Hypnotizability is associated with a few physiological characteristics also in the
normal awake state. Differences in flow-mediated dilation (FMD) have been observed
in subjects with high (Highs) or low (Lows) hypnotizability during nociceptive stimulation.
FMD is largely due to the nitric oxide (NO) produced by vascular endothelium through
the activity of NO synthase (eNOS). Endothelial NOS is encoded by the NOS3 locus.
Aim of this pilot study was to investigate the association between genetic polymorphisms
of NOS3 involved in NO blood levels and hypnotizability. Nine single nucleotide polymorphisms
(SNPs) of the NOS3 gene were analyzed in the DNA of 24 Highs, 22 Lows, and 61 newborns.
Two SNPs, rs1800783 (-1474 T/A) and rs2070744 (-786 T/C), located in the upstream
and promoter region of the gene, respectively, showed significant differences between
Highs and Lows in allele frequency. Haplotype analysis showed that the newborns were
in linkage equilibrium for these SNPs, whereas both Highs and Lows showed linkage
disequilibrium. The A-C haplotype (associated with lower NO availability in the general
population) was more frequent in Highs, and the T-T haplotype was more frequent in
Lows. Thus, the lower FMD reduction observed in Highs during nociceptive stimulation,
which is indicative of higher NO availability, should be due to greater efficacy of
shear stress-related transcriptional factors and/or to lower effects of NOS inhibitory
controls. A consequent theoretical proposal concerns the possible role of NO in the
brain vessels where, in stimulation conditions, NO diffusion to the extracellular
compartment might be involved in hypnotic responding.