SST and type 2 diabetes mellitus: The expression of 5-HT1DR had a negative correlation with somatostatin (SST) and SST receptors (SSTR) 1–5, whereas the expression of 5-HT2AR did not have any correlation with either SST or any of the SSTRs; this suggests that increased expression of HT1DR in human islet cells, as observed in T2DM islet cells, leads to decreased expression of SST and its receptors (Figure 4).