Short-term treatment with estrone oleate in liposomes (Merlin-2) does not affect the expression of the ob gene in Zucker obese rats

Young female Zucker fa/fa rats of 370-430 g were implanted with osmotic minipumps releasing 3.5 mol/dayúkg of estrone oleate in liposomes (Merlin-2) into the bloodstream for up to 14 days. Merlin-2 induced a sustained loss of appetite, and a decrease in body weight of 3.5%, which contrasts with the 8.2% increase in controls during the period studied. Plasma insulin, glucose and urea decreased, and liver glycogen increased with Merlin-2 treatment. Plasma ACTH and corticosterone increased to a maximum at the end of the experiment. The expression of the ob gene in adipose tissue was unchanged, and plasma leptin levels were also unchanged by treatment. Estrone levels increased more than 1500-fold, and estrone oleate rose 100-fold during treatment. The fact that estrone oleate had no effect on the leptin levels or expression in obese rats, in contrast with the marked inhibition observed in the lean suggests that the functionality of the leptin receptor is essential for estrone oleate inhibition of the ob gene. This also suggests that leptin may control ob gene expression in white adipose tissue and that estrone oleate may activate this process. The slimming effect of estrone oleate is, thus, not directly dependent on leptin, since both normoleptinemic and hyperleptinemic animals lose fat following treatment nor are the effects on appetite and energy expenditure mediated by leptin. However, leptin levels and the expression of the ob gene are directly linked with estrone oleate function. A possible involvement of leptin in estrone oleate action is postulated. The results support the participation of estrone oleate in the control of body weight and hint at the complexity of its regulation by leptin and glucocorticoids.     

Differential Short-Term Distribution of Estrone and Oleoyl-Estrone Administered in Liposomes to Lean and Obese Zucker Rats

Thirteen-week-old female Zucker lean (Fa/Fa) and obese (fa/fa) rats were injected through a cannula inserted in the left jugular vein with 1 mL/kg of ³H-labeled oleoyl-estrone in liposomes (Merlin-2) (i.e., 670 fmol, 84 kBq). The rats were killed 10 minutes later and dissected. The presence of intact or hydrolyzed oleoyl-estrone was later determined in all samples. The pattern of distribution of estrone was quite different from that of oleoyl-estrone both in rats that were lean and in those that were obese. Estrone was better retained by white adipose tissue than oleoyl-estrone. Liver, spleen, and lungs accumulated more oleoyl-estrone and split part of it, from 4.7% (lung, obese) to 27% (liver, lean). The overall high retention of estrone by the rat tissues results in its very low circulating levels. The fast splitting of liposome-carried oleoyl-estrone by most tissues (up to more than 67% by intestine and skin of lean rats) may help explain the rise in blood free estrone. The differences between lean and obese Zucker rats are mainly quantitative in the case of estrone, the main differences being found in blood and adipose tissues. However, when we compare the data for oleoyl-estrone, the differences cannot be dismissed simply as due to differences in body size or the extent of fat deposits. A large portion of the label remained in the blood of the rats that were obese but not in those that were lean, the tissues of which took up more label. Brown adipose tissue shows a fair affinity for oleoyl-estrone in the rats that were lean but practically does not retain label in the rats that were obese, suggesting that oleoyl-estrone may have a direct effect on brown adipose tissue. The decreased uptake of oleoyl-estrone in rats that were obese shows that the mechanism regulating the turnover or disposal of this signal is altered in this type of genetic obesity.     

K+ channels involved in contractility of rabbit small intestine

Most excitable cells, including gastrointestinal smooth muscle cells, express several types of K+ channels. The aim of this study was to examine the types of K' channels involved in the contractility of longitudinal smooth muscle of rabbit small intestine in vitro. Spontaneous contractions and KCl-stimulated contractions were reduced by atropine, phentolamine, propranolol, suramin, tetrodotoxin and indomethacin. The amplitude and tone of spontaneous contractions were increased by apamin, charybdotoxin, iberiotoxin, E4031, tetraetylammonium (TEA) and BaCl2. The frequency of contractions was reduced in the presence of apamin and TEA and increased by charybdotoxin. It was found that 4-aminopyridine increased the tone of spontaneous contractions and reduced the amplitude and frequency of contractions. Glibenclamide did not modify the amplitude, frequency or tone of contractions. KCl-stimulated contractions were increased by E4031, were not modified by apamin, glibenclamide, NS1619 or diazoxide, and were reduced by charybdotoxin, TEA, 4-aminopyridine or BaCl2. These results suggest that both Ca2+-activated K+ channels of small and high conductance, and HERG K+ channels and inward rectifier K+ channels participate in spontaneous contractions of small intestine. On the other hand, voltage-dependent K+ channels, HERG K+ channels, inward rectifier K+ channels and high conductance Ca2+-activated K+ channels are involved in KCl-stimulated contractions.     

Short-term handling of the slimming agent oleoyl-estrone in liposomes (Merlin-2) by the rat

Female adult rats were injected in the jugular vein with oleoyl-³H-estrone incorporated into liposomes. The label rapidly disappeared from the blood, being taken up by the tissues, mainly liver, spleen and lung, which filtered most of the label. However, many other tissues, such as the heart, brown adipose tissue, adrenals and visceral fat incorporated significant amounts of oleoyl-estrone. The analysis of the form in which the label remained 10 min after the injection showed that it was hydrolysed in a large proportion even in liver and lungs. However, in most tissues (brain, brown and white - periovaric - adipose tissues and ovaries), intact oleoyl-estrone accounted for less than one quarter of all tissue label, and less than 10% in the case of subcutaneous adipose tissue and uterus. This rapid destruction of oleoyl-estrone is in agreement with the active role of this compound in the control of body weight.     

Predicting muscle fatigue: a response surface approximation based on proper generalized decomposition technique

A novel technique is proposed to predict force reduction in skeletal muscle due to fatigue under the influence of electrical stimulus parameters and muscle physiological characteristics. Twelve New Zealand white rabbits were divided in four groups (\(n=3\)) to obtain the active force evolution of in vitro Extensor Digitorum Longus muscles for an hour of repeated contractions under different electrical stimulation patterns. Left and right muscles were tested, and a total of 24 samples were used to construct a response surface based in the proper generalized decomposition. After the response surface development, one additional rabbit was used to check the predictive potential of the technique. This multidimensional surface takes into account not only the decay of the maximum repeated peak force, but also the shape evolution of each contraction, muscle weight, electrical input signal and stimulation protocol. This new approach of the fatigue simulation challenge allows to predict, inside the multispace surface generated, the muscle response considering other stimulation patterns, different tissue weight, etc.     

Probabilistic analysis of the influence of the bonding degree of the stem-cement interface in the performance of cemented hip prostheses

The long-term behavior of the stem-cement interface is one of the most frequent topics of discussion in the design of cemented total hip replacements, especially with regards to the process of damage accumulation in the cement layer. This effect is analyzed here comparing two different situations of the interface: completely bonded and debonded with friction. This comparative analysis is performed using a probabilistic computational approach that considers the variability and uncertainty of determinant factors that directly compromise the damage accumulation in the cement mantle. This stochastic technique is based on the combination of probabilistic finite elements (PFEM) and a cumulative damage approach known as B-model. Three random variables were considered: muscle and joint contact forces at the hip (both for walking and stair climbing), cement damage and fatigue properties of the cement. The results predicted that the regions with higher failure probability in the bulk cement are completely different depending on the stem-cement interface characteristics. In a bonded interface, critical sites appeared at the distal and medial parts of the cement, while for debonded interfaces, the critical regions were found distally and proximally. In bonded interfaces, the failure probability was higher than in debonded ones. The same conclusion may be established for stair climbing in comparison with walking activity.