The effect of chronic nicotine and withdrawal on intra-axonal transport of acetylcholine and related enzymes in sciatic nerve of the rat

Tachyphylaxis of the intrinsic cardiac nerves to nicotine: effects on A-V nodal conduction

1. The possibility that responses of the intrinsic cardiac nerves (ICN) of the dog to nicotinic stimulation are influenced by tachyphylaxis to repeated administration of nicotine (NIC) was evaluated in an anaesthetized preparation. Prolongation of A-V conduction was used as an index of ICN responsiveness. 2. Twenty dogs were placed on cardiopulmonary bypass and an electrode was sutured over the His bundle. Both vagi were sectioned, beta-adrenoceptor blockade instituted, and the hearts were paced. Nicotine (2-100 micrograms) was administered directly into the coronary circulation via an aortic catheter. Tachyphylaxis was estimated from the rate of deterioration of negative dromotropic effect of NIC in response to various protocols of repeated doses. 3. Tachyphylaxis was not observed in response to repeated doses of acetylcholine. 4. Tachyphylaxis to nicotine was found to be both time- and dose-dependent; i.e. increasing the dose or decreasing the time between doses to less than 3 min augmented its development. 5. Tachyphylaxis was pronounced after 5 x 100 micrograms doses of NIC, even if the test doses were greater than 3 min apart and 20 min was allowed to elapse between the two series of test doses. 6. These data are descriptive in nature and no mechanism for the tachyphylaxis could be deduced. Pharmacokinetic data of this nature have not been previously reported for nicotinic stimulation of the intrinsic parasympathetic ganglia of the canine heart. Tachyphylaxis can be avoided when testing the intrinsic innervation of the canine heart if the doses used are less than 100 micrograms and are administered at least 3 min apart.

Oral administration of nicotine: its uptake and distribution after chronic administration to mice

An investigation was made of the suitability of administering nicotine to experimental animals by inclusion in the drinking water. It was found that, after an initial accommodation period of several weeks, nicotine could be administered up to a concentration of 100 micrograms/ml with no decrease in fluid intake or weight gain compared to control. An analysis of the steady-state plasma levels and distribution of nicotine was made in mice which had received nicotine in the drinking water at a concentration of 60 micrograms/ml. The average daily dose of nicotine received by these animals was 17.2 mg/kg. The steady-state plasma level of nicotine was 34.4 ng/ml, representing 6% of the total compound present at steady-state as determined by thin-layer chromatography. The distribution of nicotine or metabolite in mice which had received [methyl-14C]-nicotine orally was determined. Whole-body autoradiography, as well as direct tissue counting, demonstrated that nicotine accumulates in a number of areas, particularly the salivary gland, nasal epithelium, uterus, and liver. There was relatively little material in the blood or brain. This investigation indicates that ad libitum oral administration is an acceptable method for maintaining experimental animals on nicotine for long periods of time.

Chronic nicotine exposure in rat: a behavioural and biochemical study of tolerance

Rats received nicotine (50 mg nicotine base/1) in their drinking fluid for 28 days. The daily consumption of nicotine was about 4 mg/kg per day. Controls received plain water. Body weight, food consumption and fluid intake were registered during the whole treatment period and up to 31 days after withdrawal of nicotine. A significant lower body weight was noted in rats, treated with nicotine, in comparison with control rats during the whole treatment period. After withdrawal of nicotine the body weight returned to normal. Only slight effects were seen on the food intake (at the beginning of the nicotine treatment). The fluid intake, on the other hand, was significantly lower in the nicotine group during the whole period of treatment and a reduced intake persisted 28 days after withdrawal of nicotine. Tolerance to nicotine was measured in rats 24 hours after withdrawal of nicotine, using two behavioural tests. No tolerance to nicotine was found after 31 days of withdrawal of nicotine. The number of nicotine-like binding sites was found to be reduced in the midbrain 24 hours after withdrawal of nicotine, while no significant change was found in the cortex and hippocampus.