Expression of alpha 1 adrenoceptor subtypes in rat corpus cavernosum.

Norepinephrine mediates the antierectile role of the sympathetic nervous system. It binds to postsynaptic alpha 1 adrenoceptors present on smooth muscle fibers of the corpus cavernosum. Receptor cloning studies have evidenced three alpha 1 adrenoceptor subtypes: alpha 1A, alpha 1B and alpha 1D. We searched for the presence of these three alpha 1 adrenoceptor subtypes in the rat corpus cavernosum using in situ hybridization with specific oligonucleotide probes. Brain tissue was used as the reference of probes specificity. Autoradiographic films were studied with light illumination and computer-assisted densitometry using an image analyser. We provide evidence that the three alpha 1 adrenoceptor subtypes are expressed in the rat corpus cavernosum. These three subtypes appear to be more expressed in the trabecular smooth muscle fibers than in vascular smooth muscle fibers. Further experiments are needed to determine whether the proportion of alpha 1 adrenoceptor subtypes changes according to the etiology of erectile dysfunction. This morphological approach provides a basis for future pharmacological research of specific alpha 1 adrenoceptor subtypes blocking agents designed to treat erectile dysfunction.