The serum heat labile alkaline phosphatase activity during pregnancy

CLINICA CHIMICA ACTA

BRIEF

455

NOTES

CCA5036 The serum

heat labile alkaline

phosphatase

activity

during

pregnancy

During pregnancy maternal serum alkaline phosphatase activity increases particularly during the third trimester of pregnancy. This increase is attributed entirely to the heat stable alkaline phosphatase (HSAP) activity of placenta and it is assumed that the heat labile activity remains static during pregnancy. The work of McMaster et al.‘, supports this notion. These workers found no difference in the heat labile alkaline phosphatase activity between a group of IO women in the first and a group of 30 women in the third trimester of pregnancy. We have estimated the heat labile alkaline phosphatase activity of 333 samples of sera from pregnant women between o-42 weeks of gestation. The total and heat stable alkaline phosphatase activities -were determined by incubating IO-zo ,~l serum with $-nitrophenyl phosphate as the substrate in IOO ~1 glycine-NaOH-Mg buffer, pH 10.4~. The reaction was stopped with 0.5 ml of 0.12 M NaOH and absorbance was read at 415 nM. The HSAP activity was determined in serum that had been heated for 30 min at 65” (ref. 3.) Heat labile alkaline phosphatase activity was obtained by subtracting the HSAP activity from total alkaline phosphatase activity. The enzyme activities were assayed at 37’ in duplicate and optical densities were corrected for zero time activities. Results were discarded if the duplicates of a sample did not agree within 10% of each other. No enzyme activities could be detected when serum was omitted from the incubation mixture. One unit of phosphatase activity catalyzed liberation of I pmole of p-nitrophenol per hour of incubation.

Weeks of gestation

Fig. I. Heat labile alkaline phosphatase activity during pregnancy. The circIes and bars represent mean + 2 S.D. The number of individual random serum samples analyzed is shown at the top of each bar. Clin. Ckim. A&a, 38 (rg72)!45$-456

BRIEF NOTES

456

stages

Fig. I shows the level of heat labile alkaline phosphatase activity at different of the pregnancies studied. A definite increase in activity in the third tri-

mester is evident. Our results thus contradict those of McMaster et aZ.l. An important difference between our procedure and that of McMaster et a1.l is that these workers determined HSAP activity on serum that had been heated at 56” for 30 min. Department of Physiology, Institute of Obstetrics and Gynaecology, Chelsea Hospital fey Women, Dovehouse Street, London, S.W.3

S. P.

BISWAS

HINDOCHA

(U.K.) I Y. MCMASTER, R. TENKANT. J. S. CLUB, F. C. NEALE AND S. POSEN, J. Obstet. Gynaec. Cdtk 71 (196.4 735. 2 D. A. BESSEY, D. H. LOWRY AND M. J. BROCK, J. Biol. Chew., 164 (1964) 321. 3 R. J. HUNTER, J. Obstet. Gynaec. Brit. C&h., 76 (1969) 1057.

Received

Clin. Chim.

January Ada,

14,1972

38 (1972) 455-456

Brit