A radiometric analysis of nitric oxide synthase activity in Hymenolepis diminuta

The free radical nitric oxide (NO) is a neuronal messenger which is synthes ized from L-arginine and O-2 by nitric oxide synthase (NOS). In the synthes is NO and L-citrulline are produced in a stoichiometric 1 : 1 relation. The activity of NOS was analysed in homogenates of the rat tapeworm Hymenolepi s diminuta by measuring the formation of L-[H-3]citrulline after incubation with L-[H-3]arginine. The nature of NOS in H. diminuta was determined by s tudying the effect of 3 types of NOS inhibitors: (1) L-NAME, (2) EGTA, (3) 7-nitro-indazole. All inhibitors caused a significant but not complete redu ction in the formation of L-[H-3]citrulline. The results are discussed agai nst the background of nerve cells and fibres positive for NADPH-diaphorase staining in H. diminuta.