Structural and functional studies of the adrenal zona glomerulosa in sodium-depleted and sodium-loaded sheep

Cell and Tissue Research - The effects of alterations in sodium status upon the morphology of the adrenal zona glomerulosa in sheep have been examined qualitatively and quantitatively, using...     

Intramitochondrial bodies in sheep adrenal zona glomerulosa cells

Summary Relatively large, mostly rounded, very electron dense intramitochondrial bodies in adrenal zona glomerulosa cells of sheep are described and their nature and connection to protein in the mitochondria discussed. The so called azocarmine granules seen in the light microscope may be identical with the intramitochondrial bodies in the zona glomerulosa cells.     

Morphogenesis of the renal juxtaglomerular apparatus and peripolar cells in the sheep

Summary The morphogenesis of the juxtaglomerular apparatus and peripolar cells was studied in the metanephros of fetal sheep (from 24 to 147 days of gestation) using light and electron microscopy. The first juxtaglomerular apparatus was detected at 45 days of gestation, following constriction of the edges of Bowman's capsule and formation of the vascular pole of the renal corpuscle. Mesenchymal cells gave rise to lacis cells and to smooth muscle and epithelioid cells of the juxtaglomerular arterioles. Epithelioid cells developed only sparse cytoplasmic granulation, first detectable at 92 days. The macula densa developed from tubular cells at the junction of the middle and upper limbs of the S-shaped body of the developing nephron. Peripolar cells arose from epithelial cells in the lower limb of the S-shaped body, at the constricting edges of Bowman's capsule, and formed a cuff around the origin of the glomerular tuft. Cytoplasmic granules were first detected in peripolar cells at 53 days, and remained more prominent than epithelioid cell granulation throughout gestation.     

alpha-MSH analogues and adrenal zona glomerulosa function

Recent studies on the control of adrenal zona glomerulosa function and aldosterone secretion have focussed attention on the role of MSH-like peptides. In particular, at low concentrations, alpha-MSH has a specific stimulatory effect on rat adrenal glomerulosa cells. The synthesis of alpha-MSH analogues which have potent and prolonged effects on melanocyte systems offers new methods of examining the specificity of this response. Two peptides were tested in which potential for a beta-turn configuration was stabilised. These were: [Nle4, D-Phe7]-alpha-MSH and the cyclic [Cys4, Cys10]-alpha-MSH. In contrast to their effects on melanocyte systems, only [Cys4, Cys10]-alpha-MSH stimulated glomerulosa cells, and it was equipotent with alpha-MSH, while [Nle4, D-Phe7]-alpha-MSH and shorter fragments had no effect when added alone. [Nle4, D-Phe7]-alpha-MSH, however, augmented the response of cells already maximally stimulated with alpha-MSH and in this respect its actions resembled those of gamma-MSH and related peptides. The augmentation produced by [Nle4, D-Phe7]-alpha-MSH and gamma 3-MSH was not additive when the two peptides were added together with alpha-MSH. The results suggest that the specificity of the alpha-MSH receptors in rat adrenal glomerulosa cells and the peptide structure-function relationships in this system are different from those described for melanocytes.     

Ascorbate stimulates monooxygenase-dependent steroidogenesis in adrenal zona glomerulosa

It is well known that ascorbic acid (Asc) is highly concentrated in the adrenal gland, but its function in the gland is not thoroughly elucidated. We therefore examined the possibility that Asc participates in steroidogenic monooxygenase systems of the adrenal cortex with the aid of the regenerating system including outer mitochondrial membrane cytochrome b (OMb). When Asc availability was limited in rat mutants unable to synthesize Asc, the increase in plasma aldosterone concentration under Na-deficiency was suppressed without effect on plasma corticosterone concentration. Aldosterone formation in the isolated mitochondrial fraction of the zona glomerulosa (zG) of the adrenal cortex was stimulated by the addition of Asc and NADH, while corticosterone formation was not. Consistently zG showed a high level of Asc regeneration activity and was rich in OMb among adrenocortical zones. Taken together, the enhanced aldosterone formation that is catalyzed by one of the steroidogenic monooxygenases, P450aldo, may be supported by Asc with its regenerating system.     

Steroidogenesis in the zona glomerulosa of the adrenal cortex II. Distribution of cytochrome P-450 in the zona glomerulosa of the bovine adrenal cortex

Microsomes were obtained from the zona glomerulosa of the bovine adrenal cortex. Contamination of microsomes with other cellular organelles was examined using various marker enzymes and the electron microscope. Distribution of cytochrome P-450 in the zona glomerulosa was studied using various fractions including microsomes, described above, and mitochondria. The amount of cytochrome P-450 in mitochondria and in microsomes was determined to be 0.73 and 0.32 nmol/mg protein, respectively. The CO difference spectrum was affected not only by the concentration of added deoxycholate but also by the incubation time after addition. Approximately 40–50% of cytochrome P-450 in the samples was converted to cytochrome P-420 within 20–30 sec of incubation with deoxycholate.The content of RNA, phospholipids, and cytochromeb ₅ in microsomes obtained from the zona glomerulosa is also evaluated in comparison to that in microsomes obtained from the zona fasciculoreticularis.     

Steroidogenesis in the zona glomerulosa of the adrenal cortex I. Isolation and some properties of mitochondria from the zona glomerulosa of the bovine adrenal cortex

Isolation procedures for mitochondria from the zona glomerulosa of the bovine adrenal cortex are described and the properties of the mitochondria thus prepared are compared with those isolated from the zona fasciculoreticularis. The cristal membranes of mitochondria in the zona glomerulosa in situ are tubular or tubulovesicular, whereas those of mitochondria in the zona fasciculoreticularis in situ are vesicular. When mitochondria are isolated from the former zone, they invariably showed the condensed configuration regardless of isolation media, whereas those isolated from the latter zone in an ST medium showed the orthodox configuration. When Ca²⁺ was added to mitochondria isolated either from the zona glomerulosa or the zona fasciculoreticularis in an STE medium in the condensed configuration, a transition from the condensed to the orthodox configuration took place; the cristal membranes of mitochondria from the zona glomerulosa became tubular or tubulovesicular and those of mitochondria from the zona fasciculoreticularis became vesicular. Contaminations of mitrochondria of the zona glomerulosa with other cellular organelles were examined using various marker enzymes. There was no difference in cytochrome content between mitochondria of the two zones specified above. The coupling efficiency of mitochondria of the zona glomerulosa was found to be remarkably effected by temperature during the isolation procedures. Effects of various substrates, isolation media, and bovine serum albumin on the coupling efficiency of mitochondria of the glomerulosa are also described.     

Isolation of bovine adrenal cortex mitochondria from the zona glomerulosa

Isolation procedures for the bovine adrenal cortex mitochondria from the zona glomerulosa are described. Special care was taken to avoid contamination of the mitochondria from the zona fasciculata.     

Chronic hypoxia induced ultrastructural changes in the rat adrenal zona glomerulosa

The adrenal cortex plays an important role in adaptation to various forms of stress, including hypoxia. While physiological changes in the aldosterone metabolism during hypoxia have been extensively described, few studies have focused on the morphological changes in the adrenal glands under chronic hypoxia. We studied the ultrastructure of the zona glomerulosa of 6-month-old Wistar rats exposed to chronic normobaric hypoxia. Animals were divided into two groups: control (n=12) and hypoxic (n=12). In this latter group, the animals were kept at 7% O2 concentration after a gradual adaptation (21, 15, 12, 10, 8, 7 vol% O2). The duration of the study was 112 days. In comparison with normoxic rats, body weight and adrenal gland weight of hypoxic animals was significantly reduced by 18.5% (p=0.006) and 14.7% (p=0.001) respectively. The thickness of the zona glomerulosa decreased due to atrophy of cells. The main ultrastructural changes observed were: 1) a decrease in, or complete elimination of, lipid droplet content; 2) a marked increase in lysosome number; and 3) the presence of giant mitochondria. Our findings show that rats fail to adapt to severe chronic hypoxia. The ultrastructural changes in the zona glomerulosa found in the present study could reflect changes in the aldosterone pathway.     

Short- and long-term effects of ACTH on the adrenal zona glomerulosa of the rat

Summary Short-term ACTH treatment provoked a decrease in volume of the lipid-droplet compartment in rat zona glomerulosa cells, and a rise in plasma and intracellular concentrations of corticosterone and aldosterone. It enhanced activities of 3-hydroxysteroid dehydrogenase (3HSD), 11-hydroxylase (11OH) and 18-hydroxylase (18OH). Long-term ACTH administration produced a hypertrophy of the zona glomerulosa and its parenchymal cells, a result of the increase in volume of the smooth endoplasmic reticulum and the mitochondrial compartment. The surface area per cell of mitochondrial inner membranes increased; the tubular cristae were transformed into a homogeneous population of vesicles. The plasma and intracellular concentrations of corticosterone further increased, whereas those of aldosterone fell below basal levels (the aldosterone-escape phenomenon). The activities of 3HSD and 11OH were enhanced, that of 180H decreased. Therefore, ACTH stimulates zona glomerulosa growth and transforms parenchymal elements into zona fasciculata celltypes. Cyanoketone nullified acute ACTH effects on plasma and intracellular concentrations of corticosterone and aldosterone, but did not affect the activities of 11OH and 18OH. Chronic ACTH treatment produced similar results, although 18OH activity was not suppressed. The mechanism underlying the aldosterone-escape phenomenon may thus involve a rise in the intracellular concentration of corticosterone, caused by the enhanced synthesis and activation of 3HSD and 11OH.     

Dopamine inhibition of potassium-stimulated aldosterone biosynthesis in bovine adrenal zona glomerulosa cells

Dopamine inhibits angiotensin II-stimulated aldosterone production by an effect on the late phase of biosynthesis. This study was undertaken to investigate the effect of dopamine on potassium-stimulated aldosterone biosynthesis in adrenal glomerulosa cells in vitro. As potassium concentrations were increased from 0 to 12 mM, aldosterone production increased up to 6 mM potassium, but not beyond this concentration. Dopamine (10(-5)M) inhibited the aldosterone response to potassium. The effect of potassium on pregnenolone accumulation (the early phase of aldosterone biosynthesis) was assessed in cells treated with trilostane which inhibits the conversion of pregnenolone onward to aldosterone. Increasing potassium concentrations up to 12 mM gave increasing pregnenolone accumulation; however dopamine did not influence this effect. The potassium stimulated conversion of corticosterone to aldosterone, an index of activity in the late phase of aldosterone biosynthesis, was assessed using aminoglutethimide to prevent cholesterol side-chain cleavage. Significantly more corticosterone was converted to aldosterone at 6 mM potassium than at 0 or 12 mM; dopamine inhibited the conversion of corticosterone to aldosterone at 6 mM potassium. These data indicate that dopamine inhibits potassium-stimulated aldosterone production by an effect restricted to the late phase of the aldosterone biosynthetic pathway similar to its previously established effect on angiotensin II-stimulated aldosterone biosynthesis.     

Rat atrial natriuretic polypeptide stimulation of adrenal zona glomerulosa cell growth

Rat atrial natriuretic polypeptide (rANP) was found to stimulate [3H] thymidine incorporation into the DNA of bovine adrenal glomerulosa cells in a primary culture in a dose-dependent manner. The minimum effective dose was a very low concentration (10(-12) M of ANP), suggesting that ANP had a physiological effect. These findings are the first indication that ANP possesses growth-stimulating activity with regard to adrenal zona glomerulosa cells.