Tierärztliche Hochschule Hannover Vergleichende Studie zur

Publikation 2
associated with stress and fear. In ponies under volatile agent anaesthesia,
abdominal surgery did not induce a greater cortisol and catecholamine response than
anaesthesia alone, indicating that the adrenocortical response to anaesthesia is
already maximal and cannot be further increased by additional stimuli (Taylor et al.
1998). Similar results for cattle (Anderson & Muir 2005) suggest that general
anaesthesia itself is intensely distressful despite the absence of nociceptive
stimulation and tissue trauma from surgery. In man, inhalation anaesthesia was less
effective than neuroleptic, spinal or epidural anaesthesia in reducing the endocrine
response to surgery (Kehlet 1979). This may account for the significantly elevated
norepinephrine levels in Group INH observed immediately after incision and 65 min
into surgery.
The rise in cortisol in Group EPI when the calf was placed in dorsal recumbency
again reflects the reaction of a conscious, mildly sedated animal to unfamiliar
manipulations. However, during surgery, when actual noxious stimuli were applied, a
diminished stress response after spinal epidural anaesthesia similar to dogs (Stanek
et al. 1980) and man (Ecoffey et al. 1985; Stevens et al. 1991; Kehlet 2000)
compared to general anaesthesia could be confirmed by this study. The blunted
surgical stress response after epidural administration of xylazine is due to its local
effect on alpha-2-receptors located in the dorsal horn neurons of the spinal cord.
Activation of these receptors inhibits the release of norepinephrine and substance P,
thus decreasing neuronal activity and, in turn, inhibiting rostral transmission of
nociceptive impulses (Caron & LeBlanc 1989; Prado et al. 1999). Studies in man
found the use of epidural anaesthesia to completely suppress the stress response
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