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The Action of Steroid Hormones at the Cellular Level P POSTGRAD. MED. J. (1964), 40, 448 Postgrad Med J: first published as 10.1136/pgmj.40.466.448 on 1 August 1964. Downloaded from THE ACTION OF STEROID HORMONES AT THE CELLULAR LEVEL P. F. DIXON, B.A., M.B., B.Chir., A.R.I.C., C. H. GRAY, M.D., D.Sc., F.R.C.P., F.R.I.C., R. V. QUINCEY, B.A. Department of Chemical Pathology, King's College Hospital Medical School, London, S.E.5. Although the complex series of events which oestrogens and related compounds and showed occur when a steroid hormone is administered by viscometry and electrophoresis structural to a human subject or to an intact animal changes in the enzyme, without a change in might reflect a series of completely unre!lated molecular weight. Yielding and Tomkins activities, they are more likely to be secondary (1962) have reported a steroid-hormone induced to a few fundamental actions on the celils of loss of activity of crystalline glutamic dehydro- the body and it is with this second concept genase due to disaggregation into subunits that research in this field has been directed. functioning as alanine dehydrogenase with an There are two particular features of steroids uncovering of pyridine-nucleotide binding sites. which may be important in determining their These authors have been more concerned to mode of action. Firstly, they have oxygen show the possibility of such changes rather substituents at certain typical positions which than to attach great physiological significance readily undergo enzymatic oxido-reduction and to them. Chemical changes in receptor mole- could, therefore, act as coenzymes or pros- cules after association could account for Protected by copyright. the thetic groups of enzymes in reactions involving highly theoretical possibility of the formation hydrogen transfer. Secondly, steroids are sur- of active enzymes from inactive precursors. face active and interact with hydrophobic sur- That the receptor itsel-f could be an enzyme faces producing energy. If the energy were cofactor has been considered by Scott and to be absorbed iby a receptor molecule it could Engel (1961) who obtained physical evidence modify the structure and hence the biological for the interaction between steroid hormones activity of that molecule. A less well defined and purine dinucleotides. This interaction change is associated with the ability of steroids between hormone and a coenzyme associated to capture electrons; this has recently been with a postulated change in the structure measured by Lovelock, Simmonds and Vanden- of the coenzyme might abolish its hydrogen- heuvel (1963) who consider that the high carrying function, but there was no experi- electron affinities of adrenocortical hormones, mental evidence for this. a property unusual among organic compounds, Apart from oxido-reductive changes, might indicate their ability to participate in metabolism of the steroid molecule is nothttp://pmj.bmj.com/ or control biological oxidative processes. thought to be of physiological importance Laidler and Krupka (1961) compared the except as a mechanism for steroid inactivation. association between the steroid and a receptor However, competition for active sites on with the formation of an activated enzyme- enzymes as opposed to association with them substrate Michaelis complex. Entropy and could be of importance in influencing steroid volume changes during activation of enzymes metabolism itself. indicate that structural changes occur in the The various theories which have been pro- on September 28, 2021 by guest. enzyme molecule and such changes might ex- posed to explain the action of steroid hormones plain the disturbances of membrane perme- at the cellular level will be considered under ability in nerve cells associated with structural the following headings: changes in acetylcholinesterase. A similar 1. Effects on membrane permeability and mechanism might account for changes induced active transport. by steroids in the permeability of cell structures. 2. Effects on hydrogen transfer. In this process parts of the receptor mole- 3. Effects on enzyme induction and protein cules having specific binding properties might synthesis. be masked, unmasked, created or destroyed; as well as causing a redistribution of bound Effects on Membrane Permeability and on substrates, an alteration in enzymic properties Active Transport. might result. Kimberg and Yielding (1962) Roberts and Szego (1953) found that cestro- studied the inhibition of pyruvate kinase by gens increased the glucose uptake of rat uteri, 1964 DIXON, GRAY and QUINCEY: Steroid August, Hormones 449 Postgrad Med J: first published as 10.1136/pgmj.40.466.448 on 1 August 1964. Downloaded from and suggested that their primary action might as highly organised structures, parts of which be to facilitate the entry of glucose into the are clearly differentiated by membranes and uterine cells. Noall, Riggs, Walker and Chris- phase boundaries, a possible effect on intra- tensen (1957) showed an increased uptake of cellular substrate distribution must also ibe x -amino-iso-butyric acid (AIB) in immature considered. Information on this, however, is rat uteri 20 hours after administering aestradiol scanty and indirect. Binding to subceUlular and in rat liver 2 hours after giving hydro- particles has been studied by Westphal (1961) cortisone. Since this synthetic amino acid is who demonstrated interaction between liver not metabolised, any change in uptake must mitochondria and hydrocortisone and cortico- be due to a change in transport. Halkerston, sterone, and by Bellamy (1963) who showed a Eichhorn, Feinstein, Scully and Hechter (1960) significant binding between corticosterone and examined the effects of cestradiol on the uteri rat liver ribosomes. There is definite evidence of castrate rats using intravenous [14C] that the mitochondrial membrane is influenced labelled AIB as well as [14C] D-xylose; they by steroids. Westphal (1961) found that hydro- found no change 12 hours after cestrogen injec- cortisone and corticosterone increased the tion, although the metabolic effects on glucose swelling of rat liver mitochondria, indicating uptake and incorporation of amino acids into an increased permeability to water. Gallagher protein are detectable after one hour. After (1960) concluded that hydrocortisone inhibited six hours there was an increase in the water oxidative metabolism in liver imitochondria content of the tissue and a small increase in by increasing the membrane permeability caus- AIB and xylose accumulation. They concluded ing loss of respiratory cofactors. Blecher that there is no primary change in sugar or (1962) suggested that a similar swelling was amino acid transport and interpreted previous associated with a release of latent ATPase results as secondary effects operating at a later which inhibited metabolism of glucose byProtected by copyright. time. On the other hand Noall and Allen reducing the availability of ATP. He cited (1961) obtained more than 100 per cent increase this as a mechanism for the ilymphocytolytic in AIB uptake in uteri in vitro removed only action of steroids. 30 minutes after intravenous administration of Structural alterations in the peripheral cell cestradiol to immature rabbits. They comment membrane are generally assumed to account that in vivo experiments were unsuitalble for for changes in transport (see Tomkins and the investigation of early changes. No effect Maxwell, 1963). Controlled and variable was observed when the excised uteri were passive diffusion can be explained on a bio- treated wth cestradiol in spite of adequate chemical basis, but explanations of mechanisms penetration of the hormone. Although this of active transport in which energy is used to suggested that the increased uptake observed transfer molecules against concentration gra- after in vivo hormone administration may not dients are only speculative. Hechter and Lester have been a primary effect, they postulated (1960) present and review data suggesting that that cestradiol might be metabolised to a hypo- part of the increased glucose uptake of muscle http://pmj.bmj.com/ thetical active form but their evidence was cells in response to insulin is the apparent inconclusive. An increased uptake of AIB removal of intracellular barriers to diffusion, by rat levator ani muscles after large doses of enabling the sugar to equilibrate in a larger testosterone and of synthetic anabolic steroids fraction of the cell water. Extending this theory was shown by Metcalf and Gross (1960) but the authors outline a model cell based on the the effects were not observed until 39 hours results of their experiments on sodium and after the injection of the steroid and nine potassium distribution in the mould Neuro- hours after AIB administration. Increased spora Crassa. Potassium was taken up against on September 28, 2021 by guest. AIB uptake in isolated perfused rat livers was a concentration gradient and sodium was seen by Bass, Chamibers and Richtarick (1963) excluded from the major part of the cell water, two hours after both in vivo and in vitro but in the presence of desoxycorticosterone administrations of hydrocortisone, suggesting both ions were distributed in all of the cel an early direct effect on liver cells. water at the same concentration as in the sur- It is reasonable to conclude that steroid rounding medium. This suggested that the hormones alter transport mechanisms and thus sodium pump operated not at the cell boun- influence the availability of substrate to cells, dary but in the cytoplasm. The crystal struc-
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