L-Arginine normalizes pressure natriuresis in Dahl salt-sensitive (DS) rats. To determine the role of renal interstitial hydrostatic pressure (RIHP) in this phenomenon, we measured RIHP determined by servo-null during acute changes in renal perfusion pressure in anesthetized DS rats receiving L-arginine (300 mg.kg-1.day-1 ip) or vehicle for 3 wk. Dahl salt-resistant (DR) rats were controls. As observed previously, the slope of the pressure-natriuresis relationship was greater (P < 0.05) in L-arginine-treated DS rats than vehicle DS rats and not different from DR rats. The slope of the relationship between renal perfusion pressure and RIHP was greater (P < 0.05) in DR rats than vehicle DS rats. In L-arginine-treated DS rats the slope of this relationship was greater (P < 0.05) than that in vehicle DS rats and not different from DR rats. Removal of the renal capsule blunted the pressure-natriuresis relationship in L-arginine-treated DS rats but had no effect in vehicle DS rats. Thus L-arginine improves transmission of perfusion pressure into the renal interstitium in DS rats and may contribute to the improved pressure-natriuresis response.

Spontaneously hypertensive rats have reduced peripheral insulin sensitivity. To determine whether hypertensive rats demonstrate reduced response to the antinatriuretic effect of insulin, urinary sodium excretion was determined in hypertensive and normotensive rats (n=7 per group) before and during euglycemic insulin administration at two infusion rates (21 milliunits/kg load and 4 milliunits/kg/min or 85 milliunits/kg load and 8 milliunits/kg/min). Hypertensive and normotensive time controls received the vehicle for insulin administration. Mean arterial pressure was greater (/?<0.05) and inulin clearance was less (/?<0.05) in hypertensive than normotensive rats before insulin infusion. Baseline fractional sodium excretion was not different between groups. Low dose insulin infusion reduced (p<0.05) fractional sodium excretion from 0.81 ±0.43% to 0.31 ±0.07% in hypertensive rats and from 1.05±0.37% to 0.47±0.18% in normotensive rats. High dose insulin infusion reduced (/><0.05) fractional sodium excretion from 0.67±0.22% to 0.21 ±0.08% in hypertensive rats and from 0.81 ±0.15% to 0.30±0.09% in normotensive rats. Sodium excretion was unchanged in time controls. The reduction in sodium excretion was similar in both rat groups during low dose and high dose insulin infusions. Mean arterial pressure and inulin clearance were unchanged from baseline values during insulin infusion in all rat groups. Glucose requirement to maintain euglycemia was greater (p<0.05) in normotensive than hypertensive rats at both insulin infusion rates. Thus, while hypertensive rats have reduced sensitivity to the hypoglycemic effects of insulin, the antinatriuretic response to insulin is not different from that of normotensive rats. Furthermore, the presence of hypertension does not modulate the antinatriuretic activity of insulin. (Hypertension 1990;15:514-518) E levated plasma insulin levels and resistance to the hypoglycemic effect of insulin have been associated with hypertension in human and animal models of hypertension. -4 This observation • has led to speculation that insulin may play a role in the development of increased blood pressure.5 Such a hypothesis is strengthened by studies demonstrating that normotensive rats fed a fructose-enriched diet developed insulin resistance, hyperinsulinemia, and hypertension.3 Inasmuch as insulin reduces urinary sodium excretion, 6 " 8 an attractive hypothesis is that sodium-dependent hypertension develops as a result of persistent insulin antinatriuresis. However, no data are available that examine the effect of insulin on renal sodium reabsorption under conditions of elevated blood pressure. This information is fundamental for evaluation of any hypothesis implicating a role for insulin in development or maintenance of hypertension. The current study was performed to examine the effect of insulin on urinary sodium excretion in glucose-clamped, volumeexpanded spontaneously hypertensive rats (SHR). Effect of insulin on urinary sodium excretion in normotensive Wistar-Kyoto (WKY) rats was also perfo...

1. According to the renal body fluid feedback mechanism for long-term control, persistent hypertension can only occur as a result of a reduction in renal sodium excretory function or a hypertensive shift in the pressure natriuresis relationship. Although an abnormal relationship between renal perfusion pressure and renal sodium excretion has been identified in every type of hypertension where it has been sought, factors responsible for this effect are still unclear. 2. Nitric oxide (NO) is produced within the kidney and plays an important role in the control of many intrarenal processes that regulate the renal response to changes in perfusion pressure and, thus, help determine systemic vascular volume and blood pressure. Numerous studies have shown that long-term inhibition of NO synthesis results in a chronic hypertensive shift in renal pressure natriuresis. 3. Recent studies have shown that certain animal models of genetic hypertension and forms of human hypertension areas are associated with a decrease in NO synthesis. Reductions in NO synthesis reduce renal sodium excretory function, not only through direct action on the renal vasculature, but through modulation of other vasoconstrictor processes and through direct and indirect alterations in tubular sodium transport. 4. The causes and consequences of the disregulation of NO in hypertension and other renal disease processes remain an important area of investigation.

This study examined the contribution of endothelium-derived relaxing factor (EDRF) to the susceptibility of uninephrectomized rats to deoxycorticosterone acetate (DOCA)-salt hypertension. N omega-nitro-L-arginine, a probe for EDRF, produced smaller increases (P < 0.001) in mean arterial pressures in anesthetized hypertensive DOCA-salt rats than in sham rats. Acute L-arginine administration (300 mg/kg body wt i.v.) failed to reduce pressure in anesthetized DOCA-salt rats. Chronic oral and intraperitoneal L-arginine did not lower pressure in conscious DOCA-salt rats with established hypertension, nor did it prevent hypertension when begun in prehypertensive DOCA-salt rats. Preconstricted aortic rings from DOCA-salt rats had attenuated relaxation to acetylcholine compared with sham rats. Rings L-arginine-treated DOCA-salt rats had responses similar to DOCA-salt rats. Relaxation to nitroprusside was not different between any rat group. Thus EDRF is attenuated in DOCA-salt hypertension. However, unlike several other hypertensive models, the blunted EDRF response cannot be overcome by provision of L-arginine. These data suggest synthesis or release of EDRF may be noncompetitively inhibited in DOCA-salt hypertension.