Testicular adenosine 3':5'-monophosphate-dependent protein kinase. Regulation by follicle-stimulating hormone.

Incubation of testis seminiferous tubules with folliclestimulating hormone (FSH) results within 5 min in an activation of soluble adenosine 3’: 5’-monophosphate (CAMP)dependent protein kinase, as indicated by a conversion of the inactive holoenzyme to the active catalytic subunit. Maximal stimulation (3-fold) is achieved by 20 min. Moreover, this increased kinase activity can be directly correlated with increased intracellular accumulation of CAMP. Activation of protein kinase in isolated tubules is specific for FSH and is dependent upon time and temperature of incubation. This response to FSH is also dependent upon the age of the animal and disappears at approximately 30 days. However, sensitivity to gonadotrophin can be restored in adult animals by hypophysectomy or by addition of l-methyl3Gsobutylxanthine to the incubation medium. These results suggest that the appearance of an active phosphodiesterase may be responsible for the decreased response to FSH during spermatogenesis. Increased protein kinase activity in response to the continbed presence of FSH exhibits a half-life time of 2 to 4 hours. Furthermore, bound FSH can be recovered following treatment of the tissue of acid pH and this hormone retains the ability to activate protein kinase in fresh tissue suggesting that FSH may not be degraded while attached to testicular receptors. Excellent temporal correlation exists between binding of FSH and activation of protein kinase. Maximal enzyme activation occurs at a lower concentration of FSH than is necessary to saturate testicular binding sites.