THE RAT IN THE ASSAY OF CORTIN

¹ Research Laboratories, University of Denver

1. On the basis of short survival period, low percentage of indefinite survivals, ease of operation, care, etc., the rat appears to be an excellent test animal for the assay of cortin. In the present study, using 30-day-old males, the survival period of 422 rats not treated with cortin averaged 5.71 days; the per cent of indefinite survivals in 670 treated and non-treated animals was 3.28.

2. The cortin requirement of the rat is high, nearly as high as for a dog, but rats of the same age, weight, sex, etc., are always available, which is not usually true of dogs.

3. There does not appear to be any difference in the survival period between different strains of rats.

4. Barring the addition of salt, changes in the composition of the diet have little effect upon the survival period.

5. On the basis of parallel determinations on six preparations, oral administration of cortin is at least as effective as parenteral.

6. The assay of nine commercial preparations indicates the desirability of agreement upon a unit of potency.

7. It is suggested that a rat unit be adopted which will represent the amount of material necessary per day per rat (using a group of five 30 day old males for a period of 10 days) to produce a net gain in weight of 10 per cent, with 80 per cent of the animals surviving. Agreement upon details of administration would also be necessary and it is suggested that the material be given orally, mixed with the feed, once per day.