Vehicle control groups

It should also be kept in mind that formulating materials may have effects of their own, and a vehicle control group may be required in addition to a negative control group. 

If necessary, the test substance should be dissolved or suspended as a suitable vehicle, preferably in water, saline, or an aqueous suspension such as 0.5% methyl cellulose in water. If a test substance cannot be dissolved or suspended in an aqueous medium to form a homogenous dosage preparation, com oil or another solvent can be used. The animals in the vehicle control group should receive the same volume of vehicle given to animals in the highest-dose group. 

The test article concentration is normally the highest nonirritating concentration. Several concentrations could be tested at the same time should one wish to establish a dose-response curve for induction. The test is easiest to perform if the vehicle is a standard nonirritating organic, such as acetone, ethanol, or dimethylformamide, or a solvent-olive oil blend. Until a laboratory develops its own historical control base, it is also preferable to include a positive control group. Either 0.25% dinitricholoro-benzene or 0.05% oxazalone are recommended for positive controls. If the vehicle for the positive control is different than the vehicle for the test material, then two vehicle control groups may be necessary. 

Groups of 50 male and 50 female Fischer 344/N rats, six weeks of age, were administered diethanolamine (purity, > 99%) in 95% ethanol by dermal application on five days per week for two years. Males received 0, 16, 32 or 64 mg/kg bw and females 0, 8, 16 or 32 mg/kg bw. Survival rates for dosed male and female groups were similar to those of corresponding vehicle control groups. The mean body weight... 

Several groups of experimental animals are exposed to the test chemical in graduated concentrations for a defined period, one concentration used per group. Whenever a vehicle is used to generate an appropriate concentration of the chemical in the atmosphere, a vehicle control group should be used. Animals that die during the test are necropsied. At the conclusion of the test, surviving animals are sacrificed and necropsied as necessary. 

The test substance is usually evaluated at 4 doses, administered p.o. 60 minutes before the test, and compared with a vehicle control group. 

Fig. 8. Effects of 3 neuroleptics (tiapride, haloperidol and risperidone) on escape latencies during the first session of the Morris maze task in the rat. Note the clear decrease in escape latencies in the vehicle control group (short-term memory) and the absence of effect of the 3 substances on performance at the first trial (absence of intrinsic effects on swimming performance). Tiapride has modest but dose-dependent effects on the decrease in escape latency from trial to trial, whereas haloperidol and risperidone clearly attenuate this decrease (perturbing effect on short-term memory).

Fig. 12. Effects of scopolamine on social recognition memory in the rat. Note the clear decrease in social investigation in the vehicle control group between the first and the second exposure 30 minutes later (social memory) and the absence of effect of scopolamine on social investigation during the first exposure (absence of intrinsic effects of scopolamine on social investigation). In the scopolamine-treated animals there is no decrease in social investigation at the second exposure, demonstrating impairment of social memory.

The values for the treated groups with the candidate compound for each time point are compared to those for the vehicle control group by using appropriate statistical methods. By using several doses of the candidate compound a dose-response curve can be established. 

Mean values for aggregation in dosage groups are compared to the vehicle control groups (for rabbits control values before drug administration). Statistical significance is evaluated by means of the Student s t-test (paired for rabbits unpaired for others). 

The inclusion of untreated or a vehicle control groups is always mandatory. The additional inclusion of comparator groups (comparators of known endocrine activity) may be considered. In me majority of cases this is however not necessary, because mere is an extensive data base in me literature about me effect size of established drugs mat affect me endocrine systems. This agrees with me guideline statement in well-characterised in vivo test systems, positive controls may not be necessary . 

For each parameter, means and standard error calculated, an analysis of variance is performed and the appropriate tests of significance are applied. The mean values of each parameter of the treated groups are compared with the values of the vehicle control group. It is important to compare the results with reference to their use for the rat strain commonly-used in the Laboratory. For many studies it may be advisable to include groups treated with reference compounds of established endocrine activity. 

Number Three animals per sex per dose group with four dose groups and a vehicle control group (30 animals total)... 

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