5-HT2 RECEPTORS ARE PARTIALLY INVOLVED IN THE RELATIONSHIP BETWEEN RENIN RELEASE AND DELTA-RELATIVE POWER

A strong relationship was previously described between the nocturnal o scillations of plasma renin activity (PRA) and the sleep cycles, with levels of PRA that increase during non rapid eye movement sleep and de crease during rapid eye movement sleep. This study was designed to det ermine whether ritanserin, a 5-hydroxytryptamine-2 (5-HT2) receptor an tagonist known to increase slow wave sleep both in human and in animal s and to decrease plasma renin activity response to serotonergic stimu lation in the rat, would uncouple this relationship. Eight subjects un derwent two randomized night studies after having received either plac ebo or 5 mg ritanserin administered in the morning, They were subjecte d to 8 hour polysomnography, including spectral analysis of the electr oencephalogram and to continuous blood sampling, Blood was sampled fro m 2300 to 700h every 10 min and plasma renin activity (PRA) was measur ed by radioimmunoassay of angiotensin I, The nocturnal profiles were a nalysed using the pulse detection program ULTRA. Ritanserin produced t he expected increase in slow wave sleep (SWS) duration (132+/-10 min u nder ritanserin vs 72+/-9 min under placebo; p<0.001) and a significan t increase in delta relative power (69+/-2% under ritanserin vs 60+/-2 % under placebo; p<0.01). The mean overnight PRA levels had a tendency to decrease under ritanserin (1.66+/-0.34 ngAngl/ml per h under ritan serin vs 1.48+/-0.31 ngAngl/ml per h under placebo; p=0.08). Individua l PRA oscillations were preserved and remained strongly associated wit h delta power oscillations, PRA peak levels were similar in both exper imental conditions, but the absolute amplitude of the oscillations was decreased under ritanserin (1.50+/-0.36 ngAngl/ml per h vs 1.04+/-0.1 4 ngAngl/ml per h; p<0.05). These results demonstrate that ritanserin, at a dose that augments delta power, only weakly affects renin releas e, which suggests that 5-HT2 receptors are only partially involved in the processes coupling renin release and SWS and that other mechanisms probably control the sleep-associated variations in PRA. (C) 1996, Ed itrice Kurtis