Differential activation of the pituitary-adrenocortical axis after stress in the rat: use of two genetically selected lines (Roman low- and high-avoidance rats) as a model

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Abstract
We have examined the activation of the pituitary-adrenal axis in two lines of rats, the Roman high (RHA)- and low (RLA)-avoidance rats known to be emotionally different. These rats are selected for rapid acquisition of a conditioned avoidance response (RHA) compared with failure to acquire this response (RLA). In this study the endocrine response (ACTH, corticosterone, aldosterone) of RLA and RHA rats to two types of stress was examined: exposure to openfield stress for 10 min (Op) or exposure to ether vapours for 3 min (E). Basal plasma ACTH concentrations were lower in RLA than in RHA rats (RLA: 110·8 ± 24·5 ng/l; RHA: 252·7 ± 60·8 ng/l, PPin vivo and in vitro differed in the two lines: administration of ovine CRF (10 μg/kg body weight, i.p.) resulted in significant increases in ACTH secretion but the response was significantly lower in RHA rats (RHA: 511·1 ±41·5 ng/l; RLA: 831·4 ± 70·3 ng/l, Pin vitro compared with cells derived from the RLA rats (RHA: 750 ± 83% of control; RLA: 1374 ±79, P3H]RU28362 bound/mg protein; RLA: 173±18, P3H]aldosterone bound/mg protein; RLA: 116·7±7·3, P< 0·01). It is concluded that first, differences in pituitary activity between RLA and RHA rats are distinct from changes observed at the adrenal level, secondly, increased stress-induced ACTH output in the RLA line is associated with enhanced pituitary sensitivity to CRF and possibly with diminished corticosterone inhibitory feedback action on CRF and ACTH secretion, and thirdly, the possible involvement of differences in the pattern of CRF secretion between RLA and RHA rats on resting pituitary ACTH secretion cannot be excluded. Journal of Endocrinology (1989) 123, 477–485