Effect of dietary salt on the skeletal muscle microvasculature in Dahl rats.

Abstract

The purpose of this study was to identify microvascular alterations that could contribute to increased peripheral vascular resistance in the Dahl salt-sensitive rat with salt-induced hypertension. Intravital microscopy was used to study the spinotrapezius muscle arteriolar network in anesthetized salt-sensitive rats fed either a high salt (7% sodium chloride) or low-normal salt (0.45% sodium chloride) diet for 4 weeks. Age-matched Dahl salt-resistant rats on high and low-normal salt diets served as controls. The high salt diet had no effect on arterial pressure in salt-resistant rats but increased arterial pressure in salt-sensitive rats. Mean resting diameter of arcade arterioles in salt-sensitive rats on high salt diet was reduced by 25% compared with salt-sensitive rats on low salt or salt-resistant rats on either diet. After abolition of vascular tone with 10~3 M adenosine, arcade diameters were comparable in all groups. No difference among groups was found in either resting or passive diameter of the more distal transverse arterioles. Measurement of vessel lengths and numbers in cleared muscle specimens revealed no differences among groups in the anatomic density of either arcade or transverse arterioles. These data suggest that a reduction in the resting diameter of arcade, but not transverse, arterioles may increase spinotrapezius muscle vascular resistance in hypertensive salt-sensitive rats. The similarity in vascular densities among groups indicates that structural rarefaction of arterioles does not contribute to any increase in spinotrapezius muscle resistance at this stage of salt-induced hypertension. {Hypertension 1990;15:420-426)

Reduced influence of nitric oxide on arteriolar tone in hypertensive Dahl rats.

“…In contrast to previous findings in hypertensive DS rats fed a high salt diet for 4 weeks, 3 arcade arteriole diameters were not reduced in the current group of DS rats after 6-7 weeks of high salt intake. Longitudinal studies in DS rats and other hypertension models indicate that as hypertension progresses, the vascular alterations in a particular organ can change, often with a shift in the segments of the arterial tree that contribute to increased vascular resistance.…”

“…The right carotid artery was cannulated for arterial pressure measurement, and the right spinotrapezius muscle was exteriorized as previously described. 28 - 29 The muscle was continuously superfused with an electrolyte solution (mM: NaCl 119, NaHCO 3 25, KC1 6, and CaCl 2 3.6) warmed to 35°C and equilibrated with a mixture of 95% 1 V 5 % CO 2 (pH, 7.35-7.40). Superfusate flow was 4-6 ml/min to minimize equilibration with atmospheric oxygen.…”

“…12 Accordingly, the vascular tone of large arterioles is increased in skeletal muscle of hypertensive DS rats, reducing the average internal diameter of these vessels after 4 weeks of high salt intake. 3 Since acetylcholine (ACh) was first shown to cause vasodilation through the release of a relaxing factor from the endothelium, 4 other endothelium-derived factors have been identified and their importance in regulating vascular tone has been recognized. 5 - 6 The factor released by ACh is thought to be nitric oxide (NO) or a compound that spontaneously generates NO.…”

Effect of a High Salt Diet on Microvascular Antioxidant Enzymes

“…Hypertension that can be exacerbated by dietary salt (‘salt-sensitive’ hypertension) is characterized by distinct functional changes at the microvascular level [1, 2, 3, 4]. However, high salt intake can also lead to changes in microvascular function in the absence of elevated arterial pressure [3, 5, 6, 7, 8, 9].…”

New directions for microvascular research in hypertension.

“…It is very fitting that this new direction of research involves Dr. Phillip Hutchins because he was, if not the first, one of the first investigators to study the in vivo microvasculature of SHR. 3 Since his first study with Alice Darnell almost 2 decades past, studies of the microvasculature in virtually every organ system and type of hypertension have been published and now, with the work of Boegehold and Kotchen, 1 the Dahl form of hypertension is included. The studies by Boegehold and Kotchen 1 and le Noble et al 2 point out two ongoing issues that are common to the majority of in vivo and anatomic studies of the microvasculature.…”