Abstract:
To study the influence of acute hyperglycemia on the myogenic response in large retinal arterioles from healthy persons.
Nine healthy persons were examined in a double–blinded randomized study in the morning and in the afternoon on two days separated with at least one month. On all study days the blood glucose was controlled using clamp technique with infusion of somatostatin, insulin and glucose to either a level of normoglycaemia (5 mmol/l) or hyperglycaemia (15 mmol/l).
In five of the patients normoglycemia was maintained during the first study day, whereas on the second study day normoglycemia in the morning was followed by hyperglycemia in the afternoon. The remaining four patients were examined with the glycemia pattern in the reverse order.
On all study days the following parameters were measured during both the morning and the afternoon:: The retinal arteriolar diameter as measured by a retinal vessel analyzer (RVA) before and during isometric exercise induced by lifting a hand weight of 2 kg, mean arterial blood pressure, intraocular pressure, retinal thickness using OCT, estimation of the systolic and diastolic pressure in the ophthalmic artery, and ocular pulse amplitude using an ophthalmodynamometer (SmartLens).
The change in blood flow in the retinal arteriole was estimated using a gain factor (GF) derived from the law of Poiseuille. A GF of 1 indicates perfect autoregulation of blood flow. The measurements were compared using paired t–tests.
The results are given in table 1.
Table 1.
No significant difference was found between any of the studied parameters during normoglycaemia and during hyperglycaemia.
Acute elevation of the blood glucose does not change the myogenic response in retinal arterioles. This suggests that glucose does not have a direct effect on the regulation of retinal arteriolar smooth muscle tone.
Keywords: blood supply • diabetes