A lectin cytochemical study in the sea lamprey pituitary

In the lamprey, adrenocorticotropin (ACTH) and melanotropins (MSHs) are found in the pars distalis and pars intermedia, respectively, but they are encoded in two distinct genes. Their precursors have been shown to be glycoproteins. Moreover, there is strong evidence for the presence of gonadotropin (GTH) in the lamprey pituitary. To detect glycoconjugate in ACTH, MSH and possible GTH cells, a lectin cytochemistry was applied in the sea lamprey pituitary. A total of twenty-one kinds of lectins was tested. Three types of lectin-positive cells were observed. The first and second types of cells were identical to ACTH and MSH cells, respectively. However, the different response to several lectins in these two cells suggests the different glycoconjugate moieties on the precursor proteins, proopiocortin and proopiomelanotropin. The third type of cells was found in the ventral part of the proximal pars distalis, and was stained positively by several anti-GTH antibodies. It is suggested that those cells are most likely to be GTH cells in the sea lamprey pituitary. Thus, lectins are one of most useful cytochemical tools for studying carbohydrate moiety of endocrine cells.