Investigation of the mechanism of decreased sensitivity of the rat seminal vesicle to norepinephrine by lithium.

Li+ is reported to reduce sensitivity of alpha-adrenergic receptors to NE. The present investigation was designed to investigate the mechanism of this decreased sensitivity on the rat isolated seminal vesicle. In innervated preparations, 1.35 X 10(-3) M Li+ (i) shifted the concentration-response curves of NE, methoxamine, ACh and BaCl2 to the right and reduced their maximum responses; (ii) antagonized the leftward shift and the enhancement of maximum responses to NE by cocaine (2.9 X 10(-4) M), and (iii) reduced only the maximum responses to KCl. In denervated preparations, 1.35 X 10 (-3) M Li+ shifted the concentration response curve of NE to the left without any change in the maximum responses. The antagonistic effects of Li+ on maximal responses to NE, ACh and KCl observed in innervated preparations were significantly increased in Ca++-free medium. Li+ (1.35 X 10(-3) M) increased NE uptake by the seminal vesicle significantly. It is concluded that decreased sensitivity of the seminal vesicle to NE by Li+ could be due to an increase in the uptake of NE and to a nonspecific postsynaptic spasmolytic action.