Sugar transport from the lumen of the rat uterus

The metabolic properties of spermatozoa from the epididymis of the tammar wallaby, Macropus eugenii

The utilization of various substrates by sperm from the cauda epididymidis of the tammar was examined because the major naturally occurring sugar in the semen of this species is N-acetyl-D-glucosamine (NAG) and not furctose, as in eutherian mammals. The sperm displayed a high level of endogenous respiration that supported motility for relatively prolonged periods of time in vitro. They also metabolised exogenous 14C-labelled glucose, NAG, sucrose, and acetate through glycolytic and/or oxidative processes to produce lactate and 14CO2 at varying rates. The rate of uptake of NAG by tammar sperm was about four times greater than that of other substrates. Glucose and/or NAG stimulated the rate of oxygen consumption by about 20%, but acetate stimulated oxygen consumption by more than 40%. The most striking findings were that NAG almost completely inhibited the oxidation of glucose and sucrose by the sperm and depressed the uptake of glucose, 3-O-methylglucose, and sucrose. Acetate oxidation also was inhibited by NAG, but only by about 50%. Tammar sperm generated substantial amounts of free glucose during incubation with NAG, but this and the inhibitory effects of NAG on glucose oxidation were not mimicked by rat sperm. It is proposed that tammar sperm fail to oxidise glucose in the presence of NAG because of the rapid cellular uptake of NAG relative to glucose. Also, the intracellular glucose and acetate liberated from NAG would compete with exogenous glucose for processing in the Embden-meyerhof and tricarboxylic acid (TCA) cycle pathways. It is also suggested that tammar sperm oxidise sucrose after extracellular hydrolysis into its glucose and fructose components. The biological implications of these metabolic and transport properties of tammar sperm have as yet to be determined.

Prostanoid modulation of glucose transport in isolated diabetic rat uterus

3-O-14C-methyl-D-Glucose (3-O-MG) transport and 14C-saccharose incorporation were measured in isolated uterine strips from ovariectomized-estrogenized diabetic rats. Glucose transport was decreased in uterine strips from diabetic rats compared with control animals. PGE1 and PGE2 (10(-7) M) stimulated 3-O-MG transport, PGF2 alpha failed to modify this parameter at the same concentration, while insulin (0.5 U/ml) evoked an improvement 30% greater than PGs. In spite of the negative influence exerted by TXA2 over glucose metabolism in the isolated rat uterus, U46619, 10(-5) M (a TXA2 analogue), and OKY064, 10(-7) M (an inhibitor of TXA2 synthesis), failed to modify basal or insulin-treated hexose transport. Neither additive or synergistic interactions between PGE1 or PGE2 (10(-7) M) and insulin at 0.5 U/ml and 0.25 U/ml were detected. We conclude that the stimulatory action of PGE1 and PGE2 on glucose metabolism that has been previously described by us, involves enhancement of glucose transport.

Influence of prostaglandins on glucose transport in isolated rat uterus

Glucose transport by uterine strips from ovariectomized estrogenized rats was explored. Sugar transport was significantly different from saccharose values (non-specific diffusion) only after 60 min of incubation. The addition of cytochalasin B demonstrated that we are measuring a specific mechanism for glucose transport. Insulin-enhanced sugar transport only at 0.5 or 0.25 U/ml prostaglandin E1 (PGE1), PGE2 and PGF2 alpha (10(-7) M) significantly improved glucose transport, but indomethacin (10(-6) M) failed in modifying this parameter in either control nor insulin-treated tissues. We did not observe an additive or synergistic action between PGE2 (10(-7) M) and insulin (used at maximal or submaximal concentration).