Animal experiments indicate that inhibition of nitric oxide synthase (NOS) influences renal hemodynamics and that this effect can be reversed by L-arginine, the precursor of NO synthesis. We have therefore studied the effects of an inhibitor of NOS, N(G)-monomethyl-L-arginine (L-NMMA), and a subsequent coinfusion with L-arginine on renal hemodynamics. In a double-blind, randomized crossover design, eight healthy volunteers (means +/- 1SD, 25.6 +/- 3.1 yr) received a primed constant infusion of L-NMMA (3 mg/kg bolus infusion over 5 min, followed by 50 microg x kg(-1) x min(-1) over 120 min) with subsequent coinfusion of L-arginine (17 mg x kg(-1) x min(-1) over 30 min). In the absence of a hypertensive response, L-NMMA decreased renal plasma flow to 79% of baseline (P < 0.005); this effect was abrogated by L-arginine. Glomerular filtration rate was not affected, NO exhalation was reduced to 30% of baseline (P < 0.005) by L-NMMA, and this effect was attenuated by L-arginine. Our results demonstrate that basal NO production maintains renal blood flow in vivo in humans. In addition, the renal vasculature is particularly sensitive to inhibition of NOS, and these pharmacodynamic effects can be reversed by excess doses of L-arginine.

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Endothelial dysfunction has been implicated in the pathogenesis of diabetic vascular disorders such as diabetic retinopathy. We hypothesized that either local endogenous nitric oxide (NO) synthesis or local reactivity to endogenous NO might be impaired in patients with IDDM and that this may contribute to the development of diabetic retinopathy. Ten otherwise healthy patients with long-standing IDDM and ten healthy control subjects were studied according to an open randomized two-way cross-over design. Subjects received intravenous infusions of either N(G)-monomethyl-L-arginine, an inhibitor of NO-synthase, or L-arginine, the precursor of NO synthesis, on two separate study days. Ocular hemodynamics were assessed by laser interferometric measurement of fundus pulsations and Doppler sonographic measurement of blood flow velocity in the ophthalmic artery. N(G)-monomethyl-L-arginine decreased fundus pulsations and blood flow velocity in the ophthalmic artery and increased blood pressure in healthy subjects. The responses to NO-synthase inhibition were significantly less in diabetic subjects. In contrast, L-arginine caused a comparable increase in fundus pulsations and decrease in blood pressure in both cohorts. These results indicate that systemic and ocular hemodynamic reactivity to NO-synthase inhibition is reduced in patients with long-standing IDDM, compared with healthy control subjects. Thus, this study indicates that either NO-synthase activity is increased or NO sensitivity is decreased in patients with IDDM and supports the concept of an involvement of the L-arginine-NO system in the pathophysiology of diabetic retinopathy.

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Renal cell carcinomas, which originate within the renal cortex, constitute 80-85% of primary renal neoplasms. Patients can present with a range of symptoms due to the tumor itself (e.g., mass, pain), invasion of the urinary tract (e.g., hematuria), paraneoplastic syndromes, or the presence of metastases. Renal cell cancer is more frequently being diagnosed incidentally as a consequence of increased use of imaging procedures for other reasons. Surgery is curative in the majority of patients without metastatic disease and is therefore the preferred treatment for patients with stages I, II, and III disease. The five-year survival following the treatment correlates well with the anatomic extent of disease. Systemic therapy with molecularly targeted therapy or immunotherapy is the primary approach for patients with unresectable or recurrent disease.