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Biomedical subjects

L Milewich

Publications and source records attributed to L Milewich.

At least 73 records · Page 4Linked to original sources
PubMed1980

Steroid secretion by ACTH-stimulated human fetal adrenal tissue during the first week in organ culture.

Fetal adrenal tissue has been reported to lose its in vivo secretory pattern by virtue of a loss of fetal zone cells after the first week in culture. Consequently, we studied the steroidogenic capacity and the responsiveness to ACTH of human fetal adrenal tissue during the first week in organ culture. The culture medium was removed daily and assayed for cortisol and dehydroisoandrosterone sulfate (DS). First, as the concentration of ACTH in the medium was increased from 0 to 1 micrograms/ml steroid secretion increased. When tissue fragments were maintained in the absence of ACTH for 3 to 4 days, there was a striking increase in steroid secretion upon addition of ACTH to the medium, with larger rates of secretion of cortisol than DS being observed. Second, the steroidogenic capacity of the separate zones of the fetal adrenal gland was assessed. Tissue from the fetal zone secreted large amounts of DS and small amounts of cortisol, whereas neocortex tissue secreted similar quantities of DS and cortisol. Third, fetal zone tissue was maintained the absence of ACTH for 4 days and thereafter ACTH was added to the media for an additional 6 days. In this experiment, there was a marked increase in DS secretion rate after the addition of ACTH and a smaller increase in cortisol secretion.

Adrenal Glands↗
PubMed1980

Deoxycorticosterone biosynthesis in human kidney: potential for formation of a potent mineralocorticosteroid in its site of action.

The extra-adrenal formation of deoxycorticosterone (DOC) from plasma progesterone has been demonstrated in humans. In those studies it was shown that in some persons the volume of plasma cleared of progesterone by DOC formation was great, namely, 75 liter/24 hr. Because steroid 231-hydroxylase activity [steroid 21-monooxygenase; steroid, hydrogen-donor:oxygen oxidoreductase (21-hydroxylating), EC 1.14.99.10] could not be demonstrated in homogenates or microsome-enriched preparations of human lung or liver tissue, we speculated that the 21-hydroxylation of plasma progesterone might take place in the kidney. Employing whole tissue homogenates and microsome-enriched preparations of human kidney tissue, we demonstrated the formation of [3H]DOC from kidney tissue, we demonstrated the formation of [3H]DOC from [3H]progesterone. The rate of formation of DOC from progesterone in microsomal preparations from kidney tissues of adult humans varied from 0 to 803 pmol per mg of microsomal protein per hr. The value computed for the apparent Km of the enzyme for progesterone was 0.140 microM. On the basis of these findings, we conclude that steroid 21-hydroxylase activity is present in human kidney tissue and that the kidney may be an important site of DOC formation as well as a site of DOC action.

Cell-Free System↗
PubMed1980

Conversion of plasma progesterone to deoxycorticosterone in men, nonpregnant and pregnant women, and adrenalectomized subjects.

During the third trimester of human pregnancy the concentrations of deoxycorticosterone (DOC) in maternal plasma are 4-50 times those in nonpregnant women and men. It has been suggested that the increased amount of DOC in maternal plasma originates in the fetal compartment. We considered an alternate explanation for the high levels of DOC in plasma or near-term pregnant women, viz., that DOC may be derived in part from 21-hydroxylation of maternal plama progesterone. To test this hyposthesis we measured the fractional conversion of plasma progesterone to DOC from the relationship between the 3H:14C ratio of the infused tracers, [3H]progesterone and [14C]-DOC, and the 3H:14C ratio or urinary 3 alpha,21-dihydroxy-5 beta-pregnan-20-one (tetrahydro-DOC). The fractional conversion of plasma progesterone to DOC ([rho](BU)P-DOC), measured in this manner, was 0.007 +/- 0.001 (mean +/- SEM, n = 26) in the subjects of this study. The values for [rho](BU)P-DOC varied widely among subjects (0.002-0.022) but the range of values for [rho](BU)P-DOC was similar among women pregnant with an anencephalic or dead fetus, nonpregnant and adrenalectomized women, and men. The transfer constant of conversion of progesterone to DOC in plasma, [rho](BB)P-DOC, remained constant in a nonpregnant woman during the infusion of nonradiolabeled progesterone at rates of 0-14 mg/h. Based on the results of these studied, we conclude that DOC is formed by extra-adrenal 21-hydroxylation of plasma progesterone and that the rate of formation of DOC by this pathway is proportional to the concentration of progesterone in plasma.

Adrenalectomy↗
PubMed1979

5 alpha-Reductase activity in human placenta.

The concentration of 5 alpha-pregnane-3,20-dione in peripheral blood of pregnant women is higher than that found in blood obtained from nonpregnant women throughout the luteal phase of the ovulatory cycle. The in vitro synthesis of 5 alpha-reduced pregnanes from [3H]progesterone by placental tissue was investigated using tissue minces and homogenates in the presence of added nicotinamide-adenine dinucleotide phosphate. The metabolites, [3H]5 alpha-pregnane-3,20-dione and [3H]3 beta-hydroxy-5 alpha-pregnan-20-one, were isolated and characterized employing a combination of chromatographic techniques, derivative formation, and crystallization with authentic [14C]5 alpha-pregnane-3,20-dione and [14C]3 beta-hydroxy-5 alpha-pregnan-20-one to constant 3H:14C ratios. In short-term incubations with placenta homogenates, the apparent pH optimum for the synthesis of 5 alpha-pregnane-3,20-dione was 8.8. There was no evidence for the formation of 5 beta-reduced pregnanes from [3H]progesterone by placental tissue. The in vitro metabolism of [3H]progesterone by minces of five term placentas, during 1 hour incubations at pH 7.4, was studied. The rate of formation of 5 alpha-pregnane-3,20-dione varied from 109 to 197 pmoles/gm placental tissue/hr.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1979

The role of serum lipoproteins in steroidogenesis by the human fetal adrenal cortex.

In the present investigation it was found that human fetal adrenal tissue maintained in organ culture secreted appreciable quantities of dehydroisoandrosterone sulfate (DS) and cortisol. Pregnenolone was also secreted in significant amounts, principally as the sulfate ester. The highest rate of secretion of these steroids by fetal adrenal tissue occurred when both ACTH and whole human serum were present in the culture medium. In the absence of ACTH, steroid secretion was low. When whole serum was replaced by lipoprotein-poor serum, the steroidogenic response to ACTH was markedly attenuated but not abolished. On the basis of these findings, it is concluded (1) that the human fetal adrenal can synthesize steroid hormones de novo from cholesterol, (2) that ACTH is an important stimulant of steroidogenesis by the human fetal adrenal, and (3) that plasma lipoproteins are a major source of the cholesterol utilized by the human fetal adrenal for steroidogenesis. Hence, it is likely that factors which regulate the production of fetal plasma lipoproteins are important determinants of fetal adrenal steroidogenic activity.

Adrenal Cortex Hormones↗
PubMed1978

The effect of oral contraceptive treatment on the serum concentration of dehydroisoandrosterone sulfate.

Dehydroisoandrosterone sulfate (DS), the major C19-steroid in the human circulation, was measured in serum obtained from blood samples collected daily (8 to 10 A.M.) throughout the menstrual cycles of eight normal, presumably ovulatory women and daily throughout the treatment cycles in four women taking an oral contraceptive (norethindrone, 1 mg., plus mestranol, 80 mcg.). The serum concentrations of DS in the ovulatory women ranged from 1,025 to 4,200 ng. per milliliter; mean, 2,062 +/- 137 ng. per milliliter (mean and standard error; n = 213). Serum DS concentrations during the follicular and luteal phases of the menstrual cycles of these women were similar. In women taking the oral contraceptive, the plasma DS concentrations ranged from 475 to 1,400 ng. per milliliter (mean, 895 +/- 83; n = 119). The 24 hour secretory pattern of DS was evaluated in one subject during a nontreatment cycle and again after 20 days of oral contraceptive treatment. In this subject, the mean serum DS level was 34 per cent lower during oral contraceptive treatment than the level before treatment. The decrease in the serum concentration of DS during oral contraceptive treatment likely results from a reduction in adrenal DS secretion since DS secretion by the normal human ovary is negligible and ovarian dehydroisoandrosterone secretion is small. Therefore, it is likely that the reduced serum DS levels in women taking oral contraceptives are the consequence of reduced adrenal secretion of DS resulting from reduced release of adrenocorticotropic hormone.

Adrenal Cortex↗