Other influences

Although LH appears to be the most important hormone, Leydig cells are also target cells for other hormones. In addition, the neural network must be considered. For a long time the importance of neuronal connections between the brain and the testis was neglected, but recent data show that the neural network can regulate the sensitivity of the Leydig cells towards LH (Csaba et al. 1998; Selvage and Rivier 2003). The relative importance of this neuronal network under normal physiological conditions is yet unknown, but since current research activities are more directed to the mechanisms of fine control, interactions between the neural and endocrine network must be the subject of future investigations.

Over the past years there has been a substantial number of publications on effects of thyroid hormones and glucocorticoids on Leydig cells. Thyroid hormone actions were mainly studied in connection with stimulation of Leydig cell activities, while most effects of glucocorticoid hormones were correlated with a decrease in androgen production.

Thyroid hormone accelerates the differentiation of Leydig cells (Ariyaratne et al. 2000) and also stimulates the StAR expression and steroid production in fully developed cells (Manna et al. 1999). Glucocorticoids inhibit steroidogenic enzymes and induce apoptosis in rat Leydig cells (Gao et al. 2002). The ultimate effects of glucocorticoids in vivo depend very much on local metabolism within the target cells. In this connection the activity of 11 p-hydroxysteroid dehydrogenase as a local amplifier of glucocorticoid action is also of importance (Seckl and Walker 2001).

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