Central adrenergic receptor control of renal function in conscious hypertensive rats

The role of central nervous system alpha-adrenergic and beta-adrenergic receptors in the increased renal sympathetic nerve activity and antinatriuresis resulting from environmental stress (air stress) in conscious spontaneously hypertensive rats (SHR) was examined. Intracerebroventricular administration of the alpha 2-adrenergic receptor agonist clonidine (1, 5, and 15 micrograms) prevented the effects of air stress on renal sympathetic nerve activity and urinary sodium excretion. Clonidine, 5 and 15 micrograms, lowered baseline mean arterial pressure and renal sympathetic nerve activity and increased baseline urine flow rate and urinary sodium excretion; clonidine, 1 micrograms, had no effect on these baseline levels. Intravenous administration of 5 micrograms, but not 1 microgram of clonidine, abolished the renal responses to air stress. Intracerebroventricular administration of alpha 2-adrenergic receptor antagonists (yohimbine, rauwolscine) reversed the effects of clonidine, alpha 2-adrenergic receptor blockade alone, alpha 1-adrenergic receptor blockade (20 micrograms prazosin), or combined alpha 1-adrenergic and alpha 2-adrenergic receptor blockade (30 micrograms phenoxybenzamine) had no effect on the renal sympathetic nerve activity or antinatriuretic responses to air stress. Intracerebroventricular, but not intravenous, administration of the beta 2-adrenergic receptor antagonist ICI 118551 (30 micrograms) prevented the increased renal sympathetic nerve activity and antinatriuretic responses to air stress. In contrast, intracerebroventricular administration of the beta 1-adrenergic receptor antagonist atenolol (30 micrograms) had no effect on the renal responses to air stress. These results indicate that the increased renal sympathetic nerve activity and antinatriuresis resulting from environmental stress in conscious SHR can be prevented by pharmacological stimulation of central alpha 2-adrenergic receptors or by blockade of central beta 2-adrenergic receptors.