Abstract
Summary
Intact cockerels were injected with selected levels of corticosterone or testosterone propionate (TP) for 2 weeks. At 5 weeks of age, (immediately after hormone treatment), and at 7 weeks (2 weeks after hormone withdrawal), the weights, histology, and tissue oxygen consumptions of the bursa Fabricii, thymi, and spleens were determined. TP caused a greater involution of lymphoid organs than corticosterone, but tissue sensitivity to corticosterone was greater. Tissue size and tissue oxygen consumption were not directly correlated immediately after hormone treatment. Two weeks after hormone withdrawal the weights and oxygen consumptions of lymphoid organs in corticosterone-treated birds were increased and those in TP-treated birds decreased. This result suggests that lymphoid organs are less impaired by elevated corticosteroid levels during early developmental stages, than by elevated TP levels. For the bursa the data suggest that the mechanisms by which the two steroid hormones cause their lympholytic effect are different. The corticoids cause a transient, and androgens a permanent, effect. This contention was corroborated by histological examination which showed that the major effect of TP on the bursa is permanent and virtual replacement of lymphoid tissue by collagen, while with corticosterone there is a transient loss of lymphocytes, mainly in medullary regions.
It is postulated that the effects of TP are on the differentiation and development of stem cells necessary to the propagation of bursal lymphocytes. Corticosterone's effect is apparently more directly metabolic or lymphocytolytic, and the withdrawal of corticosterone treatment permits the lymphoid tissues to rebound.
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