Metabolism of (4-14C) cholesterol by human adrenal glands in vitro and its inhibition by metyrapone

Biosynthesis and metabolism of steroid hormones by human adrenal carcinomas

Over a 15-year period, our university-based laboratory obtained 125 adrenal tumors, of which 15 (12%) were adrenal cortical carcinomas. Of these, 6 (40% of the carcinomas) occurred in patients with clear clinical manifestations of steroid hormone excess. Adrenal cortical carcinoma cells derived from the surgically resected tumors in 4 of these patients were isolated and established in primary culture. Radiotracer steroid interconversion studies were carried out with these cultures and also on mitochondria isolated from homogenized tissues. Large tumors had the lowest steroidogenic activities per weight, whereas small tumors had more moderately depressed enzyme activities relative to cells from normal glands. In incubations with pregnenolone as substrate, 1 mM metyrapone blocked the synthesis of corticosterone and cortisol and also the formation of aldosterone. Metyrapone inhibition was associated with a concomitant increase in the formation of androgens (androstenedione and testosterone) from pregnenolone. Administration of metyrapone in vivo before surgery in one patient resulted in a similar increase in plasma androstenedione, though plasma testosterone levels were not significantly affected. In cultures of two of four tumors examined, dibutyryl cAMP stimulated 11ss-hydroxylase activity modestly; ACTH also had a significant stimulatory effect in one of these tumors. Unlike results obtained with normal or adenomatous adrenal cortical tissues, mitochondria from carcinomatous cells showed a lack of support of either cholesterol side-chain cleavage enzyme complex or steroid 11ss-hydroxylase activity by Krebs cycle intermediates (10 mM isocitrate, succinate or malate). This finding is consistent with the concept that these carcinomas may tend to function predominantly in an anaerobic manner, rather than through the oxidation of Krebs cycle intermediates.

Biosynthesis of androgens by pheochromocytomas

Homogenates from four adrenal pheochromocytomas converted 4-14C-labeled pregnenolone, 17-hydroxyprogesterone, and dehydroepiandrosterone into androstenedione and testosterone. In addition to these androgens, labeled pregnane substrates were also transformed into corticosteroids, as previously reported, and this conversion occurred in even higher yield. The formation of labeled metabolites of either pathway was greater in homogenates from intraadrenal pheochromocytomas than in those derived from an extraadrenal tumor, but less than in preparations of hyperplastic adrenal cortex. Incubations of subcellular fractions isolated from an adrenal pheochromocytoma showed that the enzyme activities involved in androgen formation from the radioactive substrates studied were associated with the microsomes and required exogenous cofactors. In contrast to adrenocortical tissue, chromaffin cell preparations uniformly failed to convert substrate [4-14C] cholesterol into either androgens or corticosteroids. The data available demonstrate the presence in chromaffin tissue of all of the enzyme activities required for the biosynthesis of androgens and corticosteroids except for those involved in the side-chain scission of cholesterol.

Kinetics of plasma corticosteroids during metyrapone infusion in man

The effect of metyrapone on plasma kinetics of cortisol (F), 11-deoxycortisol (S), corticosterone (B), 11-deoxycorticosterone (DOC), aldosterone (Aldo) and 17 hydroxyprogesterone (17 OHP) was studied in ten normal prepubertal children intravenously infused with the drug (1 gm/1.73 m2 body surface area in 4 h). Similar falls in F, B and Aldo were observed during the first hour expressing similar sensitivity of the 11 hydroxylases to the drug. The effect of the compensatory increase of endogenous ACTH could be detected after 1 hour by the rise in 17 OHP. However the concentrations of the 11-hydroxy compounds, F, B and Aldo, remained low throughout the infusion period. From the second hour onwards, facilitation of the synthesis of DOC was noticed. After the end of infusion, the levels of the precursors decreased and F and B were restored to initial values. Aldo remained low probably due to the inhibitory effect of the elevated DOC on the renin-angiotensin system.