Effects of chronic treatment with caffeine on kidney responses to angiotensin II

Previous studies demonstrate that chronic administration of caffeine causes glomerular filtration to deteriorate in rats with high-renin renovascular hypertension. A partial explanation for these findings could be that chronic administration of caffeine alters the effects of angiotensin II on the kidney. As an initial test of this hypothesis, we compared the acute effects of intrarenal infusions of angiotensin II (3 ng/min) on renal function in control rats versus rats treated with 0.1% caffeine in their drinking water for 1 week. The renal responses to angiotensin II in a group of animals receiving acute intrarenal infusions of adenosine (10 micrograms/min) were also measured to determine whether caffeine and adenosine modulated renal responses to angiotensin II in opposite directions. All studies were performed in the in situ blood perfused rat kidney. Neither caffeine nor adenosine significantly altered angiotensin II-induced changes in renal blood flow, urinary excretory function or renin release. However, caffeine augmented and adenosine attenuated the increase in filtration fraction caused by angiotensin II. The fact that caffeine potentiates angiotensin II-induced increases in filtration fraction without affecting angiotensin II-induced reductions in renal blood flow is consistent with, but does not prove, the hypothesis that chronic administration of caffeine modifies the effects of angiotensin II on the renal microvasculature. If this inference is correct, caffeine could facilitate renal damage in high-renin hypertension by exacerbating angiotensin II-induced increases in glomerular capillary hydrostatic pressure.