Evaluation of the sensitivity and specificity of (11)C-metomidate positron emission tomography (PET)-CT for lateralizing aldosterone secretion by Conn's adenomas.

CONTEXT: Identification of unilateral aldosterone-producing (Conn's) adenomas has traditionally required lateralization by the invasive and technically difficult procedure of adrenal vein sampling (AVS). (11)C-metomidate, a potent inhibitor of adrenal steroidogenic enzymes, is a positron emission tomography (PET) radiotracer that is selectively accumulated by Conn's adenomas. OBJECTIVE: The objective of the study was to compare the sensitivity and specificity of (11)C-metomidate PET-computed tomography (CT) against the current gold standard of AVS. DESIGN: The design of the study was within-patient comparison of diagnostic techniques. SETTING: The study was conducted at a single center-university teaching hospital. PATIENTS: Thirty-nine patients with primary hyperaldosteronism (PHA) and five with nonfunctioning adenomas (incidentalomas) participated in the study. INTERVENTION(S): The first six PHA patients were studied on three occasions to determine whether steroid pretreatment reduced (11)C-metomidate uptake by normal adrenal. Subsequent patients received dexamethasone for 3 d prior to injection of (11)C-metomidate 150-500 MBq. MAIN OUTCOME MEASURE(S): Maximum standardized uptake values (SUV(max)) over regions of interest determined from 35-45 min after injection were measured. RESULTS: Dexamethasone increased tumor to normal adrenal SUV(max) ratio by 25.6 ± 5.0% (P < 0.01). PET-CT visualized subcentimeter adenomas and distinguished hot from cold adenomas within a gland. In 25 patients with PHA and AVS lateralization to the side of an adenoma, SUV(max) over tumor (mean ± sem) of 21.7 ± 1.6 was greater than over normal adrenal, 13.8 ± 0.6 (P = 0.00003); this difference was absent in 10 patients without lateralization on AVS (P = 0.28) and in four of five incidentalomas. On receiver-operator characteristics analysis, an SUV(max) ratio of 1.25:1 provided a specificity of 87% [95% confidence interval (69, 104)] and sensitivity of 76% (59, 93); in tumors with SUV(max) greater than 17, the specificity rose to 100%. CONCLUSIONS: (11)C-metomidate PET-CT is a sensitive and specific noninvasive alternative to AVS in the management of PHA.

Investigating the function of an aldosterone response pathway in primary human adrenocortical cells obtained from Conn's and phaeochromocytoma patients.

The components of the classical renal aldosterone response pathway are expressed in human adrenocortical cells; however, studies in H295R cells have shown that pharmacological manipulation of this pathway has no effect on aldosterone production. We have characterised aldosterone and cortisol production by primary human adrenocortical cells and tested the hypothesis that a mineralocorticoid response pathway modulates aldosterone secretion. Aldosterone production by cells obtained from normal adrenal cortex was stimulated by angiotensin II, extracellular K(+) and a reduction in extracellular Na(+). Conn's adenoma cells, in comparison, produced higher aldosterone/cortisol ratios and were less responsive to angiotensin II and extracellular Na(+). Close coupling of aldosterone and cortisol secretion was observed in all adrenocortical cells. The mineralocorticoid receptor antagonists, eplerenone and potassium canrenoate, had no significant effect on aldosterone or cortisol production. In contrast, the glucocorticoid receptor antagonist, mifepristone, and the Na(+) uptake inhibitor, amiloride, had significant inhibitory effects on steroid production. Our current experiments do not support the hypothesis that an adrenal aldosterone-response pathway mediates the negative feedback of aldosterone on its own release, but do raise interest in the glucocorticoid receptor and downstream targets of the mineralocorticoid receptor as mediators of corticosteroid production.

Divergent cell signaling after short-term intensified endurance training in human skeletal muscle.

Endurance training represents one extreme in the continuum of skeletal muscle plasticity. The molecular signals elicited in response to acute and chronic exercise and the integration of multiple intracellular pathways are incompletely understood. We determined the effect of 10 days of intensified cycle training on signal transduction in nine inactive males in response to a 1-h acute bout of cycling at the same absolute workload (164 +/- 9 W). Muscle biopsies were taken at rest and immediately and 3 h after the acute exercise. The metabolic signaling pathways, including AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR), demonstrated divergent regulation by exercise after training. AMPK phosphorylation increased in response to exercise ( approximately 16-fold; P < 0.05), which was abrogated posttraining (P < 0.01). In contrast, mTOR phosphorylation increased in response to exercise ( approximately 2-fold; P < 0.01), which was augmented posttraining (P < 0.01) in the presence of increased mTOR expression (P < 0.05). Exercise elicited divergent effects on mitogen-activated protein kinase (MAPK) pathways after training, with exercise-induced extracellular signal-regulated kinase (ERK) 1/2 phosphorylation being abolished (P < 0.01) and p38 MAPK maintained. Finally, calmodulin kinase II (CaMKII) exercise-induced phosphorylation and activity were maintained (P < 0.01), despite increased expression ( approximately 2-fold; P < 0.05). In conclusion, 10 days of intensified endurance training attenuated AMPK, ERK1/2, and mTOR, but not CaMKII and p38 MAPK signaling, highlighting molecular pathways important for rapid functional adaptations and maintenance in response to intensified endurance exercise and training.

Aldosterone stimulates active Na+ transport in rabbit urinary bladder by both genomic and non-genomic processes.

The ability of aldosterone to stimulate Na+ transport in a range of epithelial tissues has been known for many years. Early work suggested that aldosterone had a delayed action operating by transcriptional up-regulation of proteins such as the epithelial Na+ channel. However more recent data has suggested that the hormone has a short-term non-genomic action. In this paper we investigate short and long-term actions of aldosterone on Na+ transport in the rabbit urinary bladder. We have shown that aldosterone stimulates epithelial Na+ channel activity, as measured by the amiloride-sensitive short-circuit current over a 3.75 h period and that this action is potentiated by cAMP. Using reverse transcriptase-polymerase chain reaction we have shown that aldosterone and forskolin in combination up-regulate mRNA synthesis for the beta- and gamma-subunits of the epithelial Na+ channel. Using Western blotting we have shown in the case of the beta-subunit that a corresponding increase in channel protein occurs. We have also demonstrated that aldosterone in the presence of inhibitors of phosphodiesterase can stimulate the short-circuit current across rabbit bladder epithelium over a 20 min period. An explanation for the synergistic interaction between aldosterone and cAMP is provided. We have shown that aldosterone can increase cAMP levels within urothelial cells over a 4 min period. We propose that this represents a non-genomic action of the steroid hormone.