• Brain Gα-subunit proteins;
  • GPCR;
  • CNS;
  • cardiovascular function;
  • renal excretory function;
  • α2-adrenoceptor;
  • guanabenz

BACKGROUND AND PURPOSE Activation of brain α2-adrenoceptors in conscious rodents decreases heart rate (HR) and mean arterial blood pressure (MAP) and increases urine output and urinary sodium excretion. In vitro, α2-adrenoceptor stimulation activates Gαi(1–3), Gαo and Gαs-subunit protein-gated signal transduction pathways. Here we have investigated whether these same Gα-subunit protein-gated pathways mediate the cardiovascular and renal excretory responses to central α2-adrenoceptor activation in conscious Sprague-Dawley rats.

EXPERIMENTAL APPROACH Rats were pre-treated by intracerebroventricular injection (i.c.v.) with an oligodeoxynucleotide (ODN) targeted to a Gαi1, Gαi2, Gαi3, Gαo, Gαs or a scrambled (SCR) ODN sequence (25 µg, 24 h). On the day of study, the α2-adrenoceptor agonist guanabenz (50 µg) or saline vehicle, was injected i.c.v. into ODN-pre-treated conscious rats. MAP and HR were recorded, and urine was collected for 150 min.

KEY RESULTS In vehicle- and SCR ODN-pre-treated rats, i.c.v. guanabenz decreased MAP and HR, and produced marked diuretic and natriuretic responses. Selective ODN-mediated down-regulation of brain Gαi2-subunit proteins abolished the central guanabenz-induced hypotension and natriuresis. In contrast, following selective Gαs down-regulation, the characteristic hypotensive response to i.c.v. guanabenz was converted to an immediate increase in MAP. The bradycardic and diuretic responses to i.c.v. guanabenz were not blocked by pre-treatment with any ODN.

CONCLUSIONS AND IMPLICATIONS There was functional selectivity of Gαi2 and Gαs subunit protein-gated signal transduction pathways in mediating the hypotensive and natriuretic, but not bradycardic or diuretic, responses evoked by central α2-adrenoceptor activation in vivo.