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Autonomic mechanisms underlying intraocular pressure changes during insulin-induced hypoglycaemia in normal human
D A Hepburn1, B M Fisher, I Thomson
1Department of Diabetes, Royal Infirmary, Edinburgh, Scotland, U.K.
Abstract:
1. A fall in intraocular pressure is induced by acute hypoglycaemia in humans. The role of the autonomic nervous system in mediating this response was investigated in 24 normal volunteers in whom hypoglycaemia was induced with intravenous soluble insulin, under four experimental conditions: (1) control (n = 6), (2) non-selective alpha-adrenoceptor blockade (phentolamine) (n = 6), (3) non-selective beta-adrenoceptor blockade (propranolol) (n = 6) and (4) cholinergic blockade (atropine) (n = 6). Intraocular pressure was measured by using an applanation tonometer. In 12 subjects intraocular pressure was measured during each type of pharmacological blockade of similar duration without induction of hypoglycaemia, to assess the effects of individual antagonists. 2. In the control study intraocular pressure fell during hypoglycaemia from 15 +/- 1.0 to 10 +/- 1.3 mmHg (P less than 0.01) 10 min after the autonomic reaction. beta-Adrenoceptor blockade caused a reduction in intraocular pressure from 15 +/- 1.1 to 9 +/- 1.0 mmHg (P less than 0.001) before the administration of insulin, and when hypoglycaemia was induced intraocular pressure decreased further to 7 +/- 1.0 mmHg (P less than 0.05, compared with immediately before insulin). A decrease in intraocular pressure of similar magnitude was observed with propranolol alone (16 +/- 1.0 to 10 +/- 1.0 mmHg, P less than 0.05). 3. Cholinergic blockade had no immediate effect on intraocular pressure, and the reduction in intraocular pressure during hypoglycaemia was of similar magnitude to that observed during the control study.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Acute hypoglycemia lowers intraocular pressure in humans. Beta-adrenoceptor blockade significantly reduced intraocular pressure, suggesting its role in this response.
Area of Science:
- Ophthalmology
- Autonomic Nervous System Physiology
- Endocrinology
Background:
- Intraocular pressure (IOP) regulation is complex.
- Autonomic nervous system (ANS) influences IOP.
- Hypoglycemia-induced IOP changes are not fully understood.
Purpose of the Study:
- Investigate the role of the autonomic nervous system in mediating the intraocular pressure-lowering effect of acute hypoglycemia.
- Determine the specific contributions of alpha-adrenoceptors, beta-adrenoceptors, and cholinergic pathways.
Main Methods:
- 24 healthy volunteers underwent induced hypoglycemia via intravenous insulin.
- Experimental conditions included control, alpha-blockade (phentolamine), beta-blockade (propranolol), and cholinergic blockade (atropine).
- Intraocular pressure measured using applanation tonometry; separate experiments assessed antagonist effects without hypoglycemia.
Main Results:
- Hypoglycemia induced a significant fall in intraocular pressure in the control group (15 to 10 mmHg).
- Beta-adrenoceptor blockade (propranolol) alone reduced IOP (15 to 9 mmHg) and further lowered it during hypoglycemia (to 7 mmHg).
- Cholinergic blockade did not affect IOP or alter the hypoglycemic response.
Conclusions:
- Beta-adrenergic pathways play a significant role in the intraocular pressure reduction observed during acute hypoglycemia.
- Alpha-adrenergic and cholinergic systems appear to have minimal involvement in this specific IOP response.
- Findings elucidate ANS mechanisms influencing ocular hemodynamics during metabolic stress.