A cAMP-biosensor-based assay for measuring plasma arginine-vasopressin levels.

Arginine-vasopressin (AVP), a cyclic peptide hormone composed of nine amino acids, regulates water reabsorption by increasing intracellular cyclic adenosine monophosphate (cAMP) concentrations via the vasopressin V2 receptor (V2R). Plasma AVP is a valuable biomarker for the diagnosis of central diabetes insipidus (CDI) and is commonly measured using radioimmunoassay (RIA). However, RIA has several drawbacks, including a long hands-on time, complex procedures, and handling of radioisotopes with special equipment and facilities. In this study, we developed a bioassay to measure plasma AVP levels using HEK293 cells expressing an engineered V2R and a cAMP biosensor. To achieve high sensitivity, we screened V2R orthologs from 11 various mammalian species and found that the platypus V2R (pV2R) responded to AVP with approximately six-fold higher sensitivity than that observed by the human V2R. Furthermore, to reduce cross-reactivity with desmopressin (DDAVP), a V2R agonist used for CDI treatment, we introduced a previously described point mutation into pV2R, yielding an approximately 20-fold reduction of responsiveness to DDAVP while maintaining responsiveness to AVP. Finally, a comparison of plasma samples from 12 healthy individuals demonstrated a strong correlation (Pearson's correlation value: 0.90) between our bioassay and RIA. Overall, our assay offers a more rapid and convenient method for quantifying plasma AVP concentrations than existing techniques.

Cellular adaptation of the rat medullary thick ascending limb to chronic renal failure

Chronic renal failure (CRF) is accompanied by adaptive changes in renal and extrarrenal epithelial ionic transport. Fluid reabsorption in the thick ascending limb of Henle is increased and the capacity to lower the urine osmolality in water diuresis is preserved. To study the cellular mechanism of this adaptation, we measured intracellular cAMP in microdissected medullary thick ascending limb (mTAL) segments in rats with CRF. mTAL exhibited in CRF nephrons an increase of basal cAMP from 6.0 +/- 1.5 in controls to 47.0 + 10.3 fmol. mm-1 tubule in CRF (P < 0.05). Maximally stimulated cAMP levels (10(-3) M IBMX plus 10(-5) M Forskolin) were different from basal levels in controls (6.0 + 1.5 vs 63.1 +/- 18.8, P < 0.05) but not from basal levels in CRF (47.0 +/- 10.3 vs 63.0 +/- 16.0, P = N.S.). Preincubation with the adenylate cyclase inhibitor 2'5' -dideoxyadenosine (DDA) 10(-4) M produced no changes in cAMP in controls (93.7 +/- 10.3 percent of DDA untreated samples) whereas it decreased to 76.2 +/- 8.8 percent (24 percent inhibition) in CRF (P < 0.05). No differences between controls and CRF groups were found in basal and stimulated cAMP in red blood cells and distal colon. The data would suggest that the cAMP pathway is an intracellular signal for mTAL adaptation in epithelial transport and that the adenylate-cyclase system is specifically activated in CRF.

Fluoxetine action upon human T lymphocyte proliferation

The purpose of this study was to analyze the effect of fluoxetine upon human T lymphocyte proliferation, and to assess the early signals elicited after T cell triggering and cAMP formation. Blood samples from normal human volunteers were drawn from venipuncture and T cells were cultured in the presence or absence of Concanavalin A (Con A) and fluoxetine. Protein Kinase C (PKC) levels and cyclic adenosine monophosphate (cAMP) formation were also measured. Fluoxetine exerted dual effect, depending on the degree of lymphocyte activation: at mitogenic concentrations of Con A (2 mug/ml), we observed na inhibitory effect on cellular proliferation. This inhibitory effect involves PKC degradation and cAMP formation. On the other hand, when submitogenic Con A concentrations (1mug/ml) were used, fluoxetine stimulated the cellular response and increased PKC traslocation. The participation of extracellular calcium mobilization could be involved in these mechanisms. According to our results, fluoxetine seems to modulate calcium influx which, in turn, would influence PKC traslocation, thus modulating the immune response through a mechanism that could be involving cAMP participation.

Valoración radionuclídica in vitro de la concentración plasmática de AMP-cíclico en pacientes con infarto cardíaco / In vitro radionuclide assessment of plasma cyclic AMP concentration in patients with cardiac infarction

Se realizó la determinación de los valores de AMP-cíclico plasmático en 19 pacientes con el diagnóstico confirmado de infarto cardíaca agudo, en los cuales no existían antecedentes conocidos de trastornos endocrinos; el rango de edad fue de 36 a 80 años y ambos sexos, donde predomina el masculino. El estudio se realizó en el período de 21 días posteriores a la fecha de ingreso. El AMP-cíclico fue valorado en plasma por el método radionuclídico con reactivos de la firma Amersham y como marcador del nucleótido, el tritio (8 - H3 adenosin 3,5; fosfato cíclico). Los niveles de AMP-cíclico se encuentran aumentados durante los 21 días posteriores al infarto en el grupo estudiado. En la primera semana en siete casos el promedio fue de X + 29,40 + ou - 1,4 mol/I, lo que difiere significativamente con el control (P <0.005). En la segunda semana X + 37,7 + ou - 2,35 n mol/I (P <0.005) y en la tercera semana el promedio fue X + 27,50 + ou - 4,09 n mol/I, sin encontrarse diferencia (P > 0.05). Grupo control X + 22,50 + ou - 1,00 n mol/I. Se discuten estos resultados y los datos obtenidos fueron estadísticamente precesados