GPT and Obesity: Furthermore, a recent study reported that in the visceral adipose tissue of obese humans, the expression level of both serotonin receptors, 5-HTR2a and 5-HTR2b, was increased and positively correlated with BMI, alanine transaminase (ALT), and aspartate transaminase (AST) levels, suggesting a potential role for 5-HT signaling in human obesity (21).