Les hormones gonadotropes de l'hypophyse : biochimie et biologie comparées ; spécificité et évolution

Abstract

The pituitary gonadotropic hormones : comparative biochemistry and biology ; specificity and evolution. This review summarizes recent data on the nature of pituitary gonadotropins (GTH) and their biosynthesis, secretion, control and biological effects in vertebrates. While the existence of LH-and FSH-like hormones has been demonstrated in a num-ber of tetrapods, it is still controversial in fish. With the possible exception of the stimula-tion of yolk protein uptake in oocytes, one GTH may assume the various gonadotropic functions of the pituitary. Like mammalian GTH's, the fish GTH's purified so far have two subunits. Using carp gonadotropin (c-GTH), the partial sequences of these subunits were determined to be homologous to the mammalian a and types. c-GTH(3 was also shown to be closer to mammalian LH! than to FSH P . Immunological studies have confirmed these findings and demonstrated that, from fish to mammals, the antigenic determinants were better conserved for LH! than for the rx subunits. An hybrid molecule, formed by associat-ing bovine LHa and c-GTHp, was more active in frogs than either of the mother-hormones, while it was inactive on adenylate cyclase in homogenates of rat or goldfish ovaries. This hybrid, however, was as active as c-GTH in increasing c-AMP concentration in pieces of eel ovary. Interestingly, sturgeon gonadotropin (aci-GTH) had somewhat similar biologi-cal properties. Aci-GTH subunits were partially purified, and an hybrid (bovine LHa-aci-GTH(3) was created. Both of the possible hybrids from the c-GTH and aci-GTH subunits