Biodistribution of ^99mTc-creatinine in rats with ablation nephropathy

Excerpt

Creatinine is the anhydride of creatine and is formed by non-enzymatic dehydration of creatine phosphate in muscle [1]. It is not protein-bound in plasma, has a small molecular weight, and is totally cleared by the glomeruli. In addition, it is also cleared by the gastrointestinal system to a smaller extent [2]. Since the daily production and renal excretion of creatinine is constant in healthy mammals, its serum level is fairly stable [3]. Thus, serum creatinine remains the most widely used laboratory test for estimation of renal function both in asymptomatic persons and in patients suspected of having renal disease [2]. Serum creatinine must be interpreted in light of the clinical information such as age, gender, weight, stability of renal function, muscle mass, and degree of catabolism. Serum creatinine concentration rises when more than 50% of renal function has been lost [2]. Although creatinine, as urea, is not generally considered to be an important uremic toxin, it has been shown experimentally that they are both toxic in acutely uremic rats [4]. Moreover, creatinine is one of the guanidine compounds contributing to uremic encephalopathy. The level of guanidine compounds including creatinine increases greatly in serum, cerebrospinal fluid, and brain of uremic patients. Uremic guanidine compounds have excitatory effects on the central nervous system [5]. A radioactive labeled form of creatinine has been used in the past to examine creatinine exchange between mother, fetus and amniotic fluid in rhesus monkeys [6]. However, its distribution at various tissues and the factors affecting this biodistribution has yet not been studied in detail by using radiolabeled creatinine. …