Effects of ethynyl estradiol and progesterone on triglyceride metabolism in the female rat

Dydrogesterone and norethisterone regulate expression of lipoprotein lipase and hormone-sensitive lipase in human subcutaneous abdominal adipocytes

AIM

In premenopausal women, hyperandrogenicity is associated with central obesity and an increased cardiovascular risk. The aim of this study was to investigate the effects of dydrogesterone (DYD) (a non-androgenic progestogen) and norethisterone (NET) (an androgenic progestogen) on lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and glycerol release in adipocytes isolated from subcutaneous abdominal adipose tissue.

METHODS

Adipose tissue was obtained from 12 non-diabetic women, mean age 51 years (range 37-78) and mean body mass index 25.4 kg/m(2) (range 20.3-26.4). Adipocytes were treated with increasing doses of DYD and NET for 48 h prior to protein extraction. Effects on lipogenesis and lipolysis were assessed using western blotting to determine the expression of key enzymes, LPL (56 kDa) and HSL (84 kDa) respectively. Measurement of glycerol release into the medium provided an assessment of lipolytic activity.

RESULTS

Expression of LPL was increased by DYD and NET (mean protein expression relative to control +/- s.e.), with greatest effect at 10(-8) M for DYD: 2.32 +/- 0.51 (p < 0.01) and 10(-8) M for NET: 2.06 +/- 0.19 (p < 0.01). In contrast, HSL expression was reduced by all concentrations of DYD, with maximal effect at 10(-9) M : 0.49 +/- 0.02 (p < 0.001). NET reduced HSL expression at all concentrations from 10(-9) M : 0.62 +/- 0.06 (p < 0.001) to 10(-7) M : 0.69 +/- 0.08 (p < 0.001). Glycerol measurements supported the HSL expression studies although they were not statistically significant (p > 0.05).

CONCLUSIONS

DYD and NET significantly increased LPL expression relative to control, while significantly reducing HSL expression. At the concentrations studied, similar effects were observed with the androgenic NET and the non-androgenic DYD despite differing effects on the lipid profile when taken orally in combination with oestrogen. Further work examining the effects of different progestogens on body fat distribution may enable progestogen use to be tailored to maximize benefits and minimize potential harm.

Persistent suppression of hepatic CYP2A1 expression and serum triiodothyronine levels by tamoxifen in intact female rats: dose-response analysis and comparison with 4-hydroxytamoxifen, fulvestrant (ICI 182,780), and 17beta-estradiol-3-benzoate

Tamoxifen, a nonsteroidal antiestrogen, is used widely in the treatment of breast cancer and is undergoing evaluation as a chemopreventive agent. In this study, we investigated several long-term effects of tamoxifen in intact adult female rats following acute treatment at various dosages. The effects of tamoxifen on somatic growth, growth hormone (GH) levels, thyroid hormone levels, and on hepatic cytochrome P450 (P450) expression were compared with those of fulvestrant (ICI 182,780), 17beta-estradiol-3-benzoate, and 4-hydroxytamoxifen under the same experimental conditions. Each compound was injected s.c. for two consecutive days, and rats were killed 37 days after treatment. Tamoxifen decreased body weight and serum triiodothyronine (T3) levels at dosages ranging from 0.5 to 200 mg/kg. Ovary weight, uterus weight, peak plasma GH concentration, and hepatic CYP2A1 content were decreased 37 days after treatment with tamoxifen at a dosage of 20 mg/kg, but expression of other P450 enzymes was not affected. However, tamoxifen and 4-hydroxytamoxifen could not be detected in plasma by high performance liquid chromatography analysis at this time, which suggests that the effects of tamoxifen were mediated indirectly. 4-Hydroxytamoxifen exhibited effects similar to those of tamoxifen, indicating that this metabolite contributes to the in vivo activity of tamoxifen. Estradiol benzoate decreased CYP2A1 and increased CYP3A hepatic levels, but had no effect on serum T3 concentration. In contrast, treatment with ICI 182,780 had little or no effect on the endpoints measured. In summary, 2-day tamoxifen treatment of intact adult female rats resulted in persistent suppression of somatic growth, serum T3 levels, and hepatic CYP2A1 expression.

Effect of dietary restriction on triglyceride levels in the uterus isolated from pregnant rats. Influences of prostaglandins and indomethacin

Triglyceride (TGs) concentrations in uterine strips isolated from 14 or from 21 days-pregnant rats, either normal-fed or following a restricted-diet rats (50% food intake for 14 days), were measured. Determinations were made immediately after killing (0 min time or post-isolation) as well as after a period of incubation in glucose-free medium (60 min time or post-incubation). The post-isolation levels of TGs (0 min) in the uterus from normal-fed animals at 14 or at 21 days of pregnancy, were significantly higher in implantation sites than in the interembryonic segments. These values of TGs (0 time) did not change, in comparison to post-incubation concentrations (60 min), either without additions or in the presence of indomethacin (5 X 10(-6) M) or of prostaglandins (PGs) E1, E2 or F2 alpha (10(-7) M). At 0 time, uterine TGs of rats subjected to dietary restriction, increased as pregnancy progressed, more than in normal-fed controls. The post-incubation (60 min) pattern was different depending on the days of pregnancy; i.e. at 14 days, incubation in Krebs-Ringer Bicarbonate-medium (KRB) led to a significant fall unaffected by the addition of propranolol (10(-6) M). However, in the presence of indomethacin, TGs values had a level similar to the initial one (0 time). Furthermore, exogenous PGE1 or PGE2 failed to alter the effect of indomethacin, as PGF2 alpha did.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased adenylate cyclase catalytic activity explains how estrogens "in vivo" promote lipolytic activity in rat white fat cells

Estradiol administration (5 micrograms per day x 4 days) to ovariectomized rats resulted in a 60-70% increase in the maximal lipolytic response of their white adipocytes to isoproterenol, epinephrine, IBMX and forskolin. These altered lipolytic responses were accompanied by parallel changes in the intracellular cyclic AMP levels found in response to 1 mM IBMX alone (+ 106%) or combined with submaximal concentrations of isoproterenol (+205%), epinephrine (+190%) and forskolin (235%). Studies of the adenylate cyclase activity revealed an overall increase in the stimulatory responsiveness of the enzyme (+150 to +200%) after the estradiol-treatment, regardless of the stimulatory agents tested (GTP, GppNHp, fluoride, isoproterenol, ACTH, forskolin). Finally, the finding of a 2-fold enhancement of the Mn2+ (+/- GDP beta S)-stimulated adenylate cyclase activity after the estradiol-treatment strongly suggests that increased activity of the catalytic subunit of this enzyme is the likely mechanism whereby estrogens promote lipolysis in rat fat cells.

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.

Effects of progestogens on lipemia and lipolysis in rat: effects of progesterone, megestrol acetate, norethindrone acetate, and nomegestrol acetate

Effects of 4 progestogens at equal dosages (5 mg/kg/day) on lipid metabolism and plasma glucose levels of adult female rats were compared. The 4 progestogens studied were progesterone (P) by SC injection, and megestrol acetate (MEG), norethindrone acetate (NOR), and nomegestrol acetate (NOM) PO. MEG, a 17 alpha-hydroxyprogesterone derivative, induced significant increases in glucose, total and high-density lipid (HDL) cholesterol, triglyceride, and phospholipid plasma levels. Treatment with NOR, a 19-nortestosterone derivative, resulted in a reduced gain in body wt and in a marked decrease in all plasma lipid parameters. The 19-norprogesterone derivative NOM, like P, did not alter lipid or glucose metabolism, despite a significant increase in body wt gain. In particular, no reduction in the HDL cholesterol level occurred. Plasma and tissue lipolytic activities remained unchanged. The results of this study confirm interest in the therapeutic class of 19-norprogesterone-derived progestogens, exemplified by NOM, with respect to their lack of metabolic side effects.

Sex steroid hormones and adipose tissue metabolism in ovariectomized and adrenalectomized rats

The effects of oestrogen and progesterone, alone or in combination, on regional adipose tissue metabolism and oestrogen binding were examined in rats which were not only ovariectomized but also adrenalectomized to allow a study under conditions such that no endogenous sex steroid production occurred. Under these conditions no effects on food intake of the sex steroid hormones were found. 17-beta-oestradiol plus progesterone tended to increase lipoprotein lipase in the parametrial but not retroperitoneal fat depot, but no effects were found of oestrogen or progesterone alone. Oestradiol alone or in combination with progesterone clearly increased basal and norepinephrine-stimulated lipolysis, most pronounced in the retroperitoneal depot. Progesterone alone had no effect. Cytoplasmic 17-beta-oestradiol binding was highest in the parametrial fat depot in non-substituted rats and decreased dramatically after oestrogen administration. It was concluded that in ovariectomized-adrenalectomized rats, oestrogen alone or in the presence of progesterone facilitates lipolysis, a clear effect which is thus possible to elicit without adrenal hormones. Both sex steroid hormones alone or in combination, have no or weak effects on food intake and lipoprotein lipase activity, respectively. These metabolic events as well as cytoplasmic oestrogen binding show regional variations.

Hormonal modulation of adipose tissue lipoprotein lipase may alter food intake in rats

Daily injections of 5 mg progesterone for 3 wk preferentially increased parametrial depot weight and fat cell size in ovarian intact rats. Adipose tissue lipoprotein lipase (LPL) activity was also preferentially increased in the parametrial depot. LPL activity increased at 24 h, whereas food intake did not increase until 36 h after the first injection. Parametrial fat cell size was significantly increased by 84 h and increased further by 3 wk. Daily injections of 2.5 microgram of estradiol for 3 wk decreased fat cell size and LPL activity in the parametrial depot of female rats, whereas in vitro glycerol release was unchanged. Serum triglycerides were increased, but free fatty acids were unaffected. The data suggest that ovarian hormones affected fat cell size in the rat through their modulation of LPL activity. These findings are consistent with the hypothesis that, during progesterone administration, preferential uptake of serum triglycerides into adipose stores decreases the availability of triglyceride-derived energy to the organism stimulating increased food intake.

Evolution of plasma levels of apolipoprotein B, cholesterol and triglycerides in women during long-term oral contraception

Apolipoprotein B (apo B) was measured by a sensitive and specific double antibody radioimmunoassay in plasma from 15 normal women and 47 women taking oral contraceptives. The plasma apo B concentration in normal women was 0.90 +/- 0.10 g/l (mean +/- S.D.) whereas the overall value for all women taking contraceptives was 0.69 +/- 0.19 g/l. The maximum decrease (p less than 0.001) occurred in women investigated within three months after the beginning of the steroid intake, whose mean apo B value was 0.60 +/- 0.12 g/l (n = 12); decreases found after 3--24 months of contraception were of lesser magnitude. Apo B decreases were associated with significant decreases (p less than 0.01) in total plasma cholesterol, although the latter regained normal values after one year of contraception. Apo B and cholesterol values were in the normal range in women investigated after two years of steroid intake. An inverse trend was observed for plasma triglycerides, which showed a mean increase of 29% (p less than 0.01) after three months of steroid intake, and then stayed elevated without significant change with time.