Enhanced presynaptic beta 2-adrenoceptor-mediated facilitation of the pressor responses in the prehypertensive SHR

The effects of beta-adrenoceptor agonists and antagonists on pressor responses of the isolated perfused mesenteric arteries to periarterial nerve stimulation (PNS) in the prehypertensive 4-week-old spontaneously hypertensive rat (SHR) and the age-matched Wistar Kyoto rats (WKY) were examined. The systolic arterial blood pressure (SBP) of SHR and WKY were not significantly different at this young age. The pressor responses of the mesenteric arteries to PNS at various stimulating frequencies, however, were significantly greater in SHR than WKY. Cocaine, isoproterenol (a nonselective beta-adrenoceptor agonist) and salbutamol (a selective beta 2-adrenoceptor agonist) significantly enhanced the pressor responses to PNS in SHR and WKY, with significantly greater increase in SHR than WKY. The nonselective beta-adrenoceptor antagonist (propranolol) and the selective beta 2-adrenoceptor antagonist (ICI 118,551) significantly inhibited the pressor response to PNS in SHR without affecting that in WKY. The selective beta 1-adrenoceptor antagonist (practolol) was without effect on the PNS-induced pressor responses in both SHR and WKY. These results demonstrate that the presynaptic beta 2-adrenoceptor-mediated facilitation of neurogenic pressor response in mesenteric arteries already are enhanced in 4-week-old SHR. In view of the higher concentration of circulating epinephrine (Epi) in prehypertensive SHR, the enhanced facilitatory modulation via presynaptic beta 2-adrenoceptors in prehypertensive SHR may be involved in development of hypertension.