THE ROLE OF THE ADRENAL-MEDULLA IN CARDIOVASCULAR-RESPONSES TO HYPERTONIC SALINE IN HEMORRHAGED CONSCIOUS RATS

The aim of this study was to determine if the adrenal medulla plays a role in mediating haemodynamic effects of hypertonic saline (HTS) resu scitation during haemorrhagic hypotension in conscious rats. Wistar-Ky oto rats were either adrenomedullectomized (ADMX, n = 11) or sham-oper ated (SHAM, n = 10) and implanted with intravascular catheters. Pre-ha emorrhage resting mean arterial pressure (MAP) was lower in the ADMX t han in the SHAM group. Haemorrhage was performed by withdrawal of bloo d through the venous catheter, and a MAP of 50 mmHg was maintained for 1 h by further withdrawal when necessary. Both groups responded to ha emorrhage with marked bradycardia. Plasma adrenaline (A) rose 10-fold in response to hypotension in the SHAM group, while remaining at pre-h aemorrhage levels in the ADMX group, indicating successful adrenal dem edullation. Infusion of 2.0 ml kg(-1) HTS (NaCl 8.0 mg ml(-1) i.v.) pr oduced an immediate increase in MAP and heart rate (HR) in both groups , to pre-haemorrhage values or higher. Plasma noradrenaline (NA) incre ased in both groups after HTS, while the high levels of A in the SHAM group slowly returned toward baseline. Plasma glucose and rate of haem odilution was higher in the SHAM group during and after hypotension. T he maintenance of MAP above 60 mmHg was less effective in the SHAM gro up during the first 2 h after HTS, but after 24 h, pre-haemorrhage MAP was established in both groups. In conclusion, the adrenal medulla do es not play a major role in the response to HTS resuscitation.