Effects of Adrenal Transplants upon Forelimb Regeneration in Normal and in Hypophysectomized Adult Frogs

Abstract

ABSTRACT Experiments to test the proposition that systemic factors and not fixed properties of the cells within limbs determine loss of regeneration in frogs were performed upon the forelimbs of post-metamorphic R. clamitans and R. pipiens varying in body length from 4·4 to 5·7 cm. Control experiments consisting of simple amputations through the midradius ulnar or distal humeral regions showed that the frogs at this stage were incapable of detectable regeneration. The repeated removal of the cicatricial skin in another control series elicited regeneration, of an abortive type, in only one case among fourteen limbs tested. In twenty-five hypophysectomized R. clamitans adrenals from R. pipiens were transplanted heterotopically beneath the jaw concomitantly with amputation. Weak regenerative response was observed in eleven cases. It is concluded that the absence of the pituitary in the hosts lowers the activity of the transplanted adrenals. The transplantation of R. pipiens adrenals into normal R. clamitans hosts 7 and 14 days after amputation proved most effective, since among the twenty-one limbs examined only two did not show any regeneration. It is suggested that: (1) the transplanted adrenals were functional, although at a low level of activity; (2) the time of transplantation of the adrenals is critical, since in order to elicit regeneration it must coincide with a period in amputational wound repair that is most susceptible to corticoid activity; (3) the loss of regenerative potencies after metamorphosis in Anura is attributable to changes in the endocrine system of these organisms, rather than to changes in the properties of the cells of their limbs.