The Pharmacology of Radioprotective Chemicals: On Some of the Effects of Beta-Mercaptoethylamine (MEA) and Cystamine in the Rat

Abstract

A study of the effects of MEA (125 mg/kg, intraperitoneally) and cystamine (100 mg/kg, intra-peritoneally) on arterial blood pressure, oxygen content and capacity, hemoglobin concentration and hematocrit was made to determine if the factors of hypotension and circulatory hypoxia might be common physiological factors relating to the radioprotective potential of the agents. The time course of blood sulfhydryl increase caused by these compounds was studied. Cystamine injection caused an immediate, severe, prolonged hypotension (105-73 mm Hg - duration 3 hours) in the rat while MEA caused an immediate small (9mm Hg) fall in arterial pressure. Control pressure was reached in MEA-treated rats in 10 minutes. Oxygen content in arterial and venous blood increased over the first hour after MEA injection. Hematocrits and hemoglobin values also increased. Blood oxygen saturation remained unchanged. Arterial oxygen content increased when cystamine was injected (17.8 -28.5 vol %), however there was a concommitant rise of arterial hemoglobin, resulting in little or no change in arterial blood oxygen saturation. Oxygen content of venous blood decreased (12.7 to 4.4 vol %) in 60 minutes. This was accompanied by hemoconcentration. Oxygen saturation fell to very low levels as early as 10 minutes post-cystamine treatment. MEA caused a prompt increase in SH levels (control 7 mg/ 100 ml to 16 mg/100 ml) at 10 minutes. Levels approached controls at 60 minutes. Cystamine caused a slower increase in SH, (control 6.9 mg/100 ml to 13 mg/100 ml) peak values occurring at 60 minutes. These levels were increased for more than 180 minutes. It is concluded that, while hypotension and blood hypoxia may be beneficial during cystamine-induced radioprotection, they are not present or necessary for MEA-induced protection.