Differential effects of glucose and fructose on hexose metabolism in dog spermatozoa

Abstract

ResearchIncubation of dog spermatozoa with 10 mmol l -1 glucose or fructose rapidly increased the intracellular content of glucose 6-phosphate and fructose 6-phosphate, although the effect of fructose was greater. These effects were correlated with increases in ATP, ribose 5-phosphate and glycogen contents, and in the rates of formation of Llactate and CO 2 . In all cases, except for ATP and glycogen, the effect of fructose was greater than that of glucose. The total hexokinase activity of the crude extracts of dog spermatozoa was more sensitive to fructose than to glucose at lower concentrations (0.1-3.0 mmol l -1 ). Both monosaccharides induced a fast and intense increase in the overall tyrosine phosphorylation of dog spermatozoa, although their specific induced-phosphorylation patterns differed slightly. Glut 3 and Glut 5 hexose transporters were the main hexose transporters in dog spermatozoa; however, other possible SGLT family-related hexose transporters were also localized. These data indicate that, at concentrations from 1 mmol l -1 to 10 mmol l -1 , fructose has a stronger effect than glucose on hexose metabolism of dog spermatozoa. These differences appear to be related to variations in the sensitivity of hexokinase activity. Moreover, the differential hexose metabolism induced by the two sugars had distinct effects on the function of dog spermatozoa, as revealed by the diverse patterns of tyrosine phosphorylation.

The presence of a high‐Km hexokinase activity in dog, but not in boar, sperm

“…However, recent findings support the hypothesis that sugars can play another role, at least in some mammalian species, and not only as mere energy substrates. This is especially evident in dog, where the incubation of sperm cells from fresh ejaculates with either glucose or fructose induced hexose‐specific changes in functional parameters such as motility [2] or tyrosine phosphorylation patterns [3]. These glucose‐ or fructose‐specific effects were related to specific actions on the majority of the evaluated metabolic parameters, such as intracellular levels of glucose 6‐phosphate and glycogen or production of l ‐lactate and CO 2 [3].…”

“…These glucose‐ or fructose‐specific effects were related to specific actions on the majority of the evaluated metabolic parameters, such as intracellular levels of glucose 6‐phosphate and glycogen or production of l ‐lactate and CO 2 [3]. Glucose and fructose also showed separate effects on hexokinase activity [3], and they even induced separate effects, not only on glycogen synthase activity [4], but also on the intracellular, specific location of this enzyme in dog sperm [5]. All of these results indicate that dog sperm would have very sophisticated mechanisms to specifically identify sugars that they are consuming in order to direct them to induce the sugar‐linked, functional effects.…”

“…This is especially evident in dog, where the incubation of sperm cells from fresh ejaculates with either glucose or fructose induced hexose‐specific changes in functional parameters such as motility [2] or tyrosine phosphorylation patterns [3]. These glucose‐ or fructose‐specific effects were related to specific actions on the majority of the evaluated metabolic parameters, such as intracellular levels of glucose 6‐phosphate and glycogen or production of l ‐lactate and CO 2 [3]. Glucose and fructose also showed separate effects on hexokinase activity [3], and they even induced separate effects, not only on glycogen synthase activity [4], but also on the intracellular, specific location of this enzyme in dog sperm [5].…”

“…All of these results indicate that dog sperm would have very sophisticated mechanisms to specifically identify sugars that they are consuming in order to direct them to induce the sugar‐linked, functional effects. These mechanisms might be related to the intake of sugars, since the fructose‐specific transporter, GLUT5, and the more glucose‐specific transporter, GLUT3, are located in separate zones, not only in dog sperm [3], but also in other mammalian species, such as bull, mice and human [6]. However, there are probably other systems that allow sperm to optimize these hexose‐differentiating mechanisms, at least in dog.…”

Motility and Functional State of the Membrane of Caprine Capacitated Spermatozoa under Different Chemical Agents

“…Because sugars (sucrose, raffinose, trehalose and lactose) are non-penetrating cryoprotectors of high molecular weight they are useful when applied at high cooling speeds, because the cryoprotector action is associated with its dehydrate activity and its specific interaction with the phopholipid membrane [30]. In this context, the type and sugar concentration used can modify not only the sperm motility but also the viability and acrosomal integrity [31]. In general the monosaccharides in addition to act as cryoprotector play other functions.…”