Oxidative stress impact on growth hormone secretion in the eye

To evaluate the influence of oxidative stress on extrapituitary growth hormone (GH) secretion in the eye and to analyze the interdependence between eye and serum GH levels under normal and hypoxic conditions.

Pars plana vitrectomy (PPV) was performed in 32 patients with developed proliferative diabetic retinopathy (PDR) and 49 non-diabetic controls, both of whom required this procedure as part of their regular treatment in the period from April 2013 to December 2014. During PPV, vitreous samples were taken and blood was simultaneously collected from the cubital vein. GH levels in serum and vitreous samples were measured by electrochemical luminescence assay. Oxidative stress was measured by enzyme-linked immunosorbent assay of advanced oxidation protein products (AOPP) and lipid hydroperoxide (LPO) in serum and vitreous.

Serum AOPP levels were significantly higher than vitreous levels in both groups (P<0.001 for each group) and LPO levels were significantly higher only in PDR group (P<0.001). There was a significant positive correlation between serum and vitreous LPO levels in PDR group (r=0.909; P<0.001). Serum GH levels were significantly higher than vitreous levels in both groups (P<0.001 for each group). Serum GH levels were significantly higher in PDR group than in controls (P=0.012). Vitreous GH values were slightly higher in PDR group, but the difference was not significant.

Our study confirms that GH production in the eye is autonomous and independent of oxidative stress or pituitary GH influence.