Strain and Age Effects on Immobilization Stress in JAX Rabbits 1

Abstract

Abstract

A brief immobilization stimulus was used in surveying the pituitary adrenal responsiveness of 12 strains of JAX rabbits. Healthy male adult rabbits of 7.3 to 25.3 months in age of the following strains were used: IIIVO/J, III/J, IIIEP/J, IIIC/J, WH/J, X/J, AC/J, ACEP/J, AW/J, AXBU/J, B/J, and OS/J. Blood samples were obtained daily from the marginal veins of the ears of each rabbit at 0, 10, 16, and 22 min postimmobilization for 5 consecutive days and assayed for corticosterone and cortisol by radioimmunoassay. It was observed that the average steroid level (by strain) is highest in strain III/J and lowest in strains IIIVO/J and OS/J. In regard to the changes in steroid level occurring during immobilization, at 0 min time corticosterone levels in strain X/J are significantly higher than the levels in the other 11 strains, but at 10, 16, and 22 min strain III/J corticosterone levels are significantly higher. The elevation in plasma corticosterone at 10 min postimmobilization is significant in all strains of rabbits but the response tends to plateau within 16 min. In regard to the secretion of cortisol, no significant change in the plasma level of cortisol was elicited by short periods of immobilization on 5 consecutive days. Following the survey of immobilization stress responses in 12 rabbit strains, 4 strains (X, III, AC, IIIVO) were selected to study the effect of age on this response. Three age groups were employed: 55 to 60, 100 to 109, and 318 to 412 average days age. It was observed that there are age-related increases in the response to immobilization, significant in strains III and X, and in the response to exogenous ACTH, significant in strain X.