Comparison of the effects of Althesin and sodium pentobarbitone on the regional uptake of 2-deoxyglucose by the brain and pituitary gland of the rat: selective effects on pars intermedia.

The uptake of radiolabelled 2-deoxyglucose (2DG) was used to compare the effects of the steroid anaesthetic, Althesin (alphaxalone plus alphadolone acetate) with those of sodium pentobarbitone on the regional metabolism of the brain and pituitary gland. Experiments were carried out on adult female Wistar rats. Studies on conscious animals were carried out with the aid of an indwelling intra-atrial catheter. The uptake of 2DG was measured both by liquid scintillation spectroscopy of 3H-2DG in tissue blocks and by quantitative autoradiography with 14C-2DG. Both anaesthetics significantly reduced uptake of 3H-2DG in the frontal, parietal and occipital cortex, and striatum and thalamus, but 3H-2DG uptake was significantly increased in the pituitary gland. Similar effects were found by measuring 14C-2DG uptake, and this technique showed further that Althesin, but not sodium pentobarbitone, selectively increased (2-fold) the uptake of 14C-2DG by the pars intermedia. The increase in 14C-2DG uptake by the pars intermedia in animals anaesthetized with Althesin was significantly reduced by a lesion placed in the arcuate nucleus. The most likely explanation for the effects of Althesin on the pars intermedia is that this anaesthetic increases the activity of arcuate neurons that innervate the pars intermedia.