The developmental endocrinology of the spleen in chick embryos: I. The pars distalis

Partial decapitation (‘hypophysectomy’) of the chick embryo significantly reduces body growth by 20 days (stage 46—) of incubation as indicated by body weights, 60 % of normal; the lengths of the toe and tibiotarsus, 80 % and 78 % of normal respectively; and liver growth, 47 % of normal, but the gall bladder was not apparently enlarged. It significantly increases spleen growth to 82 % greater than normal, suppresses or retards white pulp differentiation and splenic vasculogenesis but enhances red pulp development. A single pars distalis gland placed as a chorioallantoic graft into operated embryos prevents the development of these defects except for liver growth which, while improved, is still subnormal. If the number of grafts is increased by one or two there is no change in the amount of influence on growth and development of the chick embryo. This apparent regulation occurs by some unknown mechanism even in the absence of the hypothalamus. Thus body and liver growth is normally stimulated by the pars distalis but spleen growth and red pulp differentiation are suppressed even though the gland stimulates splenic white pulp histogenesis. The hypothalamus, epiphysis and pars nervosa (removed by partial decapitation) are not apparently involved in the developmental endocrinology of the spleen in chick embryos.