RESUMEN
Previous studies have shown that neural stimulation of brown adipose tissue (BAT) reorganizes the expression and activity of signaling proteins in the beta-adrenergic adenylyl cyclase pathway. Cold stress increases neural stimulation of BAT and increases alpha1-adrenergic receptor number; however, the alpha1 receptor subtype involved and the mechanism of up-regulation by cold stress have not been determined. Using reverse transcription/polymerase chain reaction analysis and nuclease protection assay, BAT was demonstrated to express mRNAs encoding alpha1a and alpha1d, but not alpha1b, receptors. Parallel pharmacologic studies of BAT membranes and recombinant alpha1a and alpha1d receptors expressed in COS-7 cells demonstrated that alpha1a receptors predominate in BAT. Exposure of rats to 4 degrees for 4 days increased alpha1a receptors and mRNA in BAT but did not alter expression of alpha1d receptors or mRNA. The induction of alpha1a receptor and mRNA level by cold stress was prevented by selective surgical denervation of BAT. Furthermore, alpha1a receptor and mRNA expression could be induced in warm-adapted rats by infusions of the selective beta3-adrenergic receptor agonist CL 316,243. These data indicate that neural activation of beta3-adrenergic receptors is an important determinant of alpha1a adrenergic receptor expression in BAT.
Asunto(s)
Tejido Adiposo Pardo/inervación , Tejido Adiposo Pardo/ultraestructura , Agonistas Adrenérgicos beta/farmacología , ARN Mensajero/metabolismo , Receptores Adrenérgicos alfa 1/metabolismo , Receptores Adrenérgicos beta/fisiología , Tetralonas , Tejido Adiposo Pardo/efectos de los fármacos , Antagonistas Adrenérgicos alfa/metabolismo , Antagonistas Adrenérgicos alfa/farmacología , Animales , Células COS/ultraestructura , Corteza Cerebral/metabolismo , ADN Complementario/genética , ADN Complementario/metabolismo , Dioxoles/farmacología , Estimulación Eléctrica , Radioisótopos de Yodo , Masculino , Fenetilaminas/metabolismo , Fenetilaminas/farmacología , Reacción en Cadena de la Polimerasa , ARN Mensajero/genética , Ensayo de Unión Radioligante , Ratas , Ratas Sprague-Dawley , Receptores Adrenérgicos alfa 1/clasificación , Receptores Adrenérgicos beta 3 , Sistema Nervioso Simpático/fisiología , Regulación hacia Arriba/fisiologíaRESUMEN
The developmental expression of the alpha-subunit of Go was examined in neuronal cultures derived from rat mesencephalon (MES) and hypothalamus (HYP). These cultures were essentially free of contaminating glia and were maintained as a stable population for periods up to 3 weeks. Immunoblotting utilizing specific antisera against Go indicated that in neurons from both brain regions, membrane concentrations of Go increased dramatically during the first 2 weeks in vitro. Thereafter, increases in the amount of Go per neuron kept pace with increasing process (axons and dendrites) formation. Multiple forms of immunoreactive Go were detected in MES and HYP neurons, and the proportions of these forms changed between 4 and 14 days in culture. Finally, increasing neuron density significantly increased membrane levels of Go in MES but not HYP cultures.