Baroreceptor modulation of regional haemodynamic responses to acute stress in rat

We examined the effects of chronic sinoaortic denervation (SAD) on regional haemodynamic responses to acute environmental stress in rats. In conscious male intact (n = 12) and SAD (2 weeks before study, n = 7) rats, arterial pressure and blood flow velocities (pulsed Doppler probes) in the subdiaphragmatic aorta, superior mesenteric artery and distal aorta (hindquarters) were simultaneously recorded. In response to air jet stress, intact rats showed modest increases in arterial pressure that were accompanied by vasoconstriction in the mesentery and vasodilatation in the hindquarters. These regional haemodynamic changes were almost balanced, as indicated by the lack of change in the subdiaphragmatic aortic conductance. SAD markedly enhanced the pressor and mesenteric vasoconstrictor responses and blunted the hindquarters vasodilatation. After acute beta-adrenoceptor blockade with propranolol, the stress-induced hindquarters vasodilatation was strongly reduced in the intact rats and was reversed into vasoconstriction in the SAD rats. These results point to an opposing interaction between centrally-induced sympathoexcitation and arterial baroreceptor reflex activation during stress. This probably favours the hyperaemic response in the skeletal muscles at a lower metabolic cost.