A quantitative study on vascular angiotensin II receptors in rats with portal hypertension

Abstract

Angiotension-I (A-I) receptor maximal binding capacity (B_max) and dissociation constants (K_d) of different blood vessels in rats with prehepatic portal hypertension were studied by radioligand binding analysis. The results showed that the A-I receptor B_max in the thoracic aorta, superior mesenteric artery and portal vein of portal hypertensive animals (113. 7±19. 4 fmol/mg protein, 206. 9 ±39. 3 fmol/mg protein and 31. 5±9. 2 fmol/mg protein respectively) was all significantly lower than that of controls (146. 8±24. 5 fmol/mg protein, 297. 2±44. 7 fmol/mg protein and 53. 4±12. 1 fmol/mg protein respectively,P<0. 01). The A-I receptor K_d in the superior mesenteric artery was markedly increased in portal hypertensive animals (1. 03±0. 11 nmol/L) compared with that in controls (0. 88±0. 08 nmol/L,P<0. 05). In the thoracic aorta and portal vein, the A-I receptor K_d in portal hypertensive animals was slightly higher than that in controls, but no significant difference was observed between the two groups. The results suggested that the vascular hyporesponsiveness to A-I in portal hypertension was caused partially by a reduction in number and a decrease in affinity of vascular A-I receptors, and these changes might possibly lead to the formation of hyperdynamic circulation.

Keywords

portal hypertension, receptors, angiotensin-II / radioligand assay