The role of the adrenal medulla in cardiovascular responses to hypertonic saline in haemorrhaged conscious rats

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Abstract
The aim of this study was to determine if the adrenal medulla plays a role in mediating haemodynamic effects of hypertonic saline (HTS) resuscitation during haemorrhagic hypotension in conscious rats. Wistar‐Kyoto rats were either adrenomedullectomized (ADMX,n =11) or sham‐operated (SHAM,n =10) and implanted with intravascular catheters. Pre‐haemorrhage resting mean arterial pressure (MAP) was lower in the ADMX than in the SHAM group. Haemorrhage was performed by withdrawal of blood through the venous catheter, and a MAP of 50 mmHg was maintained for 1 h by further withdrawal when necessary. Both groups responded to haemorrhage with marked bradycardia. Plasma adrenaline (A) rose 10‐fold in response to hypotension in the SHAM group, while remaining at pre‐haemorrhage levels in the ADMX group, indicating successful adrenal demedullation. Infusion of 2.0 ml kg‐1HTS (NaCl 8.0 mg ml‐1i.v.) produced an immediate increase in MAP and heart rate (HR) in both groups, to pre‐haemorrhage values or higher. Plasma noradrenaline (NA) increased in both groups after HTS, while the high levels of A in the SHAM group slowly returned toward baseline. Plasma glucose and rate of haemodilution was higher in the SHAM group during and after hypotension. The maintenance of MAP above 60 mmHg was less effective in the SHAM group during the first 2 h after HTS, but after 24 h, pre‐haemorrhage MAP was established in both groups. In conclusion, the adrenal medulla does not play a major role in the response to HTS resuscitation.

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