Figure 2.

Mechanisms of prostate smooth muscle contraction and assumed connections to the regulation of prostate growth. In contrast to earlier concepts, α₁-adrenoceptors in the prostate are no longer regarded as isolated receptors mediating exclusively contraction. In fact, α₁-adrenoceptors in the prostate are part of a signaling network, where different receptors and non-adrenergic mediators cooperatively regulate prostate smooth muscle tone and growth, leading to benign prostate obstruction. Prostate α₁-adrenoceptors lead to contraction by activation of the IP₃/Ca²⁺/calmodulin pathway, of DAG/protein kinase C, of the RhoA/Rho kinase pathway, and by a JNK-dependent mechanism. At least the Ca²⁺- and Rho kinase-dependent mechanisms are shared by TXA2 receptors, which cause prostate smooth muscle contraction in parallel to α₁-adrenoceptors. In addition, α₁-adrenoceptors share intracellular effectors with hormone receptors and growth factors (e. g. fibroblast growth factor): Stimulation of prostate α₁-adrenoceptors leads to activation of ERK1/2, Akt and transcription factors, which are well known to mediate growth and differentiation