POSTNATAL-DEVELOPMENT MODULATES THE RAT SEMINAL-VESICLE SENSITIVITY TO SYMPATHOMIMETIC AGONISTS

The post-natal development-related changes in the sensitivity to sympathomimetic agonists were studied in the seminal vesicle of 40-, 60- and 120-day old rats by determining the pD2 values for adrenaline, phenylephrine and methoxamine. The age-related changes in the neuronal and extraneuronal uptake of sympathomimetic agonists were also determined. The seminal vesicle sensitivity to adrenaline, phenylephrine and methoxamine increased in sexually mature rats (60- and 120-day old) (concentration-effect curves shifted to the left and pD2 values increased) when compared with immature rats (40-day old). Cocaine, a neuronal uptake inhibitor, induced supersensitivity to adrenaline at all ages, but did not affect the sensitivity to methoxamine. The ratio between the EC50 values for adrenaline in the presence and in the absence of cocaine was reduced in tissues of mature animals. This reduction suggests a loss of function of the neuronal uptake system with sexual development. In the presence of cocaine the pD2 value for adrenaline was increased during sexual development. Thus, the age-related changes in the adrenaline sensitivity were observed even when neuronal uptake was not operative, suggesting age-related changes at the post-junctional level, which was confirmed by the increase in the seminal vesicle sensitivity to methoxamine. In the presence of the extraneuronal uptake inhibitor, corticosterone, the sensitivity to adrenaline did not change and the age-related changes persisted. In conclusion, the sexual development-related changes in seminal vesicle sensitivity to sympathomimetic agonists may be due not only to an age-related loss of function of the neuronal uptake system but may also be a consequence of age-related changes at the post-junctional level.