Strain variability in Zucker rats affects their response to oral oleoyl-estrone.

There is a considerable variability in the responses of Zucker fa/fa rats in metabolic studies, which could not be solely attributed to the leprfa mutation. In order to fathom the extent of this variability, we compared the response to oleoyl-estrone (OE), a powerful lipid-mobilising agent, of two strains of Zucker lean and obese rats: Harlan (H) and Charles River (CR). Rats were given an oral gavage of 10 micromol/day/kg of OE in sunflower oil, and were compared with oil-receiving controls. Body composition, energy and water balances, and plasma parameters were studied after 10 days of treatment. H rats showed a higher water turnover than CR rats; OE treatment reduced water intake, partly compensated by metabolic water, and decreased stool water. H rats accrued more cholesterol than CR animals, which showed higher cholesterolaemia. OE facilitated cholesterol disposal in lean (CR and H) and H obese rats. CR rats had higher body and liver lipids than H animals. No differences in energy balance were found. Insulin decrease following OE treatment was greater in lean CR than in H rats, but this trend was reversed in the obese rats, lacking effective responses to leptin. The red cell glucose compartment was smaller in H than in CR rats; the higher insulin levels in H rats may be partly responsible for that difference. Obese H maintained glycaemia (and liver glycogen) with higher insulin levels than CR animals. The extent to which the leprfa mutation affects the responses of Zucker fa/fa rats could not be singled out unless the metabolic environment of the batch used is known. This variability must be taken into account when developing a metabolic or hormonal study in which this model of obesity is used.

Effect of oral oleoyl-estrone on the energy balance of diabetic rats.

We studied the effects of a 10-day oral 10 micromol/kg oleoyl-estrone (OE) treatment on streptozotocin-diabetic Wistar, Goto-Kakizaki and control Wistar rats. Streptozotocin rats lost more than half the energy ingested as urine glucose. Oleoyl-estrone induced the loss of body weight (mainly body fat) in all groups. Energy expenditure was similar in the three groups of rats studied. Water turnover was deranged in streptozotocin rats, which spent 14% of energy available heating the water drunk. Body lipids were highest in Goto-Kakizaki; lipid levels in streptozotocin rats were very low. Oleoyl-estrone decreased body lipid content in Wistar and Goto-Kakizaki; oleoyl-estrone decreased triacylglycerols (44% in Wistar and Goto-Kakizaki and 22% in streptozotocin rats) and phospholipids but did not affect body cholesterol. Oleoyl-estrone decreased insulin and leptin, did not affect blood glucose but decreased plasma glucose in all groups. There were no changes in plasma triacylglycerols or fatty acids, but HDL, LDL and cholesterol decreased in all groups. The same effects of OE on insulin, plasma (but not blood) glucose and leptin were observed in both models, but the presence of insulin seems to be needed for OE to normalise glycaemia and to facilitate the uptake and utilisation of glucose by tissues. This different handling of glucose and triacylglycerol energy accounts for the disparate effects of OE on energy balance. The main conclusion of this study is that OE function as a lipid-mobilising hormone is dependent on the mass of reserves available, which in turn is closely related to insulin status. Lack of insulin thus results in limited OE effects, and insulin resistance does not prevent or limit the effects of OE on energy homeostasis or the mobilisation of fat.

Zucker obese rats store less acyl-estrone than lean controls.

OBJECTIVE: To measure acyl-estrone levels in the plasma of Zucker obese rats. If these are lower than expected on the basis of their body-fat content, as observed in morbidly obese humans, this might provide a possible link relating obesity and low body estrone levels. We also examined the effect of pharmacological treatment with oral oleoyl-estrone on the accumulation of estrone. DESIGN: Undisturbed Wistar, Goto-Kakizaki and Zucker (lean Fa/?and obese fa/fa) rats were used to determine the relation between circulating acyl-estrone and body lipids, as well as the total body estrone/lipid ratios. One group of Wistar rats was used to measure the effect of oral gavages of oleoyl-estrone (from 0 to 20 micromol/kg/day) for 10 days on the body content of estrone. MEASUREMENTS: Body weight change and food intake. Total estrone intake, estrone accrual and excretion (by difference) in rats receiving oleoyl-estrone. Total body lipid and estrone. Circulating acyl-estrone levels. RESULTS: In lean rats (Wistar, Zucker and Goto-Kakizaki) there was a direct relation between body lipid content and circulating acyl-estrone; this relation was not found in Zucker obese rats. The estrone/lipid mass ratio was in a similar range in lean rats, but obese animals showed much lower values. Wistar rats receiving pharmacological doses of oleoyl-estrone did not accumulate significant amounts of estrone, but excreted almost all the estrone ingested. CONCLUSIONS: The pharmacological administration of acyl-estrone to rats does not result in the accrual of estrone within a wide range of doses, which confirms the safety of this compound. In rats there is a similar relation between the percentage of body lipids and circulating acyl-estrone to that found in humans. Likewise, obese rats showed lower levels of acyl-estrone than expected. The total content of estrone in the bodies of obese rats was also lower than expected from their high lipid content, which suggests that obese rats are deficient in acyl-estrone.

Effect of oral oleoyl-estrone on adipose tissue composition in male rats.

OBJECTIVE: To determine whether the oral administration of oleoyl-estrone has similar mass-decreasing effects on the main different sites of white adipose tissue (WAT). DESIGN: Adult male Zucker lean rats were given a daily oral gavage of oleoyl-estrone (OE, 10 micromol/kg) in 0.2 ml of sunflower oil for 10 days, and were compared with controls receiving only the oil. The mass of the main WAT sites: subcutaneous, epididymal, mesenteric, retroperitoneal, gluteal, perirenal and interscapular, as well as perirenal and interscapular brown adipose tissue (BAT), were dissected and studied. MEASUREMENTS: The tissue weight, DNA, protein, lipid and total cholesterol content, together with the levels of leptin and acyl-estrone in the larger WAT and BAT masses, were measured. RESULTS: The weights of WAT depots were correlated with body weight but those of BAT were not. Cell size was maximal for epididymal and mesenteric and minimal for subcutaneous and retroperitoneal WAT and BAT. Differences were detected in DNA, and in protein and lipid content between distinct WAT sites. OE treatment tended to decrease cell number and cell size in WAT; only small differences in composition were found between WAT locations inside the visceral cavity and those outside. Decreases in lipid content were maximal in mesenteric fat. Leptin and acyl-estrone content were fairly uniform at the different WAT sites, except for high concentrations in gluteal WAT. OE induced a greater decrease in leptin and acyl-estrone than in DNA and lipids; changes in these hormones were fairly parallel in all sites. CONCLUSIONS: In general, the differences in composition between visceral and peripheral subcutaneous WAT and their responses to OE were less marked than the individual differences observed between specific sites, regardless of location. WAT sites are fairly diverse in composition, but their response to OE treatment was uniform. OE decreased the weight of WAT through reduction of both cell numbers and size; but did not change the mass or composition of BAT significantly. The effects of OE are more marked in the hormonal signals (leptin and acyl-estrone) from the tissue than in its composition and mass.

Effect of oral oleoyl-estrone treatment on plasma lipoproteins and tissue lipase activities of Zucker lean and obese female rats.

OBJECTIVE: To study the effect of oral oleoyl-estrone on the plasma lipoprotein profile and tissue lipase activities in order to determine the handling of circulating lipids by adipose tissue, liver and muscle of obese female rats. DESIGN: Lean (Fa/?) and obese (fa/fa) female Zucker rats treated for 10 days with a daily gavage of 0.2 ml sunflower oil containing 0 (controls) or 10 micromol/kg of oleoyl-estrone. After sacrifice, samples of tissues and plasma were taken. MEASUREMENTS: Plasma lipoprotein classes and composition; lipoprotein lipase and hepatic lipase activities in plasma, liver, skeletal muscle and periovaric and mesenteric white adipose tissue (WAT). RESULTS: Oleoyl-estrone decreased plasma cholesterol (mainly in HDLs: 76%) of lean rats, but dramatically decreased all lipid classes in obese rats, in which chylomicra and VLDL lost most of their triacylglycerols (95 and 81%, respectively). Hepatic lipase activity decreased markedly with oleoyl-estrone in all groups, both in plasma (79% lean, 100% obese) and liver (62% in both groups). Lipoprotein lipase activity was largely unchanged by oleoyl-estrone in lean rats, but in the obese it decreased in WAT (82% in periovaric, and 49% in mesenteric), and increased in plasma (x4) and in skeletal muscle (x5); liver levels showed no change. CONCLUSIONS: The shift observed in obese rats from a decrease in liver and WAT lipoprotein lipase and hepatic lipase activities to an increase in muscle lipoprotein lipase is coincident with the hypolipemic effect of oleoyl-estrone, especially in obese rats, and indicates that muscle is a key site for the disposal of endogenous fat mobilized due to oleoyl-estrone treatment.

Oleoyl-estrone induces the massive loss of body weight in Zucker fa/fa rats fed a high-energy hyperlipidic diet.

To test whether oleoyl-estrone plus a hyperlipidic diet affects body weight in Zucker fa/fa rats, 13-week-old male Zucker obese (fa/fa) rats initially weighing 440-470 g were used. They were fed for 15 days with a powdered hyperlipidic diet (16.97 MJ/kg metabolizable energy) in which 46.6% was lipid-derived and 16.1% was protein-derived energy and containing 1.23 +/- 0.39 µmol/kg of fatty-acyl esters of estrone. This diet was supplemented with added oleoyl-estrone to produce a diet with 33.3 µmol/kg of fatty-acyl estrone. Oral administration of oleoyl-estrone in a hyperlipidic diet (at a mean dose of 0.5 µmol. kg(-1).d(-1)) resulted in significant losses of fat, energy and, ultimately, weight. Treatment induced the maintenance of energy expenditure combined with lower food intake, creating an energy gap that was filled with internal fat stores while preserving body protein, in contrast with the marked growth of controls fed the hyperlipidic diet. Treatment of genetically obese rats with a hyperlipidic diet containing additional oleoyl-estrone resulted in the loss of fat reserves with scant modification of other metabolic parameters, except for lower plasma glucose and insulin levels. The results agree with the postulated role of oleoyl-estrone as a ponderostat signal.