Kinetic parameters of the lipoprotein transport systems in the adrenal gland of the @entity35 determined in vivo. Comparison of low and high density lipoproteins of XXXX and @entity35 origin.

@entity1 @entity6239 @entity27707 @entity35 @entity165
These studies were done to characterize the rate of uptake of high (HDL) and low (LDL) density lipoprotein @entity165 by the adrenal gland of the @entity35 under in vivo conditions. Animals were pretreated for 4 days with @entity27707 to essentially eliminate endogenous plasma lipoproteins and with @entity6239 for 1 h to block conversion of @entity165 to adrenal hormones. Such animals were then infused with varying amounts of HDL and LDL from both @entity1 and @entity35 plasma, and this led to rapid accumulation of @entity165 , both free and esterified, in the adrenal glands over the subsequent 4-h period of observation. This uptake process was linear with respect to time and manifested saturation kinetics with respect to the steady state level of plasma lipoprotein @entity165 . When @entity1 lipoproteins were infused, the maximal rate of @entity165 uptake was approximately 0.45 mg/pair of adrenal glands/h for both HDL and LDL; however, the half-maximal rate of uptake (Km) was achieved at a plasma HDL @entity165 concentration of only 12 mg/dl while a concentration of 61 mg/dl was required to achieve the same velocity with LDL. When similar experiments were carried out with @entity35 HDL, the Km equaled 7.2 mg/dl and a maximal rate of uptake of 0.32 mg/pair of adrenal glands/h was achieved. It was not possible to obtain complete kinetic curves using @entity35 LDL, but at physiological plasma concentrations, there was no difference in the rate of @entity165 uptake from LDL of @entity35 or @entity1 origin. When large amounts of both HDL (5.8 times Km) and LDL (3.1 times Km) were infused into the same animals, the rate of @entity165 uptake essentially equaled the sum of the maximal transport rates for the two lipoproteins. These data provide additional support for the concept that the adrenal gland (and ovary) of the @entity35 can take up HDL and LDL @entity165 by separate mechanisms. However, from the quantitative data on the kinetics of these uptake processes, it is apparent that in this species HDL @entity165 must be the major substrate for the synthesis of adrenal hormones.
