Effects of KSG-504, a new cholecystokinin-A-receptor antagonist, on pancreatic exocrine and endocrine secretions in rats

Cholecystokinin receptors regulate sperm protein tyrosine phosphorylation via uptake of HCO3-

Cholecystokinin (CCK), a peptide hormone and a neurotransmitter, was detected in mature sperm two decades ago. However, the exact role of CCK and the types of CCK receptors (now termed CCK1 and CCK2) in sperm have not been identified. Here, we find that CCK1 and CCK2 receptors are immunolocalized to the acrosomal region of mature sperm. The antagonist of CCK1 or CCK2 receptor strongly activated the soluble adenylyl cyclase/cAMP/protein kinase A signaling pathway that drives sperm capacitation-associated protein tyrosine phosphorylation in dose- and time-dependent manners. But these actions of stimulation were abolished when sperm were incubated in the medium in the absence of HCO3-. Further investigation demonstrated that the inhibitor of CCK1 or CCK2 receptor could accelerate the uptake of HCO3- and significantly elevate the intracellular pH of sperm. Interestingly, the synthetic octapeptide of CCK (CCK8) showed the same action and mechanism as antagonists of CCK receptors. Moreover, CCK8 and the antagonist of CCK1 or CCK2 receptor were also able to accelerate human sperm capacitation-associated protein tyrosine phosphorylation by stimulating the influx of HCO3-. Thus, the present results suggest that CCK and its receptors may regulate sperm capacitation-associated protein tyrosine phosphorylation by modulating the uptake of HCO3-.

Effect of cholecystokinin1 receptor antagonist loxiglumide (CR1505) on basal pancreatic exocrine secretion in conscious rats

INTRODUCTION AND AIM

To examine the involvement of cholecystokinin (CCK) in the basal pancreatic exocrine, we investigated the effect of loxiglumide (CR1505), a CCK1 receptor antagonist, on basal pancreatic exocrine secretion in conscious rats.

METHODOLOGY

After the basal collection of pancreatic juice for 1 hour, loxiglumide (10 mg/kg/h) or saline was infused via the femoral vein continuously for 2 hours.

RESULTS

Loxiglumide significantly suppressed the basal pancreatic protein and amylase outputs. However, loxiglumide did not alter the basal pancreatic juice volume.

CONCLUSIONS

These results demonstrate that loxiglumide suppresses basal pancreatic exocrine secretion in normal rats. They also suggest that CCK is involved in basal pancreatic exocrine in conscious rats and that loxiglumide may be useful as a therapeutic agent for pancreatitis, even during fasting, by attenuating the basal pancreatic exocrine burden on the pancreas.