| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
Women’s Health Research Institute, Wyeth-Ayerst Research (S.G.L., J.M.C., R.C.W.), Radnor, Pennsylvania 19087; and Cardiovascular Research, Wyeth-Ayerst Research (M.-L.M.), Princeton, New Jersey 08852
Address all correspondence and requests for reprints to: Scott G. Lundeen, Ph.D., Women’s Health Research Institute, Wyeth-Ayerst Laboratories, 145 King of Prussia Road, Radnor, Pennsylvania 19087. E-mail address: lundees{at}war.wyeth.com
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-ethinyl
estradiol (EE) was the most potent agent to lower plasma total and high
density lipoprotein cholesterol levels, followed by 17ß-estradiol and
17-estradiol. However, 17-estradiol had the greatest separation
of uterotropic vs. cholesterol-lowering effects. EE had
the same lipid-lowering potency whether administered sc or orally to
adult rats. It had no effect on cholesterol levels in immature rats,
even though the uterotropic response was dramatic. Testosterone
propionate, dexamethasone, and progesterone did not significantly lower
cholesterol levels. The antiestrogens tamoxifen and raloxifene lowered
cholesterol levels, but with less efficacy and potency than the
estrogens. ICI 182780 had no effect on cholesterol levels. When
coadministered with EE, ICI 182780 inhibited the cholesterol-lowering
and uterotropic activities of EE, suggesting that the estrogen receptor
pathway is involved. In conclusion, although the information from the
rat is limited as a model of the low density lipoprotein-lowering
effects of estrogens in humans, it can be used to study the effects and
mechanism of action of estrogen and antiestrogens on plasma cholesterol
levels. |
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Rats have been used as a model system to study estrogenic effects on plasma lipid levels (10, 11, 12). The predominant plasma cholesterol in rats is HDL, not LDL, as it is in humans. Estrogens dramatically decrease both LDL and HDL cholesterol plasma levels in rats. Therefore, one acknowledged weakness of the rat model is that it is only useful for evaluating the mechanisms involved in the LDL-lowering effects of estrogen and provides little, if any, relevant information on potential effects on HDL. As in humans, there is little information on the molecular mechanism by which estrogens lower cholesterol in the rat. Early studies provided mechanistic clues as to how the estrogens mediate their effects on plasma lipids. It was shown that pharmacological doses of estrogens up-regulate LDL receptors in rat livers (13, 14) and in human hepatoma cell lines (15). It has also been shown that LDL binding in human liver homogenates is correlated with serum estrogen concentrations (16). Regulation of the LDL receptors has been shown to involve both transcriptional (17) and posttranscriptional (13, 14) mechanisms.
There also are few data to support the role of the classical estrogen receptor (ER) pathway in mediating the lipid-lowering effect of estrogens. Clearly, transcriptional regulation of the LDL receptor provides suggestive evidence for classical ER control. However, there are few data to support this hypothesis, and direct evidence for ER involvement is still lacking. In fact, there is evidence suggesting that a novel mechanism is involved. Firstly, the antiestrogens tamoxifen and raloxifene act as estrogen agonists in the liver, causing a decrease in total plasma cholesterol in rats and LDL in humans (11, 18, 19, 20, 21, 22). Secondly, the potencies of estrogens in the liver, as measured by changes in plasma cholesterol, do not correspond with their potencies in the uterus or their relative affinities for the ER (23).
We initiated these studies to characterize the effects of estrogens on plasma lipid levels in rats as a model for the indirect cardioprotective effects of estrogen. In doing so, we have examined several estrogenic and antiestrogenic compounds in this system and studied the role of the ER in mediating the response in the liver vs. that in the uterus.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-Ethinyl estradiol (EE), 17ß-estradiol
(17ß-E2), 17-estradiol
(17-E2), and dexamethasone were obtained from
Sigma Chemical Co. (St. Louis, MO); tamoxifen citrate was obtained from
Stuart Pharmaceuticals (Wilmington, DE); progesterone and testosterone
propionate were obtained from Steraloids (Wilton, NH). ICI 182,780 was
generously supplied by Zeneca Pharmaceuticals (Wilmington, DE).
Raloxifene was synthesized by the Wyeth-Ayerst Medicinal Chemistry
group. Stock solutions of the test compounds were prepared in either
100% ethanol or dimethylsulfoxide. The compounds were diluted into
10% ethanol in corn oil (Mazola, Best Food Division, CPC International
Inc., Englewood Cliff, NJ) vehicle before treatment of the animals.
Animals and treatment protocols
The research animals were housed in a facility accredited by the
American Association for Accreditation of Laboratory Animal Care in
accordance with the Animal Welfare Act and the Guide for the Care and
Use of Laboratory Animals, and the study was approved by the
institutional animal care and use committee of Wyeth-Ayerst Research.
Immature female (19 days old) or ovariectomized female (60 day-old)
Sprague-Dawley rats were obtained from Taconic Farms (Germantown, NY).
The ovariectomies were performed by the supplier a minimum of 8 days
before the first treatment. The animals were housed under a 12-h light,
12-h dark cycle and given Purina 5001 rodent chow (North Penn Feeds,
North Wales, PA) and water ad libitum. Upon arrival, the
rats were randomized and placed in groups of four to eight, depending
upon the experiment. The adult animals were given a minimum of 72
h to acclimate to the surroundings. The treatment of the immature rats
began 24 h after arrival to ensure that the rats did not reach
sexual maturity before the completion of treatment. After the
acclimation period, the animals were treated once a day for 4 days with
the compound(s) of interest. Doses were prepared based on milligrams
per kg mean group BW. Administration of the compound was either by sc
injection (sc) of 0.2 ml in the nape of the neck or intragastrically by
gavage (orally) in a volume of 0.5 ml. A vehicle control group was
included in all experiments. Approximately 24 h after the final
treatment the animals were killed by CO2 asphyxiation.
After death, the uteri were removed from the animals, drained of fluid,
stripped of remaining fat and mesentery, and weighed.
Plasma cholesterol measurements
Blood samples were collected by cardiac puncture after death
into vacuum tubes containing EDTA to prevent coagulation. The samples
were centrifuged (1000 x g, 10 min), and the plasma
was removed and placed in fresh tubes. Total cholesterol was determined
in whole plasma using the Boehringer Mannheim Cholesterol/HP system
pack (Boehringer Mannheim Diagnostic Laboratory Systems, Indianapolis,
IN) and the Boehringer Mannheim Hitachi 911 Analyzer (Boehringer
Mannheim Diagnostic Laboratory Systems) by the Cardiovascular Division,
Wyeth-Ayerst Research (Princeton, NJ). HDL was determined in plasma
from which the LDL and very low density lipoprotein were precipitated
using the phosphotungstic acid/magnesium chloride precipitation method
with the HDL-Cholesterol system pack as described by the manufacturer
(Boehringer Mannheim Diagnostic Laboratory Systems). Briefly, 200 µl
plasma were mixed with 500 µl precipitation reagent. The samples were
incubated at room temperature for 10–30 min, then centrifuged at
2000 x g for 10 min. The supernatant solutions were
removed and analyzed for cholesterol as described above for total
cholesterol. The Boehringer Mannheim reagent composition for
cholesterol measurement is identical in both kits. The kits were
validated for cholesterol measurement using rat serum, with an
intraassay coefficient of variation of 1.1% and an interassay
coefficient of variation of 1.8%. The reportable range for total
cholesterol is 3–800 mg/dl, and that for HDL cholesterol is 3–150
mg/dl.
Statistical analysis
The data for uterine wet weights and plasma cholesterol levels
were heterogeneous between the doses. Therefore, the uterine weights
were transformed by logarithms, and cholesterol levels were transformed
by square root to stabilize the variability. After transformation, the
Huber M-estimation weighting was used to down-weight the outlying
transformed observations (24). JMP software (SAS Institute, Cary, NC)
was used to analyze the transformed and weighted data for both the
one-way ANOVA and the nonlinear dose-response curves. In all cases, the
dose-response curves were nonlinear; that is, when the response was
plotted against the log of the concentration, the curves were
sigmoidal. Dose-response data are calculated and expressed as the
EC50 (mean ± SE) for uterotropic effects
and the IC50 (mean ± SE) for
lipid-lowering effects. The EC50 and IC50
values were calculated using the four-parameter logistic model that
calculates the minimum, maximum, Hill’s coefficient, and
ED50 (25). In cases where the dose-response curves did not
plateau or the response was too shallow, the program was unable to
calculate an EC50 or IC50 value. In these
cases, the EC50 or IC50 values were estimated
graphically.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-E2, and
17ß-E2
. When
administered orally, uterine wet weight increased in a dose-dependent
manner (Fig. 1A), and both plasma total and HDL cholesterol levels
decreased similarly (Fig. 1, B and C). The mean uterotropic
EC50 for four separate experiments was 100.8 µg/kg BW,
with IC50 values of 21.1 and 17.7 µg/kg BW for total and
HDL cholesterol, respectively. When EE was administered via the sc
route (five separate experiments), the mean EC50 for
uterine wet weight increase over vehicle was 0.3 µg/kg BW, 300-fold
lower than when EE was administered by gavage (Table 1).
However, the IC50 values of EE for plasma total and HDL
cholesterol lowering were the about the same as when EE was
administered orally (21.6 and 15.1 µg/kg BW, respectively). The data
for HDL are shown here, but will not be shown for subsequent
experiments because in all cases the effect of estrogens on plasma HDL
was similar to that on plasma total cholesterol.
|
|
-E2 and 17ß-E2 in a
similar study. The two compounds were administered at doses of 0.01,
0.5, and 5.0 mg/kg BW, both orally and sc. As with EE, the effects of
both compounds were more potent on the uterus when they were
administered sc, yet their potencies for lipid lowering were the same
regardless of the route of administration (Fig. 2).
|
-E2 and
17ß-E2 were also run in full dose-response
curves using the sc route of administration. The EC50
values for uterine wet weight increase over vehicle were 207 and 0.67
µg/kg BW, respectively (Table 1
). This difference in potencies of
17-E2 and 17ß-E2 in
the uterus correlates well with their relative affinities for the ER.
However, the potencies of the two compounds in the liver, as assessed
by plasma total cholesterol levels, were only 2-fold different;
IC50 values were 1414 and 665 µg/kg BW for
17-E2 and 17ß-E2, respectively
(Table 1).
Regulation of lipid levels in immature rats
To extend our studies to the immature rat model, we ran
dose-response curves for 17-EE in 19-day-old rats. The compound was
administered by gavage at doses ranging from 1–5000 µg/kg BW. As
expected, 17-EE increased uterine wet weight with an
EC50 of 8 µg/kg BW (Fig. 3). However,
unlike the adult rat, total and HDL cholesterol were unchanged, even at
the 5.0 mg/kg dose (Fig. 3).
|
).
Dexamethasone significantly decreased body weight about 10% and 30%
at 0.05 and 5.0 mg/kg, respectively, but had no effect on uterine wet
weight. Dexamethasone also significantly (P 
0.05)
increased LDL cholesterol levels at 5.0 mg/kg BW (Table 2).
Progesterone had no effect on uterine wet weight or plasma cholesterol
levels (Table 2).
|
). However, its
efficacy was only about 20% that of 17-EE. It had limited ability
to lower plasma cholesterol levels; treated levels differed
significantly from the control values only at 1.0 and 10.0 mg/kg BW.
Although the decrease in plasma cholesterol was significant, it was
small compared to the decrease evoked by the estrogens examined. Total
cholesterol levels dropped from the control level of 82 mg/dl to 65 and
52 mg/dl at 1.0 and 10.0 mg/kg BW, respectively (Fig. 4B). Tamoxifen is
metabolized in the liver to its active form, 4-hydroxytamoxifen (26).
Therefore, we ran a dose-response curve with tamoxifen administered by
gavage. Unlike 17-EE and the other compounds, the route of
administration did not affect the potency of the compound in either the
uterus or liver (Fig. 4).
|
), lowering total cholesterol
from the control level of 95 to 64 mg/dl at the 5.0 mg/kg BW dose.
Raloxifene also caused a small, but significant, increase in uterine
wet weight at 0.5 and 5.0 mg/kg BW (Fig. 5).
|
, A and B). ICI
182,780 was also run as an antagonist against 17-EE. In this
experiment 17-EE was administered by gavage at 0.1 mg/kg BW. This
dose, when administered orally, was about the EC50 dose for
uterine wet weight increase and the IC80 dose for lipid
lowering. ICI 182,780 was administered sc at doses ranging from
0.05–5.0 mg/kg BW. When the two compounds were coadministered, ICI
182,780 blocked the uterine wet weight increase induced by EE (Fig. 7A). It also blocked the lipid-lowering effect of EE
(Fig. 7B), suggesting that EE is acting through the ER to lower plasma
cholesterol levels. The blockage of lipid lowering was maximal at about
1.0 mg/kg; however, it was not complete even at the 5.0 mg/kg dose.
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The rat has noted differences and shortcomings as a model for human cholesterol metabolism that must be considered when using the rodent model. Most notably, in the rat HDL is the predominant form of cholesterol in plasma, comprising about 60–70% of the total cholesterol pool. Moreover, both LDL and HDL cholesterol levels decrease after estrogen treatment; in humans, estrogens decrease plasma LDL, but increase plasma HDL (7, 8, 9). One mechanism that may explain the difference in HDL metabolism is that rat HDL contains higher amounts of apoprotein E than does human HDL (10). The rat LDL receptor has high affinity for apoprotein E. Therefore, HDL particles containing apoprotein E are cleared from the blood at a higher rate in rats than in humans after estrogen treatment (10). A second mechanism that may contribute to the decrease in plasma HDL in rats is the effect of estrogen on the enzymes involved in HDL metabolism. It has been reported that estrogens decrease lipoprotein lipase (LPL) activity in rats (27, 28). Decreasing LPL activity lowers plasma HDL levels. Moreover, hepatic lipase, which is down-regulated after estrogen treatment in humans (29), is not regulated by estrogen in rats (30). Therefore, clearly, the effects of estrogen on HDL metabolism cannot be addressed in this model. Even with the differences in HDL metabolism, the rat system provides a good model to study the mechanism of LDL lowering. There is evidence that at least some aspects of the mechanism of LDL lowering are similar in rats and humans. The LDL receptor is up-regulated in rats; there is evidence for similar regulation in the human hepatoma cell line HepG2 and in human liver homogenates (13, 14, 15, 16). The validity of the model is further supported by the fact that compounds that reduce plasma total cholesterol in the rat model, such as EE, 17ß-E2, tamoxifen, and raloxifene, have beneficial effects on plasma cholesterol profiles when administered to humans (2, 22, 31).
There are conflicting reports as to whether, in humans, the beneficial effects of estrogen on plasma cholesterol requires the "first pass" through the liver. There are reports demonstrating that when estrogens are administered through transdermal patches, the compounds have little effect on plasma cholesterol levels (32). Other reports demonstrate significant effects of estrogens on plasma cholesterol when administered by either an oral or a transdermal route (33, 34). In the rat, our studies demonstrate that the potencies of five different estrogens on cholesterol lowering are unaffected by the route of administration. If the first pass through the liver was required for the effects of the estrogens, the potencies would differ when the compounds were administered orally or sc. Therefore, in the rat, the cholesterol-lowering effect of estrogen does not require the first pass through the liver.
Our studies demonstrate that estrogens have no effect on plasma cholesterol levels in the immature rat. To our knowledge, this is the first report of this finding. It has previously been shown that there is developmental regulation of components of the plasma lipoprotein particles in rats. The messenger RNA levels for both apoprotein AI and AII rapidly change between days 20 and 40, the period when the animals go through sexual maturation (35). Also, platelet-activating factor-acetylhydrolase, an enzyme that is associated with LDL and HDL particles, is estrogen regulated in adult rats, but not in immature rats (36). It has been reported that ER levels in the liver are developmentally regulated (37), low in immature animals and higher in adult animals, and may account for the developmental regulation. We are interested in this developmental regulation and are continuing to pursue its mechanism.
The effects of both tamoxifen and raloxifene on plasma lipid levels were less than reported previously (11, 18, 19, 20). This is probably due to the fact that the duration of our treatment was only 4 days, much shorter than in previous studies. cis-tamoxifen, when administered at 0.5 mg/kg BW for 12 days, decreased total plasma cholesterol 65% (19). Similarly, when tamoxifen citrate was administered weekly at 20.0 mg/kg BW for 4 weeks, both total and HDL cholesterol levels decreased about 50% from control levels (18). Raloxifene has also been reported to lower total cholesterol in rats when administered daily for 5 weeks (11, 20). Clearly, the shorter treatment time produced a much smaller response than the long term treatment. However, the 4-day period is long enough to see significant lowering of plasma lipids.
Interestingly, the potencies of 17-E2 and
17ß-E2 in the liver and uterus are very different. The
potencies we have seen in the uterus correspond well with the
affinities of these two ligands for the ER (23). However, the
difference in IC50 values for these compounds for lipid
lowering is only 2-fold. It is not believed that the liver has the
enzymatic capacity to isomerize the 17-isomer to the 17ß-isomer.
Therefore, the mechanism for estrogenic effects on lipid lowering may
be different from the mechanisms involved in the uterus.
To address the issue of whether the classical ER is mediating the lipid-lowering effect of estrogens, we used the pure antiestrogen ICI 182,780. This compound is a potent antiestrogen with little known agonistic activity and is believed to act specifically through the ER (38). ICI 182,780 administered alone had no effect on either uterine wet weight or plasma cholesterol levels, supporting its profile as a pure antiestrogen. However, when administered along with EE, it was able to block the effect of EE on both uterine wet weight and plasma cholesterol. However, the lipid levels never return to the vehicle-treated control levels when ICI 182,780 is used as an antagonist. It is not clear whether this residual response represents an effect that is mediated by a nonreceptor mechanism or the biological variability of the system. This is the first report of the effect of ICI 182,780 on rat liver and, in particular, plasma cholesterol levels. More importantly, it provides evidence for the involvement of the ER in controlling plasma lipid levels.
In summary, we have further characterized the rat as a model for estrogen-mediated plasma cholesterol lowering. It now seems likely that estrogens are functioning through the ER, but there are still many questions that need to be addressed. Primarily, what are the molecular targets through which estrogens regulate plasma cholesterol levels? The LDL receptor is one target already identified, but are there others? What relevance do the targets in rats have in regulating cholesterol levels in humans? Is there a non-ER-mediated component involved in the regulation, and what is the mechanism of the developmental regulation of the estrogen-induced lipid lowering? Studies are in progress to address some of these important questions.
|
Acknowledgments |
|---|
Received September 20, 1996.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-ethinyl estradiol. J Biol Chem 254:11367–11373-ethinyl estradiol. J Biol Chem 254:11360–11366-ethinyl estradiol. Proc Natl Acad Sci USA 83:792–796This article has been cited by other articles:
 |
|
 |
|
  N. J. MacLusky, V. N. Luine, T. Hajszan, and C. Leranth The 17{alpha} and 17{beta} Isomers of Estradiol Both Induce Rapid Spine Synapse Formation in the CA1 Hippocampal Subfield of Ovariectomized Female Rats Endocrinology, January 1, 2005; 146(1): 287 - 293. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. E. Goss, S. Qi, A. M. Cheung, H. Hu, M. Mendes, and K. P. H. Pritzker Effects of the Steroidal Aromatase Inhibitor Exemestane and the Nonsteroidal Aromatase Inhibitor Letrozole on Bone and Lipid Metabolism in Ovariectomized Rats Clin. Cancer Res., September 1, 2004; 10(17): 5717 - 5723. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J.-x. Zhang, D. C. Labaree, G. Mor, and R. B. Hochberg Estrogen to Antiestrogen with a Single Methylene Group Resulting in an Unusual Steroidal Selective Estrogen Receptor Modulator J. Clin. Endocrinol. Metab., July 1, 2004; 89(7): 3527 - 3535. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. A. Kramer, J. LeDeaux, D. Butteiger, T. Young, C. Crankshaw, H. Harlow, L. Kier, and B. G. Bhat Transcription Profiling in Rat Liver in Response to Dietary Docosahexaenoic Acid Implicates Stearoyl-Coenzyme A Desaturase as a Nutritional Target for Lipid Lowering J. Nutr., January 1, 2003; 133(1): 57 - 66. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. A. Harris, J. A. Katzenellenbogen, and B. S. Katzenellenbogen Characterization of the Biological Roles of the Estrogen Receptors, ER{alpha} and ER{beta}, in Estrogen Target Tissues in Vivo through the Use of an ER{alpha}-Selective Ligand Endocrinology, November 1, 2002; 143(11): 4172 - 4177. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Y. Chan, X. Yao, S. Y. Tsang, J.-P. Bourreau, F. L. Chan, and Y. Huang Isoproterenol amplifies 17{beta}-estradiol-mediated vasorelaxation: role of endothelium/nitric oxide and cyclic AMP Cardiovasc Res, February 15, 2002; 53(3): 627 - 633. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. M. Fitts, R. M. Klein, and C. A. Powers Estrogen and Tamoxifen Interplay with T3 in Male Rats: Pharmacologically Distinct Classes of Estrogen Responses Affecting Growth, Bone, and Lipid Metabolism, and Their Relation to Serum GH and IGF-I Endocrinology, October 1, 2001; 142(10): 4223 - 4235. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. D. Papaconstantinou, T. H. Umbreit, B. R. Fisher, P. L. Goering, N. T. Lappas, and K. M. Brown Bisphenol A-Induced Increase in Uterine Weight and Alterations in Uterine Morphology in Ovariectomized B6C3F1 Mice: Role of the Estrogen Receptor Toxicol. Sci., August 1, 2000; 56(2): 332 - 339. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. F. Couse and K. S. Korach Estrogen Receptor Null Mice: What Have We Learned and Where Will They Lead Us? Endocr. Rev., June 1, 1999; 20(3): 358 - 417. [Abstract] [Full Text]
|
|
|
|
 |
|
 M. A. Pelleymounter, M. B. Baker, and M. McCaleb Does estradiol mediate leptin's effects on adiposity and body weight? Am J Physiol Endocrinol Metab, May 1, 1999; 276(5): E955 - E963. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W. Khovidhunkit and D. M. Shoback Clinical Effects of Raloxifene Hydrochloride in Women Ann Intern Med, March 2, 1999; 130(5): 431 - 439. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. D. Sibonga, H. Dobnig, R. M. Harden, and R. T. Turner Effect of the High-Affinity Estrogen Receptor Ligand ICI 182,780 on the Rat Tibia Endocrinology, September 1, 1998; 139(9): 3736 - 3742. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Luo, A. Sourla, C. Labrie, A. Belanger, and F. Labrie Combined Effects of Dehydroepiandrosterone and EM-800 on Bone Mass, Serum Lipids, and the Development of Dimethylbenz(A)Anthracene-Induced Mammary Carcinoma in the Rat Endocrinology, October 1, 1997; 138(10): 4435 - 4444. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |
) or sc injection (
) in 10% ethanol
in corn oil vehicle once a day for 4 days. Points are
the mean from four animals per group shown with the SE.
) and
plasma total cholesterol levels (
,
Significantly different from vehicle control (P <
0.05) with sc administration.
