Adrenocortical function in 4-APP treated rats: a coupled stereological and biochemical study

Lipoproteins, lipid droplets, lysosomes, and adrenocortical steroid hormone synthesis: morphological studies

Recent studies concerning cellular cholesterol homeostasis suggest that there is a relationship between the serum lipoproteins (low density and high density lipoproteins: LDL and HDL), the intracellular storage of cholesterol (lipid droplets), lysosomes, and the steroidogenic activity of adrenocortical cells. This review surveys the current knowledge on cholesterol import from LDL/HDL by adrenocortical cells, its regulation, and the participation of lipid droplets and lysosomes in this process. The possible role of adrenocortical cell microvilli in the uptake of LDL/HDL is discussed. Under certain physiological, experimental, and pathological circumstances lysosomes accumulate unesterified and/or esterified cholesterol in the form of lipid-lysosome complexes. As suggested by the data presented in this review, lipid-lysosome complexes appear to be involved in cholesterol homeostasis, via altering lipid compartmentalization. Since previous reports do not clearly demonstrate a positive correlation between the volume of lipid- and lysosome-compartments and the rate of steroid hormone synthesis [for review, see Nussdorfer (1986) Int. Rev. Cytol., 98:1-405], the objective of this review is to provide a better understanding of the interactions of plasma lipoproteins, lipid droplets, lysosomes, and steroidogenesis.

Effects of dexamethasone on the levels of adrenal steroidogenic enzyme mRNA in rats treated with 4-aminopyrazolopyrimidine

Following three 24 hourly serial injections of 4-aminopyrazolo[3,4-d]pyrimidine (4-APP) to rats, the levels of plasma corticotropin (ACTH) and of adrenal HMG-CoA reductase, the cholesterol side chain cleavage system, 3 beta-hydroxysteroid dehydrogenase, 21-hydroxylase, and adrenodoxin increased after an initial lag of 17 h. In contrast the mRNA level of 11 beta-hydroxylase was differently regulated since it was elevated after 17 and 24 h and decreased thereafter to basal values. These increases appear to be related to ACTH secretion since they were blocked by the coadministration of dexamethasone (Dex) and 4-APP. Also 3 h after the administration of Dex to 4-APP treated rats rapid decreases in plasma corticosterone and ACTH levels were accompanied by decreases in mRNA levels of HMG-CoA reductase and low density lipoprotein receptor, two components involved in the synthesis and transport of cholesterol. The mRNA level of the electron donor adrenodoxin was also decreased, suggesting that this component participates in the short term regulation of corticosterone synthesis in the rat adrenal. The adrenal response was more readily observed with components involved in the steps preceding cholesterol biosynthesis than in those subsequent to cholesterol in the corticosteroid pathway. However, the effects of 4-APP on the latter pathway were well documented with mRNA analysis performed by Northern blot, a more sensitive technique than the Western blot used for protein quantification. The entire metabolism of the corticosterone biosynthetic pathway was thus affected in rats treated with 4-APP. Taken collectively these results indicate that under acute lipoprotein depletion rat adrenals developed a compensatory mechanism enabling them to synthesize and utilize cholesterol for corticosteroid synthesis.

Stereologic studies on the long-term effect of prazosin on rat adrenal cortex

Adult female rats were treated with prazosin, a selective alpha 1-adrenoceptor inhibitor, for 60 days in doses of 0.5 mg/kg/day or 0.5 mg/kg/8 h. Prolonged prazosin administration lowered the gain of body weight and significantly decreased systolic blood pressure and heart weight. Prazosin administered every 8 h also lowered serum triglycerides but did not change the total cholesterol level. Selective alpha 1-inhibitor treatment increased the adrenal gland weight and decreased the number of adrenocortical cells; in every 8 h treated group this effect being connected with a marked cell hypertrophy (in all adrenocortical zones). Our results suggest that prazosin induced changes in the structure of the rat adrenal cortex depend on activation of the hypothalamo-pituitary-adrenocortical axis and possibly on the small inhibition of the proliferative activity of rat adrenocortical cells.

Comparative studies on the effect of 4-APP(4-aminopyrazolopyrimidine) on hamster and rat adrenal cortex

The study aimed to compare, by means of stereologic methods, the reactivity of the adrenal cortex of the hamster and the rat to prolonged treatment with 4-aminopyrazolo-(3,4d)pyrimidine (4-APP), a drug reducing hepatic secretion of plasma lipoprotein. Adult female hamsters, intact or cortisone suppressed, were administered i.p. daily with 0.5 mg 4-APP for 5 days while intact female rats received 1 mg of the drug per dose. 4-APP resulted in a loss of body weight, with the more profound effect in the hamster. In the rat 4-APP did not change the adrenal gland weight, the volume of the adrenocortical zones, the average volume of adrenocortical cells and the number of parenchymal cells in the gland. Moreover, serum ACTH and corticosterone levels in the rat remained unchanged. In the intact hamster 4-APP decreased the adrenal gland weight, the volume of the zona fasciculata and enhanced the serum cortisol level. In steroid suppressed hamsters 4-APP lowered the adrenal weight, the volume of fasciculata and reticularis zones, the average volume of the fasciculata cells and the number of parenchymal cells in the gland. These findings may suggest the direct inhibitory effect of low 4-APP doses on the hamster adrenal cortex and clearly demonstrate higher susceptibility of the hamster adrenal cortex, if compared with the rat, to 4-aminopyrazolo-pyrimidine.

Effects of the hypocholesterolemic drug, 4-aminopyrazolo (3,4-d) pyrimidine (4-APP), on the hamster adrenal cortex. An ultrastructural and functional study

The aim of this study was to gain insight into the effects of 4-aminopyrazolo(3,4-d)pyrimidine (4-APP), a hypocholesterolemic drug, on the adrenal cortex of the hamster, representing an animal species in which steroidogenesis primarily relies on utilization of cholesterol synthesized de novo in the gland. 4-APP administration (1.5 mg/animal day for 3 days) to intact or dexamethasone-suppressed hamsters resulted in a marked proliferation of adrenocortical cells. However, the volume of parenchymal cells was unchanged in intact animals and lowered in the zona glomerulosa (ZG) and zona reticularis (ZR) of dexamethasone-administered hamsters. In both groups of animals, 4-APP strikingly increased the volume of the lipid-droplet compartment and markedly reduced the surface area of smooth endoplasmic reticulum in ZF cells, without significantly affecting the volume of the mitochondrial compartment and the surface area of mitochondrial cristae. These morphologic changes displayed no evident correlation with adrenal cortisol content and secretion. Since most of the 4-APP-induced changes were not prevented by dexamethasone, it seems legitimate to suggest that they could mainly depend on a direct effect of 4-APP on the hamster adrenocortical cells.