Sodium-phosphate cotransport and vascular reactivity

Inorganic phosphate (PO4) alters vascular reactivity in vivo as well as in vitro. In the latter condition, low PO4 reduces, while high PO4 augments reactivity. We used phosphonoformate (PFA), a phosphaturic compound, binding the renal Na-PO4 co-transporter, to examine the existence of such a transport mechanism in selected vascular smooth muscles (VSM). Strips of aorta (A), mesenteric artery (MA), and vein (MV) were obtained from normal rabbits. All tissues were either superfused in normal PO4 (Group 1: 3 mg/dL), then in modified low PO4 (Group 2: 0 mg/dL) or high PO4 (Group 3: 9 mg/dL) Ringer's solutions. The effect of angiotensin II (AII: 10-11 to 10-8M) was tested on each tissue preparation, and contraction values obtained in the presence of PFA (18.5 micrograms/ml:0.018 ml/min) were compared to control responses in the absence of the drug. In Group 1, the contractions of A were reduced by 23% during PFA, for higher doses of AII only, compared to controls (p less than 0.01). Similarly, the contractions of MA in the presence of PFA were reduced at higher doses of AII, by 22% (p less than 0.01). Finally, the contractions of MV were reduced by 75% (p less than 0.01) for all doses of AII. In Group 2, there was no difference in vascular tissue contraction between controls and PFA, whereas in Group 3, the reduction in A, MA, and MV contractions in PFA-treated tissues were approximately twice as extensive as in Group 1 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)