ACTIVITY OF PARS INTERMEDIA OF AUTOTRANSPLANTED PITUITARY GLAND IN EUROPEAN EEL

The pituitary gland was autotransplanted in the dorsal muscle of 16 eels; 2 months later, the pigmentation is quite variable, but generally darker than that of hypophysectomized animals. Also, a dark spot appears close to the graft, indicating intermedin (MSH) secretion. There is a correlation between the intensity of the pigmentation, the diameter of the black spot, and the degree of maintenance of the pars intermedia in the 13 cases where it was identified in the transplant. The intermediate lobe tissue is absent in the 3 eels which are as pale as the hypophysectomized ones. The pars intermedia normally contains 2 cell types: only the cell stainable with the leadhaematoxylin technique (H-Pb) is still present in the grafts: then, it appears responsible for the elaboration of intermedin. The other cell type, PAS positive, less abundant, is strongly regressed and can even disappear. It seems obvious that there are two distinct cell types with their own development. However, no histological criteria suggest that the H-Pb positive cells are hyperactive. As there is no permanent melano-dispersion in the grafted animals, it does not seem evident that the hypothalamus of the eel secretes a MSH-inhibiting factor (MSH-IF) similar to that described in Amphibians. Conversely, the hypothesis of a MSH-releasing factor (MSH-RF) would appear more probable despite a large degree of autonomy of the pars intermedia. These observations are compared with data published on various Vertebrates. The prolactin-like hormone secreted by the erythrosinophilic cells of the pituitary gland, identified in the 15 healthy grafts, does not seem to play an important role in the control of the pigmentation. It appears even unable to mimic the melanophoro-dispersing effect of the ovine prolactin. The corticotrophic cells present in the 15 transplants do not seem to act on the maintenance of the pigmentation, but their functional activity remains to be evaluated. © 1969 Springer-Verlag.