Norepinephrine in cochlear microcirculation of guinea pigs.

Area of Science:

• Oto-rhino-laryngology
• Cardiovascular Physiology
• Pharmacology

Background:

• Cochlear microcirculation is crucial for auditory function.
• Understanding the effects of vasoactive substances on cochlear blood flow is important for treating hearing disorders.

Purpose of the Study:

• To investigate the effects of norepinephrine on cochlear blood flow velocity and microcirculation.
• To determine the mechanisms behind norepinephrine-induced changes in cochlear hemodynamics.

Main Methods:

• Motion picture recording of blood flow in guinea pig cochlear arterioles.
• Measurement of flow velocity and vessel diameter before and after norepinephrine injection.
• Analysis of red blood cell aggregation and microemboli formation.

Main Results:

• Low-dose norepinephrine (0.01-0.15 mg/kg) increased cochlear blood flow velocity and arterial blood pressure.
• High-dose norepinephrine (1.2-2.5 mg/kg) caused transient cessation of blood flow, independent of blood pressure.
• Vessel dilatation occurred with increased blood pressure; however, high doses led to arteriole obstruction by aggregated red blood cells.

Conclusions:

• Norepinephrine affects cochlear microcirculation through dose-dependent mechanisms.
• High-dose norepinephrine can induce microemboli formation via platelet hyperaggregation, potentially disrupting cochlear blood flow.
• These findings suggest a potential mechanism for hearing impairment related to certain pharmacological interventions.