Important Aspects of Urine Sampling for Angiotensinogen Measurement: Time and Preservation Conditions in Healthy Individuals

Important Aspects of Urine Sampling for Angiotensinogen Measurement: Time and Preservation Conditions in Healthy Individuals

YOKO NISHIJIMA,¹ HIROYUKI KOBORI,^2,3 TADASHI SOFUE,¹ KUMIKO KAIFU,¹ KUMIKO MORIWAKI,¹ TAIGA HARA,¹ HIROFUMI HITOMI,² MASAKAZU KOHNO¹ and AKIRA NISHIYAMA²

¹Department of Cardio Renal and Cerebro Vascular Medicine, Faculty of Medicine, Kagawa University, Kagawa, Japan
²Department of Pharmacology, Faculty of Medicine, Kagawa University, Kagawa, Japan
³Departments of Medicine and of Physiology, and Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, LA, USA

Intrarenal renin-angiotensin system (RAS) plays an important role for the pathogenesis of renal injuries. Experimental studies have demonstrated that angiotensinogen levels in renal tissues reflect the activity of intrarenal RAS. However, dynamics of urinary angiotensinogen have not been investigated in detail. Therefore, we examined the preservation conditions of the measured values of urinary angiotensinogen concentrations and an ultradian rhythm of urinary angiotensinogen excretion in humans. Urine samples were collected from 24 healthy volunteers. The urinary concentrations of angiotensinogen were measured by using ELISA. Two different urine preservation conditions were examined. One cycle of freeze-and-thaw did not change the measured values of urinary angiotensinogen concentrations. Moreover, to keep urine samples at room temperature for 12 hours did not change the measured values of urinary angiotensinogen concentrations. Thus, preservation conditions do not change the measured values of urinary angiotensinogen concentrations. Regarding an ultradian rhythm, blood pressure and the urinary concentrations of angiotensinogen were measured at 09:00, 13:00, and 16:00. The averaged levels of blood pressure were similar over the time. The average of urinary angiotensinogen/creatinine (Cr) ratios was 8.73 ± 1.15 ng/mg Cr at 09:00, 9.53 ± 1.58 ng/mg Cr at 13:00, and 8.58 ± 1.26 ng/mg Cr at 16:00. The urinary angiotensinogen excretion in healthy volunteers does not have an ultradian change during the daytime (P = 0.482). This may be another indication that the intrarenal RAS is independent of the systemic RAS. We have to pay attention to these findings in handling urine samples for measurements of angiotensinogen.

keywords —— angiotensinogen; clinical study; preservation condition; the ultradian rhythm; urine

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Tohoku J. Exp. Med., 2012, 228, 333-339

Correspondence: Hiroyuki Kobori, M.D., Ph.D., Department of Pharmacology, Faculty of Medicine, Kagawa University, 1750-1 Ikenobe, Miki, Kita, Kagawa 761-0793, Japan.

e-mail: hkobori@kms.ac.jp