Estradiol induction of pyruvate kinase in the rat uterus

Estradiol and progesterone affect enzymes but not glucose consumption in a mink uterine cell line (GMMe)

Cells lining the uterus are responsible for storage and secretion of carbohydrates to support early embryonic development. Histotrophic secretions contain glycogen and glycolytic products such as lactate and pyruvate. Insufficient carbohydrate storage as glycogen has been correlated with infertility in women. While it is clear that changes in estrogen (17-β-estradiol (E2)) and progesterone (P4) in vivo affect the distribution of glucose in the uterine cells and secretions, the biochemical mechanism(s) by which they affect this crucial allocation is not well understood. Furthermore, in cultured uterine cells, neither E2 nor P4 affect glycogen storage without insulin present. We hypothesized that P4 and E2 alone affect the activity of glycolytic enzymes, glucose and glycolytic flux to increase glycogen storage (E2) and catabolism (P4) and increase pyruvate and lactate levels in culture. We measured the rate of glucose uptake and glycolysis in a mink immortalized epithelial cell line (GMMe) after 24-h exposure to 10 μM P4 and 10 nM E2 (pharmacologic levels) at 5 mM glucose and determined the kinetic parameters (Vmax, Km) of all enzymes. While the activities of many glycolytic enzymes in GMMe cells were shown to be decreased by E2 treatment, in contrast, glucose uptake, glycolytic flux and metabolites levels were not affected by the treatments. The cellular rationale for P4- and E2-induced decreases in the activity of enzymes may be to prime the system for other regulators such as insulin. In vivo, E2 and P4 may be necessary but not sufficient signals for uterine cycle carbohydrate allocation.

Uterine contractility is strongly influenced by steroids and glucose metabolism: an in vitro study on bovine myometrium

BACKGROUND

Energetic substrates and hormonal phase are important for uterine contractions. Etomoxir a muscle carnitine palmitoyltransferase-1 inhibitor, able to diverge uterine metabolic pathways towards glycolysis, facilitates glucose utilisation. The aim of this study was to evaluate its effect on uterine contractility in different hormonal situations.

METHODS

Uterine samples were collected from 60 cows during follicular phase, luteal phase and pregnancy. The cows were slaughtered at a local abattoir. Longitudinal strips were mounted vertically in a 30-ml organ bath connected to an isometric force transducer. Contractions were recorded with an ink-writing polygraph. After the equilibration period, etomoxir was added to the organ bath at different concentrations. The amplitude and frequency of contractions were registered before and after addition of etomoxir.

RESULTS

In 17 strips from pregnant cows, etomoxir increased the amplitude (p < 0.05) of contractions but not the frequency in comparison with basal conditions. In 15 strips from cows in the luteal phase, etomoxir increased the amplitude (p < 0.05) and frequency of contractions (p < 0.05 at 5 μM and p < 0.01 at 8 and 10 μM). In 18 strips from cows in the follicular phase, etomoxir increased the frequency of contractions but not the amplitude (p < 0.01 at 5 μM and p < 0.05 at 8 and 10 μM).

CONCLUSIONS

This study confirms the importance of glucose for uterine contractility and, moreover, it underlines different patterns of contraction with regard to the hormonal status.

13C NMR kinetic studies of the rapid stimulation of glucose metabolism by estrogen in immature rat uterus

Glucose metabolism in control and estrogen stimulated rat uteri was investigated using 13C NMR spectroscopy. By employing an NMR adapted perifusion system, and developing protocols and methods based on the application of [1-13C]glucose labeling, it was possible to measure, with a temporal resolution of 10 min, the kinetics of glucose consumption, lactate production and 13C incorporation into glutamate, alanine and glycogen. In control immature rat uteri, under aerobic conditions, the rates (+/- SEM) of [1-13C]glucose consumption and [3-13C]lactate production were 24 +/- 2 and 7.5 +/- 0.5 mmol/g wet weight/h. The rates of synthesis of [4-13C]glutamate, [3-13C]alanine and 13C labeling of glycogen at C1 of its glucose moieties were significantly lower and were in the range 0.3-0.6 mmol/g wet weight/h. Thus, ca 35% of the labeled glucose was accounted for by the glycolytic and other observed pathways. In vitro stimulation of the uteri by estrogen was found to increase significantly, within 1 h, glucose consumption by 80%, lactate production by 150% and glutamate and glycogen synthesis by 150%, in parallel to a rapid hormonal induction of mRNA for the brain type isozyme of creatine kinase.

Independent regulation of pyruvate kinase expression by cyclic AMP and prostaglandin F2 alpha in mouse mastocytoma cells

P-815 mouse mastocytoma cells express the K isozyme of pyruvate kinase and the specific activity of this enzyme is increased in response to N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate, 8-bromoadenosine 3':5'-cyclic monophosphate, cholera toxin, and epinephrine, all of which also elevate the intracellular concentration of adenosine 3':5'-cyclic monophosphate. Prostaglandin F2 alpha also increases the cellular activity of this enzyme, but does not increase the adenosine 3':5'-cyclic monophosphate levels. Under all these conditions, the increase in enzymatic activity is accompanied by an equivalent increase in the pyruvate kinase protein level. However, neither the rate of enzyme synthesis nor the level of pyruvate kinase mRNA is elevated by N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate. On the other hand, it does increase the enzyme's half-life. In contrast, prostaglandin F2 alpha increases the rate of synthesis and the level of pyruvate kinase K mRNA, but has no influence on the rate of degradation. Therefore, these cells have two mechanisms which increase pyruvate kinase K levels. One operates via an increase in cAMP level and results in a decrease in the rate of degradation, whereas the other minimizes an upsurge in cAMP levels but still increases pyruvate kinase K activity by increasing its rate of synthesis.

Ontogeny and estrogen responsiveness of creatine kinase and glycolytic enzymes in brain and uterus of rat

We have studied the postnatal ontogeny of creatine kinase (CK) and the glycolytic enzymes phosphoglycerate kinase (PGK), phosphoglycerate mutase (PGM), enolase (En), and pyruvate kinase (PK) in rat brain and uterus. In 30-day-old rat, brain and uterus express the fetal isoforms CK-B, PGK-A, PGM-B, En-alpha and PK-M2, and the differentiated isoforms En-gamma and PK-M1. The activity of glycolytic enzymes in uterus of two-day-old rat is as in brain, while CK activity is 3 times higher in brain. The activity of the glycolytic enzymes in brain began to increase (3-4-fold) 10 days after birth, in a coordinated manner. CK activity began to increase 5 days after birth in both brain (4.2-fold) and uterus (4.5-fold), suggesting the dissociation of glycolytic enzyme ontogeny from CK. In contrast to brain, the levels of glycolytic enzymes in uterus were highest at birth, suggesting the action of a tissue-specific mechanism for regulation of the constitutive levels of glycolytic isozymes. Except for PGM, all enzymes showed an increase in total activity, in response to estrogen, in uterus but not in whole brain.

Enzymology of human myometrium: variations related to the hormonal milieu

The activities of various enzymes involved in glycolysis, tricarboxylic acid cycle and fatty acid oxidation were assayed in human myometrium. A gradient of the activities from fundal to cervical myometrium was observed. In contrast to studies performed in rodents, cyclic changes of glycolytic enzymes could not be detected. Hydroxyacyl-CoA-dehydrogenase (HAD) activity was higher in secretory phase myometrium and in cases with cystic hyperplasia of the endometrium than in proliferative phase myometrium. In pregnant myometrium, lactate dehydrogenase (LDH) and glycogen phosphorylase (GLP) were increased and in postmenopausal myometrium the activities of phosphofructokinase (PFK), LDH and succinate dehydrogenase (SDH) were decreased as compared to proliferative phase myometrium. We conclude that in the human myometrium, except for HAD, activities of enzymes involved in fuel metabolism are stable throughout the menstrual cycle and that only prolonged hormonal stimulation leads to alterations of some enzyme activities.

Effect of estrogens on glucose phosphate dehydrogenase activity of liver and oviduct in the amphibian Bufo arenarum

Glucose- 6phosphate dehydrogenase (G-6PDH) stimulation by estradiol- 17beta has been studied in oviduct and liver of Bufa arenarum. OviducalG-6PDH has been found to be stimulated by a single dose of estradiol- 17beta (100 mug/100 g body weight), the stimulation being dependent on season. Hepatic G-6PDH of females is susceptible to hormonal stimulation, without seasonal variation, while in males the enzymatic activity is not modified under the same conditions. The stimulating effect of estrogen on oviducal and hepatic G- 6PDH was inhibited by Actynomicin D. The susceptibility of G- 6PDH to estrogenic action would assure NADPH production, indispensable for the biosynthesis of lipids which are required for cell growth and for hepatic vitellogenesis.