The serum levels of the low mol wt form of somatomedin-binding protein (SMBP) were 5-fold higher in both diabetic (n = 44) and nondiabetic pregnant women (n = 14) than in nonpregnant women. No difference was found between women with type 1 diabetes and those with gestational diabetes. There was a negative correlation between maternal levels of SMBP during the last trimester and the birth weight percentile of the infants (r = -0.51). There was a 2- to 3-fold elevation of maternal insulin-like growth factor (IGF-I) levels during pregnancy in both diabetic and nondiabetic women. A positive correlation (r = 0.49) was found between maternal IGF-I levels and the birth weight percentiles of their infants. The correlation between the ratio of IGF-I to SMBP, which may reflect the IGF-I available to the placenta, to birth weight percentile was higher (r = 0.57), and the SE of estimate of weight percentile was 23%. The ratio between IGF-I and SMBP in cord blood was correlated with birth weight, although cord blood IGF-I and SMBP values were not. The IGF-II levels in cord serum were 50% higher in the infants of diabetic than in those of nondiabetic mothers. These findings raise the questions of whether maternal SMBP levels influence the amount of IGF-I available for the fetal-placental unit and whether IGF-II participates in glucose homeostasis in the fetus.

A radioimmunoassay based on a monoclonal antibody, Mc-ab 1, which was raised against growth hormone but cross-reacted with human placental lactogen yielded higher GH immunoreactivity levels in serum than one based on a polyclonal antiserum. This discrepancy was noted in subjects with normal GH secretion as well as in patients with GH insufficiency. To characterize this GH immunoreactivity detected by Mc-ab 1, affinity purification and molecular sieve chromatography of serum were performed. High molecular weight proteins with GH immunoreactivity were found with both techniques. These proteins were associated with carbohydrates. Affinity cross-linking showed specific binding of radiolabelled GH to high molecular weight proteins in the serum. After fractionation of serum, the GH immunoreactivity became detectable by the polyclonal antiserum assay as well as by an immunoradiometric assay. GH immunoreactive material with an approximate mass of 80 kD was subjected to isoelectric focusing. When GH immunoreactive fractions at pH 5 were re-chromatographed, GH immunoreactivity was recovered in the elution volume corresponding to monomeric GH. Our results show that sera from normal subjects as well as from patients with deficient GH secretion contain notable amounts of high molecular weight GH which is undetectable by antibodies generally used for GH measurements, but which can be revealed after fractionation of serum.The aim of this work was to elucidate the discre¬ pancies found when growth hormone was mea¬ sured in human serum using a polyclonal antiserum (1) and a monoclonal antibody, Mc-ab 1, raised against GH but cross-reacting with human placental lactogen (2): Patients with GH insufficiency and non-detectable GH levels according to the polyclo¬ nal antiserum showed consistently detectable GH immunoreactivity with Mc-ab 1.Several monoclonal antibodies have been pro¬ duced against the closely related hormones human GH and human placental lactogen. These hor¬ mones consist of a single polypeptide chain, crosslinked by two disulfide bridges and have a mole¬ cular mass of approximately 22 kD (3). Pituitary GH does not, however, occur as only one molecular species, but shows both size and charge variations (4-6). In spite of the heterogeneity of GH, the radioimmunoassays based on monoclonal antibodies have correlated well with RIAs using polyclonal antisera (7-9). Subjects and MethodsSerum samples were obtained from 3 healthy volunteers, 2 patients with panhypopituitarism, 3 with acromegaly, and 2 with prolactinomas. The panhypopituitarism of the 2 was due to a non-secreting pituitary adenoma and a craniopharyngioma, respectively; these 2 patients had non-detectable GH levels in 24-h diurnal profiles, after oral administration of 500 mg L-dopa and during insulininduced hypoglycemia determined with the polyclonal antiserum.From the patients with acromegaly and newly diag¬ nosed disease, pieces of growth hormone producing adenomatous tissue were obtained during pituitary micro-

Seven highly purified dimeric forms of human pituitary growth hormone, composed of the monomeric forms 20 K hGH, 22 K hGH and 24 K hGH linked together by noncovalent or covalent bonds, have been characterized by an in vitro bioassay (the Nb2 assay), a radioreceptor assay and a radioimmunoassay. Considerable differences in the ability to displace labelled recombinant hGH were observed in the radioreceptor assay. The seven dimeric forms varied over a range between 22 K hGH (most effective) and 20 K hGH. The three covalently-linked dimeric forms had nearly identical affinity constants. The mitogenic action of all but one of the hGH dimers in the Nb2 assay was in the same mutual order as the receptor binding activity in the radioreceptor assay. In the RIA, all dose-response curves were parallel except for those obtained with 20 K hGH and with the dimeric form (20 K-20 K)hGH. In this assay, dimeric variants of the constituents 22 K hGH and 24 K hGH were approximately twice as active as 22 K hGH on a molar basis, suggesting about the same affinity between the antibodies and each of the monomeric forms. Determination of the amino acid compositions of the dimeric forms provided support for their content of monomeric constituents as established earlier by electrophoretic analysis.

Growth hormone (GH), placental lactogen (PL), prolactin (PRL), insulin-like growth factor I (IGF-I) and IGF binding protein-1 (IGFBP-1) were determined in serum by radioimmunoassays (RIAs) in 12 women during pregnancy. GH and PL were analyzed by two monoclonal antibodies (Mab 3 and Mab 1) raised against pituitary GH. Serum IGFBP-1 had reached maximum levels at midpregnancy while PRL, PL and IGF-I increased continuously during pregnancy. Mab 1 which cross-reacts with PL, measured consistently higher levels of PL in serum than a commercial PL RIA (p < 0.01) due to interference of cross-reacting serum proteins in the Mab 1 RIA. The GH-specific Mab 3 showed decreasing GH levels in unfractionated serum throughout gestation, but detected GH-immunoreactive proteins of approximately 40–200 kD after molecular sieve chromatography of pooled serum from late pregnancy. It is suggested that the formation of GH complexes of large molecular mass account for the successive disappearance of monomeric GH during pregnancy.

Pituitary growth hormone (GH), prolactin (PRL), placental lactogen (PL), insulin-like growth factor 1 (IGF-1) and GH-binding protein (GHBP) in plasma were determined in 12 women with gestational diabetes mellitus (GDM) and in 12 healthy pregnant women during a breakfast meal tolerance test. The women with GDM showed higher prepregnancy weight, body mass index (BMI), basal levels of glucose, insulin, and C peptide compared to the pregnant controls. No difference was found between the two groups in pituitary GH, PRL, PL and IGF-1 levels. Plasma levels of GHBP were higher in the women with GDM compared to pregnant controls. In all women there was an inverse correlation between PL and pituitary GH as well as between PL and GHBP, suggesting that PL inhibits pituitary GH secretion. A positive correlation between GHBP and BMI was found in all women, and the higher BMI in the GDM women seemed to be the cause of the higher GHBP levels in this group. In all women IGF-1, an indicator of the secretory activity of lactogenic hormones as well as of nutritional state, showed a positive correlation with the birth weights of the infants and was equally indicative in both groups.