Sildenafil, a phosphodiesterase-5 inhibitor, delays gastric emptying and gastrointestinal transit of liquid in awake rats

We studied the effect of sildenafil on gastric emptying (GE) and gastrointestinal (GI) transit in awake rats. After cervical vessel cannulation and 24 hr of fasting, the animals received an intravenous (IV) injection of sildenafil (4 mg/kg) or vehicle. Next they were gavage fed (1.5 ml) with a test meal (phenol red in 5% glucose solution, 0.5 mg/ml) and sacrificed 10, 20, or 30 min later. Experimental and control subsets consisted of 5-10 rats. Gastric and proximal, medial, and distal small intestine dye retentions (GDR and IDR, respectively) were obtained by spectrophotometry. Data were compared by ANOVA and Student-Newman-Keuls test. In sildenafil-treated animals, GDR increased (P < 0.05) by 20.3%, 46.9%, and 55,5% while medial IDR decreased (P < 0.05) by 35.1%, 43.4%, and 41.6%, respectively, at 10, 20, and 30-min intervals. Proximal and distal IDR values did not change in sildenafil-treated animals. Mean arterial pressure (MAP) decreased 25% (P < 0.05) right after sildenafil administration but normalized afterwards while in controls MAP remained unchanged. In conclusion, sildenafil delays GE and GI transit of a liquid meal while transiently decreases MAP in awake rats.