Smooth Muscle Cell Behavior in the Ventral Prostate of Castrated Rats

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Abstract
Smooth muscle cells (SMC) play roles in prostatic development and function. The cells also respond to tissue injury and hormonal variations, alternating between a fully differentiated and contractile phenotype and a dedifferentiated synthetic or secretory phenotype. However, the phenotypic changes in SMC after androgen deprivation have not yet been described. The ventral prostate of control and castrated rats was processed for routine histology, immunocytochemistry, reverse transcriptase polymerase chain reaction (RT‐PCR), and scanning electron microscopy (SEM). The maintenance of SMC phenotype was confirmed by immunocytochemistry and by RT‐PCR. Stereological analyses were done to define the relative and absolute volume of the SMC. SMC were elongated and flattened against the epithelium. After castration, the cells shortened concomitantly with pleating of the cell surface, leading to a spinous aspect. SEM showed that the smooth surface of SMC became progressively folded. Immunocytochemistry demonstrated both smooth muscle myosin heavy chain and smooth muscle α‐actin in the prostatic SMC 21 days after castration, whereas RT‐PCR amplified the message for smoothelin. Stereological analysis showed an increase in the relative volume of SMC in relation to the whole gland and the stroma. A decrease in the absolute volume of SMC occurred only within the first 7 days after castration and remained unchanged thereafter. The prostatic SMC are affected by the absence of androgens and there is a critical transition point during the first week in which the total volume occupied by SMC diminished. The remaining SMC showed a marked phenotypical change. These findings indicate that ventral prostate SMC maintain their differentiated phenotype after castration. The alterations in SMC behavior correlate with general stromal modifications taking place after castration.