Contents/Information:A. Kurtz: Cellular Control of Renin Secretion. This review focuses on the intracellular processes that govern renin release from juxtaglomerular cells. The available information is discussed in relation to background of the present knowledge on general mechanisms of secretion. It has been shown for a variety of secretory cells, including those of the adrenal and pituitary glands, exocrine and endocrine cells of the pancreas, neutrophils and platelets, that the secretory process is triggered by guanosine triphosphate-(GTP-)binding proteins, phosphoinositide turnover, intracellular levels of calcium and cyclic nucleotides. Apart from renin synthesis and secretion this review deals with the physiological environment of the juxtaglomerular cells, baroreceptors, Macula densa, sympathetic nervous system and hormones. U. Walter: Physiological Role of cGMP and cGMP-Dependent Protein Kinase in the Cardiovascular SystemThis review concentrates on the role of cGMP in the cardiovascular system, with particular emphasis on the functional significance of cGMP-dependent protein kinase and cGMP-regulated phosphorylation. Possible mechanisms of action of cGMP as well as structure, properties, cellular distribution and regulation of the cGMP-dependent protein kinases and their substrates are discussed. Major point plays the role of cGMP-dependent protein kinase and cGMP-regulated protein phosphorylation in the regulation for vascular smooth muscle cells and platelets. E. Ozawa: Transferrin as a Muscle Trophic FactorThis review attempts to offer as clear an answer to the question how is transferrin provided to muscle cells: Is it neurogenic or humoral? For this purpose muscle development, growth, and maintenance and the effect of denervation on muscle cells are first described. Followed by general biochemistry and the cell biology of transferrin in order to outline the nature of transferrin and of transferrin receptor. Thereupon "transferrinology" in muscle cells is described. And finally, a detailed discussion considers whether transferrin is provided to the muscle cells from the nerve or from tissue fluid.