Effect of inhibition of nitric oxide synthesis on the uptake of LDL and fibrinogen by arterial walls and other organs of the rat.

1. The effects of administering 3 mg ml-1 NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO), on the uptake of low density lipoprotein (LDL), fibrinogen and blood pressure were determined in conscious, unrestrained, cannulated normotensive and spontaneously hypertensive (SHR) Wistar rats. 2. The uptake of LDL and fibrinogen, labelled respectively with 125I or 131I via the adduct tyramine cellobiose ([125I]TC-LDL and [131I]TC-fibrinogen), were compared in aortic walls, heart, skeletal muscle, lung, liver, kidney and adrenal during the final 24 h of 6 days' administration of L-NAME in the drinking water. 3. In control normotensive rats, the systolic blood pressure did not change significantly over 6 days, while administration of L-NAME in normotensive rats increased the blood pressure progressively and significantly to about 170 mmHg over the same period. 4. In normotensive rats L-NAME increased significantly the uptake of both LDL and fibrinogen by aortic walls and heart, but not by muscle, lung, liver, kidney and adrenal. 5. The blood pressure in SHR was about 170 mmHg before administration of L-NAME and did not increase significantly after 6 days of treatment. In these rats the uptake of LDL or of fibrinogen was increased only in the heart but not in aortic walls nor in any of the other organs. 6. In normotensive rats the increase in blood pressure caused by inhibition of NO generation was associated with increases in the uptake of the atherogenic plasma proteins LDL and fibrinogen by the wall of the aorta and by the heart but not by the skeletal muscle, lung, liver, kidney and adrenal. The slightly higher blood pressure of SHR treated with L-NAME was not associated with increased uptake of LDL or fibrinogen by aorta nor by any organ except heart. Thus, while in normotensive rats the increase in blood pressure caused by inhibition of NO generation was associated with increase in the uptake of atherogenic plasma proteins LDL and fibrinogen by the wall of the aorta and by the heart, in SHR which showed uptakes similar to the normotensive animals, the non-significant increase in blood pressure induced by inhibition of NO generation was not associated with increased uptake of LDL or fibrinogen in any organ except the heart.7. These results are consistent with effects, demonstrated earlier, of infusing the pressor agents noradrenaline, adrenaline and angiotensin II, which produce increases in uptake of LDL and fibrinogen by aortic wall, whereas this is not so in spontaneously hypertensive rats.