Expression of insulin-like growth factor binding protein-1 mRNA in human fetal kidney

Expression of insulin-like growth factor binding protein-1 (IGFBP-1) messenger RNA (mRNA) was studied in tissues of human fetuses from 15 to 23 weeks of gestation. Northern blot analysis revealed IGFBP-1 mRNA in the fetal liver and kidney but not in other fetal tissues, including the brain, heart, lung, skeletal muscle and spleen. Studies by in situ hybridization histochemistry showed that, in all fetal kidneys tested, the IGFBP-1 mRNA was localized preferentially to the epithelial cells of the collecting ducts, as well as to the cells of developing glomeruli and in the subcapsular nephrogenic mesenchyme. Less intense labeling for IGFBP-1 mRNA was seen in the connective tissue stroma of the medullary pyramids. A weak signal was detected in the mature glomeruli, and in the cells of the medullary mesenchyme and capsular connective tissue. IGFBP-1 protein was detected by immunoperoxidase staining mostly around small blood vessels but not in the respective endothelium. The protein was also present in many epithelial cells of the collecting ducts and in stromal connective tissue. These results show that the predominant sites of IGFBP-1 transcription in the developing kidney are those with most active differentiation.

Insulin-like growth factor-binding protein-3 is functionally normal in pregnancy serum

Insulin-like growth factor-binding protein-3 (IGFBP-3) carries most of the serum IGFs as a 150K ternary complex which increases during pregnancy. However, recent studies have demonstrated that IGFBP-3 is absent in pregnancy serum when measured by ligand blotting after electrophoresis. In the present study we demonstrate that, by several criteria, IGFBP-3 appears functionally intact in pregnancy serum. Serum samples were collected from pregnant women between 2-40 weeks gestation. Serum immunoreactive IGFBP-3 and acid-labile (alpha) subunit increased linearly throughout pregnancy. Ligand blotting confirmed diminution of IGFBP-3 at 2 weeks gestation and complete absence after 4 weeks gestation or when nonpregnancy serum was preincubated with amniotic fluid. When less harsh methods (neutral chromatography or transient acidification) were used, IGFBP-3 appeared functionally normal in pregnancy serum. Fractionation of pregnancy serum by Superose-12 gel permeation chromatography showed similar elution profiles for both IGFBP-3 and alpha-subunit compared to those for nonpregnancy serum. Preincubation of nonpregnancy serum with pregnancy serum or amniotic fluid had no effect on IGFBP-3 recovery. After acidification and neutralization of serum to destroy endogenous alpha-subunit, ternary complex formation, measured by radiolabeled alpha-subunit binding, was essentially identical in all nonpregnancy and pregnancy serum, except for a slight loss of activity in first trimester serum. Since the 150K complex cannot form unless IGFBP-3 binds IGFs and alpha-subunit normally, these results suggest that IGFBP-3 in native pregnancy serum is functionally normal.

Insulin-like growth factor (IGF) binding protein-3 in pregnancy serum binds native IGF-I but not iodo-IGF-I

Although serum immunoreactive insulin-like growth factor binding protein-3 (IGFBP-3) increases during pregnancy, radioligand binding methods such as ligand blotting with iodinated IGFs fail to detect the protein in pregnancy serum. Since IGFBP-3 must bind IGF-I or IGF-II to form a complex with the acid-labile subunit (alpha-subunit), we have used ternary complex formation from [125I]alpha-subunit as a measure of IGF binding to serum IGFBP-3. High-pressure liquid chromatography fractions containing IGFBP-3 from pregnancy serum did not bind [125I]IGF-I, although the equivalent fractions from nonpregnancy serum showed dose-dependent binding. In contrast, IGFBP-3 fractions from nonpregnancy and pregnancy sera both bound [125I]alpha-subunit in the presence of either exogenous IGF-I or endogenous serum IGFs, implying that non-iodinated IGFs could bind to the IGFBP-3. Substitution of nonradioactive iodo-IGF-I for native IGF-I in the complex formation assay confirmed that the pregnancy-induced alteration in IGFBP-3, probably resulting from proteolysis, prevents it from binding iodo-IGF-I while having little effect on its binding of the native peptide. This provides an explanation for the failure to detect IGFBP-3 in pregnancy by radioligand binding methods, and raises the question of the significance of proteolysis of IGFBP-3.

Insulin-like growth factor binding protein-1 inhibits the DNA amplification induced by insulin-like growth factor I in human granulosa-luteal cells

In order to study the effects of insulin-like growth factor (IGF-I) and insulin-like growth factor binding protein (IGFBP-1) on human granulosa cell proliferation after in vitro fertilization, cells were obtained after oocyte retrieval and cultured in the presence or absence of graded amounts of recombinant IGF-I, purified IGFBP-1 and [3H]thymidine. Physiological concentrations of IGF-I (2-200 ng/ml) were found to stimulate [3H]thymidine incorporation into the cells in a concentration-dependent manner. Half-maximal stimulation of [3H]thymidine incorporation was obtained with 10 ng/ml exogenous IGF-I, which was chosen for suppression experiments with graded amounts of purified IGFBP-1. Suppression of IGF-stimulated thymidine incorporation was observed when 200 ng/ml or more of IGFBP-1 was added to the culture medium. The same concentration of IGFBP-1 also markedly inhibited binding of [125I]iodotyrosyl IGF-I to the cells. It is concluded that: (i) after a refractory period, granulosa cells from hyperstimulated follicles retained their mitogenic activity; (ii) IGF-I is capable of stimulating DNA amplification in granulosa cells; and (iii) IGFBP-1 inhibits the IGF-I stimulated proliferation in these cells. In view of our previous studies showing that IGFBP-1 is synthesized by the granulosa cells as they luteinize, the present results suggest that IGFBP-1 is one of the endogenous factors locally regulating the growth and differentiation of granulosa cells.

Oral contraceptives increase insulin-like growth factor binding protein-1 concentration in women with polycystic ovarian disease

Insulin-like growth factor-I (IGF-I) stimulates ovarian androgen production. Insulin-like growth factor binding protein-1 (IGFBP-1) inhibits IGF actions in vitro.

OBJECTIVE

To investigate the effect of oral contraceptive (OC) pills, given for 3 months, on serum gonadotropin, androgen, IGF-I, and IGFBP-1 concentrations, and glucose tolerance in seven women with polycystic ovarian disease (PCOD) and in five healthy control subjects.

PATIENTS

Seven women with PCOD and five healthy control subjects.

INTERVENTIONS

An oral glucose tolerance test (OGTT) was performed before and after treatment with OC.

RESULTS

After treatment with OC, serum luteinizing hormone, androstenedione, and free testosterone levels decreased, and sex hormone-binding globulin concentration increased in the women with PCOD as well as in the control subjects. The cumulative response of serum insulin to OGTT was larger in the women with PCOD than in the control subjects both before and after treatment. Serum IGF-I concentration, which was unchanged during OGTT, decreased from basal level of 326 +/- 70 micrograms/L to 199 +/- 28 micrograms/L after treatment with OC in the women with PCOD, whereas no change was found in the control subjects (from 235 +/- 11 micrograms/L to 226 +/- 11 micrograms/L). Treatment with OC caused an increase of the mean basal IGFBP-1 concentration from 24 +/- 7 micrograms/L to 73 +/- 14 micrograms/L in the women with PCOD. This increase was constant during the OGTT. In the control subjects, treatment with OC did not result in any significant change in IGFBP-1 concentrations (from 44 +/- 11 micrograms/L to 61 +/- 9 micrograms/L).

CONCLUSION

The combination of decreased total IGF-I concentration and increased IGFBP-1 concentration induced by OC may decrease ovarian androgen production in PCOD.

Effect of naloxone on plasma insulin, insulin-like growth factor I, and its binding protein 1 in patients with polycystic ovarian disease

Insulin and insulin-like growth factors (IGFs) stimulate ovarian steroidogenesis, and hyperinsulinemia is often accompanied by hyperandrogenemia in women with polycystic ovarian disease (PCOD). Because opioid peptides are involved in the regulation of insulin secretion, we studied the effect of naloxone-induced opiate receptor blockade on the circulating levels of insulin, IGF-I, and IGF binding protein 1 (IGFBP-1) in 13 nonobese and 7 obese PCOD patients and in 6 healthy subjects. In obese PCOD patients, the mean basal insulin concentration was significantly higher and the IGFBP-1 concentration lower than in nonobese PCOD patients. Plasma IGF-I levels were elevated both in obese and nonobese PCOD patients. After an intravenous bolus of 10 mg naloxone, no significant changes were found in the circulating insulin or IGF-I levels, whereas IGFBP-1 levels decreased in nonobese PCOD patients and remained low in obese PCOD patients. No significant decrease was found in healthy subjects. These results suggest that, in addition to insulin, endogenous opioids are involved in the regulation of serum IGFBP-1 level.

Human granulosa cells contain insulin-like growth factor-binding protein (IGF BP-1) mRNA

Previous studies have demonstrated expression of insulin-like growth factor-binding protein (IGF BP-1) in secretory and decidualized endometrium, in adult and fetal liver, and in HepG2 liver cancer cells. We have studied the expression of IGF BP-1 in various types of ovarian neoplasias, normal ovary, and granulosa cells from hyperstimulated human ovarian follicles by RNA blot hybridization. A single 1.6 kb mRNA species, similar to that present in human decidua, was identified in poly(A)RNA-containing preparations of granulosa cells and of a borderline malignant ovarian cystadenoma. This finding verifies the postulated production of IGF BP-1 by the human ovary.

Identification by hybridization histochemistry of human endometrial cells expressing mRNAs encoding a uterine beta-lactoglobulin homologue and insulin-like growth factor-binding protein-1

A beta-lactoglobulin homologue (beta LG/PP14) and insulin-like growth factor-binding protein-1 (IGFBP-1) are two major secretory proteins of the human endometrium. In the present study, we have shown that beta LG/PP14 mRNA is expressed in the endometrium in a cyclic manner, being hardly detectable in midcycle and most abundant during the late secretory phase. IGFBP-1 mRNA is also expressed in endometrium, but in amounts smaller than those encoding beta LG/PP14 and with maximal accumulation earlier in the secretory phase. The expression of these two mRNAs occurs in different cell types of the endometrium, as revealed by in situ hybridization techniques using single-stranded RNA probes. The glandular epithelial cells accumulate beta LG/PP14 mRNA during the late secretory phase of the cycle, whereas only the stromal cells of the late secretory endometrium express IGFBP-1 mRNA. In contrast to the endometrium, the two mRNAs are present at very low abundance in the fallopian tubes where they are expressed in the epithelial cells of the mucosa.

Concentrations of somatomedin-C and triiodothyronine in patients with thyroid dysfunction and nonthyroidal illnesses

We studied the possibility of an association between serum somatomedin-C (Sm-C) and thyroid hormone concentrations. For this purpose 34 hyperthyroid patients, 39 patients with primary hypothyroidism, 36 patients with severe nonthyroidal illnesses (NTI), and 63 euthyroid healthy control subjects were examined. The mean concentration of serum dialyzable free triiodothyronine (FT3) was 26.6 +/- 15.4 pmol/l (+/- SD) in hyperthyroidism, 2.8 +/- 1.2 in hypothyroidism, 4.2 +/- 1.1 in NTI, and 5.3 +/- 0.7 in controls. The lowest mean concentration of serum Sm-C (10.1 +/- 3.0 nmol/l) was found in the NTI group and the highest in the hyperthyroid group (16.8 +/- 3.2): these concentrations differed significantly from the mean control level (12.2 +/- 2.2). In NTI patients the serum FT3 and T3 levels correlated significantly with the serum Sm-C levels (r = 0.63; p less than 0.001, r = 0.65; p less than 0.001, respectively). In hypothyroid patients there was a weak correlation between the serum FT3 and Sm-C levels (r = 0.36; p less than 0.05), but no correlations were found in hyperthyroid and healthy subjects. We conclude that the lowered Sm-C levels in NTI do not reflect a hypothyroid state, as normal Sm-C levels were found in hypothyroidism, and that impaired nutritional state of the patients is the most likely explanation for the association between Sm-C and FT3 (and T3) in NTI.

Regulation of insulin-like growth factor-binding protein-1 production in human granulosa-luteal cells

Human follicular fluid contains the insulin-like growth factor-binding protein (IGFBP-1) synthesized by ovarian granulosa cells. We studied the regulation of IGFBP-1 production by the granulosa-luteal cells from the hyperstimulated follicles of patients attending an in vitro fertilization program. The cells were first allowed to attach and recover from the hyperstimulation for 2 days. Then, a protein kinase-C activator, 12-O-tetradecanoyl phorbol-13-acetate (TPA), and adenylate cyclase activators, gonadotropins, FSH, hCG, cholera toxin, or prostaglandin E2 (PGE2) were added to the cells. The gonadotropins failed to increase IGFBP-1 production, whereas it was enhanced by TPA and to a lesser extent by cholera toxin and PGE2. The maximal response to TPA occurred at the concentration of 1.0 ng/mL, and the enhancing effect of TPA was detected at 24 h. PGE2 stimulated IGFBP-1 production; the lowest effective concentration was 10(-8) mol/L. The mean highest response was 4.3-fold and occurred at the PGE2 concentration of 10(-5) mol/L. The effect of PGE2 on IGFBP-1 production became detectable at 24 h, and it continued to increase up to 72 h. PGE2 also increased granulosa-luteal cell progesterone production in a dose- and time-dependent manner. Incorporation of [35S]methionine into immunoreactive IGFBP-1, as detected by sodium dodecyl sulfate-polyacrylamide electrophoresis and fluorography, was also increased by TPA. This suggests that TPA accelerated the synthesis of IGFBP-1. Our results indicate that the production of IGFBP-1 by human granulosa-luteal cells can be regulated both via protein kinase-C- and adenylate cyclase-dependent pathways.

Elevated serum levels of endometrial secretory protein PP14 in patients with advanced endometriosis. Suppression by treatment with danazol and high-dose medroxyprogesterone acetate

The circulating concentration of endometrial protein PP14 varied during the menstrual cycle in patients with endometriosis. The highest levels were found on days 1 to 4 of the cycle (176 +/- 123 micrograms/L; mean +/- SD), and the lowest on days 5 to 20 (44.1 +/- 29.7 micrograms/L). Rising levels were observed on days 21 to 30 (58.3 +/- 62.6 micrograms/L). On days 5 to 20 (i.e., during period of the lowest levels) patients with advanced endometriosis had higher PP14 levels (63.9 +/- 39.0 micrograms/L) than those with mild endometriosis (29.3 +/- 18.2 micrograms/L; p less than 0.01). Patients with mild endometriosis had slightly higher serum PP14 levels than apparently healthy control subjects (p less than 0.05), but overlapping of values between the two groups is remarkable. Conservative surgical elimination of endometriosis significantly decreased the serum PP14 levels. Treatment with danazol (600 mg/day), or with medroxyprogesterone acetate (100 mg/day) after laparoscopy also resulted in significant decreases in the serum PP14 concentration. After 6 months of treatment, conservative surgery in combination with danazol or with medroxyprogesterone acetate, yielded more pronounced declines in serum PP14 level than conservative surgery plus placebo. No significant difference was observed between the effects of danazol and medroxyprogesterone acetate. We conclude that endometriosis tissue contributes to the circulating PP14 level, and the decline in PP14 level during danazol and medroxyprogesterone acetate treatments reflects regression of intrauterine and ectopic endometrial tissues.

Time-resolved immunofluorometric assay for placental protein 14

A sandwich-type solid phase time-resolved immunofluorometric assay (IFMA) was developed for endometrial protein PP14 (placental protein 14). The assay utilizes affinity-purified polyclonal antibodies for coating the microtiter wells and for labelling with europium (III) chelate. Maintaining specificity, the 0.6 micrograms/l sensitivity of IFMA is over 25 times higher than that of RIA. The immunofluorometric method enables detection and accurate quantitation of PP14 in all those samples in which PP14 is undetectable by RIA. The method is suitable for quantitative measurement of low PP14 levels in serum of postmenopausal and fertile-aged women and men, as well as in follicular fluid. At 14-16 micrograms/l, which is the sensitivity of radioimmunoassay, the intra-assay variation of IFMA is 6.6% and inter-assay variation 11.4%. In postmenopausal women the PP14 levels are 12.7-56.7 micrograms/l, in fertile-aged women 13.7-113.4 micrograms/l, and in men 3.1-53.1 micrograms/l. The levels in preovulatory follicular fluid are 1.2-20.5 micrograms/l. It is concluded that PP14 IFMA is highly sensitive, accurate and suitable for measurement of protein levels undetectable by other currently available methods.

Low levels of low molecular weight insulin-like growth factor-binding protein in patients with polycystic ovarian disease

Insulin-like growth factors IGF-I and IGF-II are bound to specific binding proteins in serum. The lower mol. wt binding protein (IGF-BP) has been detected in various tissues, including secretory endometrium and preovulatory follicles of the ovary. This group studied the circulating levels of IGF-BP in the serum of 23 patients with polycystic ovarian disease (PCOD) and found that one-third of them have a subnormal level. In comparison with PCOD patients with a normal level, those with a subnormal level had a higher degree of obesity and a tendency to be more hirsute. They also had a higher serum insulin concentration and testosterone/sex hormone-binding globulin (SHBG) ratio, but lower serum SHBG concentration than those with a normal IGF-BP level. PCOD is the second abnormal clinical condition, after insulinoma, in which subnormal serum IGF-BP concentrations have been reported. The significance of low serum IGF-BP levels to pathophysiology of PCOD remains to be elucidated by studies on local interaction between IGF-BP and insulin in the polycystic ovary.

Human granulosa cells synthesize low molecular weight insulin-like growth factor-binding protein

Human follicular fluid contains insulin-like growth factor I (IGF-I) and its low molecular weight binding protein (IGF-BP). We studied the synthesis of IGF-BP by the granulosa cells obtained after ovarian hyperstimulation for in vitro fertilization. The granulosa cells were cultured for 72 hours in Ham's F-10 medium supplemented with 10% fetal calf serum (FCS). Samples of the culture medium were collected every 24 hours. The IGF-BP concentration in culture medium increased from 1.2 to 2.1 micrograms/l at 48 h and to 3.3 micrograms/l at 72 h. De novo synthesis of IGF-BP was shown by incorporation of labeled methionine into immunoreactive IGF-BP, as detected by SDS polyacrylamide electrophoresis (PAGE) and fluorography. Our results demonstrate synthesis of IGF-BP in the human ovary.

Dose-response characteristics for suppression of low molecular weight plasma insulin-like growth factor-binding protein by insulin

We previously demonstrated that supraphysiological insulin concentrations reduced the plasma 34K insulin-like growth factor-binding protein (IGF-BP) concentrations in humans. In this study we examined whether physiological changes in plasma insulin concentrations regulate IGF-BP and, if so, whether the regulation is influenced by race, glucose tolerance, or rate of glucose metabolism. For these purposes we 1) analyzed the relationship between fasting plasma insulin and IGF-BP concentrations in 2 racial groups (23 caucasians and 35 southwestern American Indians), 2) measured the response of plasma IGF-BP to oral glucose in 20 normal subjects, and 3) determined the dose-response characteristics of plasma IGF-BP to glucose and insulin in 23 normal subjects at 4 different insulin and glucose concentrations. The fasting plasma insulin concentration was inversely related to the plasma IGF-BP concentration in both the caucasian and Indian groups (P less than 0.0001). In the caucasian group the mean plasma IGF-BP concentration was higher [15 +/- 4 (+/- SE) micrograms/L] than in the Indian group (8 +/- 2 micrograms/L; P less than 0.05). This difference was independent of race and glucose tolerance, and it could be explained by lower plasma insulin concentrations in the caucasian (387 +/- 50 pmol/L) than in the Indian group (215 +/- 43 pmol/L; P less than 0.001). After oral glucose administration, the insulin concentration (423 +/- 72 pmol/L) was maximal 30 min after glucose treatment, and significant suppression of the IGF-BP concentration occurred at 90 min. Analysis of the dose-response curves revealed maximal suppression of IGF-BP at about 1150 pmol/L insulin, and half-maximal suppression at about 290 pmol/L. The plasma glucose concentration or the rate of glucose metabolism had no effect on the IGF-BP concentration. These data suggest that insulin is a major regulator of plasma IGF-BP concentrations under physiological conditions.

Prolonged exercise increases serum insulin-like growth factor-binding protein concentrations

We studied the response of serum 34K insulin-like growth factor-binding protein (IGF-BP) to two types of prolonged exercise. In the first study, 11 normal men performed cycle ergometer exercise, after an overnight fast, for 3 h at the intensity corresponding to 45-50% of their maximal aerobic power. After the exercise, the mean serum IGF-BP concentration was 4.9-fold higher than the baseline level (P less than 0.01), while the IGF-I concentration did not change. Resting for the same time period resulted in a 38% fall in the serum IGF-BP level (P less than 0.01). In the second study, 10 normal men and 8 type 1 diabetic men exercised, on the average, for 7.5 h in a 75-km cross-country ski race. The mean serum IGF-BP concentration increased 5.4-fold (P less than 0.01) in the normal men and 4.2-fold (P less than 0.01) in the diabetic men. The serum IGF-I concentration decreased by 19% and 21% in the normal and diabetic men, respectively (P less than 0.01). After completion of the ski race, the serum insulin and IGF-BP levels (r = -0.70; P less than 0.05), and serum IGF-I and IGF-BP levels (r = -0.72; P less than 0.05) were inversely correlated in the normal men. No such correlations were found in the diabetic men. We conclude that 1) long term exercise increases serum IGF-BP concentrations in both normal and type 1 diabetic men; and 2) the increases are inversely related to alterations in serum IGF-I and insulin concentrations in normal men. These data suggest that IGF-BP may be involved in regulation of the biological action of IGF-I during prolonged exercise.

Insulin-like growth factor (IGF-I) and its low molecular weight binding protein in human milk

Insulin-like growth factors (IGF-I and IGF-II) are mitogenic polypeptides bound in serum to specific binding proteins. This study reports the occurrence and concentrations of IGF-I and its low molecular weight IGF binding protein (IGF BP) in human milk and serum after delivery in 41 healthy women. The levels of IGF-I in milk declined between 4 and 92 hours postpartum from 49 +/- 17 micrograms/l to 29 +/- 27 micrograms/l (p less than 0.01). The level of IGF BP also declined from 165 +/- 80 micrograms/l to 97 +/- 70 micrograms/l (p less than 0.01), whereas the serum concentration of this protein remained unchanged. A positive correlation was observed between the individual levels of IGF-I and its binding protein in milk (r = 0.49, p less than 0.01), but no correlation was found between the individual levels of 34 kDa IGF BP in milk and serum. The relative abundance of IGF BP in the first milk compared to IGF-I is intriguing and its biologic significance remains to be clarified.

Different insulin-like growth factor binding species in human placenta and decidua

Previous studies demonstrated that human decidua secretes a 34K insulin-like growth factor binding protein (34K IGF-BP) earlier designated placental protein 12, whereas placenta contains IGF receptors and IGF mRNA. We studied binding of [125I]IGF-I to paired placental and decidual tissues using competitive binding, gel filtration, RIA, and cross-linking techniques, and compared the binding characteristics of these two tissues which are located in close proximity in vivo. The effect of decidual cytosols on [125I]IGF-I binding to placental membranes also was studied. Consistent with previous data the dominating binding species in placental membranes were IGF receptors. In contrast, the binding of [125I]IGF-I to decidual membranes was mainly due to binding species with mol wts of 34K and 39K. The 34K IGF-BP was more readily detected in decidual cytosols than in decidual membranes and little was detected in placental cytosols. Purified 34K IGF-BP as well as decidual cytosols inhibited [125I]IGF-I binding to placental receptors. The inhibitory effect of decidual cytosol on IGF receptor binding was linearly correlated to the decidual content of 34K IGF-BP. The results suggest that the decidual 34K IGF-BP might act as a local modulator of the IGF action at the interface between the decidua and the placenta.

Immunofluorometric demonstration and quantification of placental protein 5 in the absence of pregnancy

This time-resolved immunofluorometric assay (IFMA) developed for measurement of placental protein 5 (PP5) involves two antibodies: a monoclonal anti-PP5 antibody attached to a solid phase and an europium(III) chelate-labeled polyclonal anti-PP5 antibody as a tracer. The measuring range is 0.05-100 micrograms/L and the detection limit is 20 times lower than that of a PP5 radioimmunoassay (RIA) performed with the same polyclonal antiserum. By IFMA, PP5 could be detected and quantified in all plasma and serum samples of nonpregnant and pregnant individuals, whereas PP5 was undetectable by RIA in serum of healthy men and nonpregnant women. The mean concentration of PP5 in sera from men was 0.43 micrograms/L (SD 0.13, range 0.19-0.75, n = 47) and in sera from nonpregnant women 0.49 micrograms/L (SD 0.19, range 0.20-0.90, n = 41). PP5 concentrations in serum showed no systematic variation during the menstrual cycle. In serum samples from 60 pregnant women the results obtained by IFMA and RIA correlated well (r = 0.97).

Immunofluorometric demonstration and quantification of placental protein 5 in the absence of pregnancy

This time-resolved immunofluorometric assay (IFMA) developed for measurement of placental protein 5 (PP5) involves two antibodies: a monoclonal anti-PP5 antibody attached to a solid phase and an europium(III) chelate-labeled polyclonal anti-PP5 antibody as a tracer. The measuring range is 0.05-100 micrograms/L and the detection limit is 20 times lower than that of a PP5 radioimmunoassay (RIA) performed with the same polyclonal antiserum. By IFMA, PP5 could be detected and quantified in all plasma and serum samples of nonpregnant and pregnant individuals, whereas PP5 was undetectable by RIA in serum of healthy men and nonpregnant women. The mean concentration of PP5 in sera from men was 0.43 micrograms/L (SD 0.13, range 0.19-0.75, n = 47) and in sera from nonpregnant women 0.49 micrograms/L (SD 0.19, range 0.20-0.90, n = 41). PP5 concentrations in serum showed no systematic variation during the menstrual cycle. In serum samples from 60 pregnant women the results obtained by IFMA and RIA correlated well (r = 0.97).

Insulin-like growth factor (IGF) binding protein from human decidua inhibits the binding and biological action of IGF-I in cultured choriocarcinoma cells

The placenta expresses genes for insulin-like growth factors (IGFs) and possesses IGF-receptors, suggesting that placental growth is regulated by IGFs in an autocrine manner. We have previously shown that human decidua, but not placenta, synthesizes and secretes a 34 K IGF-binding protein (34 K IGF-BP) called placental protein 12. We now used human choriocarcinoma JEG-3 cell monolayer cultures and recombinant (Thr59)IGF-I as a model to study whether the decidual 34 K IGF-BP is able to modulate the receptor binding and biological activity of IGFs in trophoblasts. JEG-3 cells, which possess type I IGF receptors, were unable to produce IGF-BPs. Purified 34 K IGF-BP specifically bound [125I]iodo-(Thr59)IGF-I. Multiplication-stimulating activity had 2.5% the potency of (Thr59)IGF-I, and insulin had no effect on the binding of [125I] iodo-(Thr59)IGF-I. 34 K IGF-BP inhibited the binding of [125I] iodo-(Thr59)IGF-I to JEG-3 monolayers in a concentration-dependent manner by forming with the tracer a soluble complex that could not bind to the cell surface as demonstrated by competitive binding and cross-linking experiments. After incubating the cell monolayers with [125I]iodo-(Thr59)IGF-I in the presence of purified binding protein, followed by cross-linking, no affinity labeled bands were seen on autoradiography. In contrast, an intensely labeled band at 40 K was detected when the incubation medium was analyzed, suggesting that (Thr59)IGF-I and 34 K IGF-BP formed a complex in a 1:1 molar ratio. Also, 34 K IGF-BP inhibited both basal and IGF-I-stimulated uptake of alpha-[3H]aminoisobutyric acid in JEG-3 cells. RNA analysis revealed that IGF-II is expressed in JEG-3 cells. We conclude that decidual 34 K IGF-BP inhibits the cellular binding and biological action of IGFs in JEG-3 cells. Our data show that JEG-3 cells represent a cell type that can produce IGF, but not IGF-BPs. These cells may thus provide a useful model system for a better understanding of autocrine growth regulation mediated by the IGFs.