THE CENTRAL EFFECT OF L-CYSTEINE ON CARDIOVASCULAR-SYSTEM OF THE CONSCIOUS RAT

The hemodynamic effects of intracisternal injection of the nonessential amino acid L-cysteine were studied in conscious chronically instrumented rats. Injections of L-cysteine (0.05-0.2 M in artificial cerebrospinal fluid, 10 mu l) into the cisterna magna dose-relatedly elicited an increase in arterial pressure but a decrease in superior mesenteric blood how as measured by an electromagnetic flow probe. Injections of the excitatory amino acid transmitter L-glutamate at comparable doses caused much the same presser and vasoconstrictor effects as did L-cysteine. Prior I.V. injection of vasopressin V-1-receptor antagonist, (d(CH2)(5)(1), O-Me-Tyr(2), Arg(8))-vasopressin (10 mu g/kg), markedly attenuated the effects of L-glutamate but not of L-cysteine. Ganglionic blockade with chlorisondamine (5.0 mg/kg) failed to attenuate the effects of either amino acid, whereas an additional intravenous injection of vasopressin antagonist, completely abolished the effects. These results indicate that the circulatory effects of L-cysteine are probably due to autonomic nervous activation combined with vasopressin release, unlike those of L-glutamate which acts mainly through vasopressin release. L-Cysteine may contribute to central cardiovascular control, since it induces the marked circulatory effects comparable to or greater than those of L-glutamate.