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Biomedical subjects

M E Elliott

Publications and source records attributed to M E Elliott.

44 records · Page 3Linked to original sources
PubMed1983

Cholesteryl hemisuccinate alters membrane fluidity, angiotensin receptors, and responses in adrenal glomerulosa cells.

We examined the effects of cholesteryl hemisuccinate on membrane fluidity and angiotensin II (AII) actions in bovine adrenal glomerulosa cells. Incubating cells with cholesteryl hemisuccinate decreased membrane fluidity and markedly inhibited AII binding. The effect on binding was characterized by a decrease in AII receptor number. The effects of AII on phosphatidyl inositol turnover and calcium fluxes, proposed intermediaries of AII actions on aldosterone secretion, were less impaired than AII binding by cholesteryl hemisccinate. AII stimulation of aldosterone secretion was preserved despite the decrease in AII binding after cholesteryl hemisuccinate treatment. These results indicate that AII binding can be dissociated from its effects on aldosteronogenesis by a reagent that alters membrane fluidity.

Adrenal Cortex↗
PubMed1981

Angiotensin alters 45Ca2+ fluxes in bovine adrenal glomerulosa cells.

Angiotensin II stimulated 45Ca2+ release from bovine adrenal glomerulosa cells. It also decreased the influx of 45Ca2+ into glomerulosa cells. The effects were observed within 2 min of hormone addition and were blocked by Saralasin a competitive inhibitor of angiotensin. Des-Phe8-angiotensin II, a biologically inert analog, was inactive in this system. Angiotensin II also inhibited the influx of 133Ba2+ and 54Mn2+, whereas 51Cr6+ and 57Co2+ were unaffected. Alterations in 45Ca2+ fluxes were seen with concentrations of angiotensin that stimulate aldosterone biosynthesis in bovine glomerulosa cell preparations. These results suggest that calcium plays a key role in angiotensin-stimulated aldosteronogenesis.

Adrenal Cortex↗
PubMed1979

Angiotensin and bradykinin interactions with phospholipids.

Reversible interactions were demonstrated between some phospholipids and some polypeptides related to angiotensin and bradykinin. The extent of the interaction was dependent on the structures of the lipid and peptide. The naturally occurring compounds that interacted most avidly were cardiolipin and (des-Asp1)-angiotensins. The apparent dissociation constant of this complex in chloroform was 10(-5) M. The complex contained more than one cardiolipin molecule/molecule of peptide. Kinins interacted most strongly with lecithin. The phospholipids altered the chromatographic behavior of radioiodinated derivatives of the polypeptides, and solubilized radioactive and unlabeled polypeptides in chloroform. In aqueous media, cardiolipin suspensions preferentially bound (des-Asp1)-angiotensin II, and inhibited its binding by antibody. The interactions were sensitive to pH and cations in the aqueous phase, and were reversed by some reagents added to the organic phase. These interactions have direct implications for binding reactions of peptides in vitro, and may bear upon the actions of the hormones in vivo.

Angiotensin II↗
PubMedDate not supplied

Specificity and mechanism of fatty acid inhibition of aldosterone secretion.

We have shown that unesterified, unsaturated long-chain fatty acids inhibit angiotensin II (AII) binding to receptors in adrenal glomerulosa cells. In this report, we show that oleic and arachidonic acids are specific inhibitors of the AT1 subtype of angiotensin receptor, and exert no effect on receptors of the AT2 subtype. By contrast, decanoic acid is a weak inhibitor of the AT2 subtype only. Our previous work on a post-receptor locus of inhibition by fatty acids of aldosterone biosynthesis showed that the 18-oxidase step is uniquely sensitive. In brief, the first and last steps involved in angiotensin-stimulated aldosterone secretion are particularly sensitive to inhibition by fatty acids. These results suggest a specific role for unesterified fatty acids in regulation of salt and water metabolism.

Adrenal Medulla↗
PubMedDate not supplied

Aspects of angiotensin action in the adrenal. Key roles for calcium and phosphatidyl inositol.

The steps between exposure of bovine adrenal glomerulosa cells to angiotensin and the stimulated increase in aldosterone production were studied in two ways. Binding of angiotensin to receptors, and hormone effects on phosphatidyl inositol turnover, 45Ca2+ fluxes, and aldosterone production were measured directly. Other potential intermediate steps were investigated indirectly by use of inhibitors. Angiotensin slowed calcium influx and accelerated phosphatidyl inositol turnover in proportion to hormone dose. The effects correlated with receptor binding and aldosterone production. None of the inhibitors tested, except saralasin, inhibited angiotensin's effect on phosphatidyl inositol turnover. Altered calcium flux and stimulated aldosterone production were affected by the calmodulin inhibitor trifluoperazine and the intracellular calcium antagonist 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8). Several reagents did not affect angiotensin binding, its effect on phosphatidyl inositol, or 45Ca2+ flux, but severely inhibited steroidogenesis. These included the phospholipase A2 inhibitor mepacrine, the protein synthesis inhibitor cycloheximide, and the Na+/k+-ATPase inhibitor ouabain. Colchicine had very little effect on the processes we measured, suggesting that microtubules play no role in angiotensin action in the adrenal. Based o these observations, we propose that angiotensin II affects the adrenal glomerulosa cell by first interacting with receptors, then increasing phosphatidyl inositol turnover, then altering cellular calcium distribution. Step distal to altered calcium distribution that contribute to increased steroid output include altered phospholipid metabolism, protein synthesis, and Na/k metabolism.

Adrenal Cortex↗