A Study on Influences of Various Humoral Factors to Lipoprotein Entry into Arterial Wall

Abstract

Influences of humoral factors such as renin, norepinephrin, epinephrin, angiotensin-II and insulin to serum lipoprotein entry into the arterial wall have been performed in in vitro. Rabbit thoracic aorta was incubated in Warburg's apparatus for measurement of two hours' intake of cholesterol-¹⁴C-labelled low and high density lipoproteins. During the incubation period, 95% oxygen with 5% CO² was administered. Two procedures in which the humoral factors were added into the incubation medium in various concentrations (in vitro administration) and were injected into the rabitt vein with a continuous infusion pump (in vivo administration).
Results and discussion: 1) Renin, norepinephrin and epinephrin did not show any influence to the lipoprotein entry into the arterial wall in the both study. 2) Addition of angiotensin-II into the medium at intervals of 15min. and continuous infusion in vivo significantly increased both LDL and HDL entries. 3) In the both procedure to administrate the insulin, this substance increased only LDL uptake significantly. 4) From the above mentioned results, it may be concidered that progress of vascular damage in high renin hypertention is not affected from the direct action of renin but is affected from the other factors which relate the high renin state such as angiotensin-II. Even though both catecholamine and angiotensin-II constrict the arterial wall, only angiotensin-II increased the lipoprotein entry. this may be suggests that mechanism which increased the lipoprotein entry is not the constriction of artery but the direct arterial damage caused by angiotensin-II. As compaire with the mechanism of angiotensin-II, mechanism increased the lipoprotein entry in the insulin administration may be considered as functionally since only the LDL uptake was affected by the insulin.