Changes in renal blood flow measured by radionuclide angiography following exhausting exercise in humans

We measured renal blood flow (RBF) repeatedly in six male volunteers following exhausting cycling exercise using radionuclide angiography (RA) with technetium 99 m phytate (99 mTc-phytate), which is a nondiffusible radio-active tracer for kidney imaging and which is taken up quickly by the liver after injection into the circulation. The relationships between changes in RBF and creatinine clearance (Ccr), urine volume (UV) and plasma hormone involved in the regulation of renal function were also investigated. A bolus of 99 mTc-phytate (92.5 MBq.ml-1) was injected into the brachial vein via a catheter, while each subject was maintained in a supine position with his back to a scinticamera, which was connected to a computer for data processing. The pool transit time (PTT) was calculated from the time-concentration flow curve in the left kidney following injection of the bolus. The PTT normalized by the PTT of the heart (PTTn: kidney PTT/heart PTT), and the change in the reciprocal of PTTn (1/PTTn) were used as indices of the change in RBF. The resting RBF was also measured simultaneously by both RA and the para-aminohippuric acid (PAH) clearance method (CPAH). Post-exercise RBF was measured only by RA within 60 s of exercise, then again within 30 and 60 min of exercise on different days, since RBF can be measured successively only three times even with the use of 99 mTc-phytate. The resting value of 1/PTTn was converted to the value of CPAH corrected for haematocrit, and post-exercise change of 1/PTTn (RBF) was represented as a change in the value of CPAH in order to express a definite numerical change, rather than a percentage change, from resting RBF. The RBF decreased by 53.4% immediately after exercise, and remained decreased by 17.5% 30 min after and by 21.1% 60 min after exercise in comparison with the resting value. The RBF was found to be correlated with changes in Ccr (r = 0.773, P < 0.001), UV (r = 0.598, P < 0.001), and the concentrations of plasma angiotensin II (r = -0.686, P < 0.001) and noradrenaline (r = 0.652, P < 0.001) after exercise. However, there were no significant correlations between the changes in plasma aldosterone ([Ald]) and plasma noradrenaline, or in [Ald]p1 and plasma angiotensin II concentrations. The change in [Ald]p1 did not coincide with the variation in reabsorption of Na+ in the renal tubules. Results of the present study showed that change in Ccr after exhausting exercise depended mainly on change in RBF and that changes in UV and osmolality after exhausting exercise were induced not only by change in RBF, but also by changes in reabsorption of water and solutes in the renal tubules. It is suggested that changes in reabsorption of water and solutes might be influenced by metabolites induced by exercise and an increased release of hormones, other than aldosterone, involved in the regulation of renal function.