Griselda Moreno

Orexin a stimulates hypothalamic-pituitary-adrenal (HPA) axis function, but not food intake, in the absence of full hypothalamic NPY-ergic activity.

Neonatal monosodium l-glutamate (MSG) treatment destroys hypothalamic arcuate nucleus neuronal bodies, thus inducing several metabolic abnormalities. As a result, rats develop a phenotype characterized by hyperleptinemia and by impaired NPY but normal prepro-orexin hypothalamic mRNAs expression. Thus, our study was designed to explore whether hypothalamic effects of orexin A on food intake and glucocorticoid production develop in the absence of full hypothalamic NPY-ergic activity. For this purpose we evaluated, in control and MSG-treated rats, the consequences of intracere-broventricular (icv) orexin A administration on food intake and changes in circulating levels of ACTH and glucocorticoid. Our results indicate that orexin A icv treatment stimulated hypothalamic-pituitary-adrenal (HPA) axis activity in both MSG-damaged and normal animals, with this response even more pronounced in neurotoxin-damaged rats. Conversely, food intake was only enhanced by icv orexin A injection in normal rats. Our study further supports that acute hypothalamic effects of orexin A on food intake and glucocorticoid production are due to independent neuronal systems. While intact arcuate nucleus activity is needed for the orexinergic effect induced by icv orexin A administration, conversely, orexin A-stimulated HPA axis function takes place even in the absence of full NPY-ergic activity.

Nature of changes in adrenocortical function in chronic hyperleptinemic female rats.

Neonatal treatment of rats with monosodium l-glutamate, which destroys hypothalamic arcuate nucleus neuronal bodies, induces several metabolic abnormalities; as a result, rats develop a phenotype of pseudoobesity. This study was designed to explore, in the monosodium l-glutamate-treated female rat, the influence of chronic hyperleptinemia on adrenal cortex functionality. For this purpose, we evaluated in control and hypothalamic-damaged rats: (a) in vivo and in vitro adrenocortical function, (b) adrenal leptin receptor immunodistribution and mRNA expression, and (c) whether the inhibitory effect of leptin on adrenal function remains. Our results indicate that, compared to normal counterparts, pseudoobese animals displayed (1) hyperadiposity, despite being hypophagic and of lower body weight, (2) in vivo and in vitro enhanced adrenocortical response to ACTH stimulation, (3) an in vitro adrenal fasciculata-reticularis cell hyper-sensitivity to ACTH stimulus, (4) hyperplasia of their adrenal zona fasciculata cells, and (5) adrenal fasciculata-reticularis cell refractoriness to the inhibitory effect of leptin on ACTH-stimulated glucocorticoid production due, at least in part, to decreased adrenal leptin receptor expression. These data further support that increased hypothalamo-pituitary-adrenal axis function, in the adult neurotoxin-lesioned female rat, is mainly dependent on the development of both hyperplasia of adrenal zona fasciculata and adrenal gland refractoriness to leptin inhibitory effect. Our study supports that adrenal leptin resistance could be responsible, at least in part, for enhanced glucocorticoid circulating levels in this phenotype of obesity.

Impact of estradiol on parametrial adipose tissue function : Evidence for establishment of a new set point of leptin sensitivity in control of energy metabolism in female rat ()

Estradiol has been implicated in the regulation of food intake; however, its effect seems to be exerted in a bimodal fashion. We examined whether a single im injection of estradiol valerate (E2V), lastingly effective, could induce changes in parametrial fat function that further induce a new set point of leptin sensitivity in the female rat. E2V induced severe anorexia and loss of body weight between d 4 and 12 posttreatment. E2V rats recovered normal food intake and departing body weights on wk 2 and 3 posttreatment, respectively; however, they did not reach body weights of control rats. On d 61 post-treatment, we found that unfasting E2V, vs control, rats displayed increased E2 and leptin circulating levels; reduced plasma tumor necrosis factor-α (TNF-α) concentrations; similar circulating levels of glucose, insulin, and triglyceride; and lower parametrial fat mass containing a higher number of adipocytes that, although normal in size, in vitro released more leptin. Metabolic responses to fasting indicated that unlike control animals, E2V rats did not decrease triglyceride circulating levels, and that both groups decreased plasma glucose, leptin, and insulin, but not TNF-α, levels. High glucose load experiments indicated that E2V animals displayed a better insulin sensitivity than control rats; did not significantly increase circulating leptin concentrations as control rats did; and, unlike control, significantly decreased plasma triglyceride levels. Our data strongly support a potent acute anorectic effect of E2 and that, after several weeks, E2 modified parametrial fat function and insulin sensitivity, protecting the organism against future unfavorable metabolic conditions.

Long-Term Fructose Intake Increases Adipogenic Potential: Evidence of Direct Effects of Fructose on Adipocyte Precursor Cells

We have previously addressed that fructose rich diet (FRD) intake for three weeks increases the adipogenic potential of stromal vascular fraction cells from the retroperitoneal adipose tissue (RPAT). We have now evaluated the effect of prolonged FRD intake (eight weeks) on metabolic parameters, number of adipocyte precursor cells (APCs) and in vitro adipogenic potential from control (CTR) and FRD adult male rats. Additionally, we have examined the direct fructose effects on the adipogenic capacity of normal APCs. FRD fed rats had increased plasma levels of insulin, triglyceride and leptin, and RPAT mass and adipocyte size. FACS studies showed higher APCs number and adipogenic potential in FRD RPAT pads; data is supported by high mRNA levels of competency markers: PPARγ2 and Zfp423. Complementary in vitro experiments indicate that fructose-exposed normal APCs displayed an overall increased adipogenic capacity. We conclude that the RPAT mass expansion observed in eight week-FRD fed rats depends on combined accelerated adipogenesis and adipocyte hypertrophy, partially due to a direct effect of fructose on APCs.

Relationship between the Balance of Hypertrophic/Hyperplastic Adipose Tissue Expansion and the Metabolic Profile in a High Glucocorticoids Model.

Adipose tissue (AT) expansion is the result of two processes: hyperplasia and hypertrophy; and both, directly or indirectly, depend on the adipogenic potential of adipocyte precursor cells (APCs). Glucocorticoids (GCs) have a potent stimulatory effect on terminal adipogenesis; while their effects on early stages of adipogenesis are largely unknown. In the present work, we study, in a model of high GC levels, the adipogenic potential of APCs from retroperitoneal AT (RPAT) and its relationship with RPAT mass expansion. We employed a model of hyper-adiposity (30- and 60-day-old rats) due to high endogenous GC levels induced by neonatal treatment with l-monosodium glutamate (MSG). We found that the RPAT APCs from 30-day-old MSG rats showed an increased adipogenic capacity, depending on the APCs’ competency, but not in their number. Analyses of RPAT adipocyte diameter revealed an increase in cell size, regardless of the rat age, indicating the prevalence of a hypertrophic process. Moreover, functional RPAT alterations worsened in 60-day-old rats, suggesting that the hyperplastic AT expansion found in 30-day-old animals might have a protective role. We conclude that GCs chronic excess affects APCs’ adipogenic capacity, modifying their competency. This change would modulate the hyperplastic/hypertrophic balance determining healthy or unhealthy RPAT expansion and, therefore, its functionality.

Relationship between Pituitary and Adipose Tissue after Hypothalamic Denervation in the Female Rat

Neonatal administration of monosodium glutamate (MSG) to rats produces severe lesions in certain hypothalamic nuclei, with repercussions in different neuroendocrine axes, and serves as a model for their study. In addition, adipose tissue, as a target organ, is known to be directly related to several neurondocrine axes. We used 21-day-old female Sprague-Dawley rats that had received a neonatal treatment with MSG (4 mg/g body weight, i.p., from day 2 up to day 10 of age) in addition to control rats (injected with 10% NaCl solution, on a similar schedule). We performed a specific immunohistochemical study on each anterior-pituitary cell population, along with the morphometry of these cells and of the parietal and visceral adipose tissue, and measured the levels of serum leptin and triglycerides. The MSG animals evinced significant changes in volume density (VD), cell density (CD), and cell size (CS) in the corticotropes, thyrotropes, and LH gonadotropes, but not in the somatotropes, lactotropes, and FSH gonadotropes. The modification common to the three cell types was a hyperplasia, but with different results depending on cell size. Furthermore, in the MSG rats significant changes were also observed in the VD, CD, and CS of the adipose tissue, consisting of adipogenesis and decrease of adipocyte size in visceral fat, together with probable lipogenesis as judged by an increase in adipocyte size in the parietal fat. The serum levels of leptin and triglycerides appeared significantly higher in MSG animals. For the first time in this animal model, and at the level of three neuroendocrine axes, our results suggest changes that correlate hypothalamic damage, cellular pituitary alterations, and the response of the adipose tissue as a target organ for MSG insult.