35 male sprague-dawley rats , 18 months old , were injected subcutaneously with the catecholamine precursor , l-dihydroxyphenylalanine ( l-dopa ) ( 100 mg/kg , twice daily ) , or vehicle alone , for 8 days in an attempt to increase the amplitude of growth hormone ( gh ) pulses in old male rats .
C0007412
catecholamine
C0013023
dihydroxyphenylalanine