn in Fig. 1. It is obvious that there are two peaks in the distribution and that it is possible to construct two frequency curves. This indicated that there were two types of cases in the prceclamptic
10
0.7
0.9
u
1.5 13 PLASMA P/TC RATIO
11
1.9
ji'ig, I.-The frequency distribution of values for the plasma P/TC ratio in 49 cases of preeclampsia,
group, one having a relatively normal plasma P JTC ratio and another smaller group in which the ratio was elevated as in eclampsia, An arbitrary ratio value of 1.5 was taken as the dividing line and the cases tabulated into two groups according to whether their ratio was above or below 1.5, It is recognized that a few cases of the lower ratio group might have values above 1.5 iu a Im'ge series and that a few eases of the higher ratio group might be below l,ri. To be on the safe side when a question of therapy is involved, the author advises the use of 1.4 as the lower limit for potential eclamptiCf; since values in the vfcLiss have been found in eclampsia. ' The value of 1.5 was selected now since it was desired to compare lipid values for plasma and the red blood
BOYD:
9:l9
BLOOD LIPIDS IN PREECLAMPSIA
cells in the two groups and 1.5 appeared to be the nearest delineation statistically. The value of the ratio depends, of course, upon the methods used for phospholipid and total cholesterol, but it would appear possible to employ methods other than those used by the author, providing the normal range and the range in the two groups of preeclampsia be first established. A comparison of plasma lipid values in the normal and high ratio groups of preeclampsia is giYen in Table I. The complete tabulation of all yaluefl would require the presentation of some one thousand figures. TABLE I. AN ANALYSIS OF THE LIPID VALUES FOUND IN BLOOD PLASMA IN PRE· ECLA:llPSJAi THE RESULTS ARE EXPRESSEll IN MG. PER 100 C.C'. OF PLASMA (o~{POSrrION
VALrE
LIPID
01" TOTAl, LIPID
i PHOS, _ _-,-_--;-_ _ PHO-
NEUTRAL FAT
LIPID RATIOS
Normal Ratio Group (38 Cases)
Total lipid 655 126 Maximum 'rotal lipid 1380 .553 Mean values 953 342 Htandard devia- 208 122 tion Rtandard devia- 22% 36% tion in per cent of mean
2HJ
1.04
3,48
1,48
::li4 2(\8
1.13 1.14 0.17
3.28 3.67 0.58
1.72
:n% 15%
]fl%
7 o/(~,
55
28%
21%
28%
22%
Vifi 0.12
High Ratio Group (11 Cases)
Total lipid 840 Maximum Total lipid 1350 Mean values 990 181 Standard tion Standard 18% tion in per cent of mean
97 382 352 183
482
213
2.t\2 2,4!J 2~73
0.7+ 27t}f,
and hence a statistical method has been employed. The formula used for calculating the standard deviation has been previously given in this JOURNAL. 1
It may be seen from Table I that there were no marked differences in the plasma lipid values between the two types of preeclampsia. The high ratio group tended to have higher values for all lipids except ester cholesterol which was low and consequently produced a low total cholesteroL Along with this tendency to a low ester cholesterol, plasma phospholipid was somewhat higher in the high ratio group. Comparing mean values, ester cholesterol was 28 per cent lower and phospholipid 37 per cent higher in the high than in the normal ratio group of preeclampsia. In no ease was the range of \'alues in one group beyond the
940
AMERICAN JOURNAL OF OBS'l'ETRICS AND GYNECOLOGY
range in the other as calculated from the means and standard deviations. Practically all the plasma lipid values in both groups of preeclampsia were higher than those previously found in normal pregnancy,3 but the differences were in no case sufficiently great to extend the expected range beyond that of normal gravidas. It may be concluded that this group of the toxemias of pregnancy tends to exhibit a slightly greater lipemia than normal pregnancy, but t.his is of academic interest only since cases even of eclampsia Inay show relatively low plasma lipid values. 1 From the practical point of view, one cannot distinguish preeclampsia from normal pregnane;;.' h;;.' comparing plasma lipid values in anyone given case. On the other hand there is evident a significant difference in the phospholipid to cholesterol ratios. In the normal ratio group of preeclampsia, the mean value of the plasma P ITO ratio was 1.14 with a standard deviation of 0.17. This mean plus the standard deviation in this group ( = 1.31) was t.hus lower than the mean minus the standard deviation 0.26 1.42). Statistic.ally, approxiof the high ratio group (1.68 mately 75 pel' cent of cases of the high ratio g-ronp ma:" lw t'xpected to have plasma P ITC' ratios ahove 75 per c.ent ('ases in the low or normal ratio group. Prac.tically, this would appear to he a ready means of distinguishing between these two types of preeelampsia. On reviewing the case histories in relation to the subdivision of preeclampsia hy means of the plasma P /TC ratios, it was found hnpossible to designate any further symptomatic difference between the types. In general the high ratio group showed more severe symptoms, hut this was far from an absolute rule. In view of the similarity in findings hetween the high ratio group of preeclampsia and eclampsia itself,l it is offered that the two conditions represent one and the flame disease. in the one case without and in the other rase with convulsions. On the other hand, the majority of eases now inc1uded under the diagnosis of preeclampsia do not appear to be literalJy preeclamptic. at all. Of the present series, 38 casefl out of 49 were of a normal ratio (~ noneelamptic) type or 78 per cent of the whole group. Since many milder cases diagnosed as preeclampsia were not included in this study, it. is likely that the incidence of high ratio cases (~ truly preeclamptic) would be not more than 10 per cent of the whole group. Plasma c.holesterol is composed of two fractions, a free or unbound type and cholesterol linked with fatty acids to form cholesterol esters. This latter fraction is usually designated ester cholesterol. In the plasma of normal persons, cholesterol estel'S constitute by weight the lipid of greatest bulk present. 'I'he question arose as to whether only the ratio of phospholipid to total cholesterol (P ITC) was the signifieant difference or if thel'e were also significance differences in the ratio of phospholipid to free (P /FC) and to ester cholesterol (P lEe) . Hence these latter
BOYD:
BLOOD LIPIDS IN PREECI,A}fPSTA
~l41
two ratios were also calculated and a statistical analysis OT the results included in Table 1. It may be seen that the P IFC ratio was higher in the high ratio group but that the ranges overlapped. However, Ii l'pal diffprerwe existed in the P IBC ratios: the IUelin pIns the shmdard devil!· lion of the l10rmal ratio group (1.65 ., 0.12 = ].77) was lower than the mean minus the standard deviation ot tlw high ratio group (2.73 - 0.7-1 1.99). In fact the differences were of the same order of magnitu(\(' as those of tlle P ITC ratio. There wonld thus appear to be some dis· tnrbance in the normal balance between plasma phospholipid and plasma cholesterol esters in this group of preeclampsia, and it may be notrd at this point that these two lipids constitute the bulk of all lipids normall~' present in human blood plasma. The, let us say, truly preeclamptie group may thus be distinguished from the remaining cases of' pel'· eclampsia by the plasma P lEe ratio as well as the plasma P ITC ratio. As a matter of fact it is easier to determine total cholesterol than ester cholesterol by the author's technic and by most other methods of lipid analysis. So that there is little to be gained and more work involved in determining the P lEe ratio rather than the P ITC ratio, The significanee of the phmrpholipid to cholesterol ratios is f111'th01' evidenced by a comparison of their relative variation wit.h that of the aetnal lipids, This has been shown in Tahle I under "standard dedation in perc'ent of mean." It lllay he seen that in practically all eases thel'p was less relative variation in the lipid ratios than in the aetna I lipid valnes. This would indicate that whereas the lipids themselves may ntry considerably in value, there is a tendency toward the maintenance of a relatively constant ratio between them. The lipid composition of the red blood cells in the two groups of PI'\'edampsia has been given in Table II. In general, it may be said that the red cells of the normal ratio group contained slightly more of almost all lipids than was found in the red cells of normal gravidas,3 while thosr of the high ratio group contained slightly less than healthy pregnant. women. This may be seen only in the means and is not apparent from individual eases, nor is the range of one group beyond the range of' the other. From the first few eases studied, it was calculated thai there was a significant increase in red cell neutral fat in the noncon,ulsive toxemias,9 but further studies indicated, as herein pointe(l out, that this difference was not as great as was at first thought. The relative yariations of the red cell lipids are well illustrated in Table II. Neutral fat and cholesterol esters were found to be extremely variable and usually present in small quantities only. These red cell extracts were prepared in the conventional manner by heating [or It !5hort time the alcohol-ether extract of the hemolyzed cells. This pro('edure introduced colored decomposit.ion products of hemoglobin, and fl'OllI work now in progress, it is apparent that this colored matter t.ends
942
AMERICAX JOURNAL OF OBSTETRICS AND GYNECOLOGY
to give false high values for all lipids and especially neutral fat. Rowever the same method of extraction was used in the eclamptic cases and a comparable one in normal pregnancy with (loth of which the present values have been compared. The lipids least variable in amount in the red cells were phospholipid and choleRterol, and these together constitute the bulk of red cell lipids. TABLE
II.
AN ANALYSIS OF LIPID VALUES FOUND IN THE RED BWOD CEr,LS IN PREMo. PER 100 C.C. OF RED CELLS
ECI~AMPSIA; THE RESULTS ARE EXPRESSED IN
COMPOSITION OF TOTAL LIPID TOTAL LIPID
VALUE
NEU· TRAL FAT
!
TOTAL FATTY
i.
ACIDS
.II
CHOLESTEROL TOTAl, lESTER
J
FREE
J.
PIIOS' PHOLIPID
N onnal Ratio Group Total lipid Maximum Total lipid Mean values Standard deviation Standard deviation in per cent of mean
I
418
169
289
60
1067 626 177 28%
377 103 142 138%
732
;162 142 39%
128 135 35 26%
69
0
60
191
0 20 31 155%
128 115 34 30%
562 374 95 26%
0
69
167
127 89
367 310 74 24%
High Ratio Group Minimllm
Total lipid Maximum Total lipid Mean values Standard deviation Standard deviation in per cent of mean
236 805 519 181 35%
0 311 77 118 153%
I 112 540 299 139 47%
I
127 118 37 31%
0 29 37 128%
26
29%
DISCUSSION
It has been shown that plotting the :frequency distribution o:f plasma p ITC ratios in preeclampsia reveals the presence of two types of cases, one with a normal range of ratio values and a smaller group with elevated ratios. The findings in the latter group were comparable to th{)se previously found in eclampsia. Renee, it is postulated that the high ratio group o:f preeclampsia represents cases of eclampsia without convulsions, while the normal ratio group may be an entirely separate condition. It cannot be gainsaid on present information that cases with a normal ratio may not go on to a high ratio if left untreated, and this point is being :further investigated. From the small amount of data now available, it does not appear that a normal ratio commonly, if at all, becomes an increased one. A statistical eomparison of plasma and red cell lipids revealed that no lipid value possessed a range, determined from the mean plus and minus the standard deviation, significantly different in one group from the range in the other. The high ratio group of preeclampsia tended to have a slightly greater plasma lipid content and slightly lower red cell lipid
-.<1
BOYD:
BLOOD LIPIDS IN PREECIJA){PSIA
943
f'ontent on the average. The high ratio in this group was due chiefly to relatively higher values for phospholipid and lower values for PElt!'r eholesterol. These several observations indicate some disturbance in lipid metabolism. It has been knOW"1l for many years that lipid metabolism is altered in pregnancy, and the present work has shown that there oecurs It further abnormal change in eclampsia and in a group which may be separated from what we now diagnose as preeclampsia. The nature of this disturbance in lipid metabolism has been, and still is, enveloped ill obscurity; its cause, its importance, its effect, even its nature are largely unknown. In the past few years the author has been interested in these problems, but in spite of a good deal of work barely more than the surface has been scratched. It has been shown that the lipemia of pregnaney in women is analogous chemically to lipemias in other conditions and is eharacterized by an orderly increase in plasma lipid values with no change in the lipids of the red blood ce11s.3 Following parturition, the lipemia gradually subsides, but if normal lactation be prevented. a further lipemia supervenes which may be taken to indicate that the drying up of the breasts, though frequently resorted to, is in reality pathologic. lO At the end of prt!gnancy, the leucocyte count is usually elevated, but the lipid content of the white cells is not significantly changed: after labor there is an increase in the phospholipid and free cholesterol of the blood leueocytes (indicative of increased activity) and an increase in neutral fat which latter probably represents a scavenger action on the part of the white cells in removing debris fat from the involuting uterusY Evidenee has been presented that the human placenta is "permeable" to lipids and that a good deal of fatty substances, especially phospholipids, is absorbed by the human fetus from the umbilical circulation, suggesting that one result of the lipemia in the mother may possibly be the nourishment of the infant in utero.12 The latter part of pregnancy in rabbits 13 and guinea pigs14 was found associated with evidence of increased lipid metabolism in the placenta, suggesting that the placental tissues may be actively engaged in the transfer of lipids from the mother to the offspring. In the rabbit it was found that a marked increase in the lipid content of the fetus does not occur until the latter third or so of gestation,t3 at which time the lipid metabolism of the placenta also increases. It does not appear that the lipemia of pregnancy in women is of toxic origin, since an even greater lipemia may occur in the lower animals, for example guinea pigs. is There is a certain amount of dil'ect evidence that the changes in endocrine balance during pregnancy may have something to do ",ith the changes in the concentration of blood lipids. By comparing blood lipid values in pregnant and pseudopregnant rabbits, it was possible to show that in early gestation certain
944
AMERICAN JOURNAL OF OBSTETRICS AND GYNECOLOGY
changes may be rlne to the direct or indirect effects of the products of conception and other changes to the direct or indirect effects of the presence of the corpus luteum.lfi In the rabbit, in which a lipopenia or decrease in blood lipid values occnrs rlnring' pregnancy (for the use of the term lipopenia see Boyd17 ), there is a marked rise and fall in the lipid composition of the ovary. 18 On the other hand a lipemia is found during pregnancy in guinea pigs as in women I !> and practically no change occurs in the lipid content of guinea pig ovaries throughout gestation. '9 The author has also found in unpublished experiments the phospholipid and free cholesterol content of the human ovary to he quite low at the end of pregnancy in one or two cases studied. This evidence points to the endocrine system as a factor in the disturbed lipid metabolism of pregnancy hut is far from sufficient to establish the exact relationship. SUM:\IARY
The lipid composition of blood plasma and of the red blood cells was determined by oxidative micromethods in 49 cases of preeclampsia. On the basis of the plasma P ITC ratio it was possible to show that these eases could be divided into two groups, one with a normal P ITC ratio and one in which the ratio was elevated As in eclampsia. Cases with a high plasma P ITC ratio tended to have slightly higher plasma lipid valnes and slightly lower red cell lipid values than cases of a normal ratio. The increase in the plasma P ITC ratio was due chiefly to relatively high plasma phospholipid and relatively low plasma ester cholesterol values. It is offered that cases of preeclampsia with a high ratio are in reality eclampsia without convulsions, while the remaining normal ratio cases are not literally preeclamptic at all. The significance of changes in lipid metabolism during gestation has been discussed. REFERENCES
(1) Boyd, E. M.: AM. J. OBST. & GY:>lEC. 30: ::23, 19:15. (2) Kurten, H.: Klin. \\,(·hn~ehr. 3: 1216, 1924. (3) Boyd, E. le.: J. Clin. Inve8tigation 13: 347, 1934. (4) Idem: J. BioI. Chern. 110: 61,1935. (5) Bayd, E. M., and 1'weddeU, H. J.: Trans. Royal Soc. Canada, Sect. V 29: 113, 1935. (6) Boyd, E. M.: .T. BioI. Chern. 114: 223, 1936. (7) Idem: J. BioI. Ohem. 91: 1, 1931. (8) Idem: J. BioI. Chern. 101: 323, 1933. (9) Idem: Unpublished data presented before the Royal Soc. Canada, Hamilton, Ontario, May, 1935. (10) Idem: AM. J. OnST. & GYNEC. 29: 797, 1935. (11) Idem: Surg. Gynec. Obst. 59: 744, 1934. (12) Boyd, E. M., and Wilson, K. M.: J. Clin. Investigation 14: 7,1935. (13) Boyd, E. M.: Biochern. J. 29: 985,1935. (14) Idem: Oamtd .•J. Researeh B. 14: 155, 193!5. (15) Boyd, E. M., and Fellows, M.: Am. J. Physiol. 114: 635, 1936. (16) Boyd, E. M.: J. Physiol. 86: 250, 1936. (17) Idem: Canad. M. A. J. 32: 500, Ill35. (18) Idl'tn: J. BioI. Chern. 108: 607, 193fi. (11) Idem: .T. BioI. Ohern. 112: 591,1935·1936.