Presence of alternative splicing or post-translational modifications in proteins (such as glycosylation, phosphorylation, proteolytic processing, lipid modification, etc.) explains these basic numerical differences. Interestingly, fluids such as semen appear, in the context of protein identification and relation to function, really complex, ranging from few relevant proteins in spermatozoa towards hundreds

in SP.15 Moreover, the fact that ejaculation is in many species fractionated adds a new dimension to the action of SP proteins (and their interaction) on sperm function and on female reactivity. This paper attempts to review aspects of the composition of the seminal plasma of mammals, with a particular focus on its proteomics and the CH5424802 order differential functions this fluid would play in relation to sperm function and signalling to the female, with an ultimate focus on its role in modulating fertility. As already mentioned, collection of a naturally fractionated ejaculate (as in humans, pigs or horses) into a single vial represents a non-physiological situation, because such bulk ejaculate where all fluids mix at a single time does

not exist in vivo. During coitus, individuals from these exemplified species deliver spurts of fluid Lenvatinib in a sequential manner and to a specific location in the female. In primates and some artiodactila, sperm deposition is performed tuclazepam deep in the vagina, in front of the cervical opening or in the vaginal fornix while in other species of ungulates, sperm deposition occurs intracervically or even intrauterine.2 The first secretion (pre-ejaculate) presented to the urethra is that of the urethral and/or bulbourethral glands (Littré and Cowper for human, a secretion

containing mainly mucin, sialic acid, galactose and salts in a slightly viscous, clearly aqueous fluid). This is followed by the emission of spermatozoa from the caudae epididymides to the urethra accompanied by secretion from the prostate, followed by ejaculation proper (e.g. expulsion of semen into the female) in a series of spurts. The initial spurts are usually called the sperm-rich fraction of the ejaculate, because most spermatozoa are present there,16 with a blend of the acidic cauda epididymides and ampullar fluids together with the slightly acidic citrate and zinc-rich prostate fluid, which also contains specific peptides and proteins [as acid phosphatase and prostate-specific antigen (PSA) in humans]. In the following spurts, there is a gradual dominance of secretion from the seminal vesicles (rich in fructose, peptides, proteins, prostaglandins (PGs), etc., which is clearly basic in nature)2,17 as well as gradual diminution of sperm numbers.