Effect of salmon calcitonin on the lethality of quinolinic acid, an excitatory amino acid

The effect of salmon calcitonin (SCT) on the lethality of quinolinic acid (QA), an endogenous excitatory amino acid, was investigated in relation to the excitatory amino acid receptor/ion channel complex. SCT increased the LD50 value of QA in a bell-shaped fashion, but the difference was not significant. The non competitive N-methyl-D-aspartate (NMDA) receptor antagonists MK-801 and phencyclidine (PCP) inhibited QA lethality dose- dependently. SCT potentiated the inhibitory effects of these antagonists. The competitive and glycine site antagonists 3-((±)-2-carboxypiperazin-4- yl)propyl-1-phosphonic acid (CPP) and 7-chlorokynurenic acid (7C1K), respectively, inhibited QA lethality in a dose-dependent fashion. SCT did not potentiate the effect of either drug. These results suggest that SCT inhibits NMDA receptors by interacting with Ca ion channel.