Autonomic mechanisms underlying intraocular pressure changes during insulin-induced hypoglycaemia in normal human subjects: effects of pharmacological blockade.

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)