INTERACTION BETWEEN HEAD-DOWN TILT AND ANTERIOR-CHAMBER INFUSIONS ON INTRAOCULAR-PRESSURE OF ANESTHETIZED RATS

Head-down tilt or infusions of a balanced salt solution into the anter ior chamber of the eye raise intraocular pressure. Mie measured intrao cular pressure directly in adult male Sprague-Dawley rats, anesthetize d with pentobarbital, and subjected to 45 degrees head-down tilt alone , tilt with an anterior chamber infusion (0.087 mu l min(-1)), or tilt with an infusion containing arginine vasopressin. The intraocular pre ssure of the three groups differed during the 1 hr tilt and recovery p eriods. In the case of tilt alone. intraocular pressure quickly reache d a peak after tilting, partially decreased during the tilt period, re covered to baseline immediately after tilt, then a secondary rise occu rred. Combined infusion and tilt caused a slower rise to peak intraocu lar pressure, and only a partial recovery occurred during the 1 hr rec overy period. Combined vasopressin infusion and tilt caused a gradual rise in intraocular pressure of a lesser magnitude than the other grou ps, followed by a rapid recovery to baseline pressure and no secondary rise. Systemic arterial pressure was stable within and between the gr oups. The underlying mechanism for these differing response patterns i s unknown. However, some evidence indicates that infusions are indepen dent of aqueous synthesis rate, and that vasopressin, acting on a V-1 receptor subtype reached from the anterior chamber, exerts a vascular effect. (C) 1996 Academic Press Limited