Inner ear pressure changes modify adh secretion in freely moving guinea pig

The present study was designed to elucidate the relationship between endoly mphatic 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 cmH(2)O to the inner ear. The experimental proto col was designed to avoid any interference on ADH release caused by anesthe sia and surgical stress. There was no change in blood pressure, heart rate, plasma Na (pNa) and osmolality (pOsm) after inner ear pressure (IEP) modif ications. 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. Thes e results confirm that structures in the inner ear help control of ADH rele ase.