STUDIES OF ZINC AND ALKALINE PHOSPHATE ISOENZYMES IN NORMAL AND TOXAEMIC PREGNANCIES IN NIGERIANS

Abstract

ABSTRACT There is at present no information on the metabolism of zinc It during pregnancy in Nigerians. A study of zinc and a zinc melalloenzyme was therefore considered worthwhile in normal and toxaemic pregnant Nigerian women. Alkaline phosphatase (a zinc metalloenzyme) is easily measured in plasma and is a diagnostic index in clinical medicine, although its function is not yet clear. Toxaemia of pregnancy (pre-eclampsia and eclampsia) is a common problem in pregnancy in Nigeria and has been shown to be one of the three commonest causes of high mortality rates in Nigerian women (Waboso, 1973; Balachandran, 1975; Medical Officer of Health, Lagos, 1975). The following categories of patients and biological materials were selected for the investigations: (a) Normal controls comprising of 118 women of child-bearing age who were neither pregnant nor using any form of contraceptive device. (b) Normal pregnant patients comprising of 108 women who were in various stages of normal uncomplicated pregnancies. (c) 91 normal pregnant women at term. (d) 20 women suffering from Toxaemia of pregnancy but who here nevertheless delivered of their babies either prematurely or at term. (e) 36 placentas obtained from normal healthy women who had had uncomplicated full-term deliveries. (f) 21 placenta obtained from toxaemic pregnant women at the times of deliveries. (g) 3 young patients with biochemically, radiologically and clinically confirmed rickets. (h) Liver biopsy from one patient undergoing hepato-portal enterostomy. (i) 18 normal and toxaemic pregnant women who were investigated from 24 weeks gestation to term. Zinc was estimated by Atomic Absorption Spectroscopy using the Atomic Absorption Spectrophotometers Beckman Model 495 (Beckman instruments International, S.A.. Switzerland) and Pye Unicam, SP 90A Series (Pye Unicam, Cambridge , England). Total plasma alkalin. phosphatase (A.P.) and A.P. of tissue extracts were estimated by the method of Wootton (1964), phenol released by the enzymatic hydrolysis of phenyl disodium phosphate under defined conditions of time, temperature and pH was estimated calorimetrically. Heat-stable placental A.P. fraction in the plasma, in the leucocyte suspensions and in placental extracts was measured by first heating the di1uted sample at 70˚C for 30mins in the presence of 20mM exogenous, Mg2 when the activities of all A.P. from other sources, except that from the placenta, are completely destroyed (Neale, Clubb',, iiotchkis and Posen, 1965; Hunter, 1969; Hunter, Pinkerton and Johnson, 1970; Merrett and Hunter, 1973). The specificity of this technique for the determination of placenta A.P. in the human plasma for example, is comparable to the specificity of a recently developed double antibody solid phase radioimmunoassay for placenta A.P. in human serum (Holmgren, Stigbrand, Damber and Schoultz, 1978). A.P isoenzymes were separated by polyacrylamide gel electrophoresis using a modification of the method of Smith, Lightstone and Perry. (1968). Leucocytes were separated from whole blood using the method of Dennes, Tupper and Wormall, (1961). Haemoglobin screening of patients' whole blood for anaemia was done by the specific gravity method of Phillips, Van Slyke, Hamilton, Dole, Emerson and Archibald, 195O. Packed cell volume values of patients were measured by the method of Dacie and Lewis, 1975. Urine specimens were tested for glucose, ketone bodies and protein using Multistix reagent strips (Ames Co. Stoke, Poges, Bucks, England). In all cases, Blood Pressure measurements were taken using a standard sphygmomanometer (Accoson, England) and a standard adult Cuff size (Accoson, England). Standard statistical methods were used to determine differences between test groups and controls and all result were expressed in Means ± S.E.M. The following observations were made: (1) Total maternal plasma A.P. in normal pregnant women was significantly higher than in non-pregnant control women (P <0.001). (2) Total maternal plasma A.P. in normal pregnant women was significantly higher than in toxaemic women (P <0.01). (3) A.P. from placenta partly accounted for the increased total plasma A.P. in both groups of patients. (4) A.P. from bone partly accounted for the increased total plasma A.P. in both groups of patients. (5) The placental A.P. appeared in the maternal circulation during the 15th week of gestation. (6) Maternal leucocyte alkaline phosphatase (LAP) in normal pregnant women was significantly increased compared with normal non-pregnant controls (P <0.001). (7) Maternal LAP in normal pregnant women was significantly greater than in toxaemic women (P <0.001). (8) Total cord plasma A.P. of infants of normal pregnant women was significantly higher than in infants of toxaemic mothers (P <0.00). (9) Total A.P. of placental extracts from normal pregnancies was higher than in placental extracts from toxaemic pregnancies (P <0.001). (10) Maternal plasma zinc in normal pregnancies was significantly decreased compared with non-pregnant controls (P <0.001). (11) There was no change in the plasma zinc of toxaemic women when compared with non-pregnant controls (P >0.10). (12) Maternal leucocyte zinc, cord plasma zinc and placental tissue zinc were all significantly higher in normal pregnancies than in toxaemic pregnancies (P <0.01; P<,0.001, P<0.001 respectively). (13) There were highly significant negative correlations between maternal leucocyte zinc, cord plasma zinc and placental zinc on one hand and maternal plasma zinc on the other (r =-0.64, P <0.001; r = -0.41, P<0.05; r = -0.88, P <0.001 respectively). Such observations were not made in toxaemic pregnancies. (14) Between 24 weeks and the time of delivery, there seems to be a correlation between the trend of plasma placental A.P. and the Apgar score of the infant. It appears that if the plasma placental A.P. suddenly falls and the pregnancy is not interrupted shortly thereafter, an infant with an Apgar score of 6 or less, may result if the trend of the plasma placental A.P. is steady and reaches its peak value at term, an infant with an Apgar score of 7 or above may result. (15) From observations made in paragraph 14, there seems to be a need for re-evaluating the usefulness of the circulating placental A.P. in predicting the outcome of pregnancy in toxaemia.