Vol. 46, No. 4 Printed in U.SA.

Journal of Clinical Endocrinology and Metabolism Copyright © 1978 by the Endocrine Society

Somatomedin Bioactivity in Serum and Amniotic Fluid during Pregnancy* R. M. BALA.f C. WRIGHT, A. BARDAI, AND G. R. SMITH Division of Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 1N4 ABSTRACT. Somatomedin bioactivity (SMA) in maternal serum, as measured by hypophysectomized rat cartilage assays, was low during early and late pregnancy but was similar to normal nonpregnant control levels near 28 weeks and at term pregnancy. At term, the mean level of SMA in cord serum was significantly less than in maternal serum, and greater than in amniotic

fluid. The mean level of SMA in amniotic fluid was higher at term than in early pregnancy. No significant correlation was noted between SMA levels in amniotic fluid, maternal serum or cord serum, or between the SMA levels in these samples and the usual amniotic fluid parameters used as indices of fetal maturity. (J Clin Endocrinol Metab 46: 649, 1978)


OMATOMEDINS (SM) are GH-depend- these women were healthy and not taking medicaent tissue growth factors (1). The possi- tions other than routinely prescribed vitamins. All ble role of SM in regulation of fetal growth serum samples were stored at —20 C until assayed. AF samples were obtained at the time of memand development is not clearly defined. Varying levels of SM activity in maternal and fetal brane rupture during normal term delivery of 41 cord serum have been reported (2-6). SM healthy women (20 samples were obtained from the groupd of 24 women noted above). Eighteen samactivity in amniotic fluid, as measured by ples of AF were obtained by standard amniocentesis bioassays (7) and radioreceptor assays (8), has techniques performed on 18 women (12 at 12-16 been partially characterized (9, 10). weeks and 6 at 33-36 weeks of pregnancy) for the In this study, we have compared SM bioac- usual indications. AF samples obtained at term tivity (SMA) in maternal serum (MS), fetal delivery of patients with a variety of medical or cord serum (CS), and amniotic fluid (AF) ob- obstetrical problems were not included in this tained at term delivery. SMA was also mea- study. The AF samples were centrifuged to remove sured in MS and AF at various intervals dur- cellular contaminants, then stored at —20 C until assayed. Samples obviously contaminated with ing normal pregnancies. blood were not used for these studies. SMA in serum and AF was measured by an in Materials and Methods vitro bioassay by utilizing hypophysectomized rat Serum samples were obtained from 7 nonpreg- costal cartilage segments as previously described nant women and 67 women at various times during (9, 11). SMA was expressed as a potency ratio pregnancy (serial samples were obtained from 7 compared to a reference serum pool obtained from women). Duration of pregnancy was recorded as normal adult males, which was assumed to contain weeks since the onset of the last menstrual period. 1 U of SM bioactivity/ml. In the SM bioassays, the Samples of MS were obtained just before (1-8 h) percentages of concentration in the final incubates normal term delivery of 24 of these women. CS were 6.25, 1.25, 0.25, and 0.125 for the reference samples were obtained at the time of normal term serum; 6.25, 1.25, and 0.25 for MS and CS; and 25, delivery of 22 of this group of 24 women. All of 12.5, and 6.25 for AF samples. All samples were assayed in quadruplicate at each dose level. The index of precision (s/b) (12) revealed a mean A Received August 30, 1976. value of 0.29 (range, 0.11-0.39), whereas parabolic * These studies were supported by grants from the regression analysis revealed an r value of 0.95 in Medical Research Council of Canada and a Research and standard curves (n = 24) by using reference serum Development Grant from Foothills Hospital, Calgary. t To whom all requests for reprints should be ad- in the dilutions noted. Individual assays were condressed. sidered valid if the interassay variability, in mea649

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surement of SMA in a normal serum standard, was less than 15%. Estimations of SMA, at each dose level of sample assayed, were considered to be valid if the mean was at least 2.5 times its SD. The mean SMA of the test samples was determined from at least two dose levels showing acceptable parallel dose responses. Samples which showed inhibitory or significantly non-parallel dose responses as compared to the reference pooled serum (greater than 25% difference in sample SMA as calculated after adjustment for the different dose levels) were reassayed. AF creatinine concentration, lecithin-sphingomyelin (L/S) ratio, and the percentage of cells showing positive fat stain were determined by standard techniques (13).

Results The level of SMA in MS at normal term delivery (1.05 ± 0.06 SEM; range, 0.56-1.60; n = 24) was similar to that found in normal nonpregnant women (1.04 ± 0.06 SEM; range, 0.77-1.20; n = 7). The mean levels of SMA in MS at different intervals of pregnancy are

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shown in Fig. 1. SMA in MS was low before 24 weeks of pregnancy, near normal at 25-28 weeks, fell to low levels by 36 weeks, then returned to normal by the term delivery day. The levels of SMA in serial serum samples obtained from seven normal women at various intervals of pregnancy followed an approximately similar pattern (serum samples were not obtained at all 4-week intervals from all patients), even though the levels of SMA were different in individual women. The mean level of SMA in AF was significantly lower at 12-16 weeks than at 33-36 weeks of pregnancy or at term delivery (Table 1). The mean levels of SMA in AF, MS, and CS, obtained at term delivery of 24 patients (Table 2), were significantly different (P < 0.001). The correlation between SMA in AF, MS, and CS was low (highest correlation, r = 0.27) and was not statistically significant (P > 0.05). The levels of SMA in AF, MS, or CS


FIG. 1. Comparison


mean 0.9

(±SEM) SMA in MS measured at

various intervals during normal pregnancy. The number of MS assayed at each pregnancy interval is shown in brackets. One unit of SM activity is defined as the total SMA in 1 ml pooled normal adult male reference serum. The mean levels of SMA in MS at various intervals of pregnancy are compared for statistical difference (Student's t test) with MS at term delivery (**, P < 0.01; ***, P < 0.001; NS, P > 0.05) and with maternal serum during the 25-28week pregnancy interval (++, P < 0.01; +++, P < 0.001; NS, P > 0.05).


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Somatomedin bioactivity in serum and amniotic fluid during pregnancy.

Vol. 46, No. 4 Printed in U.SA. Journal of Clinical Endocrinology and Metabolism Copyright © 1978 by the Endocrine Society Somatomedin Bioactivity i...
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