Changes in mammary fat pad composition and lipolytic capacity throughout pregnancy.

Changes in rat mammary fat pad during pregnancy were assessed by studying differences in the morphology and composition of the pad and in the levels of proteins involved in the accumulation and mobilization of fat stores. During pregnancy, the mammary fat pad weight had increased 1.8-fold by day 20, as compared with control rats. DNA content had increased two-fold by day 13 and remained stable until day 20. Protein content showed a two-fold increase on day 20, compared with control rats. As pregnancy advanced, both the percentage of mammary gland cells with respect to the whole mammary fat pad and the size of the adipocytes increased. The specific content of the different elements of the lipolytic pathway, viz. (alpha(2A)-adrenergic receptor (AR), beta(3)-AR, cAMP-dependent protein kinase and hormone-sensitive lipase (HSL)) underwent a decrease as pregnancy progressed, although adenylate cyclase increased greatly. The lipoprotein lipase (LPL) content per gram of tissue increased with pregnancy and the HSL-to-LPL ratio reflected a continuous increase in the triglyceride storage throughout pregnancy. Thus, the mammary fat pad undergoes extensive morphological, compositional and metabolic transformation during pregnancy, attributable to the development of the mammary gland. The various elements of the lipolytic pathway and LPL undergo major changes during the development of the mammary gland focused towards the increase of fat stores and allowing the accumulation of lipid droplets in the epithelial mammary cells and an increase in adipocyte size.

Pregnancy effects on rat adipose tissue lipolytic capacity are dependent on anatomical location.

Pregnancy is characterized by changes in maternal adiposity. The aim of this study was to carry out a detailed analysis of the different steps of the adrenergic pathway, lipoprotein lipase (LPL) levels and adipocyte size, in order to evaluate the response of white adipose tissue (WAT) to the metabolic changes during pregnancy depending on the anatomical location. In general, the levels of the proteins of the lipolytic pathway decreased with pregnancy. In retroperitoneal WAT adenylate cyclase (AC) levels decreased from 100% in controls to 44% by day 13 and 11% by day 20. In mesenteric WAT the alpha (2A)/beta (3)-adrenergic receptor balance seemed to be one of the main regulatory points of the lipolytic pathway and the reduction in the postreceptor element levels was clearly lower than for the other two depots (PKA levels reduced from 100% in controls to 72% by day 20, while in the other two depots it decreased to 30%, and AC and HSL levels did not show statistically significant changes in this depot). In contrast, the LPL-to-HSL ratio may be a major regulatory point in gonadal WAT. In summary, we describe regional differences in the regulation of WAT metabolism throughout pregnancy, which may be of great importance to determine the role of the different fat depots during late pregnancy. Thus, gonadal and mesenteric WAT changed to a lipolytic state to sustain the rapid foetal growth, although with differences between them in the main regulatory points, while retroperitoneal WAT could have a role later on, during lactation.

Rat brown adipose tissue thermogenic features are altered during mid-pregnancy.

Brown adipose tissue (BAT) thermogenesis is inhibited during late-pregnancy and lactation in the rat. However, scarce information concerning BAT functionality during mid-pregnancy is available. The aim of this work was to investigate uncoupling proteins and leptin expression during placentation in rat BAT as well as other key parameters in the thermogenic function of the tissue. BAT mitochondrial content was found to be reduced 50% in 11 and 13 day pregnant rats as compared to nonpregnant controls, although uncoupling protein 1 (UCP1) content was not modified. Furthermore, UCP3 mRNA levels were found to be highly increased during this period. beta3-adrenergic receptor (beta3-AR) decreased expression resulted in a higher alpha2/beta3 ratio. Finally, leptin mRNA levels in BAT were found to be 3-fold up-regulated in pregnant animals. In conclusion, we show the existence of profound changes in thermogenic features in BAT during gestational days 11 and 13, pointing to the importance of this tissue during mid-pregnancy.

alpha2- to beta3-Adrenoceptor switch in 3T3-L1 preadipocytes and adipocytes: modulation by testosterone, 17beta-estradiol, and progesterone.

Sex steroid hormones are important factors in the determination of fat distribution and accumulation. The aim of this study was to investigate the effect of testosterone (T), 17beta-estradiol (17betaE), and progesterone (P) on adrenergic receptor (AR) gene expression in 3T3-L1 preadipocytes and adipocytes and their relation to the proliferation and differentiation processes. Our data clearly show that alpha(2A)-AR was the highest AR subtype expressed in preadipocytes, whereas in mature adipocytes was by far beta(3)-AR. In the differentiation process to adipocytes, alpha(2A)-AR expression was decreased to 0.3-fold (P < 0.01), whereas beta(3)-AR was upregulated 578-fold (P < 0.001) compared with preadipocytes. In addition, the expression of alpha(2A)-AR in preadipocytes was increased upon incubation with T, 17betaE, and P, and a stimulation of proliferation was also observed in 17betaE- and P-treated cells. In mature adipocytes, 17betaE and P enhanced both alpha(2A)- and beta(3)-AR gene expression (although the effects on beta(3)-AR mRNA levels could be more relevant, since beta(3)-AR was the most highly expressed), whereas T only increased alpha(2A)-AR mRNA levels. Leptin and adipocyte fatty acid-binding protein mRNA levels were higher after 17betaE and P treatment, possibly indicating a proadipogenic effect of these hormones. In conclusion, this study indicates that AR gene expression is affected by these hormones in both preadipocytes and adipocytes, which could have potential importance when considering the role of ARs in the mechanisms underlying the sex-related differences in adipose tissue regional distribution.

Gender-related differences in morphology and thermogenic capacity of brown adipose tissue mitochondrial subpopulations.

To investigate the possible existence of a gender dimorphism in the morphology and functionality of brown adipose tissue (BAT) mitochondrial subpopulations, we obtained three mitochondrial fractions - heavy, medium and light - by differential centrifugation. Electron microscopic analysis was carried out and mitochondrial protein content, cytochrome c oxidase and ATP synthase activities, mitochondrial DNA content and UCP1 protein levels were measured in each mitochondrial fraction. Female rats showed a greater mitochondrial size than males, with a different distribution pattern of the subpopulations. These differences were accompanied by higher oxidative and thermogenic capacities and a higher protein content in female rat BAT. This tissue also showed a greater tendency to respiratory chain uncoupling, as well as a close coordination between the oxidative, phosphorylative and thermogenic processes. These differences were found in the heavy subpopulation but not in the light one. Our results demonstrate that female rat BAT shows a highly differentiated mitochondrial pool, with the heavy mitochondrial subpopulation as the main responsible for the greater thermogenic activity of this tissue. In addition, it seems that there is a differential regulation of the mitochondrial growth cycle between genders in BAT, which leads to enhanced thermogenic capacity in female rat mitochondria.

Sex-dependent thermogenesis, differences in mitochondrial morphology and function, and adrenergic response in brown adipose tissue.

Gender-related differences in brown adipose tissue (BAT) thermogenesis of 110-day-old rats were studied by determining the morphological and functional features of BAT. The adrenergic control was assessed by studying the levels of beta(3)- and alpha(2A)-adrenergic receptors (AR) and by determining the lipolytic response to norepinephrine (beta(1)-, beta(2)-, beta(3)-, and alpha(2)-AR agonist), isoprenaline (beta(1)-, beta(2)-, and beta(3)-AR agonist), and CGP12177A (selective partial beta(3)-AR agonist but beta(1)- and beta(2)-AR antagonist) together with post-receptor agents, forskolin and dibutyryl cyclic AMP. The female rats that had greater oxygen consumption showed higher UCP1 content, a higher multilocular arrangement, and both longer cristae and higher cristae dense mitochondria in BAT indicating heightened thermogenic capacity and activity; this picture is accompanied by a more sensitive beta(3)-AR to norepinephrine signal (EC(50) 10-fold lower for CGP12177A) and a lower expression of alpha(2A)-AR than male rats. Taken together, our results support the idea that the BAT hormonal environment could be involved in the control of different elements of lipolytic and thermogenic adrenergic pathways. Gender dimorphism is both at receptor (changing alpha(2A)-AR density and beta(3)-AR affinity) and post-receptor (modulating the links involved in the adrenergic signal transduction) levels. These changes in adrenergic control could be responsible, at least in part, both for the important mitochondrial recruitment differences and functional and morphological features of BAT in female rats under usual rodent housing temperatures.

Gender effects on adrenergic receptor expression and lipolysis in white adipose tissue of rats.

OBJECTIVE: To investigate the effects of short-term (15 days) cafeteria-diet feeding on the expression of alpha- and beta-adrenergic receptors (AR) and its association with lipolytic stimulation in isolated retroperitoneal white adipocytes. RESEARCH METHODS AND PROCEDURES: Six female and 6 male Wistar rats (4 weeks old) were fed a cafeteria diet plus standard diet for 15 days. The remaining 12 age- and sex-matched rats received a standard diet only. White retroperitoneal adipose tissue was isolated and used for the determination of both alpha(2) and beta-AR expression and for in vitro studies of lipolytic activity. RESULTS: In female control rats, we found higher lipolytic capacities located at the postreceptor level and a lower alpha(2)/beta(3)-AR ratio than male rats. Cafeteria-diet feeding for 15 days decreased lipolytic activity in both male and female rats and altered the alpha(2A)- and beta(3)-AR protein levels with an increase of alpha(2A)-AR in males and a beta(3)-AR decrease in females. DISCUSSION: Our results indicate that a 15-day cafeteria-diet feeding induced an increase in the alpha(2)/beta(3)-AR balance and impaired adipose tissue lipolytic activity, which was higher in males and may contribute to the development of increased fat mass. The higher functionality of alpha(2)-AR, together with the minor role developed by beta(3)-AR and lower lipolytic capacities located at the postreceptor level in cafeteria-diet-fed male rats compared with female rats, may be responsible for the gender-dependent differences observed in this study.