Effect Of Endokinin A/B On Rats Gastric Motility And Related Mechanism

Background:Tachykinins receptors in gastrointestinal tract are widely expressed both on neurons and effector cells.It is essential for maintaining normal gastrointestinal function.Tachykinins peptides are encoded by three different genes:TAC1,TAC3 and TAC4,of which TAC4 encodes HK-1 and Endokinins?EKs?:Endokinin A?EKA?,Endokinin B?EKB?,Endokinin C?EKC?and Endokinin D?EKD?.There are many reports fucused on gastrointestinal function of tachykinins encoded by TAC1 and TAC3,but the study of TAC4-related tachykinins on gastrointestinal system is limited to HK-1.The effect of EKA and EKB on gastrointestinal function is still unclear.Purpose:This study will explore the effect of Endokinin A/B?EKA/B,the common C-terminal decapeptide in EKA and EKB?on rats gastric motility and related mechanisms.Methods:In vivo,the effect of EKA/B on rats gastric motility was firstly assessed by measuring the effect of EKA/B?intraperitoneal injection?on gastric emptying rate.In vitro,in order to determine whether EKA/B directly acts on the stomach and the exact site of action of EKA/B in the stomach,the effect of EKA/B on intra-gastric pressure and on the contraction of muscle strips from stomach?fundus,corpus,and antrum?were measured.Tachykinin receptor antagonists?SR140333,GR159897,SR142801?and neural blocking agents?tetrodotoxin,atropine,hexamethonium,naloxone,phentolamine,propranolol?are used to examine the mechanism of EKA/B regulating gastric motility.In addition,in view of the region-dependent difference in the effects of EKA/B,at the molecular level,qPCR was used to detect the expression of TAC4 and TACR1 mRNA in different regions of the stomach?fundus,corpus,and antrum?to further explore its mechanism.Results and Conclusion:In vivo,EKA/B?1,3,10,30,or 100 nmol/rat,i.p.?dose-dependently increased gastric emptying rate in rats.In vitro,similar to SP,EKA/B(10^-9 M-10^-6 M)dose-dependently increased intra-gastric pressure in rats,indicating that EKA/B directly affects gastric motility in rats by directly acting on the stomach.EKA/B(10^-9 M-10^-6 M)dose-dependently contracted the gastric longitudinal muscle strips from the fundus but not corpus or antrum.Moreover,NK1 receptor antagonists can block the contraction of EKA/B on longitudinal muscles of the gastric fundus,but neither of the neural blocking agents can.Our results suggested that EKA/B might stimulate gastric motility mainly through the direct activation of myogenic NK1receptors located in the fundus.The results of qPCR showed that TAC4 and TACR1mRNAs were equally expressed through fundus,corpus and antrum of rat gastric.In other words,the region-dependent differences of EKA/B responses are not due to the different expression levels of NK1 receptors in various gastric regions.We speculate that it may be related to NK1 receptor subtypes and new family receptors of EKA/B.Our findings provide a point of important reference for the following EKA/B experiments,and provide new insights into the physiological role of tachykinins in gastric motility.