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

Enhancement of aldosterone-induced catecholamine production by bone morphogenetic protein-4 through activating Rho and SAPK/JNK pathway in adrenomedullar cells

Here we investigated the effects of mineralocorticoid in the regulation of catecholamine biosynthesis using rat pheochromocytoma PC12 cells. Expression of mineralocorticoid receptor (MR) was confirmed in undifferentiated PC12 cells. Aldosterone stimulated dopamine production by PC12 cells without any increase in cAMP activity. Aldosterone-induced dopamine accumulation was enhanced in accordance with the increase in the rate-limiting enzyme tyrosine hydroxylase (TH). Blocking MR with eplerenone suppressed aldosterone-induced increases of TH mRNA and dopamine production. A glucocorticoid receptor (GR) antagonist, RU-486, attenuated dexamethasone- but not aldosterone-induced TH expression. Cycloheximide reduced both aldosterone- and dexamethasone-induced TH mRNA. A SAPK/JNK inhibitor, SP600125, suppressed aldosterone-induced TH mRNA expression; however, the aldosterone-induced TH expression was not affected by inhibition of ERK1/2, p38-MAPK, Rho-kinase, PI 3-kinase, and PKC. It was of note that cotreatment with eplerenone and SP600125 restored aldosterone-induced TH mRNA expression to basal levels. To investigate the involvement of bone morphogenetic protein (BMP) actions in aldosterone-induced catecholamine production, we examined the effects of BMP-4 and BMP-7, which are expressed in the adrenal medulla, on catecholamine biosynthesis. BMP-4 preferentially enhanced aldosterone-induced TH mRNA and dopamine production, although BMP-4 alone did not affect TH expression. The BMP-4 enhancement of aldosterone-induced TH expression was not observed in cells treated with eplerenone. BMP-4 did not affect MR expression of PC12 cells; however, it did enhance aldosterone-induced SAPK/JNK phosphorylation. Inhibition of SAPK/JNK or Rho suppressed BMP-4 enhancement of aldosterone-induced TH expression. Collectively, our findings demonstrate that aldosterone stimulates catecholamine biosynthesis in adrenomedullar cells via MR through genomic action and partly through nongenomic action by Rho-SAPK/JNK signaling, the latter of which is facilitated by BMP-4. A functional link between MR actions and endogenous BMP may be involved in the catecholamine production.

Evidence for a tonic inhibitory role of nifedipine-sensitive calcium channels in aldosterone biosynthesis

This study investigated the effects of the calcium channel blockers nifedipine (a dihydropyridine) and verapamil (a papaverine derivative), on aldosterone production utilizing isolation of the early and late phases of aldosterone biosynthesis. Pregnenolone production (the early phase of aldosterone biosynthesis) was assessed in trilostane-treated bovine glomerulosa cells, used to inhibit the conversion of pregnenolone onwards to aldosterone. Conversion of exogenous corticosterone to aldosterone, an index of late phase activity, was assessed using aminoglutethimide to inhibit endogenous aldosterone production. Low concentrations of nifedipine, 10(-11)-10(-9) M, stimulated basal total aldosterone biosynthesis by enhancing the late phase although the early phase was inhibited. In the presence of 12 mM potassium (K+), which is less effective in stimulating aldosterone production than lower K+ concentrations, aldosterone production was enhanced by nifedipine, 10(-8) M, by an effect on the late phase. At K+ 6 and 8 mM, nifedipine, 10(-4) M, inhibited the early phase. Nifedipine 10(-5) inhibited angiotensin II (AII)-stimulated total aldosterone biosynthesis by independent effects on the early and late phases. Verapamil, 10(-4) M, inhibited total and early phase aldosterone production at K+, 4 mM and inhibited both phases at K+, 8 mM, stimulation was not observed using verapamil. Verapamil, 10(-4) M, also inhibited AII-stimulated aldosterone production. Basal and AII-stimulated pregnenolone production were inhibited by verapamil, 10(-4) M (basal) and 10(-6) M (AII-stimulated). These studies using nifedipine have revealed subtle calcium-dependent mechanisms involved in the tonic inhibition of activity in the late phase of aldosterone biosynthesis and the reversal of the inhibitory effect of high K+ concentrations also on the late phase. In addition, the data reported indicate that both AII and K+ independently enhance activity in the early and late phases of aldosterone production by calcium-dependent mechanisms.

Guanabenz-induced inhibition of aldosterone secretion from isolated rat adrenal glomerulosa cells

The authors examined the effects of the alpha 2-adrenergic agonist guanabenz and other alpha-adrenergic ligands on aldosterone secretion and cyclic nucleotide content in isolated rat adrenal glomerulosa cells. Guanabenz inhibited aldosterone secretion stimulated by potassium, angiotensin II (AII), and adrenocorticotropic hormone (ACTH), exhibiting IC50 values of 35 microM, 43 microM, and 58 microM for stimulation by 10 mM K+, 1 nM AII, and 10 pM ACTH, respectively. Guanabenz did not affect the cGMP content of purified adrenal glomerulosa cells but inhibited ACTH stimulation of cAMP accumulation. Guanabenz inhibition of ACTH-induced cAMP may represent a mechanism for inhibition of aldosterone secretion, however, guanabenz also inhibited aldosterone secretion stimulated by the cAMP analog dibutyryl cAMP. The effect of guanabenz on the early and late pathways of steroidogenesis was tested in the isolated rat glomerulosa cells using 25-OH cholesterol and steroid precursors to aldosterone. Guanabenz inhibited the steroidogenic response to 25-OH cholesterol stimulation of aldosterone secretion but induced a much smaller inhibition of the steroidogenic response to exogenous pregnenolone, progesterone, and 11-deoxycorticosterone. These results suggested that guanabenz inhibited aldosterone secretion primarily through inhibition of the early component of the steroidogenic pathway prior to pregnenolone formation. The effects of guanabenz were not mimicked by other alpha-adrenergic ligands suggesting that these effects of guanabenz were not mediated through activation of alpha-adrenergic receptors.

The role of dopamine in the control of corticosteroid secretion and metabolism

The relation between aldosterone and its trophins is altered by electrolyte status and in some hypertensive conditions in man by a mechanism or mechanisms not understood. Dopamine has been suggested as the agent for the altered sensitivity of plasma aldosterone to angiotensin II based on the results of studies with dopamine itself, both in vivo and in vitro, and with pharmacological agonists and antagonists. The evidence derived from these studies is presented and discussed. Questionable specificity of the agents used makes interpretation difficult. Similarly, dopamine infusion rates used in man and animals have resulted in plasma concentrations far in excess of those found normally and these pharmacological concentrations have been shown to alter both the clearance rate of exogenous angiotensin II, and the pattern of steroid response to ACTH. Direct study of adrenal tissue has provided more promising results. The adrenal cortex possesses specific dopamine receptors and dopamine has been shown to modify aldosterone biosynthesis in vitro. Moreover, dopamine is present in adrenocortical tissue in concentrations in the range calculated to operate the receptors. However, there is, as yet, no evidence that dopamine concentrations change in a physiological meaningful way, for example, during changes in sodium status.