Day-night variation in the in vitro contractility of aorta and mesenteric and renal arteries in transgenic hypertensive rats

TGR(mREN2)27 (TGR) rats develop severe hypertension and an inverted circadi an blood pressure profile with peak blood pressure in the daytime rest phas e. The present study investigated the in vitro responsiveness of different arteries of TGR rats during day and night. Twelve-week-old TGR rats and nor motensive Sprague-Dawley (SPRD) controls, synchronized to 12h light, 12h da rk (LD 12:12) (light 07:00-19:00), were killed at 09:00 (during rest) and 2 1:00 (during activity), and endothelium-dependent relaxation by acetylcholi ne and vascular contraction by angiotensin II were studied by measuring iso metric force in ring segments of abdominal aorta and mesenteric and renal a rteries. In SPRD rats, consistent day-night variation was found, with great er responses to angiotensin II during the daytime rest span. In TGR rats, b iological time-dependent differences were found in the renal vasculature, b ut not in the aorta and mesenteric artery. Relaxation of SPRD rat aorta and mesenteric artery by acetylcholine was greater at 09:00, whereas in TGR ra ts, day-night variation was absent (mesenteric artery) or inverted (aorta). In conclusion, based on the study of two time points, day-night variation in vascular contractility of aorta and mesenteric artery is blunted in TGR rats, whereas renal artery segments showed an unchanged day-night pattern c ompared to SPRD controls.