Growth of the adrenal gland of the normal human fetus during early gestation

The weights of 182 adrenal glands obtained from presumably normal human fetuses delivered by elective abortion between 6 and 17 weeks post-conceptional gestational age were measured. There was little increase in adrenal weight between 6 and 12 weeks gestation. Thereafter, the rate of increase in adrenal weight was rapid. There were no significant differences between the adrenal gland of male and female abortuses of similar gestational ages.

Growth of the kidney in the normal human fetus during early gestation

The weights of kidney obtained from 200 presumably normal human abortuses of postconceptional gestational ages between 6 and 17 weeks were measured. The weight of the normal human fetal kidney increases in an exponential manner between 6 and 14 weeks gestation. Thereafter, the rate of increase in weight is slower. No significant differences were found between the weights of kidneys of male and female abortuses of 7-15 weeks postconceptional gestational ages.

Synthesis of cholesterol in the human fetus: 3-hydroxy-3-methylglutaryl coenzyme A reductase activity of liver microsomes

The specific activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase in microsome-enriched fractions prepared from normal human fetal liver tissue was assessed. The mean specific activity was 0.58 +/- 0.18 nmol mevalonate formed min-1 mg-1 protein. The activity of the enzyme was inhibited by preincubation of microsomes with ATP (4 mM) and was greatly reduced when microsomes were prepared from tissue homogenized in the presence of NaF (50 mM). It can be computed that the activity of HMG CoA reductase in human fetal liver microsomes is adequate to provide cholesterol to meet the requirements of the fetal adrenal for steroid precursor provided that cholesterol synthesized in the fetal liver appears in the plasma in the form of low density lipoprotein.

The role of cyclic adenosine 3',5'-monophosphate in cholesterol metabolism and steroidogenesis by the human fetal adrenal gland

In the present investigation we studied the role of cAMP as a mediator of ACTH action in human fetal adrenal (HFA) tissue. We have characterized the response to ACTH, dibutyryl adenosine 3',5'-cyclic monophosphoric acid (dbcAMP), and cholera toxin (CT) with respect to steroidogenesis, low density lipoprotein (LDL) binding, degradation of LDL, and the rate of de novo synthesis of cholesterol. The rate of dehydroisoandrosterone sulfate secretion was similar in HFA tissue maintained in the presence of ACTH, dbcAMP, or CT. In contrast, cortisol secretion by HFA tissue was more sensitive to dbcAMP and CT than to ACTH. In membrane preparations obtained from HFA tissue maintained in the presence of ACTH, dbcAMP, or CT, there was a 2 to 3-fold increase of specific binding of [125I]iodo-LDL. In HFA tissue maintained in the presence of ACTH or CT, the rate of degradation of LDL was significantly increased compared to tissue maintained in the lipoprotein-poor serum alone. Finally, in HFA tissue maintained in the presence of ACTH, dbcAMP, or CT there was a 6- to 10-fold stimulation of the rate of incorporation of [14C]acetate into cholesterol. We conclude that steroidogenesis, LDL binding, and degradation, as well as de novo synthesis of cholesterol, are probably stimulated in HFA tissue via a cAMP-mediated pathway.

Plasma lipoprotein regulation of progesterone biosynthesis by human corpus luteum tissue in organ culture

The role of plasma lipoproteins in supplying cholesterol for progesterone biosynthesis by human corpus luteum tissue in culture was investigated. Progesterone secretion by tissue fragments maintained in organ culture reached a maximum rate by the third day and subsequently declined. Maximal secretion of progesterone was dependent on the presence of both low density lipoprotein (LDL) and hCG in the culture medium, whereas high density lipoprotein (HDL) was ineffective in supporting progesterone biosynthesis. Human corpus luteum tissue degraded [125I]iodo-LDL by a mechanism which was saturable, and degradation of [125I]iodo-LDL was stimulated by hCG. Although 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was present in microsomes prepared from fresh human corpus luteum tissue, the activity of this enzyme in microsomes prepared from tissue maintained in culture for 3 days was virtually undetectable. Fresh human corpus luteum tissue contained 3 times more unesterified cholesterol than esterified cholesterol. It is concluded that LDL, but not HDL, is the major source of cholesterol used by the human corpus luteum for progesterone biosynthesis.

Effects of adrenocorticotropic hormone on low density lipoprotein receptors of human fetal adrenal tissue

In the present investigation, the mechanism(s) whereby ACTH stimulates low density lipoprotein (LDL) metabolism in human fetal adrenal was evaluated. Plasma membrane fractions were prepared from fetal adrenal tissue fragments incubated in lipoprotein-poor serum with or without ACTH, and the binding of [125I]iodo-LDL to such membrane fractions was examined. The mean specific binding capacity for [125I]iodo-LDL by membrane fractions prepared from four separate fresh human fetal adrenal glands was 1370 +/- 168 ng mg-1 protein (mean +/- SE), and the concentration of [125I]iodo-LDL producing half-maximal binding was 20.8 +/- 1.2 ng ml-1. Thus, the presence of high affinity, low capacity binding sites for LDL in human fetal adrenal tissue was confirmed. When human fetal adrenal tissue was maintained in organ culture for 2 days in medium containing lipoprotein-poor serum in the absence of ACTH, and plasma membrane fractions were subsequently prepared, the binding capacity for LDL in such membrane fractions was the same as or slightly greater than that in membrane fractions prepared from fresh tissue. When ACTH was present in the culture medium, the binding capacity for LDL was doubled compared to that in membrane fractions prepared from tissues incubated in the absence of ACTH. The rate of [125I]iodo-LDL degradation by human fetal adrenal tissue maintained in medium containing ACTH was also twice that of tissue maintained in the absence of ACTH. These results demonstrate that ACTH causes an increase in the number of LDL-binding sites in human fetal adrenal tissue in vitro. This is one mechanism whereby ACTH stimulates LDL metabolism in this tissue.

Maternal plasma adrenocorticotropin and cortisol relationships throughout human pregnancy

Adrenocorticotropin (ACTH) and cortisol in plasma were measured weekly from early in gestation through delivery in five women whose pregnancies were normal. During the twelfth week of pregnancy, the concentration of ACTH in plasma of blood samples obtained between 0800 and 0900 hours was 23 +/- 4.6 pg/ml (mean and SEM) and rose progressively to 59 +/- 16 pg/ml at 37 weeks. The levels of ACTH in plasma were significantly lower throughout pregnancy than those found in nonpregnant women. During labor and delivery, ACTH levels rose strikingly to values of 301 +/- 137 pg/ml. As pregnancy advanced, the concentration of cortisol in plasma increased progressively from 149 +/- 34 ng/ml (mean and SEM) at 12 weeks to 352 +/- 90 ng/ml at 26 weeks' gestation but changed minimally thereafter until labor commenced, during which values of 706 +/- 148 ng/ml were achieved. ACTH and cortisol secretory patterns over a 24-hour period were also investigated in one subject during each trimester of pregnancy. Diurnal variations were observed that were qualitatively similar to those seen in nonpregnant women. From the results of these studies, we conclude that ACTH levels are suppressed in plasma of normal pregnant women but are higher in late pregnancy than in early pregnancy. The rise in plasma ACTH concentrations, as pregnancy advances, in spite of increasing levels of plasma cortisol, estrogens, and progesterone, is suggestive of the possibility that a source of ACTH exists that is not subject to negative feedback control, that the clearance of free cortisol increases as pregnancy advances, or that there is an alteration in the metabolism of the ACTH precursor protein produced by the pituitary and/or placenta.

Lipoprotein utilization and cholesterol synthesis by the human fetal adrenal gland

A model proposed for regulation of steroidogenesis, lipoprotein utilization and cholesterol metabolism in HFA tissue is presented in Fig 17. We envision that the role of ACTH and cAMP in steroidogenesis and cholesterol metabolism is as follows. ACTH binds to specific receptors on the surface of the cells of the HFA gland and as a consequence, adenylate cyclase is activated, leading to increased formation of cAMP. cAMP causes activation of protein kinase that leads, presumably, to phosphorylation of specific proteins. This leads to the initiation of reactions that give rise to increased activity of key enzymes and levels of proteins involved in adrenal cholesterol metabolism. Presumably, the action of ACTH causes an increase in the activity of cholesterol side chain cleavage, the rate-limiting step in the conversion of cholesterol to steroid hormones. We suggest that once the mitochondrial cholesterol side-chain cleavage system is fully activated by ACTH, the supply of cholesterol to the mitochondria becomes rate-limiting for steroidogenesis. To meet this demand for cholesterol, a further action of ACTH results in an increase in the number of LDL receptors. LDL binds to specific receptors on the cell surface that are localized in coated pits. LDL is internalized by a process of adsorptive endocytosis and the internalized vesicles fuse with lysosomes and the protein component of LDL is hydrolyzed by lysosomal proteolytic enzymes to amino acids. The cholesteryl esters of LDL also are hydrolyzed to give rise to fatty acids and cholesterol. The liberated cholesterol is available for utilization in the biosynthesis of steroid hormones and other cellular processes. In addition, ACTH stimulates the activity of HMG CoA reductase and, thus, the rate of de novo cholesterol biosynthesis. In this way sufficient cholesterol is obtained to provide for precursor cholesterol to maintain the high rate of steroid synthesis by the HFA. HDL is not utilized as a source of cholesterol by the HFA. Because of the rapid rate of utilization of LDL by the HFA, fetal plasma levels of LDL are low and the activity of the HFA is a primary determinant of these levels. Thus, in the case of anencephaly, in which the activity of the adrenal is very low, plasma levels of LDL are 2--3 times higher than in normal fetuses, whereas plasma HDL levels are similar. In addition, in the normal neonate plasma LDL levels rise rapidly after birth, and this event is coincident with the involution of the fetal zone of the adrenal. The fetal liver is likely to be the major source ultimately of the LDL-cholesterol utilized by the HFA. Consequently, factors that regulate cholesterol and lipoprotein synthesis in the fetal liver may, in turn, affect the steroidogenic activity of the HFA through regulation of the supply of cholesterol precursor. Thus, if trophic factors for the HFA other than ACTH exist, an important site of their action might be the fetal liver, rather than a direct action to influence the rate of synthesis of steroids by the fetal adrenal.

Plasma lipoproteins in follicular fluid of human ovaries

Human corpus luteum tissue, maintained in organ culture, is dependent upon low-density lipoprotein (LDL) as a source of cholesterol for maximal progesterone secretion whereas high-density lipoprotein (HDL) does not support progesterone biosynthesis by human corpus luteum tissue. In the present investigation, follicular fluid of human ovaries was found to contain little or no LDL or very low-density lipoprotein. The concentration of HDL in follicular fluid approached that found in plasma. We suggest that one reason that granulosa cells of the preovulatory follicle produce limited quantities of progesterone is because of the absence of LDL-cholesterol in follicular fluid. Following ovulation, vascularization of the corpus luteum provides a means by which LDL is available to the luteinized granulosa cells and thence progesterone biosynthesis can commence.

Metabolism of high density lipoprotein by human fetal adrenal tissue

The role of lipoproteins as a source of the cholesterol utilized for steroidogenesis by human fetal adrenal (HFA) tissue was investigated previously. It was found that low density lipoprotein (LDL) was the lipoprotein preferred as a source of cholesterol for steroidogenesis by the HFA. [125I]Iodo-LDL was taken up and degraded by HFA tissue in organ culture, and the degradation of [125I]iodo-LDL was stimulated when ACTH (1 microgram X ml-1) was present in the culture medium. Others have shown that high density lipoprotein (HDL) is utilized as a source of cholesterol for steroidogenesis by rat adrenocortical cells in vitro and by the adrenals of the adult rat in vivo. In the present investigation we evaluated the metabolism of [125I]iodo-HDL by HFA tissue. [125I]iodo-HDL uptake by the HFA tissue increased in a linear manner with time and as the concentration of [125I]iodo-HDL in the culture medium was increased. However, there was little degradation of [125I]iodo-HDL by HFA. Moreover, preincubation of HFA tissue in medium containing ACTH (1 microgram X ml-1) or HDL, in various concentrations, did not affect the rate of uptake and degradation of [125I]iodo-HDL. The rate of degradation of [125I]iodo-LDL was found to decrease to low levels as the concentration of nonradiolabeled LDL in the culture medium was increased, whereas nonradiolabeled HDL had little effect on the degradation of [125I]iodo-LDL. HFA tissue fragments were incubated in medium containing ACTH plus lipoprotein-poor serum (LPPS) alone or LPPS plus HDL in various concentrations (50-1000 microgram X ml-1). The medium was changed daily and assayed for dehydroisoandrosterone sulfate and cortisol. In the presence of HDL, steroid secretion rates were no greater than those attained by HFA maintained in medium containing LPPS. It is concluded that the HFA utilizes cholesterol derived from LDL for steroidogenesis and that HDL is not metabolized efficiently by the human fetal adrenal.

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.

Steroid production in a woman with gonadal dysgenesis, breast development, and clitoral hypertrophy

Androgen and estrogen production was measured in a 46,XX woman with gonadal dysgenesis, breast development, and clitoral hypertrophy. The production rates of androstenedione (438 micrograms/24 hr), estrone (26 micrograms/24 hr), and estradiol-17 beta (13 micrograms/24 hr) were low compared to values obtained in normal young women. The production rate of testosterone (239 micrograms/24 hr) was similar to that of normal women. Bilateral nodular streaks were found in the usual anatomic site occupied by ovaries. By microscopic examination of the streaks, fibrous tissue containing nests of hilar cells was found. The karyotype of skin, peripheral leukocytes, and gonadal streak fibroblasts in culture was 46,XX. The possible causes and implications of breast development and clitoral enlargement in subjects with gonadal dysgenesis are discussed.

Inverse relation between low-density lipoprotein-cholesterol and dehydroisoandrosterone sulfate in human fetal plasma

A striking inverse correlation was found in umbilical cord plasma between the concentrations of dehydroisoandrosterone sulfate and low-density lipoprotein (LDL)-cholesterol but not high-density lipoprotein-cholesterol or very low density lipoprotein-cholesterol. Dehydroisoandrosterone sulfate is a major secretory product of the human fetal adrenal and the principal precursor of placental estrogen production. The data suggest that the concentrations for LDL-cholesterol in fetal plasma are influenced by the rate of utilization of LDL-cholesterol by the fetal adrenal for steroidogenesis and are not necessarily related to a genetic predisposition for hypercholesterolemia or other lipoprotein disorders.

Regulation of steroid secretion by adrenal tissue of a human anencephalic fetus

ACTH-stimulated adrenal tissue of a human anencephalic fetus, when maintained in organ culture, secreted appreciable quantities of cortisol but little dehydroisoandrosterone sulfate or pregnenolone sulfate. In the absence of ACTH, cortisol secretion was severely attenuated. Arginine vasopressin or alpha MSH, when added to the culture medium, did not stimulate steroid secretion. When whole human serum was present in the culture medium bathing the adrenal tissue of the anencephalic fetus, the rate of cortisol secretion was similar to that attained when lipoprotein-poor serum was in the medium. Based on these findings, it is concluded that in the presence of ACTH, the adrenals of the anencephalic fetus secrete principally cortisol, and the failure of dehydroisoandrosterone sulfate and pregnenolone sulfate secretion is due to the absence of the fetal zone. The lack of stimulation of cortisol secretion by lipoprotein is probably due to a reduced number of low density lipoprotein receptors resulting from diminished ACTH stimulation before birth.

Plasma levels of adrenocorticotropin and cortisol in women receiving oral contraceptive steroid treatment

The secretion rate and plasma concentration of the adrenocortical steroid cortisol is modified in subjects treated with estrogenic and/or progestational steroids. The effects of contraceptive steroids on the secretion of ACTH are poorly documented, however, In the current investigation, we found that concentrations of ACTH and cortisol in plasma obtained at 0800--0900 h from a group of women with normal cyclic menses (n = 4) ranged from 78--120 pg/ml and 77--137 ng/ml, respectively. Although significant cyclic changes in the plasma levels of LH, FSH, 17 beta-estradiol, and progesterone occurred during the ovarian cycle, no obvious cyclic fluctuations in plasma levels of ACTH or cortisol were observed. In women treated with Norinyl 1 + 80 (1.0 mg norethindrone plus 0.08 mg mestranol), plasma concentrations of LH, FSH, 17 beta-estradiol, and progesterone were significantly lower (P less than 0.001) than plasma levels of these hormones in normal women during the ovarian cycle. The mean daily plasma concentrations of ACTH were significantly lower (P less than 0.001), whereas plasma cortisol levels were significantly higher (P less than 0.001) in women treated with oral contraceptive steroids compared to the levels of these hormones in the untreated ovulatory women.

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.

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.