An enzyme-linked immunosorbent assay has been developed to measure human Müllerian inhibiting substance (MIS) in biological fluids. The enzyme-linked immunosorbent assay is specific for MIS, with a sensitivity in human serum to 0.5 ng/ml and does not recognize transforming growth factor-beta 1 or -beta 2, LH, or FSH. It similarly fails to recognize other proteins secreted from the cell type into which the MIS gene was cloned. MIS was detected in the serum of normal newborns, infants, children, and adults. In males the serum level of MIS is 10-70 ng/mL at birth. The level increases slightly after birth, and then decreases to a basal level of 2-5 ng/mL after the first 10 yr of life. Newborn male urine contains minimal amounts of MIS (0.5 ng/mL). In females MIS is barely detectable in serum at birth, but rises to the basal level equal to that seen in males after 10 yr of age. Similar basal levels of MIS were found in adult ovarian follicular fluid. MIS levels were high in the serum of a female patient with a sex cord tumor (3200 ng/mL), but fell to 100 ng/mL after multiple excisional operations. In addition, a serum MIS level of 20 ng/mL was detected in a patient with an ovarian granulosa cell tumor. A sensitive assay for MIS could be useful in the diagnosis of patients with congenital abnormalities of sexual development and patients with Sertoli cell and/or other MIS-producing neoplasms. Other applications may also be recognized as the biology of MIS in both males and females is further elucidated.

Male neonates develop respiratory distress syndrome (RDS) with a greater incidence and mortality than do female neonates; the cause of this male disadvantage remains obscure. Male fetuses are exposed to higher levels of androgens and Müllerian inhibiting substance (MIS). Androgens have been shown to inhibit fetal lung maturation, and recent evidence in vitro indicates that MIS, a Sertoli cell-derived glycoprotein made early in ontogeny of the testis, may also inhibit lung development. To study whether this fetal regressor might inhibit maturation of the fetal lung in vivo, we injected human recombinant MIS (rMIS) into fetal rats, measured serum levels of rMIS using an enzyme-linked immunosorbent assay, and analyzed fetal lung tissue histologically and for protein, glycogen, DNA, and disaturated phosphatidylcholine content. Peak serum levels of recombinant MIS were measured at 6 h, with an apparent elimination half-life of 3 h, and without leakage into adjacent littermates injected with vehicle alone. Female fetal rat lung tissue exposed to recombinant MIS (10(-9) M, 10(-8) M) revealed depressed disaturated phosphatidylcholine content both 48 and 72 h after injection compared with female vehicle-injected littermates. Male lungs of the same gestational age appeared inhibited at a higher (10(-8) M) rMIS dose. These inhibitory effects observed in vivo confirm those previously seen in vitro and suggest that MIS, as well as androgens, may play a causative or important ancillary role in the sexual dimorphism that characterizes the neonatal respiratory distress syndrome.

Summary. Esterase activity was investigated in blood cells of peripheral blood and bone marrow in healthy subjects and in various pathological conditions. As substrates were used: α‐naphthyl acetate, naphthol AS‐D acetate and naphthol AS‐D chloroacetate. Fast blue B and fast garnet G. B. C. were used as coupling agents. The distribution of AS‐D acetate esterase in different blood cells was described. Strong α‐naphthyl acetate esterase activity was found in monocytes, reticulum cells, megakaryocytes and in monoblasts in cases of monocytic leukaemia. Weak activity was shown in thrombocytes, and in lymphocytes. With naphthol AS‐D chloroacetate as substrate strong enzymatic activity was demonstrated in the cells of the neutrophilic myelocytic series. The activity was strong in the more mature cells. Blasts from acute myelocytic leukaemia showed enzymatic activity. The use of α‐naphthyl acetate and naphthol AS‐D chloroacetate as substrates proved to be of help in differentiating between the three types of acute leukaemia. In cases with megaloblastic erythropoiesis only strong α‐naphthyl acetate esterase activity was demonstrated in the megaloblasts. Successful treatment of pernicious anaemia with B12, resulted in disappearance of megaloblasts and cessation of the strong esterase activity. There seems to be a correlation between strong naphthyl acetate esterase activity and the presence of megaloblasts. An explanation of this phenomenon is suggested.