NITROGLYCERIN-INDUCED PENILE ERECTION AND YAWNING IN MALE-RATS - MECHANISM OF ACTION IN THE BRAIN

The effect of the central administration of nitroglycerin, a potent organic nitrate vasodilator, on penile erection and yawning was studied in male rats. When given intracerebroventricularly (ICV), nitroglycerin (33-99 mu g) induced the above responses dose-dependently. The minimal effective dose was 33 mu g, which was active in 60% of the rats. Nitroglycerin (1.65-6.6 mu g) induced penile erection and yawning also when injected in the paraventricular nucleus of the hypothalamus. Nitroglycerin responses were prevented by methylene blue (200-400 mu g ICV), by d(CH2)(5)Tyr(Me)(2)-Orn(8)-vasotocin (0.5-1 mu g ICV) but not hemoglobin (100-200 mu g ICV). In contrast methylene blue (10-20 mu g), d(CH2)(5)Tyr(Me)(2)-Orn(8)-vasotocin (0.05-0.1 mu g) and hemoglobin (10-20 mu g) were ineffective when injected in the paraventricular nucleus. Systemic haloperidol (0.5-1 mg/kg IP) was also ineffective. The results suggest that nitroglycerin induces penile erection and yawning by activating brain oxytocinergic transmission through the formation of nitric oxide in the paraventricular nucleus of the hypothalamus.