Hormonal Regulation of Cellular Metabolism

Abstract

Several classes of animal hormones are known, all of which exert control over intracellular metabolism. Steroid hormones, for example, are thought to penetrate the plasma membrane, bind to cytoplasmic receptors, and travel to the nucleus where the hormone receptor complex influences gene expression. By contrast, prostaglandins, catecholamines, and peptide hormones probably exert their regulatory effects at the level of the plasma membrane. Specific hormone receptor proteins have been postulated to account for the action of the latter compounds on the activities of membrane-associated enzyme systems that catalyze solute transport and the synthesis of cyclic nucleotides. Prostaglandins are water-insoluble compounds, which probably intercalate into the phopholipid matrix of the membrane before binding to a hydrophobic receptor site within the membrane. Some evidence exists to suggest that prostaglandin receptors (which have not been isolated or characterized biochemically) may mediate the action of other hormones and thus function as transducer elements in the membrane. Catecholamines (epinephrine, norepinephrine) are simple derivatives of the amino acid, tyrosine, and can penetrate most biologic membranes via specific transport systems.

To me life consists simply in this, in the fluctuation between two poles, in the hither and thither between the two foundation pillars of the world.

Hermann Hesse