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 f ollowing exhausting cycling exercise using radionuclide angiography (R A) with technetium 99 m phytate Tc-99m-phytate), which is a nondiffusi ble radio-active tracer for kidney imaging and which is taken up quick ly by the liver after injection into the circulation. The relationship s between changes in RBF and creatinine clearance (C-cr), urine volume (UV) and plasma hormone involved in the regulation of renal function were also investigated. A bolus of (99 mc)-phytate (92.5 MBq . ml(-1)) was injected into the brachial vein via a catheter, while each subjec t was maintained in a supine position with his back to a scinticamera, which was connected to a computer for data processing, The pool trans it 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 (C-PAH) Post-exerci se RBF was measured only by RA within 60 s of exercise, then again wit hin 30 and 60 min of exercise on different days, since RBF can be meas ured successively only three times even with the use of Tc-99m-phytate . The resting value of 1/PTTn was converted to the value of C-PAH corr ected for haematocrit, and post-exercise change of 1/PTTn (RBF) was re presented as a change in the value of C-PAH in order to express a defi nite numerical change, rather than a percentage change, from resting R BF. The RBF decreased by 53.4% immediately after exercise, and remaine d decreased by 17.5% 30 min after and by 21.1% 60 min after exercise i n comparison with the resting value. The RBF was found to be correlate d with changes in C-cr(p=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 angiote nsin 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 C-cr after exhausting exercise depended mainly on change in RBF and that changes in UV and osmolalit y after exhausting exercise were induced not only by change in RBF, bu t also by changes in reabsorption of water and solutes in the renal tu bules, It is suggested that changes in reabsorption of water and solut es might be influenced by metabolites induced by exercise and an incre ased release of hormones, other than aldosterone, involved in the regu lation of renal function.