5.1 STRESS-INDUCED SYMPATHETIC ACTIVITY AND THE RETINAL VASCULATURE: THE SABPA PROSPECTIVE STUDY

Abstract

Objectives: Retinal vessels are part of the intracranial vasculature and analysis thereof complements behavioural and brain measures. Mental stress was related to downregulation of norepinephrine in Africans. Hence we continue by assessing prospective associations between sympathetic nervous system activity and retinal vessel calibres. Methods: Black and Caucasian participants (n = 275; 45 ± 9 years) were stratified into tertiles according norepinephrine:creatinine (NE:Cr) ratio at baseline. Three year prospective % changes (Δ) for depression (PHQ-9), urinary NE:Cr, serum cortisol and High-Density-Lipoprotein (HDL, neuronal-membrane-integrity and ischemic stroke risk marker) were obtained. At 3yr-follow-up, retinal microvascular calibres were quantified from digital images in the mydriatic eye and salivary cortisol (sC) and α-amylase (sAA), adrenergic activity marker were obtained. Results: Only the low NE:Cr-tertile group (44% Black; 64% Men), showed chronic depression and hypertension prevalence. Over 3yrs, their NE:Cr increased whereas cortisol and HDL decreased. At 3yr-follow-up, wider venules (stroke risk marker) were apparent in the low- compared to the high-tertile group (Figure 1). In the low-tertile group, chronic depression was associated with stroke risk markers, wider venules [OR 1.7; P = 0.03] and lower HDL [OR 4.8; P = 0.04]. In this group, arteriole narrowing was associated with ΔNE:Cr, Δcortisol and sAA; whilst a wider venule was associated with ΔNE:Cr and sC. Conclusions: In reaction to depression and low NE:Cr levels, homeostatic reflexes facilitated upregulation of norepinephrine and concurrent downregulation of cortisol. Stress-induced sympathetic nervous system activity however disturbed myogenic tone, neuronal-membrane-integrity and retinal venular widening; increasing the susceptibility for ischemic stroke.