Routine heparin therapy inhibits adrenal aldosterone production

While heparin-induced aldosterone deficiency has been sporadically reported, it is not known whether heparin always inhibits aldosterone production to a variable extent or if this is an idiosyncratic effect, nor is the mechanism underlying the phenomenon known. We have examined plasma aldosterone, PRA, and aldosterone to renin activity ratios in 20 patients before, during and after treatment with heparin. Aldosterone cell during heparin treatment from 73.5 +/- 20.5 to 36.8 +/- 11.2 pg/ml (P less than 0.05) and rose after its withdrawal to 94.8 +/- 37.1 p/ml (P less than 0.05). PRA rose with heparin treatment from 2.8 +/- 1.0 to 6.1 +/- 1.6 ng/ml . h (P less than 0.05) and fell to 2.4 +/- 0.5 ng/ml . h (P less than 0.05) when the drug was withdrawn. Aldosterone to renin activity ratios, which are indices of aldosterone responsiveness to angiotensin, fell from 59.5 +/- 1.7 to 25 +/- 14.9 (P less than 0.01) with heparin treatment and rose after withdrawal of the drug to 58.5 +/- 24.9 (P less than 0.01). There was a significant small fall in serum sodium levels with the introduction of heparin, but none of the patients developed clinical mineralocorticoid deficiency. Although heparin consistently perturbs aldosterone production in the glomerulosa cell, this effect is not clinically significant when normal adjustments can be made in the generation of angiotensin. However, where limitations in the renin-angiotensin-aldosterone axis exist, e.g. in diabetes mellitus, mineralocorticoid insufficiency may be precipitated by heparin.     

Features of adrenal cortex function in heterozygous carriers of 21-hydroxylase deficiency

Adrenocortical function in carriers of 21-hydroxylase insufficiency and in persons without it was investigated by change in the levels of 17-hydroxyprogesterone and dehydroepiandrosterone before and against a background of prolonged ACTH stimulation. Differences in change of the basal concentrations of these hormones in both groups were absent. Change of adrenocortical function in the carriers was observed against a background of ACTH stimulation only by the blood level of 17-hydroxyprogesterone. Prolonged ACTH stimulation revealed not only quantitative but also qualitative traits of adrenocortical function in carriers of 21-hydroxylase insufficiency. An algorithm for diagnosing this insufficiency was worked out.     

Beta-adrenergic stimulation of aldosterone production by rat adrenal capsular explants

Adrenal glomerulosa was examined for the presence of an adrenergic influence on aldosterone production. Cultured rat adrenal capsular explants were transferred to a perifusion system where the effect of exposure to catecholamines on aldosterone production was assessed. At 10(-6) M, isoproterenol greater than epinephrine greater than norepinephrine significantly stimulated aldosterone production, whereas at 10(-8) M only isoproterenol showed significant stimulation. Propranolol, a beta-adrenoreceptor antagonist, inhibited stimulation by epinephrine, and the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine, enhanced stimulation by a submaximal dose of epinephrine. Epinephrine and norepinephrine were found by radioenzymatic assay to be present in fresh as well as cultured capsular tissue, although levels were considerably lower in tissue that had been in culture (about one tenth that of fresh tissue). The epinephrine-norepinephrine ratio was similar in capsule and medulla, suggesting a medullary source of capsular catecholamines. Whether catecholamines in the capsule arose from the in vitro manipulation of adrenal tissue or existed in vivo is unclear. In summary, beta-agonists stimulate aldosterone production in cultured rat capsular explants.     

Effect of osmolarity on aldosterone production by rat adrenal glomerulosa cells

The effect of osmotic changes on aldosterone production, [Ca2+]i and voltage-gated Ca2+ currents, was studied in cultured rat glomerulosa cells. Alteration of osmolarity by sucrose addition in the 250-330 mosM range did not influence aldosterone production per se, but it substantially affected K+-stimulated aldosterone production. Hyposmosis markedly increased the hormone response evoked by raising [K+] from 3.6 to 5 mM, whereas hyperosmosis had a mild decreasing effect. Cytoplasmic [Ca2+]i, measured in single glomerulosa cells, did not show detectable change in response to either hyposmotic or hyperosmotic exposure, but the [Ca2+]i signal evoked by elevation of [K+] to 5 mM was augmented in hyposmotic solution. The osmosensitivity of the transient (T)-type and long-lasting (L)-type voltage-gated Ca2+ currents was studied using the nystatin-perforated voltage-clamp technique. Lowering osmolarity to 250 mosM significantly increased the amplitude of the T-type current, and it had a transient augmenting effect on L-type current amplitude. Hyperosmotic solution (330 mosM) reduced L-type current amplitude but did not evoke significant change in T-type current. These results indicate that the responsiveness of rat glomerulosa cells to physiological elevation of [K+] is remarkably influenced by changes in osmolarity by means of modulating the function of voltage-gated Ca2+ channels.     

Homeostatic responses in the adrenal cortex to the absence of aldosterone in mice

To study the effects of decreased amounts or absence of aldosterone on development and endocrine function, we have disrupted the mouse gene, Cyp11b2, coding for aldosterone synthase (AS) by replacing its first two exons with sequences coding for enhanced green fluorescent protein. The null pups fail to thrive postnatally, and about 30% die between d 7 and 28. Aldosterone in plasma and AS mRNA in adrenal glands are undetectable in the null mice. Adult AS-null mice are small, weigh 75% of wild type, are hypotensive, have increased concentrations of plasma K(+) and corticosterone, and a decreased concentration of plasma Cl(-). Their plasma renin and angiotensin II concentrations are 45x and 4x wild type. The adrenal cortex is disorganized and has cells that contain marked accumulations of lipid. The zona glomerulosa is widened and includes easily detectable renin-containing cells, not seen in the wild-type adrenal gland. In the AS-/- adrenals, the level of mRNA for Cyp11b1, coding for 11beta-hydroxylase, is 150% wild type. The adrenal glands of the null mice consequently show evidence of a greatly activated renin-angiotensin system and up-regulation of glucocorticoid production. In the AS-null mice enhanced green fluorescent protein fluorescence is mainly at the boundary between the cortex and medulla, where apoptotic cells are numerous. These data are consistent with the absence of aldosterone in the AS-null mice inducing an increased cell-turnover of cells in the adrenals that normally become AS expressing and their migration to the medullary boundary where they apoptose.     

Maternal dietary choline deficiency alters angiogenesis in fetal mouse hippocampus

We examined whether maternal dietary choline modulates angiogenesis in fetal brain. Pregnant C57BL/6 mice were fed either a choline-deficient (CD), control (CT), or choline-supplemented diet (CS) from days 12 to 17 (E12-17) of pregnancy and then fetal brains were studied. In CD fetal hippocampus, proliferation of endothelial cells (EC) was decreased by 32% (p < 0.01 vs. CT or CS) while differentiated EC clusters (expressing factor VIII related antigen (RA)) increased by 25% (p < 0.01 vs. CT or CS). These changes were associated with > 25% decrease in the number of blood vessels in CD fetal hippocampus (p < 0.01 vs. CT and CS), with no change in total cross-sectional area of these blood vessels. Expression of genes for the angiogenic signals derived from both endothelial and neuronal progenitor cells (NPC) was increased in CD fetal hippocampus VEGF C (Vegfc), 2.0-fold, p < 0.01 vs. CT and angiopoietin 2 (Angpt2), 2.1-fold, (p < 0.01 vs. CT)). Similar increased expression was observed in NPC isolated from E14 fetal mouse brains and exposed to low (5 μM), CT (70 μM), or high choline (280 μM) media for 72 h (low choline caused a 9.7-fold increase in relative gene expression of Vegfc (p < 0.001 vs. CT and high) and a 3.4-fold increase in expression of Angpt2, (p < 0.05 vs. CT and high). ANGPT2 protein was increased 42.2% (p < 0.01). Cytosine-phosphate-guanine dinucleotide islands in the proximity of the promoter areas of Vegfc and Angpt2 were hypomethylated in low choline NPC compared to CT NPC (p < 0.01). We conclude that maternal dietary choline intake alters angiogenesis in the developing fetal hippocampus.     

Molecular mechanism of cytochrome P-450-dependent aldosterone biosynthesis in the adrenal cortex.

In the adrenal cortex, the potent mineralocorticoid, aldosterone, is produced in the zoba glomerulosa but not in the zona fasciculata/reticularis. In rodents and humans, two distinct species of P-450(C18) (aldosterone synthase) and P-450(11beta) (11beta-hydroxylase) are expressed in the adrenal cortex. The selective expression of cytochrome P-450 species in different zones contributes to zone specificity of aldosterone synthesis. In the cow and pig, only one molecular species of P-450(11beta) having both 11beta-hydroxylase and aldosterone synthase activity is expressed throughout the adrenal cortex. P-450(11beta) in the zona fasciculata/reticularis catalyzes the formation of corticosterone but not that of aldosterone from 11-deoxycorticosterone; the same enzyme in the zona glomerulosa produces aldosterone from the same substrate, indicating that a local factor in mitochondria is likely to be involved in the selective suppression of the aldosterone synthetic activity of P-450(11beta) in the zona fasciculata/reticularis. The zone specificity of aldosterone synthesis catalyzed by P-450(11beta) in the bovine adrenal cortex appears to be due to differences in interactions between P-450(11beta) and P-450(SCC) in mitochondria in different cortical zones. Thus, two modes exist for aldosterone biosynthesis in mammals: rodent-human and bovine-porcine modes.     

Angiotensin II receptors and aldosterone production in rat adrenal glomerulosa cells.

Specific receptors for angiotensin II (A II) were demonstrated in membrane fractions and collagenase-dispersed cells from the zona glomerulosa of the rat adrenal gland. The equilibrium association constant (Ka) of the A II binding sites was similar in particulate fractions (2.0 +/- 0.4 (SE) X 10(9) M-1) and intact glomerulosa cells (1.8 +/- 0.3 X 10(9) M-1). Specific binding of [125I]iodo-A II was enhanced by increasing sodium concentration, and in the presence of dithiothreitol, EDTA, and EGTA. Plasma membrane fractions prepared by density gradient centrifugation showed increased binding of [125I]iodo-A II, and were correspondingly enriched in adenylate cyclase and sodium-potassium-dependent ATPase. Steroid production by collagenase-dispersed adrenal glomerulosa cells was highly responsive to A II and ACTH. Significant increases in aldosterone and corticosterone production were elicited by A II concentrations as low as 3 X 10(-11) M, equivalent to normal blood levels of A II in rats (5 X 10(-11) M). The maximum increase in aldosterone production, of 6--7 times the basal value, was obtained at 10(-9) M A II. Dispersed capsular cells were also highly sensitive to ACTH, responding to concentrations down to 3 X 10(-12) M with increased aldosterone production, reaching a maximum aldosterone response of 20-fold above the basal value. The magnitudes of the aldosterone and corticosterone responses to A II in capsular and fasciculata-reticularis cells were commensurate with the distribution of A II receptors, which were 11-fold more concentrated in capsular cells. The ability of A II to evoke aldosterone production at physiological concentrations, and the correspondence between A II binding and steroidogenesis in capsular cells, demonstrate the functional importance of A II receptor sites in the zona glomerulosa of the rat adrenal cortex.