Nitric oxide-mediated erectile effects of galantide but not galanin in vivo

The purpose of this study was to investigate the in vivo effects of intraca vernosal injections of galanin and galantide (a specific galanin receptor a ntagonist) on penile erection in the anesthetized cat. Erectile responses t o galanin and galantide were compared with responses to a standard triple d rug combination [1.65 mg papaverine, 25 mu g phentolamine, and 0.5 mu g pro staglandin E-1 (PGE(1))]. Intracavernosal injections of galanin (3-100 nmol ) and galantide (0.1-3 nmol) induced penile erection in a dose-dependent ma nner. In terms of relative potency, galantide was approximately 100-fold mo re potent than galanin at increasing cavernosal pressure. The maximal incre ases in intracavernosal pressure in response to galanin and galantide were 83 and 95%, respectively, of the control triple drug combination. The total durations of erectile response caused by these peptides were significantly shorter (P < 0.05) than those by the triple drug combination. The nitric o xide synthase inhibitor L-NAME (20 mg) significantly decreased the erectile response in the cat to galantide but not to galanin, while the K-ATP(+), c hannel antagonist U-37883A (3 mg) had no effect on the erectile response to galanin nor galantide. The results of the present study demonstrate that g alantide, a putative antagonist for the galanin receptor, has more potent a gonist activity than galanin in increasing intracavernosal pressure in the cat. Moreover, these data suggest that galantide, but not galanin, causes p enile erection by an NO/cGMP-dependent mechanism. This is the first study t o demonstrate that galanin may play a role in the physiology of penile erec tion. (C) 2000 Academic Press.