Synergistic Effect of Angiotensin II and a High Sodium Diet on the Vascular Glycosaminoglycan Synthesis of Rats

Abstract

The effect of dietary sodium supplementation on angiotensin II (ANG II)-induced stimulation of vascular glycosaminoglycan (GAG) synthesis of rats was investigated. Measurements were performed both ex vivo and in vivo to validate the in vivo measurements and to estimate the relative contribution of intrinsic and extrinsic influences to ANG II-stimulated GAG synthesis in sodium-fed rats. Male Sprague-Dawley rats on normal (0.7% NaCl) and high sodium (4.0% NaCl) diets were infused with 100 ng/kg/min ANG II intraperitoneally for 48 h, or sham operated (controls). To measure tissue GAG synthesis, 35SO 4 was added to the incubation medium (ex vivo) or injected intravenously into rats (in vivo). Systolic blood pressure of ANG II-treated rats on normal sodium diet was unchanged, but it increased by 13 mm Hg ( P < .05) in the rats on the combined treatment of ANG II and a high sodium diet. ANG II or high sodium diet by itself had no effect on GAG synthesis. On the combined treatment, GAG synthesis of the aorta was increased by 17% ( P < .05) when measured ex vivo, and by 38% ( P < .01) when measured in vivo. In vivo, there was also increased GAG synthesis of mesenteric arteries ( P < .01) and of vena cava ( P < .02); GAG synthesis of nonvascular tissue (diaphragm, bladder, and kidney) was unchanged. The synergistic effect of ANG II treatment and high sodium diet on GAG synthesis appears to be, in part, arterial pressure independent and vascular tissue specific. The greater effect of combined treatment in vivo than ex vivo suggests that humoral or neural stimuli may be contributing to the interaction.