ACTH activity in the pituitary and brain of the least brook lamprey, Lampetra aepyptera.

Research on the lamprey pituitary has not revealed whether these cyclostomes possess the same pituitary cell types and trophic hormones as other vertebrates (Percy et al., 1975). For example, Weisbart er al. (1980) indicate that there is no substantive evidence for the presence of ACTH in cyclostomes. The report of ACTH in Myxine and Lampetra (Strahan, 1959) is unreliable in view of the insensitivity of the bioassay and the absence of experimental details and quantitative data. As evidenced by a positive lead hematoxylin staining reaction, there is histological evidence for ACTH-secreting cells in the mesoadenohypophysis of lampreys (Larsen and Rothwell, 1972). However, the evidence for hypophyseal control of the interrenal is inconclusive (Hardisty, 1979) considering the small amount of interrenal tissue in lampreys (Hardisty, 1972) and the extremely low levels of plasma corticosteroids (Idler and Truscott, 1980). Plasma corticosteroid levels in hagfish are elevated by injections of mammalian ACTH (Weisbart et al., 1980), but corticosterone levels in Lampetra fluviatilis are unaffected by this treatment (Buus and Larsen, 1975). In both larval and adult sea lamprey, Petromyzon marinus, however, administration of mammalian ACTH produces ultrastructural changes in the interrenal cells similar to those seen in the adrenocortical cells of other vertebrates after ACTH stimulation (Youson, 1973). Based on the results of a sensitive rat adrenal bioassay, we present evidence for the existence of ACTH activity in the pituitary and brain of both larval and adult Lampetra aepyptera, the least brook lamprey, a nonparasitic species inhabiting small creeks in the east central United States.