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Biomedical subjects

M Levitz

Publications and source records attributed to M Levitz.

At least 73 records · Page 4Linked to original sources
PubMed1978

The transfer and metabolism of corticosteroids in the perfused human placenta.

The transfer and metabolism of cortisol, prednisolone, betamethasone, and dexamethasone were investigated in vitro in the perfused human placenta. Maternal and fetal circuits were established but the steroid was added to the former only. The clearance expressed as a fraction of the antipyrine transfer rate varied from 0.27 to 0.50, but there were no significant differences among the four steroids. All the steroids were metabolized extensively to their respective 11-ketosteroids and again there were no material differences among the steroids. The metabolic conversions of dexamethasone and betamethasone were far greater in the perfused placenta than in minced placenta. From the standpoint of placental transfer and metabolism, as observed in the perfusion studies, none of the four corticosteroids offers a decisive advantage in the antepartum maturation of the fetal pulmonary surfactant system.

Antipyrine↗
PubMed1978

Steroid metabolism in human breast cancer cell lines.

The metabolism of 1,2-3H-androstenedione was studied in 2 cell lines, MCF-7 (estrogen responsive) and BT-20 (estrogen nonresponsive) over 48 hrs. Water soluble and unconjugated metabolites were separated by solvent partition and the former was submitted to chromatography on Sephadex LH-20 and enzyme hydrolysis. The resulting unconjugated steroids were separated by paper chromatography and identities were established by reverse isotope dilution. The unconjugated steroids initially obtained were separated by chromatography and identified by reverse isotope dilution. About 70% of the androstenedione was metabolized by both cell lines. However, the respective conversions to conjugates by MCF-7 and BT-20 were 31% and 0.32%. In the former, glucosiduronates predominated (94%) and consisted of androsterone (55%), etiocholanolone (9.4%) and androstanediol (5alpha-androstane-3alpha,17beta-diol) (9.3%). Androsterone comprised most of the unconjugated metabolites in both cell lines. Androstanediol was found in both cell lines, 2% in MCF-7 and 12% in BT-20. Testosterone, 5alpha-androstane-3,17-dione and 3beta-hydroxy-5alpha-androstan-17-one were isolated only from MCF-7. The metabolism of 3H-estriol was studied in a similar way. Both cell lines produced about equal amounts of estriol-3-sulfate (9%) and a compound with properties of estriol-3-glucosiduronate (0.15--0.5%). The results worthy of emphasis are: 1. The far greater conjugation of androgens exhibited by the MCF-7 cell lines as compared to the BT-20 cell lines; 2. In MCF-7, the high conversion of androstenedione to etiocholanolone (glucosiduronate form), a metabolite reported to form only in liver and sebaceous cysts; 3. The possible formation in both cell lines of estriol-3-glucosiduronate, normally a metabolite of the intestine.

Androstenedione↗
PubMed1978

Prevention of normal mouse uterine maturation by antipain and elastatinal: suppression of peroxidase activity.

We had shown previously that the serine protease inhibitors, antipain and leupeptin, restrict uterine DNA snythesis and function in adult mice. The present study is an extension, focusing on the perimaturation period. The protease inhibitors, antipain and elastatinal were tested and the end points were uterine development and peroxidase activity in the uterus. Four week old mice were treated with eigher antipain (3 mg), elastatinal (5 mg) or vehicle (control) twice daily for 3 weeks. The uteri were excised, weighed and homogenized. Subcellular fractions were prepared by differential centrifugation. Each fraction was analyzed for peroxidase activity. The weights and protein content of uteri from control mice averaged greater than twice those in either antipain or elastatinal treated mice (p less than 0.001). Peroxidase activity was sharply curtailed by both inhibitors, antipain being more active than elastatinal. Mechanistically, antipain and elastatinal may act directly on the uterus either by inhibiting key enzymes or by preventing the formation of macromolecules crucial to normal function. Alternatively, the protease inhibitors may interfere with ovarian function, thereby restricting normal uterine development.

Animals↗
PubMed1978

Effect of protein binding on transfer and metabolism of cortisol in perfused human placenta.

The transfer and metabolism of cortisol and cortisone and the effect of protein binding on these processes have been investigated in vitro in the perfused human placenta. The clearance of cortisol in buffer, expressed as a fraction of the antipyrine transfer rate (clearance index), was 0.50 +/- 0.05 SEM in either direction. Extensive conversion to cortisone (85%) occurred during transfer. Addition of corticosteroid-binding globulin (CBG) in amounts sufficient to bind 50% of the cortisol reduced the clearance (0.40 +/- .026) insignificantly, whereas human serum albumin (HSA) in amounts sufficient to bind 50% of the cortisol reduced the clearance to 0.28 +/- 0.012 (P less than 0.001) even though the association constant for albumin is approximately 1000-fold less. The percent of conversion to cortisone did not change significantly with protein binding. The clearance index of cortisone from a protein-free perfusate was 0.74. With CBG and albumin in the same concentrations as used in the cortisol experiments, the binding of cortisone to CBG was 23% and its clearance was 0.70; with albumin, the binding was 45% and the clearance index was 0.45. The addition of albumin and CBG to the same perfusate resulted in a cortisol clearance equal to that obtained with perfusate containing only albumin. Binding to albumin may be more significant than binding to CBG in controlling the transfer rate of cortisol to the fetus.

Carrier Proteins↗
PubMed1977

Antipain and leupeptin restrict uterine DNA synthesis and function in mice.

As in rats, administration of estradiol to ovariectomized mice results in a trypsin-like proteolytic activity in the uterus. After fractionation of uteri from estradiol-treated ovariectomized mice the protease activity was found in the 12,000 times g pellet and the nucleus, appearing first in the former. Further fractionation of the pellet by discontinuous sucrose gradient centrigugation resulted in sedimentation of the protease with 5'-nucleotidase, a marker enzyme for plasma membrane and separate from mitochondrial and lysosomal enzyme markers. Solubilization was best accomplished by lysis at 37 degrees. The soluble enzyme from mouse uterus had optimal activity at about 43 degrees and pH 8.3 and was inhibited by diisopropylfluorophosphate, tosylarginine methyl ester, antipain, and leupeptin, but not by soybean trypsin inhibitor. Inhibition in vitro by antipain and leupeptin, two low molecular weight peptides, prompted the study of their effect in vivo on the mouse uterus. After intact, cycling female mice received subcutaneous injections of antipain and leupeptin for 16 days, their uteri showed significant diminution in weight and total DNA when compared to untreated controls. Fertility rates were also diminished. Trypsin-like protease activity may be essential to normal uterine metabolism and function.

Animals↗
PubMed1977

Estriol conjugates in human breast cyst fluid and in serum of premenopausal women.

A sensitive method was developed for the assay of the four major estriol (E3) conjugates in human breast cyst fluid and in serum during the menstrual cycle. In the cyst fluid, estriol-3-sulfate (E3-3S) was found in each of ten samples, the concentrations ranging from 240-4310 pg/ml. Estriol-16-glucosiduronate (E3-16G) was detected in six samples at levels of 19-153 pg/ml; estriol-3-glucosiduronate (E3-3G) in five samples, 13-79 pg/ml and estriol-3-sulfate-16-glucosiduronate (E3-3S-16G) in four samples, 28-152 pg/ml. Unconjugated estriol was found in three of the ten cases (12-30 pg/ml). Serum samples obtained in the follicular and luteal phases of the cycle from eight different subjects were assayed in the same way. There was considerable variation between subjects and many values were indistinguishable from zero. But preliminary data suggest that E3-3G is the predominant E3 conjugate in the serum and E3-3S-16G is quantitatively least important. It appears that E3 conjugates in the cyst fluid are not derived from the blood directly, but are produced locally from precursors which have not been identified.

Adult↗
PubMed1976

Renal clearances of estriol conjugates in normal human pregnancy at term.

In late human pregnancy more than 90 per cent of the total estriol (E3) in body fluids consists of four conjugates, estriol-3-sulfate (E3-3S), estriol-16-glucosiduronate (E3-16G), estriol-3-glucuronide (E3-3G), and estriol-3-sulfate-16-glucosiduronate (E3-3S-16G). Since the relative amounts of E3 in blood and urine would be determined by the kidney, the renal clearance of each conjugate was determined and compared with inulin and p-aminohippuric acid (PAH) clearance, as measures of glomerular filtration rate (GFR) and the effective renal plasma flow. Five women were studied in the lateral decubitus position with inulin and PAH infusion. Samples of blood and urine were collected at 40 minute intervals and analyzed. The method for E3 conjugates involved separation of the four conjugates on Sephadex LH-20, enzyme hydrolysis, and radioimmunoassay. Renal clearances for E3-3S and E3-3S-16G were below inulin. E3-3G approximated inulin; E3-16G exceeded inulin and approached PAH. In plasma E3-3S-16G represented 48.4 +/- 7.2 per cent; in urine E3-16G represented 69.5 +/- 7.3 per cent of total E3. Thus, different conjugates predominate in blood and urine.

Aminohippuric Acids↗
PubMed1976

16-sulfates of estriol in body fluids of human pregnancy at term.

A method was developed for the assay of estriol-16-sulfate (E3-16S) and estriol-3, 16-disulfate (E3-3,16-diS) in maternal serum, cord serum and amniotic fluid at delivery in human pregnancy. Tritiated E3-16S and E3-3,16-diS are added to the fluid being analyzed. The conjugates are separated and purified by sequential chromatography on alumina, Celite and Sephadex LH-20. Each conjugate is hydrolyzed with Glusulase and the released estriol is quantified by radioimmmunoassay. E3-3,16-diS was found in each fluid, most concentrated in the cord serum. Small amounts of E3-16S were found in some amniotic fluids, and this conjugate was virtually absent from the sera. These new estriol conjugates comprise less than 1 percent of total, estriol, apparently too low to be of diagnostic value in human pregnancy.

Amniotic Fluid↗
PubMed1976

Transfer across perfused human placenta. IV. Effect of protein binding on free fatty acids.

The effect of protein binding on the rate of placental transfer of hexanoic (C 6) and decanoic (C 10) acids was investigated in an in vitro perfusion system of human placenta. As much as 30% of transferred C 6 was converted to more polar compounds, so that the observations related to the combined effects on transfer and metabolism. Less than 10% of C 10 was similarly metabolized. Both fatty acids are soluble in buffered salt solutions at the concentrations used (40 muM) and both are bound to serum albumin, C-10 having higher association constants (K' for C 6, 1.48 X 10(4); for C 10, 1.03 X 10(5). When the placenta is perfused with buffered salt solution, the transfer of C 6 is 22% more rapid than that of C 10. It is suggested that binding within the placenta retards C 10 more than C 6. The addition of 1 g/100 ml bovine serum albumin to the maternal perfusate reduces the transfer rate of C 10 by 80%, whereas 2 g/100 ml serum albumin has a more moderate effect on C 6 (a reduction of 50%). The addition of 1 g/100 ml serum albumin to the fetal perfusate increases transfer rate of both free fatty acids (FFA), C 6 by 25% and C 10 by about 250%. With equivalent concentrations of serum albumin in maternal and fetal perfusates, the transfer rate of C 10 was reduced by 65%, whereas there was no detectable effect on transfer of C 6 in two of three experiments. The transfer rate of FFA increase logarithmically with progressive shortening of the carbon chain from C 16 to C 8 when maternal and fetal perfusates contain serum albumin. Protein binding is apparently the determining factor. The rate of transfer falls off at C 6 and C 4, 4ven though protein-binding continues to decrease. The determining factor may be the hydrophilic nature of these molecules.

Fatty Acids, Nonesterified↗
PubMed1975

Serum unconjugated estriol in the menstrual cycle and early pregnancy.

A radioimmunoassay for serum unconjugated estriol in the menstrual cycle with a sensitivity of about 5 pg/ml is described. 8 cycles were studied. In 2 cycles, single spikes of 22 and 30 pg/ml were obtained. In 3 cycles, concentrations of 4-5 pg/ml were found whereas in the other 3 studies, no estriol was detected. In general, peaks of estriol corresponded to peaks in estradiol plus estrone. Patients in 4-12 weeks of gestation were also studied. Concentrations as high as 262 pg/ml were found but in isolated instances, no estriol was detected. The results support the view that in contrast to the pregnant state, in the normal menstrual cycle, the bulk of the estriol produced is conjugated before release into the blood.

Estriol↗