title: Low serum testosterone and increased diastolic ocular perfusion pressure: a risk for retinal microvasculature.
abstract: BACKGROUND
  Low levels of testosterone in men and changes in retinal microvascular calibre are both associated with hypertension and cardiovascular disease risk. Sex hormones are also associated with blood flow in microvascular beds which might be a key intermediate mechanism in the development of hypertension. Whether a direct association between endogenous testosterone and retinal microvascular calibre exists is currently unknown. We aimed to determine whether testosterone is independently associated with ocular perfusion via a possible association with retinal vascular calibre or whether it plays only a secondary role via its effect on blood pressure in a bi-ethnic male cohort.
  
  
  METHODS
  A total of 72 black and 81 white men (28-68 years of age) from the follow-up phase of the Sympathetic activity and Ambulatory Blood Pressure in Africans (SABPA) study were included in this sub-study. Ambulatory pulse pressure and intraocular perfusion pressures were obtained, while metabolic variables and testosterone were measured from fasting venous blood samples. Retinal vascular calibre was quantified from digital photographs using standardised protocols.
  
  
  RESULTS
  The black men revealed a poorer cardiometabolic profile and higher pulsatile pressure (>50 mm Hg), intraocular pressure and diastolic ocular perfusion pressure than the white men (p≤0.05). Only in the white men was free testosterone positively associated with retinal calibre, i.e. arterio-venular ratio and central retinal arterial calibre and inversely with central retinal venular calibre. These associations were not found in the black men, independent of whether pulse pressure and ocular perfusion pressure were part of the model.
  
  
  CONCLUSIONS
  These results suggest an independent, protective effect of testosterone on the retinal vasculature where an apparent vasodilatory response in the retinal resistance microvessels was observed in white men.
authors.affiliation: 1 Hypertension in Africa Research Team, Faculty of Health Sciences, North-West University, Potchefstroom, South Africa.
authors.forename: Nico T
authors.initials: NT
authors.lastname: Malan
authors.affiliation: 1 Hypertension in Africa Research Team, Faculty of Health Sciences, North-West University, Potchefstroom, South Africa.
authors.forename: Wayne
authors.initials: W
authors.lastname: Smith
authors.affiliation: 2 Department of Psychosomatic Medicine, Clinic Barmelweid, Barmelweid, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: von Känel
authors.affiliation: 3 Department of Epidemiology and Public Health, University College of London, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Hamer
authors.affiliation: 1 Hypertension in Africa Research Team, Faculty of Health Sciences, North-West University, Potchefstroom, South Africa.|4 MRC Research Unit for Hypertension and Cardiovascular Disease, North-West University, Potchefstroom, South Africa.
authors.forename: Alta E
authors.initials: AE
authors.lastname: Schutte
authors.affiliation: 1 Hypertension in Africa Research Team, Faculty of Health Sciences, North-West University, Potchefstroom, South Africa.|4 MRC Research Unit for Hypertension and Cardiovascular Disease, North-West University, Potchefstroom, South Africa.
authors.forename: Leoné
authors.initials: L
authors.lastname: Malan
mesh_terms: D000328:Adult; D044383:Black People; D001794:Blood Pressure; D006801:Humans; D008297:Male; D008833:Microcirculation; D055806:Microvessels / Q000503:physiopathology*; D008875:Middle Aged; D009798:Ocular Hypertension / Q000097:blood / Q000175:diagnosis / Q000208:ethnology / Q000503:physiopathology*; D065840:Protective Factors; D015861:Retinal Neovascularization / Q000097:blood / Q000175:diagnosis / Q000208:ethnology / Q000503:physiopathology*; D012171:Retinal Vessels / Q000503:physiopathology*; D018570:Risk Assessment; D012307:Risk Factors; D013019:South Africa / Q000453:epidemiology; D013739:Testosterone / Q000097:blood / Q000172:deficiency*; D014655:Vascular Resistance; D014664:Vasodilation; D044465:White People
chemical_list: D013739:Testosterone
keywords: Testosterone; diastolic ocular perfusion pressure; intraocular pressure; pulse pressure; retinal microvascular calibre