HPA Axis Responsiveness Associates with Central Serotonin Transporter Availability in Human Obesity and Non-Obesity...

Alterations of hypothalamic-pituitary-adrenal (HPA) axis activity and serotonergic signaling are implicated in the pathogenesis of human obesity and may contribute to its metabolic and mental complications. The association of these systems has not been investigated in human obesity.

To investigate the relation of HPA responsiveness and serotonin transporter (5-HTT) availability in otherwise healthy individuals with obesity class II or III (OB) compared to non-obesity controls (NO).

Twenty-eight OB (21 females; age 36.6 ± 10.6 years; body mass index (BMI) 41.2 ± 5.1 kg/m²) were compared to 12 healthy NO (8 females; age 35.8 ± 7.4 years; BMI 22.4 ± 2.3 kg/m²), matched for age and sex.

HPA axis responsiveness was investigated using the combined dexamethasone/corticotropin-releasing hormone (dex/CRH) test, and curve indicators were derived for cortisol and adrenocorticotropic hormone (ACTH). The 5-HTT selective tracer [¹¹C]DASB was applied, and parametric images of the binding potentials (BP_ND) were calculated using the multilinear reference tissue model and evaluated by atlas-based volume of interest (VOI) analysis. The self-questionnaires of behavioral inhibition system/behavioral activation system (BIS/BAS) with subscales drive, fun-seeking and reward were assessed.

OB showed significant positive correlations of ACTH curve parameters with overall 5-HTT BP_ND (ACTH_AUC: r = 0.39, p = 0.04) and 5-HTT BP_ND of the caudate nucleus (ACTH_AUC: r = 0.54, p = 0.003). In NO, cortisol indicators correlated significantly with BP_ND in the hippocampus (cortisol_AUC: r = 0.59, p = 0.04). In OB, BAS reward was inversely associated with the ACTH_AUC (r = -0.49, p = 0.009).

The present study supports a serotonergic-neuroendocrine association, which regionally differs between OB and NO. In OB, areas processing emotion and reward seem to be in-volved. The finding of a serotonergic HPA correlation may have implications for other diseases with dysregulated stress axis responsiveness, and for potential pharmacologic interven-tions.