Blood pressure and sleep in the rat in normotension and in neurogenic hypertension.

1. Blood pressure was recorded in normotensive rats (114 +/- 2 mmHg) and in those made hypertensive by baroreceptor denervation (135 +/- 4 mmHg) during natural sleep. The different states of the wakefulness-sleep cycle were identified by analysis of the frontal electrocorticogram, the cervical electromyogram and by behavioural changes. 2. During synchronized sleep the arterial pressure in the control animals usually remained unchanged as compared to values prevailing when the rats were awake and quiet. The blood pressure usually attained higher levels in the sino-aortically denervated rats during this state. 3. Coincidently with the short episodes of electrocortical desynchronization of the synchronized sleep the blood pressure exhibited rapid oscillations. These fluctuations were greater in the rats with neurogenic hypertension where there were large pressure drops. 4. During desynchronized (REM) sleep arterial pressure underwent marked oscillations. While in the control rats the pressure usually rose, the baroreceptor-denervated rats showed a severe reduction in pressure. Arterial pressure in denervated animals became lower than that of the control rats, 106 +/- 2 and 121 +/- 2 mmHg, respectively. 5. We interpret these results to mean that in the rat alterations in the sensitivity of the baroreceptor reflex could be an important factor in preventing the arterial pressure from rising to hypertensive levels during syndhronized sleep and from dropping to low values during desynchronized (REM) sleep.