The mechanism of the effect of K + on the steroidogenesis of rat zona glomerulosa cells of the adrenal cortex: role of cyclic AMP

The effects of various concentrations of extracellular K + (3.6 - 13 mM) on the steroid (corticosterone and aldosterone) and cyclic AMP outputs of capsular cells (95% zona glomerulosa) of the rat adrenal cortex were studied at different concentrations of extracellular Ca 2+ . Small amounts of EGTA (50 μM) were added to reduce the free Ca 2+ concentrations effectively to zero at the lowest possible total Ca 2+ concentration. At a total extracellular concentration of 2.5 mM Ca 2+ , in 27 experiments the mean values of the steroid and cAMP outputs showed a maximum at 8.4 mM K + . The increase in steroid and cAMP outputs at 5.9, 8.4 and 13 mM K + compared with that at 3.6 mM were highly significant ( p < 0.01). The overall correlation of either corticosterone or aldosterone with cAMP outputs was also highly significant and was even better from 3.6 to 8.4 mM K + . Lowering the effective free concentration of Ca 2+ to zero decreased the steroid and cAMP outputs significantly at all K + concentrations, and no output was then significantly higher than at 3.6 mM. With the pooled data on outputs at all total Ca 2+ (2.5, 0.5, 0.25, 0.10, 0.05 and 0.0 mM) and K + (3.6, 5.9, 8.4 and 13 mM) concentrations, the correlation of either steroid with cAMP outputs was highly significant (but again optimally from 3.6 to 8.4 mM K + ). Nifedipine (10 -6 to 10 -4 M) was added to the incubations with the aim of specifically inhibiting Ca 2+ influx at total extracellular Ca 2+ concentra­tions of 2.5, 1.25 and 0.25 mM and with the usual K + concentrations. The cAMP outputs were reduced at all K + concentrations above 3.6 mM K + . The effect was highly significant at 10 -4 M nifedipine and a total Ca 2+ of 1.25 mM, which with the incubation conditions used, corresponds to the free Ca 2+ concentrations in vivo . These results indicate that cAMP plays a significant role in the stimulation of steroid output by K + particularly between 3.6 and 8.4 mM K + . In this range of K + concentrations the stimulation of cAMP seems to be controlled by increases in Ca 2+ influx. The correlation of steroid and cAMP output at the higher K + concentra­tions (between 8.4 and 13 mM K) and at the various total Ca 2+ concentra­tions is less significant. Also, with all concentrations of added nifedipine there is an ‘anomalous’ increase in steroid output at 13 mM K + and at total Ca 2+ concentrations of 2.5 and 1.25 mM. However, at the same K + concentrations and at 0.25 mM Ca 2+ , nifedipine decreases steroid outputs. Our previous data, obtained after addition of maximally effective amounts of cAMP, indicated that there were also non-cAMP mechanisms involved in the stimulation of steroidogenesis by K + in z. g. cells. The present data confirm this conclusion, particularly at K + concentrations above 8.4 mM. They also indicate that at these higher K + concentrations, by non-cAMP mechanisms increasing intracellular Ca 2+ concentrations probably inhibit steroidogenesis. We conclude, however, that in the physiological range of K + concentra­tions, the role of cAMP in zona glomerulosa cells is at least comparable in importance to that of non-cAMP mechanisms.

1995 ◽  
Vol 145 (2) ◽  
pp. 283-289 ◽  
Author(s):  
J P Hinson ◽  
L A Cameron ◽  
S Kapas

Abstract Neuropeptide Y (NPY) has been identified in nerves supplying the adrenal cortex of several mammalian species, although its function in this tissue is unknown. The present studies, employing adrenocortical cells prepared by collagenase digestion, have shown that NPY, in the absence of other stimulants, has no effect on steroid secretion by the rat adrenal over a range of peptide concentrations (10−11 to 10 −6 mol/l). However, in the presence of physiological concentrations of ACTH, which are submaximal for the stimulation of aldosterone secretion, NPY (10−6 mol/l) significantly enhanced the secretion rate of aldosterone by rat zona glomerulosa cells in response to ACTH. This effect was specific to the rat zona glomerulosa as NPY had no effect on the response to ACTH in rat zona fasciculata cells. The effect of NPY appears to be biphasic, however, as NPY significantly attenuated the steroidogenic response to supramaximal ACTH concentrations: in rat zona glomerulosa cells the aldosterone response to 10 −8 mol ACTH/l was significantly inhibited by NPY. The effect of NPY on the ACTH response appeared to be mediated by changes in the cAMP response. NPY had no effect on the steroidogenic response to potassium ions (K+), but enhanced the response to angiotensin II. NPY (10 −6 mol/l) significantly stimulated inositol 1,4,5-trisphosphate (InsP3) production although this concentration of peptide had no effect on steroid secretion. The effects of NPY on InsP3 production were additive with those of angiotensin II. These results suggest that the role of NPY in the adrenal cortex may be to regulate the sensitivity of the zona glomerulosa to peptide stimulation. Journal of Endocrinology (1995) 145, 283–289


2016 ◽  
Vol 594 (20) ◽  
pp. 5851-5860 ◽  
Author(s):  
Paula Q. Barrett ◽  
Nick A. Guagliardo ◽  
Peter M. Klein ◽  
Changlong Hu ◽  
David T. Breault ◽  
...  

1991 ◽  
Vol 129 (3) ◽  
pp. 391-397 ◽  
Author(s):  
S. J. Purdy ◽  
B. J. Whitehouse ◽  
D. R. E. Abayasekara

ABSTRACT The actions of forskolin have been investigated to determine to what extent its effects on steroidogenesis in rat adrenal preparations are dependent on activation of adenylate cyclase. In zona glomerulosa preparations, stimulation of both aldosterone and corticosterone production was obtained at concentrations of forskolin between 1 and 10 μmol/l. The effects of 10 μmol forskolin/l were additive with those of low doses (1 pmol/l) of corticotrophin (ACTH), but not with those of high doses (1 nmol/l) of ACTH. In contrast, in zona fasciculata/reticularis cells, doses of forskolin up to 10 μmol/l produced no significant stimulation of corticosterone production either alone or in the presence of ACTH (1 pmol/l and 1 nmol/l). The response to 1 nmol ACTH/l was attenuated in the presence of forskolin (10 μmol/l) in both zona glomerulosa and zona fasciculata/reticularis cell preparations. Cyclic AMP production increased progressively with dose up to 100 μmol forskolin/l in zona glomerulosa cells, whereas corticosterone production was maximal between 10 and 30 μmol forskolin/l and decreased at 100 μmol forskolin/l. In zona fasciculata/reticularis cells, cyclic AMP production was also increased by forskolin (1 and 10 μmol/l). The stimulation of zona glomerulosa steroido-genesis by forskolin (1–10 μmol/l) and ACTH (1–100 pmol/l) were both reduced by the adenylate cyclase inhibitor, N6-phenylisopropyladenosine (100 μmol/l). The calcium channel inhibitor, nifedipine, only reduced the steroidogenic response to forskolin (3 μmol/l) at doses of 300 μmol/l whereas the response to 8·4 mmol K+/l was inhibited at 10 μmol nifedipine/1. Although there is some dissociation between the effects of forskolin on cyclic AMP and steroidogenesis, the results are generally consistent with the view that the effects of forskolin in rat zona glomerulosa cells are mainly dependent on activation of adenylate cyclase. This contrasts with the effects of forskolin in bovine fasciculata cells which are reported to be mediated by activation of voltage-regulated calcium channels. Journal of Endocrinology (1991) 129, 391–397


1974 ◽  
Vol 185 (1081) ◽  
pp. 375-407 ◽  

The densities of latex spheres and biological cells can be reliably determined from their sedimentation rate in an albumin gradient under unit gravitational force. The densities of zona glomerulosa and fasciculata cells of rat adrenals were found to be 1.072 ± 0.004 and 1.040 ± 0.001 respectively. Purified zona glomerulosa cells of rat adrenals can be prepared by gravitational sedimentation of dispersed cells from capsule strippings of the gland, which originally contain 3 to10% zona fasciculata contamination. Electron and phase microscopic examination of the sedimented glomerulosa cells and their steroidogenic response to ACTH and cyclic AMP indicate that they are reasonably free of contamination from zona fasciculata cells. Electron microscopic examination of the purified glomerulosa cells indicates that most of them are reasonably normal in structure. Their basal production of corticosterone is decreased after sedimentation. However, their maximal response of corticosterone output to serotonin and potassium and their response to all potassium concentrations is not significantly altered, indicating normal function for the cells producing steroids. Their maximal responses to ACTH, valine angiotensin II and cyclic AMP are decreased, but, at the doses used, steroidogenesis by the zona fasciculata contamination in the unfractionated preparation would be stimulated by these substances. Purified zona glomerulosa cells have about the same maximal response of corticosterone output (about twofold) to potassium, valine and isoleucine angiotensin II, serotonin and ACTH. The maximal response of the purified zona glomerulosa cells to cyclic AMP is similar to that elicited by valine and isoleucine angiotensin II, potassium, serotonin or ACTH. This indicates that if these stimuli act by increasing cyclic AMP output, then the maximal response of corticosterone output (about twofold) is defined by the limited response of the biosynthetic pathways to cyclic AMP.


1979 ◽  
Vol 237 (5) ◽  
pp. C200-C204 ◽  
Author(s):  
D. J. Stewart ◽  
J. Sax ◽  
R. Funk ◽  
A. K. Sen

Stimulation of salt galnd secretion in domestic ducks in vivo increased the cyclic GMP concentration of the tissue, but had no effect on cyclic AMP levels. Methacholine, which is known to stimulate sodium transport by the glands both in vivo and in vitro, stimulated ouabain-sensitive respiration in salt gland slices. Cyclic GMP stimulated ouabain-sensitive respiration to the same extent as methacholine. Guanylate cyclase stimulators, hydroxylamine and sodium azide, also stimulated ouabain-sensitive respiration. The stimulation of ouabain-sensitive respiration by methacholine was blocked either by atropine or by removal of calcium from the incubation medium. The stimulation of ouabain-sensitive respiration by cyclic GMP still occurred in the absence of calcium. The above observations seem to indicate that cyclic GMP acts as a tertiary link in the process of stimulus-secretion coupling in the tissue.


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