K. Witte et al., EFFECTS OF SCN LESIONS ON CIRCADIAN BLOOD-PRESSURE RHYTHM - IN NORMOTENSIVE AND TRANSGENIC HYPERTENSIVE RATS, Chronobiology international, 15(2), 1998, pp. 135-145
Transgenic hypertensive TGR(mREN2)27 (TGR) rats, carrying an additiona
l mouse renin gene, have been found to show inverse circadian blood pr
essure profiles compared to normotensive Sprague-Dawley rats. In order
to evaluate the contributions of the suprachiasmatic nucleus (SCN) an
d the neurohormone melatonin to cardiovascular circadian regulation in
TGR(mREN2)27 rats and Sprague-Dawley (SPRD) controls, we investigated
the effects of melatonin agonist and antagonist treatment in SCN-lesi
oned and nonlesioned rats, which were kept under conditions of alterna
ting light and darkness (LD). After destruction of the SCN, circadian
rhythmicity in blood pressure, heart rate (HR), and motor activity (MA
) was almost abolished in rats of both strains. One week of treatment
with a synthetic melatonin agonist S-21634 was not able to restore cir
cadian variation in the parameters monitored. In nonlesioned TGR(mREN2
)27 rats and Sprague-Dawley control rats, the melatonin antagonist S-2
2365 had no suppressive effect on LD-synchronized circadian rhythmicit
y, indicating that LD itself may have a stronger influence on the SCN
than endogenous melatonin.