Patients with Parkinson's disease (PD) often suffer from delayed gastric emptying, but the underlying mechanism remains unclear. We have shown previously that a PD rat model comprising bilateral substantia nigra destruction by 6-hydroxydopamine (6-OHDA rats) exhibits gastroparesis with alteration of neural nitric oxide synthase (nNOS) and acetylcholine in gastric corpus. However, changes in pyloric motility in the 6-OHDA rats have not been characterized. Solid gastric emptying test, immunofluorescence, Western blot, and in vitro pyloric motility recordings were used to assess pyloric motor function in the 6-OHDA rats. The 6-OHDA-treated rats displayed delayed solid gastric emptying and a lower basal pyloric motility index. In the 6-OHDA rats, high K+-induced transient contractions were weaker in pyloric sphincters. Electric field stimulation (EFS)-induced pyloric sphincter relaxation was lower in the 6-OHDA rats. NG-nitro-l-arginine methyl ester (l-NAME), a nonselective inhibitor of NOS, markedly inhibited the EFS-induced relaxation in both control and 6-OHDA rats. Pretreatment of tetrodotoxin abolished the effect of EFS on the pyloric motility. In addition, nNOS-positive neurons were extensively distributed in the pyloric myenteric plexus, whereas the number of nNOS-immunoreactive neurons and the protein expression of nNOS were significantly decreased in the pyloric muscularis of 6-OHDA rats. However, sodium nitroprusside-induced pyloric relaxations were similar between the control and 6-OHDA rats. These results indicate that the pyloric sphincters of 6-OHDA rats exhibit both weakened contraction and relaxation. The latter may be due to reduced nNOS in the pyloric myenteric plexus. The dysfunction of the pyloric sphincter might be involved in the delayed gastric emptying.NEW & NOTEWORTHY Reduced nitrergic neurons in pyloric myenteric plexus potently contributed to the attenuated relaxation in 6-hydroxydopamine (6-OHDA) rats, subsequently affecting gastric emptying. SNP could well improve the relaxation of pylori in 6-OHDA rats. The present study provides new insight into the diagnosis and treatment of delayed gastric emptying in patients with PD.
Keywords: 6-OHDA rat; gastric emptying; nNOS; pyloric motility.