title: Cardiovascular Responses to Tonic Pain in REM Sleep-Deprived Rats: Role of Melatonin and Beta Endorphin.
abstract: OBJECTIVE
  Chronic pain is associated with increased incidence of hypertension. Sleep deprivation, common in patients with chronic pain, is associated with increased blood pressure and heart rate. This study was designed to determine whether sleep deprivation induces increased cardiovascular responses to pain. In addition; we examined the role of melatonin and endorphins in mediating these responses.
  
  
  METHODS
  The study was conducted in Sprague-Dawely rats divided into a control group (n=8) and Rapid Eye Moment sleep deprived (REMSD) group (n=8). REM sleep deprivation was done for three days using the inverted flowerpot technique. Systolic BP and HR were recorded at baseline as well as 5, 10 and 30 minutes after intra-plantar formalin injection. In addition, serum melatonin and endorphin levels were determined.
  
  
  RESULTS
  Under basal conditions, BP and HR and following acute pain (1(st) phase of formalin injection) were comparable with non-sleep deprived (non-SD) state. In contrast, the REMSD rats showed significantly greater increases in HR and BP during the 2(nd) phase of formalin pain as compared to non-SD state. These changes were associated with significant reductions in serum melatonin and endorphin levels in REMSD rats.
  
  
  CONCLUSIONS
  These data indicate that exaggerated blood pressure and HR responsiveness to pain in sleep deprivation could be mediated through reductions in melatonin and endorphin.
authors: Department of Physiology, College of Medicine and Medical Sciences, Arabian Gulf University, P.O. Box 22979, Manama, Bahrain.
authors: Salah
authors: S
authors: Kassab
authors: Usha
authors: U
authors: Sachdeva
authors: Nagalla
authors: N
authors: Das
authors: Tarik
authors: T
authors: Al-Shaibani
authors: Usha
authors: U
authors: Nayar