Central Beta-Adrenergic Receptors Mediate Renal Nerve Activity During Stress In Conscious Spontaneously Hypertensive Rats

The effects of intracerebroventricular (i.c.v.) administration of beta-adrenergic receptor antagonists (d,l-propranolol or timolol, 30 micrograms in 2 microL of isotonic saline) on the increased renal sympathetic nerve activity and decreased urinary sodium excretion (UNaV) responses to stressful environmental stimulation (air jet to head) in conscious spontaneously hypertensive rats (SHR) were examined. Before i.c.v. d,l-propranolol or timolol, air stress increased renal activity (68% from 10.6 +/- 2.1 and 63% from 8.2 +/- 0.9 integrator resets/min respectively). In contrast, after i.c.v. d,l-propranolol or timolol in the same conscious SHR, air stress had no effect on renal sympathetic nerve activity (+7% from 8.1 +/- 1.7 and +7% from 5.5 +/- 1.0 integrator resets/min respectively). Air stress decreased UNaV in conscious SHR given i.c.v. saline vehicle (25% from 2.8 +/- 0.5 microEq/min/100 g body weight), but had no effect on effective renal plasma flow or glomerular filtration rate. In contrast, after i.c.v. d,l-propranolol or timolol, air stress had no effect on UNaV (0% from 2.8 +/- 0.5 and +9% from 3.3 +/- 0.3 microEq/min/100 g body weight respectively). Mean arterial pressure increased similarly during air stress with i.c.v. saline-vehicle or beta-adrenergic receptor antagonists. Intravenous administration of the same doses of d,l-propranolol or timolol did not prevent the increased renal sympathetic nerve activity or decreased UNaV responses resulting from air stress. These results suggest that central nervous system beta-adrenergic receptors mediate the increased renal sympathetic nerve activity and decreased UNaV responses resulting from stressful environmental stimulation in conscious SHR.