No abstract

Background/Aims: Phosphodiesterase type 4 (PDE4) has been previously shown to regulate colonic contractile activity in vitro. In this study, the effects of PDE4 inhibition were assessed in a model of stress-induced defecation previously demonstrated to be due to increased colonic transit/evacuation. Methods: Rats were individually placed in a mild restraint cage and placed into a 12°C environment (cold-restraint stress) for 60 min. Mice received restraint (only) stress at room temperature for 30 min. Loperamide (positive control compound) or two different PDE4 inhibitors (rolipram and roflumilast) were administered orally at several doses to the rodents 1 h before stress began. Vehicle alone was administered for comparison. The number of fecal pellets expelled during stress (fecal pellet output), total fecal pellet wet weight and total fecal water content were measured. Results: Loperamide produced a dose-related decrease (ID₅₀s in mg/kg) in fecal pellet output (rat = 7.4, mouse = 0.7) and significantly decreased fecal wet weight (72.9%) and decreased fecal percent water content (9.4%). The two PDE4 inhibitors produced a similar dose-related inhibition of fecal pellet output. Rolipram exhibited ID₅₀s in rat and mouse of 14.1 and 27.1, respectively. Rolipram significantly decreased fecal wet weight (58.8%) but increased fecal percent water content (15.0%). For roflumilast, ID₅₀s were 24.2 mg/kg and 12.4 in the rat and mouse, respectively. Although roflumilast also significantly (p < 0.05) decreased fecal wet weight (47.2%), it did not significantly increase fecal percent water content. Conclusions: These data indicate that PDE4 inhibition is effective in reducing rodent stress-induced defecation, provides the first functional data on a potential role for PDE4 activity in the colonic evacuation response to stress, and indicates the potential utility of PDE4 inhibitors in functional bowel disease such as irritable bowel syndrome requires further evaluation.

In the marble burying test, we focused on the 5 distinctive behavioral parameters of mice other than burying marbles, i.e. digging, latency to the first digging, exploration around marbles, rearing and locomotor activity. Typical anxiolytics or antidepressants with different mechanisms, fluvoxamine (30 mg/kg, selective serotonin reuptake inhibitor), bupropion (60 mg/kg, noradrenaline and dopamine reuptake inhibitor), imipramine (60 mg/kg, tricyclic antidepressant) and diazepam (10 mg/kg, benzodiazepine) were used to examine whether these behavioral parameters are sensitive to pharmacological treatments. Each of the drugs demonstrated an individual action pattern on the 4 behavioral parameters (latency to the first digging, exploration around marbles, rearing and locomotor activity). On the other hand, all 4 drugs reduced burying marbles and digging, which were correlated with each other. These results suggest that the former 4 behavioral parameters are sensitive to pharmacological treatment and that pharmacological regulation mechanisms of them may be different from burying marbles and digging. They could be useful to identify the type of action of a test drug like selective serotonin reuptake inhibitor, noradrenaline and dopamine reuptake inhibitor, tricyclic antidepressant or benzodiazepine.

No abstract

No abstract