Activation of neuronal endothelin B receptors mediates pressor response through alpha-1 adrenergic receptors.

Abnormalities in activity of the endothelin (ET) system have been widely reported in a number of cardiovascular disease states such as hypertension and heart failure. Although the vascular responses to ET are well established, the interaction between ET and other important modulators of blood pressure, such as the sympathetic nervous system, are less understood. Previous reports implicate ET signaling through ET type B (ET) receptors in increasing neuronal activity. Therefore, we hypothesized that activation of ET receptors on sympathetic nerves would increase blood pressure through an adrenergic-mediated mechanism. Thus, we used anesthetized ET-deficient rats, which only express functional ET receptors on adrenergic neurons, and genetic controls, which express functional ET receptors in vascular tissue and kidney epithelium. We determined the pressor response to the selective ET receptor agonist sarafotoxin c (S6c). Separate groups of rats were treated with the -adrenergic receptor antagonist prazosin or the -adrenergic receptor antagonist propranolol to elucidate the role of adrenergic signaling in mediating the blood pressure response. We observed a dose-dependent pressor response to S6c in ET-deficient rats that was reversed by prazosin treatment and augmented by propranolol. In genetic control rats, the effects of S6c on sympathetic neurons were mostly masked by the direct activity of ET receptor activation on the vasculature. Heart rate was mostly unaffected by S6c across all groups and treatments. These results suggest that ET activation on sympathetic neurons causes an increase in blood pressure mediated through -adrenergic receptor signaling.