Effect of dietary salt on arteriolar nitric oxide in striated muscle of normotensive rats

Abstract

This study evaluated the influence of high dietary salt intake on nitric oxide (NO) activity in the arteriolar network of rats resistant to salt-induced hypertension. The spinotrapezius muscle microvasculature was studied in inbred Dahl salt-resistant (SR/Jr) rats fed low (0.45%)- or high (7%)-salt diets for 4-5 wk. Arterial pressures were not different between groups at any time during the study. NO synthesis inhibition with NG-nitro-L-arginine-methyl ester (L-NAME) constricted arcade arterioles in low-salt SR/Jr and dilated arcade arterioles in high-salt SR/Jr. Arcade arteriole dilation to acetylcholine (ACh), but not sodium nitroprusside (SNP), was impaired in high-salt SR/Jr. In contrast, transverse and distal arteriole responses to L-NAME, ACh, and SNP were identical in high- and low-salt SR/Jr. These findings indicate that high salt intake, in the absence of increased arterial pressure, suppresses the influence of basal and evoked NO on vascular tone in arcading arterioles, but not in smaller transverse and distal arterioles. Unaltered SNP responses in high-salt SR/Jr suggest that this effect does not involve a change in arteriolar smooth muscle responsiveness to NO.

High-salt diet impairs vascular relaxation mechanisms in rat middle cerebral arteries

“…Previous studies have suggested that overproduction of vasoconstrictor factors, such as PGH 2 and TxA 2 via cyclooxygenases, can contribute to an impaired relaxation in response to endotheliumdependent vasodilator stimuli in spontaneously hypertensive rats (1,28) and spontaneously hypertensive hamsters (34). The results of the present study suggest that TxA 2 plays a role in mediating the paradoxical constriction in response to reduced PO 2 in MCA of animals on a high-salt diet because TxA 2 production was significantly elevated during resting conditions in vessels from rats on high-salt diet and TxA 2 release tended to increase during hypoxia in vessels from animals on high-salt diet.…”

“…Effect of endothelium removal on response to reduced PO 2 and iloprost in arteries of animals on high-and low-salt diet. The effect of endothelium removal on the response to hypoxia and iloprost in MCA isolated from animals on short-term low-and high-salt diets is shown in Fig.…”

“…Thromboxane release by arteries from animals on a low-salt diet decreased significantly during exposure to reduced PO 2 , whereas thromboxane release by vessels from animals on a high-salt diet tended to increase during hypoxia. 2 and other dilator stimuli. Several recent studies (2, 3, 8-10, 12, 17-19) indicate that elevated salt intake leads to significant changes in the reactivity of resistance vessels to vasoconstrictor and vasodilator stimuli in normotensive rats.…”

“…Endothelial function also appears to be altered by elevated salt intake, because short-term exposure to high-salt diet eliminates acetylcholine-induced dilation of MCA. It also appears that short-term exposure to high-salt diet leads to significant alterations in arachidonic acid metabolism in MCA, because these vessels exhibited significant increases in both PGI 2 and TxA 2 release in response to high-salt diet. In addition, the pattern of PGI 2 and TxA 2 release was also altered by high-salt diet, such that vessels of animals on a low-salt diet exhibited an increase in PGI 2 production and a decrease in TxA 2 production during exposure to hypoxia, whereas PGI 2 production was reduced and TxA 2 production tended to increase when vessels from animals on a high-salt diet were exposed to reduced PO 2 .…”

Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle

“…Of these, the rat spinotrapezius muscle possesses the following singular advantages: 1) it can be exteriorized and transilluminated without disruption of the nervous or primary vascular supplies (2,12,28,40); 2) it comprises a mosaic of the three principal fiber types found in mammalian muscle (8); and 3) the oxidative capacity approximates that found in the untrained human quadriceps (8,22). Consequently, it is not surprising that intravital microscopy of the spinotrapezius has been integral to our understanding of muscle microcirculation in health (4,21,23,25,31,37,39) and chronic diseases such as heart failure (15), Type 1 diabetes (18), and hypertension (13).Within the past two years, it has been possible to measure spinotrapezius capillary hemodynamics during muscle contractions (17,33). This raises the exciting possibility that the spinotrapezius can be utilized to understand the effects of physiological adaptations, for example, to exercise training on capillary hemodynamics and O 2 exchange in contracting muscle.…”