A Histochemical Study on Uptake of Serum Low density Lipoprotein into Arterial Wall

In this in vivo study, uptake of serum LDL into the arterial wall obtained from normocholesterolemic rabbits has been investigated under the condition of 6 hours continuous infusion of various humoral factors such as norepinephrine, epinephrine, hog renin, angiotensin II and insulin. Concentration of the humoral factors were as follows: 1.0μg/kg/min. for norepinephrine, 0.1μg/kg/min. for epinephrine, 0.05 Goldblatt units/kg/min. for hog renin, 0.003μg/kg/min. for angiotensin II and 1.0U/kg/hr. for insulin. Blood pressures during the infusions were less than 150 mmHg. Blood sugar was maintenined between 70-90mg% during the insulin infusion. Uptake of the LDL into the arterial wall was observed by immunofluorescent technique.RESULTS: No immunofluorescent of LDL was observed by the infusions of norepinephrine, epinephrine, and hog renin. On the other hand, uptake of LDL was observed when angiotensin II and insulin were given.DISSCUSSION and CONCLUSION: Previously, we had report that LDL u0take of arterial wall increased in the renovascular hypertensive rabbit. It should be obvious that blood pressure plays important role to the increase of the LDL uptake. However, it seems that effect of the humoral factors can not be disregard. It is of interest that only the angiotensin II among the various substances which affect the blood pressure increase the permeability of arterial wall to the LDL. Mechanism which angiotensin II increase the endotherial permeability to the LDL may be considered that this substance cause the organic change of endotherial cell but not constriction of the cell since the both catebholamines and angiotensin II constrict the arterial wall.In this. experiment, insulin increased the LDL uptake into the arterial wall but precise mechanism is still unknown.