Effects of microinjection of melatonin and its receptor antagonists into anterior hypothalamic area on blood pressure and heart rate in rats.
OBJECTIVE
To examine the effects of microinjection of melatonin and its receptor antagonists into the anterior hypothalamic area (AHA) on blood pressure (BP) and heart rate (HR) in normotensive and stress-induced hypertensive rats.


METHODS
Melatonin and its receptor antagonists were microinjected into the AHA, then BP, mean arterial pressure (MAP), and HR were synchronously recorded.


RESULTS
Microinjection of melatonin produced a fall in MAP. Prazosin, an antagonist of melatonin ML2 receptor, could not antagonize the depressive response induced by melatonin. While luzindole, a competitive antagonist of melatonin ML1 receptor, was able to almost completely prevented the depressive response induced by injection of melatonin.


CONCLUSIONS
Melatonin acts as a hypotensive factor and the effects are mainly due to activation of ML1 receptors in rat brain, and the AHA may be one of the important central areas where melatonin can exert modulatory effects on BP and HR.
Ding
C N
CN
Department of Physiology, Medical Center of Fudan University, Shanghai 200032, China.
Cao
Y X
YX
Zhou
L
L
Zhu
D N
DN
Shen
Z Y
ZY
Fei
M Y
MY
Yu
P
P
D000818:Animals; D007025:Anterior Hypothalamic Nucleus / Q000187:drug effects* / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D008845:Microinjections; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000378:metabolism; D044094:Receptors, Melatonin; D014363:Tryptamines / Q000494:pharmacology
D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin; D014363:Tryptamines; C057154:luzindole; D008550:Melatonin; D011224:Prazosin