Effects of intraventricular histamine and H2 receptor antagonists on intraocular pressure

Central nervous system control of intraocular pressure

Normal intraocular pressure (IOP) is the result of an equilibrium between aqueous humor (AH) production, AH outflow and episcleral venous pressure. Most available antiglaucoma agents produce their effects by interacting with autonomic mechanisms (beta-blockers, epinephrine or parasympathomimetics). In contrast, the role of the central nervous system (brain and nerves) in the regulation of IOP remains unclear in view of the complex haemodynamic, metabolic or hormonal changes which occur under experimental conditions. In this paper, we discuss a basic understanding of the anatomic and physiological relationships between central nervous system and IOP and describe how the brain can affect functions in ciliary body and trabeculum meshwork.

Central mediation of tracheal pressure through H1 and H2 receptors after histamine administration to the fourth ventricle of anesthetized rabbit

Administration of 1.5, 5.0 and 15 nmol histamine (HA) into the fourth ventricle (IVth) decreased tracheal pressure (PT) dose-dependently in anesthetized rabbits. Maximum decrease of PT occurred 0.9 +/- 0.1 min (mean +/- S.E.M., n = 9) after administration of 15 nmol, and recovery occurred at 4.5 +/- 1.0 min (n = 9). The decrease of PT was blocked by the H1 receptor antagonist, pyrilamine administration into the IVth, or intravenous injection of the alpha-adrenoceptor antagonist, phentolamine. Recovery from the PT decrease was delayed by the H2 receptor antagonist, cimetidine. The results suggest that HA centrally decreases PT through H1 receptors, which action is mediated by the sympathetic nervous system, and this decrease may be modulated through H2 receptors.