and Dairy and Swine R&D Centre (M.-F.P.), Agriculture and Agri-Food Canada, Sherbrooke, Canada J1M 0C8 The polyamines are ubiquitous polycationic compounds. Over the past 40 yr, investigation has shown that some of these, namely spermine, spermidine, and putrescine, are essential to male and female reproductive processes and to embryo/fetal development. Indeed, their absence is characterized by infertility and arrest in embryogenesis. Mammals synthesize polyamines de novo from amino acids or

more »

... ort these compounds from the diet. Information collected recently has shown that polyamines are essential regulators of cell growth and gene expression, and they have been implicated in both mitosis and meiosis. In male reproduction, polyamine expression correlates with stages of spermatogenesis, and polyamines appear to function in promoting sperm motility. There is evidence for polyamine involvement in ovarian follicle development and ovulation in female mammals, and polyamine synthesis is required for steroidogenesis in the ovary. Studies of the embryo indicate a polyamine requirement that can be met from maternal sources before implantation, whereas elimination of polyamine synthesis abrogates embryo development at gastrulation. Polyamines play roles in embryo implantation, in decidualization, and in placental formation and function, and polyamine privation during gestation results in intrauterine growth retardation. Emerging information implicates dietary arginine and dietary polyamines as nutritional regulators of fertility. The mechanisms by which polyamines regulate these multiple and diverse processes are not yet well explored; thus, there is fertile ground for further productive investigation. FIG. 1. A, Molecular structure of the major polyamines-putrescine, spermidine, and spermine. B, De novo polyamine biosynthesis. Polyamines are synthesized from Larginine or L-proline through L-ornithine (157) and L-methionine via decarboxylated S-adenosylmethionine, the decarboxylated product formed by SAMDC (8). Ornithine decarboxylase catalyzes the decarboxylation of L-ornithine to yield putrescine. Putrescine combined with decarboxylated S-adenosylmethionine is then transformed into spermidine and spermine via spermidine synthase and spermine synthase, respectively, and through the formation of methylthioadenosine. Spermidine can be converted back into putrescine and spermine into spermidine by the combination of SAT1 and the polyamine oxidase (16). This back conversion leads to intermediate acetylated polyamines, namely N 1 -acetylspermidine and N 1 -acetylspermine.