Proton relaxation enhancement in tissue due to ingested manganese chloride: time course and dose response in the rat

MnCl2, a potential NMR contrast agent, was force fed by cannula to 27 fasted rats in an attempt to establish the efficacy of this route of administration. The animals were sacrificed and the relaxation times (T1 and T2) of liver, spleen, kidney, heart, and skeletal muscle were determined in vitro. One group of rats was subject to a range of doses (8.3-333.3 mg/kg) and sacrificed at 90 minutes. Another group received a single large dose (500 mg/kg) with animals sacrificed at intervals from 15-225 minutes. The single large dose caused a rapid and prolonged reduction in liver T1 (-93% of normal) and to a lesser degree affected the other organs. The dose response data shows that liver T1 is also affected at significantly lower dosages than the other tissues tested. These results suggest the oral route as a possible alternative to IV Mn+2. Further studies with inorganic and organic manganese are indicated.