Cardiovascular toxicity and tissue proton T1 response to manganese injection in the dog and rabbit

Paramagnetic substances that shorten proton T1 relaxation time have promise as nuclear magnetic resonance (NMR) contrast agents. The cardiovascular toxicity and tissue T1 response to 0.01-0.1 mM/kg intravenous doses of MnCl2 in rabbits and dogs were studied. There were dose-dependent changes in cardiac electrophysiology and arterial blood pressure consistent with the calcium-blocking properties of manganous ion. There were also dose-dependent and organ-specific changes in tissue proton T1. The sensitivity of organ T1 was expressed as the dose of manganese required to shorten the normal T1 by 50%. Liver, kidney, and heart were most sensitive, while skeletal muscle and adipose tissue were insensitive. MnCl2 is an effective NMR contrast agent, but its toxicity may be excessive for clinical use.