Platelet-derived growth factor regulation of type-5 phosphodiesterase in human and rat penile smooth muscle cells.

INTRODUCTION: Relaxation of cavernous smooth muscle cells (SMCs) is a key component in the control of the erectile mechanism. SMCs can switch their phenotype from a contractile differentiated state to a proliferative and dedifferentiated state in response to a change of local environmental stimuli. Proliferation and contraction are both regulated by the intracellular second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), which are degraded by phosphodiesterases (PDEs). The most abundant PDE present in corpora cavernosa is the electrolytic cGMP-specific phosphodiesterase type 5 (PDE5). AIM: We investigated the cellular localization of PDE5 in in vitro cultured corpora cavernosa cells and the effect of mitogenic stimulation on PDE5 expression. METHODS: Biochemical ad molecular techniques on cultured SMCs from human and rat penis. MAIN OUTCOME MEASURES: We studied the ability of the quiescent SMC phenotype vs. the proliferating phenotype in modulation of PDE5 expression. RESULTS: We demonstrated that PDE5 is localized in the cytoplasm, in the perinuclear area, and in discrete cytoplasmic foci. As previously demonstrated in human myometrial cells, the cytoplasmic foci may correspond to centrosomes. In corpora cavernosa, PDE5 protein levels are strongly regulated by the mitotic activity of the SMCs, as they were increased in quiescent cultures. In contrast, treatment with platelet-derived grow factor (PDGF), one of the most powerful mitogenic factors for SMCs, reduces the expression of PDE5 after 24 hours of treatment. CONCLUSION: We found that PDGF treatment downregulates PDE5 expression in proliferating SMCs, suggesting that PDE5 may represent one of the markers of the contractile phenotype of the SMCs of corpora cavernosa.

Ontogenetic profile of the expression of thyroid hormone receptors in rat and human corpora cavernosa of the penis.

INTRODUCTION: In the last few years, various studies have underlined a correlation between thyroid function and male sexual function, hypothesizing a direct action of thyroid hormones on the penis. AIM: To study the spatiotemporal distribution of mRNA for the thyroid hormone nuclear receptors (TR) alpha1, alpha2 and beta in the penis and smooth muscle cells (SMCs) of the corpora cavernosa of rats and humans during development. METHODS: We used several molecular biology techniques to study the TR expression in whole tissues or primary cultures from human and rodent penile tissues of different ages. MAIN OUTCOME MEASURE: We measured our data by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) amplification, Northern blot and immunohistochemistry. RESULTS: We found that TRalpha1 and TRalpha2 are both expressed in the penis and in SMCs during ontogenesis without development-dependent changes. However, in the rodent model, TRbeta shows an increase from 3 to 6 days post natum (dpn) to 20 dpn, remaining high in adulthood. The same expression profile was observed in humans. While the expression of TRbeta is strictly regulated by development, TRalpha1 is the principal isoform present in corpora cavernosa, suggesting its importance in SMC function. These results have been confirmed by immunohistochemistry localization in SMCs and endothelial cells of the corpora cavernosa. CONCLUSIONS: The presence of TRs in the penis provides the biological basis for the direct action of thyroid hormones on this organ. Given this evidence, physicians would be advised to investigate sexual function in men with thyroid disorders.