Induction of steady-state blood alcohol levels: application to the study of within-session alcohol tolerance in rats.

BACKGROUND: The study of within-session alcohol tolerance in the rat has been hampered by methodological difficulties related to the measurement of dependent variables at predictable blood alcohol concentrations (BAC) during a single session of alcohol exposure. This study characterizes a method for maintaining steady-state blood alcohol levels over several hours in the rat, referred to as the "alcohol clamp." METHODS: Wistar rats were implanted with an indwelling catheter in the carotid artery for blood sampling and another in the external jugular vein for alcohol infusion. To clamp BAC at a predetermined level, rats first were infused with a priming dose of alcohol to establish the desired or "target" BAC, followed by a continuous infusion of alcohol at a rate equal to that of alcohol metabolism in the rat. This maintained BAC at a constant level over time. BACs of 100, 200, or 300 mg% were maintained over several hours in separate groups of rats. The alcohol clamp was applied to the study of acute (within-session) alcohol tolerance in rats selectively bred for high and low alcohol drinking. Alcohol-induced hypothermia was used to index tolerance, and within-session alcohol tolerance was defined as a return of body temperature toward baseline during the course of the alcohol infusion while BAC was maintained at a constant level. RESULTS: The continuous alcohol infusion procedure maintained BAC in a steady state throughout the 3 hr alcohol infusion session at each of the three target BAC levels. Alcohol infusion induced a drop in body temperature, followed by a return of temperature toward baseline during the course of infusion, which indicated the development of within-session alcohol tolerance. CONCLUSIONS: The continuous alcohol infusion procedure (alcohol clamp) maintained BAC in a steady state, both within and between subjects, across a wide range of blood alcohol levels. The alcohol clamp appears to be a useful tool for subsequent studies of within-session alcohol tolerance in the rat.

Contribution of the opioid system to alcohol aversion and alcohol drinking behavior.

The effect of blocking delta opioid receptors on alcohol aversion was examined in female alcohol-preferring (P) rats using a conditioned taste aversion (CTA) paradigm. In experiment 1, alcohol naive P rats were given i.p injections of 0.5, 1.0 or 1.5 g alcohol/kg BW or saline, paired with consumption of a banana-flavored solution during 5 conditioning trials. Alcohol in a dose of 0.5 g/kg was not aversive while the two higher doses (1.0 and 1.5 g/kg) were both aversive in the CTA paradigm. In experiment 2, the effect of the selective delta opioid receptor antagonist, naltrindole (NTI), on alcohol aversion was examined. Rats were pretreated with NTI in doses of 2.5, 5.0, 10.0 or 20.0 mg/kg before conditioning using the nonaversive dose of alcohol from Experiment 1. As in experiment 1, the 0.5 g/kg dose of alcohol did not produce a CTA. Administration of NTI alone in doses of 2.5, 5.0 or 10.0 mg/kg did not produce a CTA. However, when the nonaversive dose of alcohol (0.5 g/kg) was combined with NTI in a dose of either 5.0 or 10.0 mg/kg, an aversion to alcohol was seen. The highest dose of NTI (20 mg/kg) produced a CTA when given either alone and in combination with alcohol. The results indicate that blocking the action of opioid peptides at the delta opioid receptor can make a nonaversive dose of alcohol aversive which suggests that opioid peptides, acting via the delta opioid receptor, play an important role in regulating alcohol aversion.

Audit of blood transfusion policy in head and neck surgery.

There is current concern about the possible adverse affects of blood transfusion on patient survival after cancer surgery. In addition, blood transfusion is associated with a low incidence of morbidity and mortality in any patient. 100 patient records have been examined retrospectively to outline the problems with blood transfusion policy in head and neck surgery. The current situation lacks standardization on a scientific basis and represents an area of resource over-utilization. A new approach to this subject in head and neck surgery is proposed and a recommended 'new policy' suggested.

Effect of nasogastric tubes on eustachian tube function.

The Eustachian tube acts as pressure equalizing tube between the nasopharynx and the middle ear. It also functions as a conduit for removal of secretions from the middle ear and mastoid air cell system into the post nasal space. Eustachian tube function may be assessed objectively using tympanometric measurements. (Brooks, 1968, Lutman, 1987). The post-operative use of nasogastric Ryles tubes is associated with reduced peak middle ear pressure (mmH2O) and reduced peak compliance volumes (ml) as assessed by tympanometry. In addition changes in the appearance of the tympanic membrane may occur with the protracted use of Ryles tubes. This phenomenon is a transient one. Nasogastric tube-induced Eustachian tube dysfunction is a previously unreported entity.