Mammalian sperm energy resources management and survival during conservation in refrigeration

The present review has as its main aim to present an overview regarding the mechanisms utilized by mammalian sperm to manage its intracellular energy levels. This management will strongly influence the sperm's ability to maintain its overall function during its entire life span. Thus, the precise knowledge of these mechanisms will be of the utmost interest to optimize the systems utilized to conserve mammalian sperm for a medium-to-long time-lapse. Briefly, utilization of hexoses as energy substrates by mammalian sperm is very finely regulated from the very first step of its metabolization. Furthermore, the equilibrium among the separate, monosaccharide metabolization pathways in mammalian sperm depends on many factors. This prevents the possibility to draw a general vision of sperm energy utilization, which explains the results of all mammalian species in all points of the sperm life-cycle. To complicate the matter further, there are separate energy phenotypes among mammalian spermatozoa. The precise knowledge of these phenotypes is of the greatest importance in order to optimize the design of new extenders for sperm conservation in refrigerated conditions. Moreover, sugars can act on sperm not only as passive metabolic substrates, but also as direct function activators through mechanisms like specific changes in the tyrosine phosphorylation status of distinct proteins. Finally, mammalian sperm utilizes non-glucidic substrates like citrate and lactate to obtain energy in a regular form. This utilization is also finely regulated and of importance to maintain overall sperm function. This implies that the exact proportion of glucidic and non-glucidic energy substrates could be very important to optimize the survival ability of these cells in conservation.