Central angiotensin alters blood pressure regulation during natural sleep.

Sino-aortic denervation (SAD) in rats alters completely the pattern of pressure changes during sleep: from unchanged to a rise in SS and from slight increase to a market drop in DS. Rats with mild renal hypertension (1K - 1C) behaved like normotensive rats, whereas in those rats with hypertension accompanied by overactivity of RAS, the pattern of MAP changes during sleep was similar to SAD rats. Since acute SAD also produced overactivity of RAS we studied SAD rats treated with Captopril or when RAS was normal at the chronic phase of SAD and we showed that impairment of baroreceptor function per se determines the typical alteration of BP during sleep. Intracerebral infusion of angiotensin modifies the pattern of pressure changes during sleep in a way similar to that produced by impaired baroreceptor function (SAD), probably by altering the central integration of the baroreceptor reflexes. Therefore the pattern of pressure changes during sleep seems to be a sensitive index of the functional integrity of the baroreceptor reflex.

Alteration in baroreceptor function in rats produces typical pressure changes during sleep.

We have shown previously that both sinoaortic denervation (SAD) and high renin hypertension in the rat produce a pronounced alteration in the pattern of pressure change during sleep, namely from unchanged to a rise in pressure during synchronized sleep (SS) and from a slight rise to a marked fall during desynchronized sleep (DS). Since acute SAD also produces overactivity of the renin-angiotensin system (RAS), we investigated if this overactivity is essential for the development of the alterations. In rats studied 1 day after SAD (138 +/- 1.0 mm Hg) the MAP rose during SS (+14 +/- 0.7 vs. +1.0 +/- 0.16 mm Hg in the controls) and fell during DS (-27.2 +/- 1.5 vs. 4.9 +/- 0.6 mm Hg in the controls). Captopril-treated rats, studied 1 day after SAD (89 +/- 1.2 mm Hg), also exhibited rise in pressure during SS (+12.3 +/- 0.6 mm Hg) and fall during DS (-12.8 +/- 1.7 mm Hg). Similar alterations were observed in rats studied 10 days after SAD (116 +/- 0.7 mm Hg) when RAS activity was normal (PRA: 1.3 +/- 0.2 vs. 10.4 +/- 2.7 ng AI/ml/h for SAD-1 day); the MAP rose during SS (+6.5 +/- 0.3 mm Hg) and fell during DS (-5.0 +/- 0.9 mm Hg). These data indicate that impairment of the baroreceptor function per se determines the typical alteration in the pattern of pressure change during sleep in the rat.