Effects of ethynyl estradiol on incorporation of (1-14C) oleate into triglyceride and ketone bodies by the liver

Estrogen induction of fatty liver in dairy cattle

Two trials were conducted to determine if estrogen contributes to development of fatty liver in dairy cattle. During trial 1, eight late lactation, nonpregnant cows were assigned to 0 or 15 mg estradiol-17 beta benzoate/d treatment. Days 1 to 3 of the trial were for baseline measurements, and treatments were given from d 4 to 21; on d 20 and 21 animals were fasted. Short-term feed deprivation resulted in increased plasma FFA concentrations and rapid accumulation of triglyceride into liver tissue obtained by biopsy. During starvation, plasma FFA concentration and liver triglyceride content were lower for cows receiving the estradiol-17 beta treatment relative to cows receiving control treatment. Very low density lipoprotein concentration in blood increased dramatically in three of four animals during estradiol-17 beta administration. Because of the decrease in milk production during estradiol-17 beta treatment, it was not known whether this represented a decrease in very low density lipoprotein clearance from blood or reflected a lipotropic response to estradiol-17 beta. Therefore, a second trial was conducted employing nonlactating cows, and control and estradiol-17 beta-treated animals were pair fed. The trial was 33 d with d 1 to 3 for baseline measurements, and treatments were administered from d 4 to 33. All animals were starved from d 19 to 23. Estradiol-17 beta increased hepatic lipid and triglyceride accumulation and plasma very low density lipoprotein concentration during starvation. Plasma FFA concentration was also increased by estradiol-17 beta during this time; therefore, a direct or indirect effect of estrogen on hepatic lipid metabolism could not be delineated.

Use of combined oral contraceptive preparations alters the insulin sensitivity of fatty acid and ketone metabolism

Eight women taking low-dose-oestrogen combined oral contraceptive preparations were compared to eight women in the luteal phase of the menstrual cycle during hourly incremental insulin infusions of 0 (basal), 0.005, 0.01 and 0.05 U/kg/h short-acting insulin. Dose-response relationships between insulin and intermediary metabolites were sought by analysis of variance applied to regression. For insulin (log) and glucose the slope of the relationship was significantly shallower in the oral contraceptive group. For insulin (log) and non-esterified fatty acids the slopes of the regression lines were not different between groups but lines were significantly displaced. For insulin (log) and total ketone bodies (log) slopes of the regression lines were not different but significant displacement was observed. At identical insulin concentrations women taking an oral contraceptive had higher non-esterified fatty acids (NEFA) (difference between groups +0.15 mmol/l, P less than 0.001) and total ketone bodies (log: -0.26 mmol/l, P less than 0.001). The potency of insulin action in oral contraceptive users versus the luteal group was 0.47 (P less than 0.01) for NEFA and 0.38 (P less than 0.001) for total ketone bodies. The results demonstrate, for the first time, in-vivo insulin resistance of NEFA and ketone bodies' metabolism induced by oral contraceptive use.

Effects of estradiol-17 beta on the net hepatic extraction of triglyceride in vivo in fed and fasted sheep

The effects of estrogen and fasting on hepatic metabolism were studied by an arteriovenous difference technique in six multicatheterized ewes. In each experiment samples were collected during fed and 3- and 5-day fasted states before, and 10 to 17 days after the animals had been implanted with 550 mg of estradiol-17 beta. The implants elevated plasma estradiol five- to seven-fold. Plasma concentrations of insulin and triglyceride (TG) were increased (P less than 0.01) by 131% and 62% respectively by estradiol in fed sheep. Concurrent circulating concentrations of glucose, glycerol, free fatty acids, and beta-hydroxybutyrate were unaffected. During fasting estradiol elevated circulating concentrations of beta-hydroxybutyrate slightly, while levels of other metabolites and insulin were not different from fasted controls. In fed animals estradiol had no effect on the net hepatic uptake (NHU) of TG or glycerol but during fasting estradiol reduced the NHU of TG and glycerol by 47% and 31% (P less than 0.01) respectively. In addition, estradiol reduced the net hepatic production of beta-hydroxybutyrate in fed, but not in fasted animals. Net hepatic exchanges of glucose, or FFA were not affected by estradiol in either the fed or fasted state. Fasting increased the NHU of TG (P less than 0.05) and glycerol (P less than 0.01). The results of this study suggest that estradiol, at physiological concentrations, has lipotropic and anti-ketogenic effects on the ruminant liver. However, the anti-ketogenic effect is not apparent in fasted animals. Secondly, it appears that the hepatic lipidosis which often occurs in ruminants during negative energy balance is due largely to an increase in the NHU of circulating TG.

Metabolic effects of combined oral contraceptive preparations

Fasting intermediary metabolite concentrations were measured in comparable groups of women either in the follicular or luteal phase of the menstrual cycle or taking low-dose estrogen combined oral contraceptive preparations. Blood total ketone bodies concentrations were significantly elevated in oral contraceptive users (p less than 0.05 v follicular and luteal groups) whilst blood alanine levels were lower (p less than 0.01 v follicular).

Stimulation by acetoacetate of hepatic triacylglycerol synthesis

The factors responsible for the huge accumulation of hepatic triacylglycerols in the ketotic diabetic state are not established. Our earlier work suggested a role for ketone bodies in the increased hepatic triacylglycerol synthesis observed in the ketotic diabetic state. Isolated hepatocytes obtained from normal fed rats were incubated with sodium acetoacetate or sodium chloride (control) and [1-14C]palmitate in Krebs-albumin buffer. Acetoacetate stimulated triacylglycerol synthesis in a concentration-dependent manner without increasing palmitate uptake or inhibiting palmitate oxidation. Beta hydroxybutyrate showed no effect on palmitate esterification to triacylglycerols. Isolated hepatocytes of normal fed rats were incubated with either sodium acetoacetate or sodium chloride and the nuclear-free homogenate was incubated with [U-14C]glycero-3-phosphate and cofactors. The synthesis of triacylglycerol and the activity of the cytosolic phosphatidate phosphohydrolase were increased in the cells pre-incubated with acetoacetate. The results of this study demonstrate that the increases in triacylglycerol synthesis and the cytosolic activity of phosphatidate phosphohydrolase previously observed by us in the ketotic diabetic liver, could be reproduced in normal fed rat liver cells by incubating them with acetoacetate. The results identify acetoacetate as a potential factor, in the regulation of hepatic triacylglycerol synthesis and for hepatic accumulation of triacylglycerols observed in the ketotic diabetic state.

Effects of estradiol on tissue distribution of newly-synthesized fatty acids in rats and hamsters

Estradiol treatment decreases body weight and adiposity in ovariectomized (OVX) rats and hamsters partly by increasing energy expenditure. Other manipulations which increase energy expenditure (e.g., cold exposure or overfeeding) enhance thermogenesis in brown adipose tissue (BAT) and stimulate BAT fatty acid synthesis/uptake. We examined the effect of estradiol treatment on the in vivo distribution of newly-synthesized fatty acids in OVX rats and hamsters. In both species estradiol treatment increased BAT fatty acid synthesis/uptake (incorporation of tritium from (3H)2O into lipid), consistent with the possibility that enhanced thermogenesis in BAT may contribute to estradiol-induced energy expenditure. Estradiol treatment increased BAT lipoprotein lipase (LPL) activity in hamsters, but not in rats. Thus, hamsters may utilize fatty acids synthesized in other tissues as a fuel for BAT thermogenesis, whereas rats may rely more on in situ lipogenesis. Estradiol-induced decreases in carcass adiposity (white adipose tissue mass) may be accomplished by different means in rats and hamsters. Estradiol treatment reduced white adipose tissue LPL activity and fatty acid synthesis/uptake in rats, but not in hamsters. While there are some species differences in the effects of estradiol on lipid metabolism, it appears that in both rats and hamsters estradiol acts to direct metabolic fuels (especially lipids) away from white adipose tissue storage depots and into tissues where they are oxidized (e.g., BAT). Finally, cold acclimation and estradiol had similar effects in OVX hamsters including increases in BAT fatty acid synthesis/uptake, BAT LPL activity, and energy expenditure. These findings, too, are consistent with a role for BAT in estradiol-induced thermogenesis.

Lipotropic effect of estradiol-17 beta in fed and fasted lactating cows

The lipotropic effect of estradiol-17 beta was measured in seven nonpregnant Holstein-Friesian cows 2 to 5 wk into lactation. The experiment was divided into an initial 3-day control period, 19 days treatment, and 2 days fast. Jugular blood samples were taken twice daily during the control period, the last 2 days of treatment, and the fast. After the control period, four cows received daily injections of estradiol-17 beta benzoate (15 mg) in sesame oil for the remainder of the experiment whereas three cows received injections of sesame oil only. Estradiol-17 beta did not change triglyceride concentration of plasma during the treatment period but increased it markedly during fast. Estradiol-17 beta increased the free glycerol concentration of plasma during treatment. Cholesterol concentrations of plasma showed a consistent trend lower in the estradiol group during treatment and fast. No differences were apparent in glucose and blood ketone concentrations. The concentration of insulin in plasma was lower for the estradiol group during treatment. Estradiol-17 beta appears to have a similar effect on lipid metabolism in dairy cows to other species. However, it exerted a strong lipotropic effect only under fasting.

Metabolic effects of progesterone

Progesterone has important effects on carbohydrate, lipid and protein metabolism. This steroid induces hyperinsulinemia, possibly by direct action on pancreatic islets, while promoting glycogen storage in the liver. Paradoxically, it antagonizes the effects of insulin on glucose metabolism in adipose tissue and skeletal muscle. Progesterone stimulates deposition of body fat but had catabolic effects on protein metabolism. Provisional evidence is offered that the steroid may influence ketone body production by the liver as well. When these steroid actions are considered together, their most relevant expression appears to be the physiologic changes observed during normal pregnancy.

Metabolic response to starvation. I. Relative effects of pregnancy and sex steroid administration in the rat

Increased sensitivity to a fast with rapid onset of ketosis, hypoalaninemia, and hypoglycemia is characteristic of rat and human gestation. The present study examines the role of sex steroids in the development of these metabolic changes. Subgroups of female rate received 10 microgram of estradiol (E), 10 mg of progesterone (P), or the two in combination (E + P) s.c. daily for 5 days. Control rats (C) received sesame oil alone. Different groups were starved 12, 24 and 48 hr during days 4 and 5 or treatment. Plasma substrate and insulin responses were measured and compared to results of similar studies performed on rats in late gestation. Administration of E or P along had no significant effects on measured parameters as compared to control values. However, the combined E + P regimen resulted in significantly higher ketonemia, greater hypoalaninemia, and relatively higher triglyceride concentrations than in control groups during fasting. Plasma triglyceride, free fatty acid, and ketone concentrations in the pregnant group exceeded values of both the E + P and control animals. However, plasma free fatty acids in the E + P group were significantly lower as compared to control values during starvation. These data suggest that the combined effects of estradiol and progesterone enhance ketogenesis and hypoalaninemia independent of the fetal-placental unit during starvation in pregnancy. Since the ketogenic effect was associated with a relative suppression of plasma free fatty acids, this may be indicative of a direct action of these hormones on hepatic disposition of free fatty acids and/or the biosynthetic pathways for ketone body production.

The influence of hormonal changes of pregnancy on maternal metabolism

Mammalian pregnancy is characterized by progressive hyperinsulinaemia, raised plasma lipids and increased vulnerability to ketosis after food deprivation. The present investigations were performed to assess the role of two placental steroids, oestradiol and progesterone, in the development of these changes, since plasma titres of these hormones progressively increase during human gestation. In both human subjects and adult female rats it was demonstrated that these two steroids, separately or in combination, augment plasma insulin concentration in vivo, cause hypertrophy of pancreatic islets and promote exaggerated secretion of insulin, but not glucagon, by pancreatic islets in vitro. Hypertriglyceridaemia induced by oestrogen alone or combined with progesterone was associated with increased splanchnic production of triglyceride as well as altered tissue lipoprotein lipase (EC 3.1.1.34) and circulating apoproteins that influence activity of this enzyme. The combined regimen also increased hepatic glycogen storage and suppressed gluconeogenesis in vivo in the rat while accelerating the onset of ketosis during starvation in human subjects and in the animal model. Oestradiol and progesterone appear to effect metabolic changes in nonpregnant animals and human subjects that simulate maternal adaptations to advancing gestation, including altered endocrine pancreatic function, triglyceride metabolism and metabolic fuel storage and mobilization.