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Placental transfer of fluoride and calcium
FETUS, PLACENTA, AND NEWBORN
Placental transfer of fluoride and calcium W.
D.
LEOl\ EDGAR Mtnneapolis,
ARMSTRONG. SINGER, L.
M.D. PH.D.
MAKOWSKI,
M.D.
Minnesota
Maternal (uterine) artery, maternal (uterine) vein, umbilical artery, and umbilical vein blood were obtained simultaneously at the time of 16 cesarean sections. Calcium determinations of these blood plasma samples and those from women in their ninth month of pregnancy suggest either that a calcium “jump” operates in the placenta sufiplying a higher concentration of calcium to the fetal blood supply than is found in the maternal circulation or that the calcium homeostatic mechanisms operate at different levels in the maternal and fetal organisms. The fluoride concentrations found in the blood plasmas suggest that the placental barrier to the transport of fluoride ion does not operate so as to maintain a diflerence in concentration of fluoride between the maternal and fetal body fluids.
%I P ICI N A N D Babeaux14 reviewed the world’s literature on placental transfer of fluoride. There can be no question that fluoride passes the placenta since fluoride is found in tlrc fetal blood and calcified tissues. There is, however, evidence indicating that the pls:enta acts as a partial barrier affecting the rate of fluoride transport from the maternal to the fetal circulation. Bawden, M’olkoff, :md Flowers,1 who administered radiofluoride (lSF) to pregnant ewes, found fetal blood plasma levels of radiofluoride to he relatively low compared to the maternal plasma levels. Similar results were obtained by Erkssorl and Malmn%” in studies with
rabbits and with 4 women who were submitted to therapeutic abortion and sterilization. These last authors found the human fetal blood concentration of radiofluoride never to exceed one-fourth that of the maternal blood during periods of up to 10 minutes after intravenous injection of the isotope. The mean fluoride content of maternal whole blood of pregnant women, shortly before delivery, and of the umbilical cord blood obtained after delivery of the placenta was found by Gedalia and associates” not to be significantly different. These reports emphasize the necessity to determine the fluoride contents of both maternal and fetal arterial and venous blood, collected without disturbance of the normal hemodynamics, to answer the question of whether or not a partial placental barrier to the transport of fluoride is sufficient to produce an alteration of equilibrium concentrations of fluoride in the maternal and fetal body fluids.
Fr,~rn the Departments of Biochemistry and Obstetr.:cs and Gynecology, College of Medical !;ciences, Iiniversity of Afrnnesota. 7‘his ruork Leas supported by Grant DR-1850 frcm the National Institute Dental Rese,arch, National Institutes Health, Bethesda, Maryland.
o{ of 432
Placental
Radioactive fluoride investigations without analytical studies and inadequate sampling of the fetal and maternal blood have not provided the arxswers. In this study the maternal and cord blood samples were obtainei. at the time of cesarean section. Thus, it cart bf* assumed that the blood samples were -procured with the absolute minimum of disturbance of their physiologic concentrations. Furthermore, the analyses were carried out LL~OII plasma rather than upon whole blood. In this way the effects of unequal distribution of fluoride between plasma and erythrocytes and of variations of the value of thie hematocrit on the results were eliminated. Calcium and fluoride are closely related in the mineral part of skeletal tissues but studies bearing on the concomitant placental transfer of these ions at a. time of active calcification of tie fetal skeleton have not been undertaken. Although there are independent reports of either the calcium or fluoride content of blood sera obtained from the mother, umbilical cord, or newborn infant, none has relat’ed the simultaneous concentrations of these: ions in the arterial and venous blood of the maternal and fetal circulations. The level of the maternal blood serum calcium at the time of cesarean section has not been well investigated, although some inve:;tigatorP, ’ have reported that the cesarean operation is sometimes associated with hypocalc,emia in the newborn infant. The failu.re to investigate the maternal blood serum c,alcium under this condition is surprising since Denzer, Reiner, and Weiner3 found that immediately after birth the concentration of calcium in infant serum is higher than that in the respective maternal serum. Mull7 obtained cord blood and maternal blood after delivery and also found that the serum calcium of cord blood is higher than in the maternal blood obtained just prior to the delivery. Denzer, Reiner, and Weiner,3 however, established that there is E. close agreement between the calcium contents of cord blood and blood taken from the child within 5 hours of birth. The maternal blood serum calcium concentration
transfer
433
is reported to be at its lowest concentration about the eighth month of pregnancy.’ The circumstances of the present stucly, like those with respect to fluoride, permitted determinations of the serum cakium concentrations in the maternal and fetal circulations under conditions of the least possible physiologic disturbances. Material
and
methods
Four blood samples Tvere obtained nearly simultaneously from the maternal (uterine) (uterine) vein, umbilical artery, maternal artery, and umbilical vein at the time of each of 16 cesarean sections. III addition: venous blood was obtained from 6 women in their ninth month of pregnancy who jvere to be delivered by the vaginal route. All blood samples were collected in sterile disposable syringes using hcparin from fresh bottles as a11 anticoagulant. The plasma was harvested in special fluoride-low glassware. The plasma samples were analyzed for their fluoridell and calcium contents.10a I3 It is possible, from recent work,l’ which we have confirmed, that the results for fluoride content of plasma represent the total fluoride contents better than ionic fluoride concrntrations. Results
The results in Table I indicate that near the end of pregnancy the calcium content of fetal blood plasma is generally higher than that of the maternal blood plasma and thus confirm the findings of Denzer, Reiner, and Weiner,” and of Mull.’ The mean calcium content of the arithmetically combined arterial and venous maternal blood plasmas was 7.5 t 0.15 (SE.) mg. per cent as compared with a mean value of 9.1 + 0.21 (SE.) for the similarly combined fetal plasmas, This difference is mathematically highly significant (p < 0.001). The mean calcium concentration in the maternal venous blood plasma obtained from 6 women in the ninth month of normal pregnancy, who were later to be delivered by the vaginal route, was 7.8 + 0.12 mg. per cent and was not different mathematically from the mean calcium con-
434
Armstrong,
Singer,
Table I:. Calcium
and
and fluoride
Mean Maternal
vein
Maternal
artery
Makowski
results
contents
of maternal
Calcium
(mg.
2 S. E. M.
Umbilical
vein
7.5 7.94 7.5 7.79 9.2
Umbilical
artery
9.1 2 0.26
---~-
Amer.
-? 0.25 + 0.176 + 0.15 + 0.124 2 0.32
tents of maternal plasmas obtained at the time of cesarean sections. The mean fluoride contents of the sa:me plasma samples was 0.18+0.011 (S.E.) p.p.m. These results do not imply that the placenta secretes calcium into the fetal blood circulation since th.e difference in calcium concentrations may be caused by the calcium homeostatic mechanisms operating at a different level in the maternal and fetal organisms. The fact that the maternal plasma calcium concentrations found in this series are below the concentrations accepted as “normal” blood pl,asma contents is recognized. Representative samples of these plasma samples analyzed by both a calorimetric methodlo and by atomic absorption analyses13 with a ,Jarrell-Ash instrument were in good agreement. The reliability of these methods was further confirmed by comparison with
REFERENCES
J. W., Wolkoff, A. S., and Flowers, 1. Bawtjen, C. E:., Jr.: J. Dent. Res. 43: 678, 1964. 2. Clark, E. P., and Collip, J. B.: J. Biol. Chem. 63: 461, 1925. B. S., Reiner, M., and Weiner, S. B.: 3. Denzer, Amer. J. Dis. Child. 57: 809, 1939. 4. Ericsson, Y., and MalmnHs, Cl.: Acta Obstet. Gynec. Stand. 41: 144, 1962. I., Bryzezinski, A., Bercovici, B., 5. Gedalia, and Lazaron, E.: Proc. Sot. Exp. Biol. Med. 106: 147, 1961. 6. Gittleman, I. F., Pincus, J. B., Schmerzler, E., and Saito, M.: Pediatrics 18: 721, 1956.
Fluoride
of
1, 1970 Gynec.
and fetal plasmas
%) No.
June J. Obstet.
subjects
16 12 16 14 16 15
Mean
results
+ S. E. M.
(f.p,m.) No.
of subjects
0.10 + 0.008
14
0.11 t 0.011
13
0.142 0.142
15 14
0.013 0.010
the results with those obtained by the ClarkCollip method2 for calcium determination. The fluoride concentrations in the maternal venous, maternal arterial, fetal venous, and fetal arterial blood plasma specimens -are quite similar and the data do not support the concept of a placental fluoride barrier, operating to a degree sufficient to maintain a disequilibrium of fluoride concentrations in the maternal and fetal circulations. Actually, the mean maternal blood plasma fluoride value for arterial and venous maternal plasma is 0.11 t 0.007 (S.E.) p.p.m. and compared with a mean of 0.14 + 0.008 (SE.) p.p.m. for fetal plasma. An inspection of the results obtained from the specimens from an individual mother and her child did not reveal a consistent pattern of fluoride concentration between the maternal and fetal circulations.
7. Mull, J. W.: J. Clin. Invest. 15: 513, 1936. 8. Newman, R. L.: AMER. J. OBSTET. GYNEC. 65: 796, 1953. P. D., and 9. Saville, Kretchmer, N.: Biol. Neonat. 2: 1, 1960. 10. Singer, Leon, Armstrong, W. D., and Colman, L. M.: Anal. Biochem. 9: 217, 1964. 11. Singer, Leon, and Armstrong, W. D.: Anal. Biochem. 10: 495, 1965. 12. Taves, D. R.: Talanta 15: 1015, 1968. 13. Zettner, Alfred, and Selegsin, David: Clin. Chem. 10: 869, 1964. 14. Zipkin, I., and Babeaux, W. L.: J. Oral Ther. 1: 652, 1965.
Placental transfer of fluoride and calcium W.
D.
LEOl\ EDGAR Mtnneapolis,
ARMSTRONG. SINGER, L.
M.D. PH.D.
MAKOWSKI,
M.D.
Minnesota
Maternal (uterine) artery, maternal (uterine) vein, umbilical artery, and umbilical vein blood were obtained simultaneously at the time of 16 cesarean sections. Calcium determinations of these blood plasma samples and those from women in their ninth month of pregnancy suggest either that a calcium “jump” operates in the placenta sufiplying a higher concentration of calcium to the fetal blood supply than is found in the maternal circulation or that the calcium homeostatic mechanisms operate at different levels in the maternal and fetal organisms. The fluoride concentrations found in the blood plasmas suggest that the placental barrier to the transport of fluoride ion does not operate so as to maintain a diflerence in concentration of fluoride between the maternal and fetal body fluids.
%I P ICI N A N D Babeaux14 reviewed the world’s literature on placental transfer of fluoride. There can be no question that fluoride passes the placenta since fluoride is found in tlrc fetal blood and calcified tissues. There is, however, evidence indicating that the pls:enta acts as a partial barrier affecting the rate of fluoride transport from the maternal to the fetal circulation. Bawden, M’olkoff, :md Flowers,1 who administered radiofluoride (lSF) to pregnant ewes, found fetal blood plasma levels of radiofluoride to he relatively low compared to the maternal plasma levels. Similar results were obtained by Erkssorl and Malmn%” in studies with
rabbits and with 4 women who were submitted to therapeutic abortion and sterilization. These last authors found the human fetal blood concentration of radiofluoride never to exceed one-fourth that of the maternal blood during periods of up to 10 minutes after intravenous injection of the isotope. The mean fluoride content of maternal whole blood of pregnant women, shortly before delivery, and of the umbilical cord blood obtained after delivery of the placenta was found by Gedalia and associates” not to be significantly different. These reports emphasize the necessity to determine the fluoride contents of both maternal and fetal arterial and venous blood, collected without disturbance of the normal hemodynamics, to answer the question of whether or not a partial placental barrier to the transport of fluoride is sufficient to produce an alteration of equilibrium concentrations of fluoride in the maternal and fetal body fluids.
Fr,~rn the Departments of Biochemistry and Obstetr.:cs and Gynecology, College of Medical !;ciences, Iiniversity of Afrnnesota. 7‘his ruork Leas supported by Grant DR-1850 frcm the National Institute Dental Rese,arch, National Institutes Health, Bethesda, Maryland.
o{ of 432
Placental
Radioactive fluoride investigations without analytical studies and inadequate sampling of the fetal and maternal blood have not provided the arxswers. In this study the maternal and cord blood samples were obtainei. at the time of cesarean section. Thus, it cart bf* assumed that the blood samples were -procured with the absolute minimum of disturbance of their physiologic concentrations. Furthermore, the analyses were carried out LL~OII plasma rather than upon whole blood. In this way the effects of unequal distribution of fluoride between plasma and erythrocytes and of variations of the value of thie hematocrit on the results were eliminated. Calcium and fluoride are closely related in the mineral part of skeletal tissues but studies bearing on the concomitant placental transfer of these ions at a. time of active calcification of tie fetal skeleton have not been undertaken. Although there are independent reports of either the calcium or fluoride content of blood sera obtained from the mother, umbilical cord, or newborn infant, none has relat’ed the simultaneous concentrations of these: ions in the arterial and venous blood of the maternal and fetal circulations. The level of the maternal blood serum calcium at the time of cesarean section has not been well investigated, although some inve:;tigatorP, ’ have reported that the cesarean operation is sometimes associated with hypocalc,emia in the newborn infant. The failu.re to investigate the maternal blood serum c,alcium under this condition is surprising since Denzer, Reiner, and Weiner3 found that immediately after birth the concentration of calcium in infant serum is higher than that in the respective maternal serum. Mull7 obtained cord blood and maternal blood after delivery and also found that the serum calcium of cord blood is higher than in the maternal blood obtained just prior to the delivery. Denzer, Reiner, and Weiner,3 however, established that there is E. close agreement between the calcium contents of cord blood and blood taken from the child within 5 hours of birth. The maternal blood serum calcium concentration
transfer
433
is reported to be at its lowest concentration about the eighth month of pregnancy.’ The circumstances of the present stucly, like those with respect to fluoride, permitted determinations of the serum cakium concentrations in the maternal and fetal circulations under conditions of the least possible physiologic disturbances. Material
and
methods
Four blood samples Tvere obtained nearly simultaneously from the maternal (uterine) (uterine) vein, umbilical artery, maternal artery, and umbilical vein at the time of each of 16 cesarean sections. III addition: venous blood was obtained from 6 women in their ninth month of pregnancy who jvere to be delivered by the vaginal route. All blood samples were collected in sterile disposable syringes using hcparin from fresh bottles as a11 anticoagulant. The plasma was harvested in special fluoride-low glassware. The plasma samples were analyzed for their fluoridell and calcium contents.10a I3 It is possible, from recent work,l’ which we have confirmed, that the results for fluoride content of plasma represent the total fluoride contents better than ionic fluoride concrntrations. Results
The results in Table I indicate that near the end of pregnancy the calcium content of fetal blood plasma is generally higher than that of the maternal blood plasma and thus confirm the findings of Denzer, Reiner, and Weiner,” and of Mull.’ The mean calcium content of the arithmetically combined arterial and venous maternal blood plasmas was 7.5 t 0.15 (SE.) mg. per cent as compared with a mean value of 9.1 + 0.21 (SE.) for the similarly combined fetal plasmas, This difference is mathematically highly significant (p < 0.001). The mean calcium concentration in the maternal venous blood plasma obtained from 6 women in the ninth month of normal pregnancy, who were later to be delivered by the vaginal route, was 7.8 + 0.12 mg. per cent and was not different mathematically from the mean calcium con-
434
Armstrong,
Singer,
Table I:. Calcium
and
and fluoride
Mean Maternal
vein
Maternal
artery
Makowski
results
contents
of maternal
Calcium
(mg.
2 S. E. M.
Umbilical
vein
7.5 7.94 7.5 7.79 9.2
Umbilical
artery
9.1 2 0.26
---~-
Amer.
-? 0.25 + 0.176 + 0.15 + 0.124 2 0.32
tents of maternal plasmas obtained at the time of cesarean sections. The mean fluoride contents of the sa:me plasma samples was 0.18+0.011 (S.E.) p.p.m. These results do not imply that the placenta secretes calcium into the fetal blood circulation since th.e difference in calcium concentrations may be caused by the calcium homeostatic mechanisms operating at a different level in the maternal and fetal organisms. The fact that the maternal plasma calcium concentrations found in this series are below the concentrations accepted as “normal” blood pl,asma contents is recognized. Representative samples of these plasma samples analyzed by both a calorimetric methodlo and by atomic absorption analyses13 with a ,Jarrell-Ash instrument were in good agreement. The reliability of these methods was further confirmed by comparison with
REFERENCES
J. W., Wolkoff, A. S., and Flowers, 1. Bawtjen, C. E:., Jr.: J. Dent. Res. 43: 678, 1964. 2. Clark, E. P., and Collip, J. B.: J. Biol. Chem. 63: 461, 1925. B. S., Reiner, M., and Weiner, S. B.: 3. Denzer, Amer. J. Dis. Child. 57: 809, 1939. 4. Ericsson, Y., and MalmnHs, Cl.: Acta Obstet. Gynec. Stand. 41: 144, 1962. I., Bryzezinski, A., Bercovici, B., 5. Gedalia, and Lazaron, E.: Proc. Sot. Exp. Biol. Med. 106: 147, 1961. 6. Gittleman, I. F., Pincus, J. B., Schmerzler, E., and Saito, M.: Pediatrics 18: 721, 1956.
Fluoride
of
1, 1970 Gynec.
and fetal plasmas
%) No.
June J. Obstet.
subjects
16 12 16 14 16 15
Mean
results
+ S. E. M.
(f.p,m.) No.
of subjects
0.10 + 0.008
14
0.11 t 0.011
13
0.142 0.142
15 14
0.013 0.010
the results with those obtained by the ClarkCollip method2 for calcium determination. The fluoride concentrations in the maternal venous, maternal arterial, fetal venous, and fetal arterial blood plasma specimens -are quite similar and the data do not support the concept of a placental fluoride barrier, operating to a degree sufficient to maintain a disequilibrium of fluoride concentrations in the maternal and fetal circulations. Actually, the mean maternal blood plasma fluoride value for arterial and venous maternal plasma is 0.11 t 0.007 (S.E.) p.p.m. and compared with a mean of 0.14 + 0.008 (SE.) p.p.m. for fetal plasma. An inspection of the results obtained from the specimens from an individual mother and her child did not reveal a consistent pattern of fluoride concentration between the maternal and fetal circulations.
7. Mull, J. W.: J. Clin. Invest. 15: 513, 1936. 8. Newman, R. L.: AMER. J. OBSTET. GYNEC. 65: 796, 1953. P. D., and 9. Saville, Kretchmer, N.: Biol. Neonat. 2: 1, 1960. 10. Singer, Leon, Armstrong, W. D., and Colman, L. M.: Anal. Biochem. 9: 217, 1964. 11. Singer, Leon, and Armstrong, W. D.: Anal. Biochem. 10: 495, 1965. 12. Taves, D. R.: Talanta 15: 1015, 1968. 13. Zettner, Alfred, and Selegsin, David: Clin. Chem. 10: 869, 1964. 14. Zipkin, I., and Babeaux, W. L.: J. Oral Ther. 1: 652, 1965.