ABSTRACT
We have investigated the changes in urinary sodium excretion during an oral glucose tolerance test [OGTT] through the associated changes in plasma atrial naturetic peptide [ANP], endogenous insulin and renal kallikrein excretion, in 10 normatensive obese and 10 healthy non-obese pre-menopausal females. Baseline blood glucose did not differ between obese and non-obese females. Blood glucose levels during the OGTT were significantly higher in obese than in non -obese females [P<0.01]. Obese females had significantly higher values of serum insulin at baseline and 2 hours after oral glucose load in comparison to non-obese females [P<0.01, <0.0001 respectively]. A similar finding was also obtained regarding fasting insulin resistance index [FIRI][P<0.0001] Prior to OGTT, urine sodium and kallikrein excretion did not differ between obese and non-obese subjects. After oral glucose load there were significant reduction of urine sodium [P<0.0001] and kallikrein excretion [P<0.0001] only in non-obese females. Obese females had insignificant decrease in urine sodium excretion and insignificant increase in urine kallikrein excretion. The decrease in urine sodium excretion was similar in obese and non-obese females. The plasma ANP level was significantly higher both in obese [P<0.0001] and non-obese [P<0.0001] females after glucose load. However, the percent increase was less in obese than in non-obese females [P<0.05]. In conclusion, changes in endogenous insulin induced by oral glucose were associated with a similar decrease in urine sodium excretion in obese and non-obese normatensive pre-menopausal females but the decrease was only significant in non-obese females. Insignificant reduction in urine sodium excretion in obese females could be due to the counteracting natriuretic effects of renal kallikrein and ANP