title: Isoprenaline-induced facilitation of the Eustachian tube opening.
abstract: Isoprenaline was given i.v. to rats and its ability to change the air pressure necessary to open the Eustachian tube (ET) was studied. Air was injected once a minute into the middle ear via a tube glued to a hole in the tympanic bulla. The rate of pressure increase was 0.7 kPa/sec. The air pressure at which the ET opened was in 10 rats 3.4 +/- 0.3 (SE) kPa. Isoprenaline in a dose of 1 microgram/kg decreased this pressure opening level (Pol) by 0.14 +/- 0.03 kPa and with 10 micrograms/kg by 0.22 +/- 0.03 kPa. These effects were reduced by propranolol. Isoprenaline did not act via released adrenaline. A surface tension lowering substance, Tween 20, instilled into the middle ear, decreased Pol by about 0.9 kPa. It is suggested that isoprenaline evokes a decreased Pol via secretion of surface tension lowering substances.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000399:Air Pressure; D000818:Animals; D005064:Eustachian Tube / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013500:Surface Tension
chemical_list: D000318:Adrenergic beta-Agonists; D011433:Propranolol; D007545:Isoproterenol