Abstract
Li+ is reported to reduce sensitivity of α-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 10–3M 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 KC1. In denervated preparations, 1.35 x 10–3M 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 KC1 observed in innervated preparations were significantly increased in Ca++-free medium. Li+ (1.35 x 10–3M) 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.