Inner ear pressure changes modify ADH secretion in freely moving guinea pig.

The present study was designed to elucidate the relationship between endolymphatic pressure and plasma ADH levels in conscious guinea pigs. Plasma ADH (pADH) was measured in basal conditions and after having applied positive or negative pressure of 20 cmH2O to the inner ear. The experimental protocol was designed to avoid any interference on ADH release caused by anesthesia and surgical stress. There was no change in blood pressure, heart rate, plasma Na (pNa) and osmolality (pOsm) after inner ear pressure (IEP) modifications. However, pADH was inversely related with IEP: pADH averaged 31.4 +/- 7.0 pg/ml (mean +/- S.D.) in basal conditions, rising to 48.8 +/- 19.3 when IEP was lowered and falling to 16.6 +/- 10.3 when IEP was raised. These results confirm that structures in the inner ear help control of ADH release.