ACUTE, SUBACUTE, and CHRONIC X-RAY-EFFECTS ON GLOMERULAR HEMODYNAMICS in RATS

In order to evaluate the effects of x-rays on glomerular hemodynamics, surgically exposed left kidneys of Munich-Wistar rats were irradiated with 15 Gy in a single dose. the animals were studied 45 min (acute group, n = 8), 14 days (subacute group, n = 7), and 60 days (chronic group, n = 7) after irradiation and compared with their respective controls. A decrease in total glomerular filtration (55%) and renal plasma flow (40%) rates with marked elevation of total renal vascular resistance (180%), p < 0.05, occurred within 45 min. Significant changes also occurred in the microcirculation; i.e., single-nephron glomerular filtration (SNGFR), glomerular plasma flow (Q(A)), and glomerular capillary hydraulic pressure (P-GC) declined by 35%, 40%, and 12%, respectively, due to an increase in total arteriolar resistance (90%), p < 0.05. Within 14 days, SNGFR was similar to control in spite of a moderate elevation of afferent arteriolar resistance (26%) and reduction in P-GC (11%), p < 0.05, and Q(A) (20%). K-f was significantly elevated (46%), p < 0.05. the chronic group presented a response pattern similar to that of the acute group, although less severe. Histopathological changes were not relevant and were restricted to tubules. the present results suggest that: (a) Acutely, there was a marked reduction in filtration, flow, and P-GC with significant elevation of resistances. (b) Within 14 days, the maintenance of SNGFR was probably the result of an offsetting effect between Q(A) and P-GC decreases and K-f elevation. (c) After 60 days, the homeostatic mechanism was not sufficient to maintain normal renal function. (d) A functional effect is probably the most important pathogenetic mechanism, at least during the initial phase, for the development of radiation nephropathy since no morphological alterations were observed.ESCOLA PAULISTA MED,DEPT MED,DIV NEPHROL,BR-04023062 São Paulo,BRAZILESCOLA PAULISTA MED,DEPT MED,DIV NEPHROL,BR-04023062 São Paulo,BRAZILWeb of Scienc