The acute action of adrenocorticotropic hormone on adrenal steroidogenesis

Controle de dopagem de anabolizantes: o perfil esteroidal e suas regulações

O conceito de perfil esteroidal é discutido neste artigo. As principais vias biossintéticas são apresentadas. A importância do monitoramento do perfil esteroidal é demonstrada dentro da clínica médica e da medicina esportiva. Parâmetros da literatura para a identificação de dopagem por esteróides endógenos são apresentados, assim como os fatores que acarretam alterações no perfil esteroidal normal. É dada atenção especial a essa última abordagem.

Gamma 3-melanotropin promotes mitochondrial cholesterol accumulation in the rat adrenal cortex

Gamma 3-melanotropin (gamma 3-MSH) facilitates a rapid, dose-dependent, and cycloheximide-insensitive increase in the concentration of mitochondrial free cholesterol in the adrenals of hypophysectomized rats. Physiological concentrations of various synthetic and native preparations of gamma 3-MSH are potent, while gamma-MSH is not. This cholesterol accumulation coincides with the activation of cholesteryl ester hydrolysis by gamma 3-MSH, while the rates of cholesterol esterification and of mitochondrial cholesterol side-chain cleavage are unaffected. Conversely, ACTH inhibits cholesterol ester esterification. Therefore, gamma 3-MSH and ACTH together may coordinate a substantial shift in the set-point of cholesteryl ester in equilibrium cholesterol cycling toward the right. Because ACTH also activates cholesterol side-chain cleavage, this coordinate effect on the flux of cholesterol substrate is manifest as a potentiation of corticosteroidogenesis by gamma 3-MSH. These data extend our previous studies demonstrating that pro-gamma-MSH polypeptides have an endocrine influence on the rat adrenal cortex.

On the mechanism of action of ACTH: the role of actin

The discovery of a role for the cytoskeleton in the responses to ACTH and cyclic AMP was somewhat unexpected - at least this was the case 9 years ago (1). In fact, many endocrinologists are forced to confess that they were innocent of any understanding of the cytoskeleton and were not even aware that all mammalian cells possess microfilaments and microtubules. A new generation of endocrinologists has arrived on the scene who have been brought up with the cytoskeleton so that we can expect to see considerable progress during the coming decade in our understanding of the role of the cytoskeleton in endocrine cells.

The effect of ether stress and cycloheximide treatment on cholesterol binding and enzyme turnover of adrenal cortical cytochrome P450scc

Relative rate constants for the formation of pregnenolone from cytochrome P450scc bound cholesterol in adrenal cortical mitochondria of stressed, stressed plus cycloheximide treated and dexamethasone treated rats were calculated from the ratios of initial rates of pregnenolone formation and the pregnenolone induced difference spectrum. In mitochondria from adrenals removed under aerobic conditions in vivo, the rate constant for the enzyme in stressed rats is twice a high as the rate constant for the enzyme from the stressed plus cycloheximide group, and four times as high as that for the enzyme from dexamethasone treated rats. Anoxia for 5 min in the intact gland increases the rate constant in all groups. Pregnenolone difference spectra are higher in mitochondria from stressed plus cycloheximide treated rats than in mitochondria from stressed rats, when adrenals are removed aerobically. It is concluded that ACTH increases cholesterol binding to cytochrome P450scc, by increasing either the enzymes affinity for its substrate or the availability of cholesterol and in addition promotes turnover of the enzyme. Both of these effects of ACTH are inhibited by cycloheximide.

Pro-adrenocorticotropin/endorphin-derived peptides: coordinate action on adrenal steroidogenesis

A synthetic peptide, representing a portion of the 16K (16,000 dalton)-fragment sequence within the pro-adrenocorticotropin/endorphin precursor molecule, potentiates the steroidogenic action of the 1 to 24 portion of adrenocorticotropin [ACTH(1-24)] on the rat adrenal cortex. The peptide has 27 amino acid residues and consists of gamma-melanotropin with a carboxyl terminal extension. It affects both the inner and outer adrenocortical zones of hypophysectomized animals, as evidenced by a synergistic augmentation of corticosterone and aldosterone production, respectively. The peptide can be distinguished from adrenocorticotropin by its activation of cholesterol ester hydrolase and its failure to stimulate cholesterol side-chain cleavage.

Non-esterified cholesterol-rich adrenal lipid fractions. Preparation, properties and preferential utilization for cholesterol side-chain cleavage by corticotropin-stimulated adrenal mitochondria

Rat adrenal 105,000 g supernatant contains two lipid moieties, 'lipid-I' and 'lipid-II' which contain non-esterified cholesterol and stimulate cholesterol side-chain cleavage in soluble or mitochondrial enzyme systems. Lipid-I contains relatively large low-density heat-stable particles, whereas lipid-II particles are smaller, more dense and heat-labile. Lipid-I and lipid-II can be separated from clear cytosol by ultracentrifugation and gel filtration respectively. Corticotropin plus cycloheximide treatment increases the non-esterified cholesterol concentrations in the lipid fractions, and stimulatory effects of lipids on cholesterol side-chain cleavage appear to correlate with non-esterified cholesterol concentrations therein. On addition of saturating amounts of cholesterol-rich lipid, pregnenolone synthesis and cholesterol binding to cytochrome P-450 are stimulated more in mitochondria from corticotropin-stimulated adrenals than in mitochondria from control or corticotropin-plus cycloheximide-stimulated adrenals. These results support the contention that the corticotropin-induced increase in mitochondrial cholesterol side-chain cleavage involves an increase in cholesterol utilization as well as an increase in cholesterol availability.

Regulation of cholesterol metabolism in rat adrenal mitochondria

Addition of cholesterol to rat adrenal mitochondria resulted in a stimulation of pregnenolone synthesis. The slow step of the mitochondrial cholesterol side-chain cleavage reaction could be the interaction of the sterol with cytochrome P-450. The rate of cholesterol binding to this enzyme as observed spectroscopically correlated with the equilibration period (20 min) of the mitochondria and exogenous cholesterol required for maximal rates of pregnenolone synthesis. It is suggested that translocation of cholesterol between different sterol pools occurs within the mitochondria. Potential intracellular effectors that could be of importance in the movement or regulation of mitochondrial cholesterol include bivalent metallic ions, prostaglandins, cyclic nucleotides, polyamines and polylysine. Of the effectors studied, only calcium ions and polylysine markedly stimulated pregnenolone synthesis. These effectors might stimulate steroidogenesis by lateral displacement of cholesterol in the mitochondrial membrane into a compartment easily accessible to the cholesterol side-chain cleavage enzyme complex.

Mitochondria from human term placenta. III. The role of respiration and energy generation in progesterone biosynthesis

The interrelationships among the processes of progesterone biosynthesis, respiration and energy production in human term placental mitochondria were examined. All substrates (citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, malate, glutamate, glycerol 3-phosphate, ascorbate + N,N,N',N'-tetramethyl-p-phenylenediamine) previously found to stimulate oxygen uptake and ATP synthesis in placental mitochondria supported progesterone synthesis from endogenous and exogenous cholesterol. Citrate support of progesterone synthesis was stimulated by NADP+ but not NAD+. It was inhibited by fluorocitrate and trans-aconitate but not by arsenite, rotenone, antimycin, cyanide or 2,4-dinitrophenol. Ascorbate-N,N,N',N'-tetramethyl-p-phenylenediamine support of progesterone synthesis was stimulated by NAD+ and NADP+ and was inhibited by ADP, rotenone, antimycin, cyanide and 2,4-dinitrophenol. Cyanide inhibition was relieved by an exogenous ATP regenerating system and ADP inhibition was reversed by oligomycin. Progesterone synthesis supported by alpha-ketoglutarate + malonate was stimulated by NAD+ and NADP+, and was completely inhibited by arsenite. 2,4-Dinitrophenol was strongly inhibitory both in the absence and presence of rotenon or antimycin. Stimulation by ATP was enhanced by rotenon, antimycin and oligomycin and inhibited by 2,4-dinitrophenol. Thus, metabolic control of progesterone synthesis by the energy status of the mitochondrial system was demonstrated when reducing equivalents were supplied via NADH or the respiratory electron transport chain.

Different effects of cycloheximide and chloramphenicol on corticosterone production by isolated rat adrenal cells

Cycloheximide and chloramphenicol both inhibit the stimulating effect of adenocorticotropic hormone (ACTH) on adrenal steroid production. To test whether these inhibitors had andy effect on adrenal steroid production, independent fromthe mechanism of action of ACTH we investigated their effect on the conversion of 25-hydroxycholesterol into corticosterone in isolated rat adrenal cells. Cycloheximide, both in the absence and in the presence of ACTH, had no effect on this conversion. Chloramphenicol inhibited the conversion of 25-hydroxycholesterol into corticosterone whether ACTH has no direct efeect on the cholesterol side-chain cleaving system. The inhibition by chloramphenicol of the ACTH-stimulated steroid production is at least partly due to inhibition of one or more of the processes involved in the conversion of 25-hydroxycholesterol into corticosterone.

Effects of 25-hydroxycholesterol and aminoglutethimide in isolated rat adrenal cells. A model for congenital lipoid adrenal hyperplasia?

The production of corticosterone from 25-hydroxycholesterol by isolated rat adrenal cells is inhibited by aminoglutethimide phosphate (AGI); half-maximal inhibition is obtained at ca. 10 muM. AGI also inhibits ACTH-stimulated steroid production from endogeneous substrates; here half-maximal inhibition is obtained with ca. 40 muM AGI. In the presence of ACTH + AGI, 25-hydroxycholesterol causes additive inhibition. This effect of 25-hydroxycholesterol is dose-dependent. ACTH-stimulated steroid production from endogeneous substrates is partially inhibited by 5-cholene-3 beta,24-diol. These results may just reflect substrate competition for the side-chain cleaving system or may be due to some seocndary toxic effect on the cells.

Studies on isolated rat adrenal cells metabolism of hydroxylated sterols

Corticosterone production by isolated rat adrenal cells in the absence of ACTH is stimulated by 20alpha-hydroxycholesterol, 22R-hydroxycholesterol and 25-hydroxycholesterol. This effect is also seen at sub-maximal ACTH concentrations. Aminoglutethimide (AGI) inhibits the stimulation caused by the three hydroxylated cholesterols. In the presence of ACTH, AGI also inhibits steroid production both under control conditions and in the presence of the sterols. The stimulation by 25-hydroxycholesterol is dose-dependent, both in the presence and absence of a sub-maximal ACTH concentration. At maximal ACTH concentrations 25-hydroxycholesterol does not give additional stimulation. Cycloheximide has no effect on corticosterone production from 25-hydroxycholesterol whether ACTH is present or not. Our results indicate that 25-hydroxycholesterol is a good substrate for the study of the cholesterol side-chain cleaving system and the mechanism of action of ACTH at the levels of the intact cell.