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The endothelial nitric oxide synthase (eNOS) is involved in the regulation of vascular tone and cardiac functions influencing the haemodynamics. Therefore, eNOS deficient knockout mice (eNOS−/−) have been studied in comparison to the wildtype C57BL mice. No data are available for these knock-out animals regarding the 24-h profiles in blood pressure and heart rate. We investigated by radiotelemetry (radiotelemetric probe: TA11PA-C40; DataSciences, Minnesota, USA) the 24-h profiles in systolic (SBP), diastolic blood pressure (DBP), HR and motor activity (MA) in 4 eNOS−/− and in 5 wild-type mice under a light:dark schedule of 12h:12h. Data collection started 5 weeks after transmitter implantation, data from 1 week were analysed. The results showed that eNOS−/− mice had a significant higher SBP/DBP (mmHg) than the wildtype with unchanged day:night pattern (higher BP during night, activity period). HR (beats/min) was greatly decreased in eNOS−/− mice compared to the wildtype, but interestingly displayed no circadian rhythm but stayed constant within 24 hours, MA (counts/15min) rhythm was unchanged with higher activity during the night, indicating a normal night-active animal. (See Table) 24h-Mean Day Mean Night Mean N-D-Difference SBP eNOS−/− 136.6 ± 13.0* 127.9 ± 10.8* 145.3 ± 16.6* 17.5 ± 10.3 (mmHg) C57BL 114.0 ± 4.3 109.2 ± 5.8 118.7 ± 3.1 9.5 ± 2.2 DBP eNOS−/− 115.0 ± 10.0* 107.5 ± 8.2* 122.4 ± 12.6* 15.0 ± 7.4 (mmHg) C57BL 89.3 ± 5.9 84.0 ± 7.7 94.6 ± 4.3 10.6 ± 1.7 HR eNOS−/− 386.4 ± 71.9* 386.4 ± 64.5* 386.0 ± 79.5* −0.7 ± 16.8 (b/15min) C57BL 519.8 ± 18.1 483.3 ± 18.4 556.4 ± 21.2 73.1 ± 23.3 Means ± SD, eNOS vs C57BL * p < 0.05. In conclusion, the genetic deletion of the eNOS lead to higher a BP and a lower HR. While the circadian rhythm in BP was unchanged, the rhythm in HR was abolished. This could be due to different activation of the eNOS in the endothelium (sheer stress, acetylcholine-receptor) and cardiomyocytes (b3-adrenoceptor) as well as due to a modulation of the baroreceptor reflex.

P-127 Means ± SD, eNOS vs C57BL;*>p < 0.05. Key Words: eNOS Knock-Out Mice, Blood Pressure and Heart Rate, Circadian Rhythms