Cyclic adenosine 3′,5′-monophosphate-phosphodiesterases in epididymis and prostate of castrate and of aged rats

Abstract

The activities of the low- K m and high- K m forms of cyclic AMP phosphodiesterase (PDE) were determined in extracts prepared from epididymis and prostate taken from adult (10–12 months) and from aged (32–35 months) rats. The maximum velocity V of low- K m PDE in the epididymis of normal adult rats (approx. 300 pmoles/min per mg protein) was increased after castration by 80%, whereas V of the high- K m form remained unchanged, suggesting that only the low- K m PDE is subject to regulation by the animals' endocrine status. In the epididymis of aged rats V of low- K m PDE was unchanged, whereas V of high- K m PDE (approx. 3000 pmoles/min per mg protein) was decreased by 40%; in the prostate of aged rats V of both low- K m (approx. 225 pmoles/min per mg protein), and of high- K m PDE (approx. 1500 pmoles/min per mg protein) were decreased by 50–60%. The absence of interdependence of the two forms of the enzyme in their response to changes in environmental conditions in each organ suggests different mechanism of control of their activities and adds validity to the reported age-related decline of low- K m-PDE activity in prostate.