Transducing systems in the hormonal regulation of steroidogenesis in rat Leydig cells

The studies described in this thesis have mainly been concerned with the elucidation of several of the second messenger systems present in the Leydig cell and the regulation of steroidogenesis through pathways that involve cAMP and calcium ions as second messengers. A general, albeit simplified scheme for transmembrane signalling which result in stimulation of steroid production is given in figure 1 .1. To affect Leydig cell function specific stimulators (dbcAMP, phorbol esters etc.} or inhibitors (P-site agonists, diltiazem etc.) of the different second messenger systems were used in addition to physiological stimuli. The effects of these probes were measured by determining (1) the activity of adenylate cyclase through measurements of the intracellular levels of cAMP, {2) the activity of protein kinases by studying electrophoresis patterns of proteins labelled with 32Po 4 , (3) stimulation of de novo protein synthesis by studying the electrophoretic patterns of proteins labelled with 35s-methionine and (4) the activity of the cholesterol side chain cleavage enzyme by measuring the production of pregnenolone from endogenous precursors. The results of these studies are described in detail in chapters 3-6 and in the appendix papers 1, 2, 4 and the appendix chapter. Results of studies on the involvement of cAMP and calcium as second messengers in LH action are described in chapter 4. The mechanism of action of LHRH is discussed in chapter 5 and data on the presence of GTP-binding proteins N s and Ni in Leydig cells are given in chapter 6. In chapter 7 an integrated model of the regulation of properties of Leydig cell function is discussed with special derived from the results in summarized