Effect Of ?-Blockers On The Renal Excretion Of Metformin Interpreted By Organic Cation Transporter Protein 2 In Rats

Aim1.Investigate the effect of propranolol on the renal excretion of metformin in rats.2.Investigate the effect of atenolol on the renal excretion of metformin in rats with different ages.3.To clarify the effect of atenolol on the renal excretion of metformin and the underlying mechanisms in rats with different ages.Methods1.20 male Wistar rats(aged 3 months)were randomly divided into 2 groups,one group of rats were treated with propranolol(0.8 mg·kg-1,i.v.)and metformin(25 mg·kg-1,i.v.),the other were treated with metformin(25 mg·kg-1,i.v.)only.The urine samples were collected at 0?2,2?4,4?6.6?8,8?10,10?12 and 12?24 h after drug administration,and the metformin concentrations in urine were determined by HPLC in order to obtain the cumulative urinary excretion-time curves.The software of DAS 2.0 was used to calculate the renal excretion parameters(t1/2?Ke?cumulative urinary excretion)of metformin.2.20 male Wistar rats(aged 3 months)were randomly divided into 2 groups,one group of rats were treated with atenolol(10 mg·kg-1,i.v.)and metformin(25 mg·kg-1,i.v.),the other were treated with metformin(25 mg·kg-1,i.v.)only.The urine samples were collected at different time points.After urine collection,rats were sacrificed and the kidneys were collected and stored in-80?.The metformin concentration in urine was determined by HPLC so as to obtain the cumulative urinary excretion-time curves.The software of DAS 2.0 was used to calculate the renal excretion parameters(t1/2?Ke?total cumulative urinary excretion)of metformin.The method for the treatment of 10 male rats(aged 12 months)was as same as that descript above.3.To investigate the effect of age on renal organic cation transporter 2(rOct2)expression,the localization and expression level of rOct2 were evaluated by immunofluorescent analysis and western blot technique.Results1.Rats pretreated with propranolol significantly increased t1/2(2.844±0.37 h)of metformin(P<0.05)and decreased Ke(0.249±0.58 h-1)when compared to the metformin-treated group(2.109±0.30 h and 0.342±0.45 h-1),while the total cumulative urinary excretion of metformin in these two groups did not show significantly difference(P>0.05).2.The rats aged 12 months pretreated with atenolol,the T1/2,Ke,and total cumulative urinary excretion of metformin in urine were all significantly altered(3.03±0.67 h,0.228±0.05 h-1,3239.972±446.61 ?g)when compared to that of metformin treated group(2.002±0.51 h,0.346±0.07 h-1,4287.087±458.08 ?g)(P<0.05),but no significant difference was found in rats aged 3 months(P<0.05).3.Results from Western blot analysis indicated that renal rOct2 expression in rats aged 12 months decreased 36%when compared to rats aged 3 months.Results form immunofluorescent analysis showed that rOct2 mainly located in renal proximal tubule,and their location did not changed much with age alteration.Conclusion1.At the dose equivalent to clinical use.propranolol administration significantly affected the renal excretion of metformin in rats.Concerning the renal excretion of metformin,there was a singnificant difference in rats aged 3 months and 12 months,the renal excretion of metformin was significantly decreased in rats aged 12 months when compared to that of 3 months.2.The expression of rOct2 in kidney was markedly decreased in rats aged 12 months when compared to the rats aged 3 months,which may explain why atenolol significantly reduced the renal excretion of metformin in rats aged 12 months.