Inhibition of aldosterone secretion by atrial natriuretic peptide in chicken adrenocortical cells

Invited review: Adrenocortical function in avian and non-avian reptiles: Insights from dispersed adrenocortical cells

Herein we review our work involving dispersed adrenocortical cells from several lizard species: the Eastern Fence Lizard (Sceloporus undulatus), Yarrow's Spiny Lizard (Sceloporus jarrovii), Striped Plateau Lizard (Sceloporus virgatus) and the Yucatán Banded Gecko (Coleonyx elegans). Early work demonstrated changes in steroidogenic function of adrenocortical cells derived from adult S. undulatus associated with seasonal interactions with sex. However, new information suggests that both sexes operate within the same steroidogenic budget over season. The observed sex effect was further explored in orchiectomized and ovariectomized lizards, some supported with exogenous testosterone. Overall, a suppressive effect of testosterone was evident, especially in cells from C. elegans. Life stage added to this complex picture of adrenal steroidogenic function. This was evident when sexually mature and immature Sceloporus lizards were subjected to a nutritional stressor, cricket restriction/deprivation. There were divergent patterns of corticosterone, aldosterone, and progesterone responses and associated sensitivities of each to corticotropin (ACTH). Finally, we provide strong evidence that there are multiple, labile subpopulations of adrenocortical cells. We conclude that the rapid (days) remodeling of adrenocortical steroidogenic function through fluctuating cell subpopulations drives the circulating corticosteroid profile of Sceloporus lizard species. Interestingly, progesterone and aldosterone may be more important with corticosterone serving as essential supportive background. In the wild, the flux in adrenocortical cell subpopulations may be adversely susceptible to climate-change related disruptions in food sources and to xenobiotic/endocrine-disrupting chemicals. We urge further studies using native lizard species as bioindicators of local pollutants and as models to examine the broader eco-exposome.

Mineralocorticoid receptor antagonism confers cardioprotection in heart failure

The symptoms and signs constituting the congestive heart failure (CHF) syndrome have their pathophysiologic origins rooted in a salt-avid renal state mediated by effector hormones of the renin-angiotensin-aldosterone and adrenergic nervous systems. Controlled clinical trials, conducted over the past decade in patients having minimally to markedly severe symptomatic heart failure, have demonstrated the efficacy of a pharmacologic regimen that interferes with these hormones, including aldosterone receptor binding with either spironolactone or eplerenone. Potential pathophysiologic mechanisms, which have not hitherto been considered involved for the salutary responses and cardioprotection provided by these mineralocorticoid receptor antagonists, are reviewed herein. In particular, we focus on the less well-recognized impact of catecholamines and aldosterone on monovalent and divalent cation dyshomeostasis, which leads to hypokalemia, hypomagnesemia, ionized hypocalcemia with secondary hyperparathyroidism and hypozincemia. Attendant adverse cardiac consequences include a delay in myocardial repolarization with increased propensity for supraventricular and ventricular arrhythmias, and compromised antioxidant defenses with increased susceptibility to nonischemic cardiomyocyte necrosis.

Natriuretic peptides are negative modulators of adrenocortical cell function of the eastern fence lizard (Sceloporus undulatus)

Elucidation of the role of natriuretic peptides (NPs) in vertebrate adrenal steroidogenesis has been facilitated by the use of freshly dispersed adrenocortical cells. Our recent characterization of lizard adrenocortical cells [Carsia, R.V., John-Alder, H.B., 2003. Seasonal alterations in adrenocortical cell function associated with stress-responsiveness and sex in the Eastern Fence Lizard (Sceloporus undulatus). Horm. Behav. 43, 408-420] provided the opportunity to examine the influence of atrial natriuretic peptides (ANPs) and related NPs on reptilian adrenal steroidogenesis at the cellular level. In the present report, the action of NPs on lizard adrenal steroidogenesis was investigated using freshly dispersed adrenocortical cells derived from the Eastern Fence Lizard (Sceloporus undulatus). Basal production rates of aldosterone and corticosterone and maximal angiotensin II (ANG II)-induced production rates of these corticosteroids were inhibited with high efficacy (75-90%) by rat ANP at potencies of 0.4-0.7 nM. By contrast, rat ANP had no effect on maximal production rates of these corticosteroids in response to a maximal steroidogenic concentration of adrenocorticotropin (ACTH; 1 nM). However, rat ANP inhibited aldosterone and corticosterone production rates in response to a half-maximal steroidogenic concentration of ACTH (10 pM; approximately 50 pg/ml), albeit with less efficacy ( approximately 50%) and potency (approximately 6 nM) than for ANG II. Rat and eel ANP and rat and chicken brain natriuretic peptide (BNP) were equally efficacious at inhibiting maximal ANG II-induced aldosterone and corticosterone production but with different potencies. The order of inhibitory potency was rat ANP = chicken BNP > eel ANP > rat BNP. However, a specific peptide ligand for the NP clearance receptor was without effect. This study indicates that ANP and related NPs are efficacious inhibitors of lizard adrenal steroidogenesis by acting directly at the level of the adrenocortical cell.

Effects of nitric oxide on aldosterone synthesis and nitric oxide synthase activity in glomerulosa cells from bovine adrenal gland

This study investigated the effects of two NO-releasing agents, diethylenetriamine-NO (deta-NO) and sodium nitroprusside (SNP), on basal, ACTH-, and angiotensin II (AngII)-stimulated aldosterone production in glomerulosa cells from bovine adrenal gland. NO donors inhibited basal and ACTH- or AngII-stimulated aldosterone synthesis in a concentration-dependent manner. Deta-NO and SNP also provoked a concentration-dependent stimulation of cGMP production. However, cGMP was not responsible for the inhibition of aldosterone secretion, because a cGMP analog did not reproduce the inhibitory effect. Moreover, soluble guanylyl cyclase or protein kinase G inhibitors did not revert the inhibitory effect of NO on aldosterone production. NO donors did not modify ACTH-stimulated cAMP production or AngII-stimulated PLC activity stimulation, but inhibited 22[R] hydroxycholesterol- or pregnenolone-stimulated aldosteronogenesis. NO can be synthesized in bovine glomerulosa cells because nitrite production was determined and characterization of NOS activity was also performed. Nitrite accumulation was not modified in the presence of ACTH, AngII, or other factors used to induce iNOS. NOS activity that showed a Michaelis-Menten kinetic was NADPH- and calcium-dependent and was inhibited by two competitive inhibitors, L-NAME and L-NMMA. These results show that NO inhibits aldosterone production in glomerulosa cells acting on P450scc and other P450-dependent steroidogenic enzymes, and these cells display NOS activity suggesting that NO can be produced by constitutive NOS isozymes.

Nitric oxide potently inhibits the rate-limiting enzymatic step in steroidogenesis

This study tested the hypothesis that nitric oxide (NO) inhibits the rate-limiting catalytic step in steroidogenesis, cytochrome P450 cholesterol side-chain cleaving enzyme (CYP11A1), independent of soluble guanylyl cyclase (GC-S) stimulation. To assess CYP11A1 activity, pregnenolone levels were quantified in murine adrenocortical Y1 cells in the presence of the 3beta-hydroxy-Delta(5)-steroid dehydrogenase inhibitor, 2alpha-cyano-17beta-hydroxy-4,4',17alpha-trimethylandrost-5-ene-3-one. The NO donor, (Z)-1-[2-(2-aminoethyl-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate(deta nonoate), inhibited vasoactive intestinal peptide-, forskolin- and 22alpha-hydroxycholesterol (22HC)-facilitated pregnenolonogenesis in the absence of GC-S activation and in the presence of a GC-S inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). CYP11A1 was also heterologously expressed in monkey COS7 cells. Deta nonoate inhibited 22HC-facilitated activity of the over-expressed enzyme in the absence of GC-S activation and in the presence of ODQ. The NO-independent, GC-S agonist, 1-benzyl-3-(5'-hydroxymethyl-2'-furyl)indazole did not inhibit steroidogenesis. The IC(50) for effects of free NO on CYP11A1 was potent and in the 0.4-2 microM range. These results support the hypothesis that NO inhibits the rate-limiting enzyme in steroidogenesis independent of GC-S activation.

Evidence for the involvement of nitric oxide in the control of steroid secretion by the frog adrenal gland

Nitric oxide (NO) has been found to modulate the response of rat, bovine and human adrenocortical cells to corticotropic factors. The aim of the present study was to investigate the possible involvement of NO in the control of corticosteroid secretion in the frog Rana ridibunda. Histochemical studies using the NADPH-diaphorase reaction and immunohistochemical labeling with antibodies against NO synthase (NOS) revealed that NOS is exclusively expressed in chromaffin cells. The NO donor sodium nitroprusside (SNP) and the NO synthase inhibitor Nw-nitro-L-arginine (L-NO(2)Arg) did not modify the spontaneous production of corticosterone and aldosterone by perifused adrenal slices. Similarly, L-NO(2)Arg had no effect on the secretory responses induced by ACTH, angiotensin II (AII) and endothelin-1 (ET-1). In contrast, SNP significantly inhibited the stimulatory effects of ACTH, AII and ET-1 on corticosterone and aldosterone secretion. These data provide the first evidence for a modulatory role of NO on adrenocortical cell activity in amphibians.

Dietary protein restriction stress in the domestic chicken (Gallus gallus domesticus) induces remodeling of adrenal steroidogenic tissue that supports hyperfunction

The stress of dietary protein restriction in the immature domestic turkey (Meleagris gallopavo) induces adrenal steroidogenic hypofunction that is associated with an alteration in the proportion of density-dependent subpopulations of steroidogenic cells within the adrenal gland. In contrast, when imposed on immature chickens, this nutritional stressor induces long-term enhancement of adrenal steroidogenic function. However, whether this alteration in function is accompanied by a remodeling of chicken adrenal steroidogenic tissue as in the turkey is not known. To address this question, immature cockerels (2 weeks old) were fed established isocaloric synthetic diets containing either 20% (control) or 8% (restriction) soy protein for 4 weeks. Adrenal glands were processed for the isolation of defined, density-separable, adrenal steroidogenic cell subpopulations: three low-density adrenal steroidogenic cell subpopulations [LDAC-1 (rho = 1.0285-1.0430 g/ml), LDAC-2 (rho = 1. 0430-1.0485 g/ml), and LDAC-3 (rho = 1.0485-1.0500 g/ml)] and one high-density subpopulation [HDAC (rho = 1.0510-1.0840 g/ml)]. The steroidogenic function of these cell subpopulations was assessed. Protein restriction consistently, but differentially, enhanced maximal ACTH-induced corticosterone production by the subpopulations: values of LDAC-1, -2, and -3 and HDAC from protein restricted birds were, respectively, 116, 43, 33, and 20% greater than those of corresponding cell subpopulations from control birds. However, it had contrasting influences on maximal ACTH-induced aldosterone production by the cell subpopulations. Whereas the value of LDAC-1 from protein-restricted birds was 70% greater than that from control birds, the values for LDAC-2 and -3 were not different from those of the control, and the value for HDAC was 22% less than that of the control. Protein restriction also altered the cell subpopulation composition of the adrenal gland: compared to control, it increased the proportion of LDAC-1 by 46% and decreased the proportion of LDAC-3 and HDAC by 34 and 20%, respectively. Thus, dietary protein restriction increased the proportion of cells (i.e., LDAC-1) having the greatest enhancement in corticosteroid production. This pattern of remodeling of chicken adrenal steroidogenic tissue in response to dietary protein restriction contrasts sharply with the pattern that occurs in another galliform species, the domestic turkey.

Nitric oxide inhibits human aldosteronogenesis without guanylyl cyclase stimulation

Deta nonoate (deta-NO), a zwitterion nitric oxide (NO) donor, potently inhibited forskolin- and angiotensin II-stimulated aldosterone production in human adrenocortical H295R cells in a concentration-dependent manner (0.1-1000 microM). The half-maximal and maximal inhibition of forskolin-evoked aldosteronogenesis occurred at 0.6 and 100 microM deta-NO, respectively. The respective half-maximal and maximal deta-NO-mediated inhibition of angiotensin II-stimulated aldosterone generation occurred at 150 microM and 1 mM. In H295R cells, deta-NO and sodium nitroprusside did not stimulate cGMP production, and the soluble guanylyl cyclase inhibitor oxadiazoloquinoxalinone (10 microM) did not block deta-NO-mediated attenuation of aldosteronogenesis. 25-Hydroxycholesterol (10 microM)-facilitated aldosterone synthesis was also diminished with half-maximal and maximal inhibition occurring at 120 microM and 1 mM deta-NO, respectively. Taken together, these results demonstrate that NO inhibits human aldosteronogenesis without stimulating guanylyl cyclase in H295R cells.

Dietary protein restriction stress in the domestic turkey (Meleagris gallopavo) induces hypofunction and remodeling of adrenal steroidogenic tissue

In the present study, we investigated the influence of dietary protein restriction stress on adrenal steroidogenic function of the domestic turkey. Immature male turkeys (2 weeks old) were fed isocaloric synthetic diets containing either 28% (control) or 8% (restriction) soy protein for 4 weeks. Trunk plasma was processed for the determination of adrenocorticotropin (ACTH), corticosterone, aldosterone, and total 3, 5, 3'-triiodothyronine (T3). In addition, adrenal glands were processed for the isolation of defined, density-separable, adrenal steroidogenic cell subpopulations: three low-density adrenal steroidogenic cell subpopulations [LDAC-1 (rho = 1.0350-1.0490 g/ml). LDAC-2 (rho = 1.0490-1.0570 g/ml), and LDAC 3 (rho = 1.0370-1.0585 g/ml)] and a high-density subpopulation [HDAC (rho = 1.0590-1.0720 g/ml)], and the steroidogenic function of these cell subpopulations was evaluated. Protein restriction did not influence plasma ACTH However, it increased relative adrenal weight (mg/100 g body wt) (+37.8%) and plasma corticosterone (+317%). By contrast, it depressed plasma aldosterone (-51.2%). In addition, it caused a modest depression in plasma T3 (-25.9%). At the cellular level, protein restriction induced panhypofunction. Basal corticosteroid (aldosterone and corticosterone) production values of LDAC-1, -2, and -3 and HDAC from protein-restricted birds were, respectively, 42.9, 47.9, 30.8, and 57.5% less than those of corresponding cell subpopulations from control birds. In addition, maximal corticosteroid production values of LDAC-1, -2, and -3 and HDAC from protein-restricted birds, in response to ACTH, angiotensin II (AngII), and 25-hydroxycholesterol support, were depressed by 56.8, 55.1, 22.7, and 42.9%, respectively. Interestingly, LDAC-3 was relatively refractory to the influence of this stressor. By contrast, there was the lack of a concentration-dependent aldosterone response of LDAC-1 and -2 to AngII with protein restriction. This was not due to a failure in cell function since aldosterone responses of these cell subpopulations to ACTH and to 25-hydroxycholesterol support were apparent. In addition, the concentration of AngII receptors of cell subpopulations from protein-restricted turkeys, if anything, was greater than that of cell subpopulations from control turkeys. Protein restriction also altered the cell subpopulation composition of the adrenal gland: compared to control, it decreased the proportion of LDAC-2 by 42.3% and increased the proportion of LDAC-3 and HDAC by 68.7 and 302%, respectively. Thus, dietary protein restriction induces adrenal steroidogenic hypofunction in turkeys. In addition, the present study suggests that this nutritional stressor induces marked remodeling of the steroidogenic tissue in the turkey adrenal gland.

Effects of atrial natriuretic factor on the renin-aldosterone system: in vivo and in vitro studies

We investigated the effect of high physiological plasma levels of human varies; is directly proportional to atrial natriuretic factor (ANF) on renin and aldosterone secretion in normal sodium deplete men. In short term infusion studies (2 or 8 h duration), ANF plasma levels as observed after sodium loading (50-70 pg/ml) lowered basal renin (PRA) and aldosterone, but had only a marginal effect on angiotensin II-stimulated aldosterone secretion. Preliminary results of a study with long term infusion (6 days) of ANF during a period of dietary sodium depletion argue against a significant tonic inhibitory effect of ANF on the renin-aldosterone system in the preceding period of sodium repletion: the plasma aldosterone response to sodium depletion was similar with and without ANF infusion. The second messenger of ANF for the direct inhibition of aldosterone secretion from zona glomerulosa cells is still unknown. To test the hypothesis, that cGMP is the second messenger of ANF, we produced a rise in intracellular cGMP in rat and rabbit zona glomerulosa cells using the unspecific phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) and the more cGMP specific phosphodiesterase specific inhibitor M + B2948 (Zaprinast). Both inhibitors simulated the action of ANF in suppressing steroid secretion and elevating cGMP levels. The results are compatible with the view that cGMP is of importance as a second messenger for ANF in adrenal zona glomerulosa cells. Selective inhibition of phosphodiesterases in combination with endopeptidase inhibition may be an interesting principle to enhance the action of endogenous and exogenous ANF.