Maternal high fructose diet exacerbates white adipose tissue thermogenic process in offspring upon exposure to cold temperature.

AIM: An adverse endogenous environment during early life predisposes to metabolic disorder development. We previously reported adverse metabolic and adipose tissue effects in adult male rats born to dams fed with a fructose-rich diet (FRD). The aim of this work was to determine the effect of a FRD consumed by the pregnant mother on the white adipose tissue (WAT) browning capacity of male offspring at adulthood. MAIN METHODS: Adult SD male offspring from control (C) and FRD-fed mothers were exposed during one week to a cold stimulus. WAT browning capacity was studied through in vivo and in vitro approaches. KEY FINDINGS: After cold exposure, WAT browning was higher in fructose-programmed animals as evidenced by an increase in ucp-1 gene expression, protein levels, and higher UCP-1 positive foci. Moreover, pgc1-α gene expression was increased. In vitro studies showed a lower adipogenic capacity in cells of prenatally fructose-exposed animals differentiated with a white differentiation cocktail, while a higher ucp-1 expression was noted when their cells were treated with a pro-beige differentiation cocktail. SIGNIFICANCE: For the first time we demonstrate that pre-natal fructose exposure predisposes programmed male rats to a higher WAT browning-induced response, under stimulated conditions, despite an apparent lower basal thermogenic capacity. These results should be considered in future studies to generate new therapeutic approaches to deal with adverse programming malnutrition effects.

Efecto de esteroides sexuales sobre la función endocrina adipocitaria e insulinosensibilidad periférica / Effect of sexual steroids over the adipocyte and outlying insulin sensitivity

Es conocido que las hormonas esteroideas sexuales modulan la composición corporal y otras funciones endocrinas. El objetivo del presente trabajo fue estudiar el impacto de la administración de esteroides sexuales sobre la insulinosensibilidad periférica y la función secretora adipocitaria. Grupos de ratas hembra recibieron vehículo (C) o valerato de E2 o propionato de T. Se monitoreó el peso corporal y la ingesta de alimento hasta el día experimental, que fueron sacrificados en condición basal o sometidos a un test de sobrecarga con glucosa. Se evaluaron las concentraciones de leptina, E2, T, glucosa, triglicéridos e insulina (INS). Se ponderó el tejido adiposo parametrial y se aislaron los adipocitos e incubaron con o sin INS. E2 indujo una temprana (p < 0,05) hipofagia, contrariamente, T indujo una moderada (p < 0,05) hiperfagia. Los animales E2 resultaron con menor peso y masa adiposa parametrial que los C (p < 0,05). Los niveles plasmáticos no se modificaron en los animales E2 ni T, salvo el desarrollo de hiperleptinemia en el grupo E2 (p < 0,05). El test de tolerancia a la glucosa mostró (p < 0,05) aumento y disminución en la insulinosensibildad en los animales E2 y T, respectivamente. Finalmente, los adipocitos aislados de animales E2 como los T desarrollaron una disminuida (p < 0,05 vs. C) respuesta a INS. Nuestro estudio pone en evidencia los efectos de E2 y T sobre la sensibilidad a insulina y la función adipocitaria.

Sex hormones are known to modulate body composition and endocrine functions. The aim of the present study was to analyze the impact of sexual steroids administration on the outlying insulin-sensibility and adipocyte secretory function. Groups of female rats received either vehicle (C), E2 valerate, or T propionate. Daily food intake and body weight were recorded until sacrifice under basal conditions or after high glucose load test. Plasma concentrations of leptin, E2, T, glucose, triglycerides, and insulin (INS) were evaluated. The parametrial adipose tissue was pondered and adipocytes were isolated and then incubated with or without INS. E2 induced early hypophagia (p< 0,05); contrarily, T induced moderate hyperphagia (p<0,05). Weight and fatty parametrial mass values were lower for E2- than C-treated animals (p<0,05). Plasma levels remained unmodified either for E2 or T groups, though E2 animals developed hyperleptinemia (p<0.05). The high glucose load test showed increased and decreased insulin-sensitivity (p<0.05) in E2 and T groups, respectively. Finally, E2 and T isolated adipocytes were less sensitive to insulin-induced leptin secretion than C cells (p<0.05 vs. C). Our study reveals that E2 and T hormones affect sensibility to insulin as well as adipocyte functions.

Testis structure and function in a nongenetic hyperadipose rat model at prepubertal and adult ages.

There are few data for hormonal levels and testis structure and function during postnatal development in rats neonatally treated with monosodium L-glutamate (MSG). In our study, newborn male pups were ip injected with MSG (4 mg/g body weight) every 2 d up to 10 d of age and investigated at prepubertal and adult ages. Plasma levels of leptin, LH, FSH, prolactin, testosterone (T), corticosterone, and free T4 (FT4) were measured. MSG rats displayed elevated circulating levels of corticosterone and hyperadiposity/hyperleptinemia, regardless of the age examined; conversely, circulating prolactin levels were not affected. Moreover, prepubertal MSG rats revealed a significant (P < 0.05) reduction in testis weight and the number of Sertoli (SC) and Leydig cells per testis. Leptin plasma levels were severalfold higher (2.41 vs. 8.07; P < 0.05) in prepubertal MSG rats, and these animals displayed plasma LH, FSH, T, and FT4 levels significantly decreased (P < 0.05). Taken together, these data indicate that testis development, as well as SC and Leydig cell proliferation, were disturbed in prepubertal MSG rats. Adult MSG rats also displayed significantly higher leptin plasma levels (7.26 vs. 27.04; P < 0.05) and lower (P < 0.05) LH and FSH plasma levels. However, T and FT4 plasma levels were normal, and no apparent alterations were observed in testis structure of MSG rats. Only the number of SCs per testis was significantly (P < 0.05) reduced in the adult MSG rats. In conclusion, although early installed hyperadipose/hyperleptinemia phenotype was probably responsible for the reproductive axis damages in MSG animals, it remains to be investigated whether this condition is the main factor for hypothalamus-pituitary-gonadal axis dysfunction in MSG rats.

Impact of maternal undernutrition on hypothalamo-pituitary-adrenal axis and adipocyte functions in male rat offspring.

Malnutrition induces profound deleterious effects on several metabolic and neuroendocrine functions. In the present study, we examined the impact of maternal food restriction, during gestation and lactation, on the metabolic-neuroendocrine function of their male offspring at 21 and 60 d of age. Well-nourished (WN) and undernourished (UN) pregnant rats were used, during gestation and lactation, until pups were weaned. Twenty-one-day-old WN and UN male pups were studied in basal and postinsulin conditions. Additional groups of weaned (WN and UN) male rats were fed either ad libitum (WN-WN and UN-WN) or in a restricted fashion (WN-UN and UN-UN) until experimentation at age 60 d. Body weights of mothers and their male offspring were monitored. Basal and postinsulin plasma concentrations of several metabolic fuels were evaluated. Our results indicate that 21-d-old UN male rats exhibited (vs their WN counterparts), decreased body weights, similar basal and postinsulin glycemia, similar basal plasma adrenocorticotropic hormone (ACTH) and corticosterone levels but diminished ACTH response to insulin treatment, and basal hypoleptinemia and significant insulin-induced leptin release. Finally, at 60 d of age, long-term UN (WN-UN and UN-UN) rats showed lower plasma (basal and postinsulin) glucose, and basal triglyceride levels than their counterparts (WN-WN and UN-WN). Sixty-day-old rats submitted to either food restriction protocol also showed a reduced hypothalamo-pituitary-adrenal axis response to insulin-induced hypoglycemia and basal hypoleptinemia, in spite of restoration of normal body weights. These results further indicate a clear metabolic-neuroendocrine dysfunction in male pups of UN mothers, with the abnormality partially present at weaning and deteriorated by adulthood, even after the recovery of normal body weight. Our study strongly supports the importance of the irreversibility of a deleterious allostatic state resulting from fetal and early postnatal undernutrition.

Maternal undernutrition induces neuroendocrine immune dysfunction in male pups at weaning.

The present study was designed to assess the effect of maternal undernutrition, during gestation and lactation, on the neuroendocrine [hypothalamo-pituitary-adrenal (HPA)]-immune axis response to endotoxin (LPS) administration. For this purpose, 21-day-old male rats from both well-nourished (WN) and undernourished (UN) mothers were examined 2 h after injection (i.p.) of vehicle alone (VEH) or containing LPS (130 microg/kg BW). Circulating levels of glucose (GLU), ACTH, corticosterone (B), tumor necrosis factor-alpha (TNFalpha) and leptin were explored. The results indicate that: (a) mother body weight was significantly (p < 0.05) reduced, as a consequence of UN, at the second and third weeks of pregnancy; (b) no differences in basal glycemia were found in the two groups of pups, and LPS treatment did not induce hypoglycemia, in either group; (c) basal plasma ACTH, B and TNFalpha levels were similar in the two groups, and LPS-induced ACTH, B and TNFalpha secretions, although severalfold higher than respective VEH values (p < 0.05) in pups from WN mothers, were fully (ACTH and B) and partially (TNFalpha) abolished in products from UN mothers; (d) both mean body weights and basal plasma leptin levels were significantly (p < 0.05) lower in pups from UN than from WN mothers, and LPS administration did not modify plasma leptin values in products from both groups. In addition, results of dispersed total adrenal cells incubated in vitro indicate that: (a) both basal and ACTH (22 pM)-induced B secretion were significantly (p < 0.05) lower in cells from UN than WN pups, and (b) leptin (100 nM) was able to inhibit partially ACTH-stimulated B output by adrenal gland (AG) cells from WN pups; however, it failed to inhibit ACTH-stimulated glucocorticoid release by AG cells from UN pups. The present results indicate that undernutrition in mothers, during the very critical periods of gestation and lactation, induces in their male pups at weaning: (a) reduced circulating leptin levels and body weight values; (b) metabolic adaptation to normal carbohydrate metabolism; (c) hyporesponsiveness of the HPA and immune (TNFalpha) axes during endotoxemia, and (d) leptin resistance at the adrenocortical level. This study strongly supports that undernutrition of mothers results in neuroendocrine immune dysfunction of their pups; however, adrenal resistance to the inhibitory effect of leptin on glucocorticoid output is developed, probably as an adaptive mechanism to counteract unfavorable metabolic conditions.

Circulating and mitogen-induced tumor necrosis factor (TNF) in malnourished children.

Malnutrition in children is associated with an increased risk of infection and death. Multiple abnormalities in the inflammatory-immune response, including cytokine production, have been described in protein energy malnourished (PEM) children and could account for increased severity and frequency of infection. The aim of the present study was to determine whether there are abnormal basal tumor necrosis factor (TNF) serum concentrations in PEM children, to relate it with serum cortisol and plasma corticotrophin levels and to explore simultaneously the in vitro production of TNF by peripheral blood leukocytes (PBL). No differences were found in basal plasma corticotrophin and serum cortisol concentrations in malnourished as compared with normal, well-nourished control children. Basal TNF serum concentrations were significantly higher in malnourished children than in controls. Conversely, mitogen induced TNF production by PBL in vitro was significantly reduced in PEM children compared with controls. Abnormalities in circulating and mitogen-induced TNF production are present in malnourished children even in absence of elevated serum cortisol concentrations. These abnormalities potentially could modify inflammatory-immune responses to infectious stimuli in malnourished children.

Sexual dimorphism in the hypothalamo-pituitary-adrenal (HPA) axis and TNFalpha responses to phospholipase A2-related neurotoxin (from crotalus durissus terrifcus) challenge.

Neuroendocrine-immune interactions are vital for the individual's survival in certain physiopathological conditions such as sepsis and tissular injury. It is known that several snake venoms (SV) are potent neurotoxic compounds and that their main component is a specific phospholipase type 2 (PLA2). It has been recently described that the venom from crotalus durissus terrificus (SV) possesses a cytotoxic effect in different in vitro and in vivo animal models. In the present study we investigated whether SV is able to stimulate both TNFalpha and neuroendocrine functions in a sexual dimorphic fashion. For this purpose the modulatory role of endogenous sex steroids during neurotoxemia was evaluated. Our results indicate that SV (25 microg/animal) stimulates the hypothalamo-pituitary-adrenal axis and TNFalpha secretion when administered (ip) to adult male mice, such responses were characterized by a time-related enhance in plasma glucose, ACTH, corticosterone and TNFalpha levels. SV-stimulated glycemia, corticosteronemia and adrenal glucocorticoid were sexually dimorphic. Twenty-day gonadectomized mice showed a similar sexual dimorphism to that found in intact animals, however, they additionally showed a sexual dimorphic pattern in cytokine release in plasma 30 min post-SV. Estradiol (E2) treatment, in gonadectomized mice, abolished some characteristics of the sexual dimorphism, such as hyperglycemia, hypercorticosteronemia and hypercytokinemia. Finally, in vitro experiments indicate that: a) gonadectomy increased spontaneous and SV-stimulated cytokine output by incubated peripheral mononuclear cells (PMNC), regardless of the sex; and b) despite E2 treatment, in gonadectomized, did not modify the pattern of basal and SV-elicited TNFalpha secretion induced by orchidectomy, fully reversed the enhance in basal and SV-stimulated cytokine release found after ovariectomy alone. Our results further indicate that neurotoxemia, due to SV challenge, induces several symptoms common to those of inflammatory stress; they also strongly support that both gender and endogenous sex steroids are responsible for neuroendocrine-immunological sexual dimorphism.

Modulatory role of the epinergic system in the neuroendocrine-immune system function.

It is well recognized that the reciprocal interaction established between the immune and neuroendocrine systems is crucial for the homeostatic adaptation of individuals during septicemia. In the present study, using an in vivo rat model, we investigated the degree of participation of central and peripheral epinergic systems in the modulation of the hypothalamic-pituitary-adrenal and immune axes' functions during endotoxemia. For this purpose, acute endotoxemia was induced in adult male rats pretreated intraperitoneally with either different inhibitors of phenylethanolamine-N-methyltransferase (PNMT) [which are active either peripherally (SKF 29661) or both peripherally and centrally (SKF 64139), thus lowering epinephrine (EPI) synthesis] or vehicle only (CTRL). Twelve hours after pretreatment, animals were intraperitoneally injected with vehicle alone (basal) or vehicle containing bacterial lipopolysaccharide (LPS) and sacrificed 2 h later. A significant (p < 0.05 vs. the respective basal value) hypoglycemia was found in all groups studied. No pretreatment modified basal plasma adrenocorticotropic hormone (ACTH), glucocorticoid and cytokine concentrations. Endotoxin-stimulated ACTH secretion was severalfold (p < 0.05) higher than the respective basal value in CTRL and in SKFs-pretreated rats; however, the plasma ACTH levels after LPS were significantly (p < 0.05 vs. CTRL and SKF-29661 values) reduced in SKF-64139-pretreated rats. All groups studied showed an appropriate adrenal response to endotoxin challenge. Although no differences were found in basal anterior pituitary (AP) ACTH content among groups, LPS treatment significantly (p < 0.05 versus the respective basal value) decreased AP ACTH in CTRL and SKF 29661 groups. No pretreatment modified the basal medial basal hypothalamus (MBH) corticotropin-releasing hormone (CRH) content. Conversely, SKF 64139 pretreatment significantly (p < 0.05 vs. CTRL and SKF 29661 values) reduced basal median eminence (ME) CRH content, and LPS administration significantly (p < 0.05) decreased ME CRH in CTRL and SKF-29661-pretreated rats. SKF 64139 pretreatment significantly (p < 0.05) enhanced basal MBH and ME arginine vasopressin (AVP) contents. LPS administration significantly (p < 0.05) decreased MBH AVP in CTRL and SKF-29661-pretreated rats and diminished (p < 0.05 vs. basal values) ME AVP in all groups. The plasma tumor necrosis factor alpha (TNFalpha) concentrations were enhanced severalfold (p < 0.05 vs. basal values) after LPS treatment in CTRL rats, but not in SKFs-treated animals. In order to explore the reduced cytokine release after LPS in PNMT-inhibited rats, additional ex vivo experiments were performed by using peripheral mononuclear cells (PMNC) from both CTRL and SKF-29661-pretreated rats. The results of these experiments confirmed an immune dysfunction after inhibition of peripheral EPI synthesis; in fact, basal and concanavalin-A-stimulated TNFalpha secretions were significantly (p < 0.05) lower in SKF-29661-treated than in CTRL PMNC, while, interestingly, addition of EPI (10(-7) M) to the medium fully restored these effects. These data demonstrate that: (1) the mechanism whereby LPS-induced hypoglycemia was independent of epinergic activity; (2) selective central inhibition of epinergic function reduced endotoxin-stimulated ACTH secretion, an effect that could mainly be due to a decrease in CRH-ergic activity; (3) the central epinergic system positively and negatively modulates CRH- and AVPergic functions, respectively, and (4) inhibition of peripheral PNMT activity reduced immune system function in vivo and ex vivo. It is further suggested that low peripheral levels of EPI could be beneficial for the body's defense mechanisms during endotoxic shock.

Metabolic, neuroendocrine and immune functions in basal conditions and during the acute-phase response to endotoxic shock in undernourished rats.

Chronic malnutrition is one of the most important causes of several metabolic, immune and neuroendocrine dysfunctions. The aim of the present study was to determine the influence of chronic food restriction on basal neuroendocrine, immune and adipocyte functions and during the acute-phase response to endotoxic shock in female rats. The effect of refeeding of undernourished rats on the above-mentioned functions was also investigated. For these purposes, plasma total protein, glucose, triglycerides, ACTH, corticosterone, tumor necrosis factor-alpha (TNF) and leptin (LEP) levels were determined in basal condition and 2 h after endotoxin (LPS; 180 microgram/kg body weight, i.p.) administration in 3 different groups: (1) well-nourished (WN) controls; (2) undernourished (UN) rats as a consequence of chronic food restriction, and (3) UN rats re-fed to restoration of their body weights in the WN rat range. The results indicate that UN rats, in comparison with WN controls, developed an arrest in body weight gain as well as in basal hypoglycemia, hypotriglyceridemia, hypoleptinemia, hypercorticosteronemia and enhanced adrenal glucocorticoid content; however, no changes in basal total protein, ACTH and TNF plasma levels and in anterior pituitary ACTH concentrations were found. When endotoxic shock was induced, the LPS-induced hypoglycemia developed in WN rats was abolished in UN animals, and both ACTH and TNF plasma concentrations after endotoxin, albeit significantly (p < 0.05) higher than the respective basal values, were significantly (p < 0.05) lower in UN than in WN control rats. Despite the high basal plasma corticosterone concentration in UN vs. WN rats, the LPS-induced glucocorticoid release was similar in WN and UN rats. Additionally, LPS treatment did not modify basal plasma LEP levels, regardless of the group. Interestingly, UN rats fed ad libitum for 15 days restored their body weight to WN rat range values, and the various metabolic dysfunctions seen in UN rats in both basal and post-LPS conditions were fully normalized. Our results clearly indicate that chronic undernutrition not only affects, as earlier described, reproductive function but also metabolic, neuroendocrine, immune and adipocyte functions, and that the effects induced by undernutrition can be fully reversed after recovery of normal body weight. The present study strongly supports the involvement of the metabolic status in the effectiveness of the defense mechanisms developed in patients in inflammatory stress conditions.

Food intake-induced leptin secretion modulates hypothalamo-pituitary-adrenal axis response and hypothalamic Ob-Rb expression to insulin administration.

The mutation of the ob gene is known to induce a phenotype of obesity accompanied by symptoms including enhanced production of glucocorticoid. Chronic administration to ob/ob mice of leptin, the ob gene product, reverses hypercorticosteronemia. This establishes a clear relation between adipocyte and hypothalamo-pituitary-adrenal (HPA) axis functions. In the present study we investigated the acute modulatory effects of food intake-stimulated leptin secretion on HPA axis activity and hypothalamic leptin receptor (Ob-Rb) expression in 24-hour fasting, adult female, BALB/c mice after insulin-induced hypoglycemia. Our results indicate that: (1) food supply for 45 min to 24-hour fasting mice increased plasma glucose levels and reversed both hypercorticosteronemia and hypoleptinemia; (2) the insulin-induced hypoglycemia produced a marked HPA axis activation in animals with no access to food but this response was fully prevented by food intake and the consecutive increase in plasma leptin levels; (3) the inhibitory effect of leptin on the HPA axis response to insulin-induced hypoglycemia was corroborated by i.p. administration of murine leptin, and (4) fasting-induced hypothalamic Ob-Rb overexpression is not modulated by insulin itself but by leptin, since increase in leptin levels by food intake or by administration of exogenous leptin completely reversed this Ob-Rb overexpression. These results confirm the inhibitory effect of leptin on the HPA axis response to various stress stimuli. They clearly demonstrate that acute food intake in 24-hour fasting mice: (a) rapidly reduced fasting-induced hypercorticosteronemia by enhancing both spontaneous and insulin-elicited endogenous leptin secretion; (b) fully prevented HPA axis response to insulin administration, by rapidly increasing endogenous leptin secretion and probably also by diminishing the extent and the duration of insulin-induced hypoglycemia, and (c) abolished hypothalamic Ob-Rb overexpression induced by fasting itself combined with insulin treatment. The present data strongly suggests an inhibitory effect of endogenous leptin on insulin-induced HPA axis response, an interaction relevant to the physiological adaptation to starvation and caloric excess, and further supports the pivotal role played by the hypothalamus in restoring homeostasis in different allostatic states.

A phospholipase A2-related snake venom (from Crotalus durissus terrificus) stimulates neuroendocrine and immune functions: determination of different sites of action.

Immune neuroendocrine interactions are vital for the individual's survival in certain physiopathological conditions, such as sepsis and tissular injury. It is known that several animal venoms, such as those from different snakes, are potent neurotoxic compounds and that their main component is a specific phospholipase A type 2 (PLA2). It has been described recently that the venom from Crotalus durissus terrificus [snake venom (SV), in the present study] possesses some cytotoxic effect in different in vitro and in vivo animal models. In the present study, we investigated whether SV and its main component, PLA2 (obtained from the same source), are able to stimulate both immune and neuroendocrine functions in mice, thus characterizing this type of neurotoxic shock. For this purpose, several in vivo and in vitro designs were used to further determine the sites of action of SV-PLA2 on the hypothalamo-pituitary-adrenal (HPA) axis function and on the release of the pathognomonic cytokine, tumor necrosis factor alpha (TNF alpha), of different types of inflammatory stress. Our results indicate that SV (25 microg/animal) and PLA2 (5 microg/animal), from the same origin, stimulate the HPA and immune axes when administered (i.p.) to adult mice; both preparations were able to enhance plasma glucose, ACTH, corticosterone (B), and TNF alpha plasma levels in a time-related fashion. SV was found to activate CRH- and arginine vasopressin-ergic functions in vivo and, in vitro, SV and PLA2 induced a concentration-related (0.05-10 microg/ml) effect on the release of both neuropeptides. SV also was effective in changing anterior pituitary ACTH and adrenal B contents, also in a time-dependent fashion. Direct effects of SV and PLA2 on anterior pituitary ACTH secretion also were found to function in a concentration-related fashion (0.001-1 microg/ml), and the direct corticotropin-releasing activity of PLA2 was additive to those of CRH and arginine vasopressin; the corticotropin-releasing activity of both SV and PLA2 were partially reversed by the specific PLA2 inhibitor, manoalide. On the other hand, neither preparation was able to directly modify spontaneous and ACTH-stimulated adrenal B output. The stimulatory effect of SV and PLA2 on in vivo TNF alpha release was confirmed by in vitro experiments on peripheral mononuclear cells; in fact, both PLA2 (0.001-1 microg/ml) and SV (0.1-10 microg/ml), as well as concavalin A (1-100 microg/ml), were able to stimulate TNF alpha output in the incubation medium. Our results clearly indicate that PLA2-dependent mechanisms are responsible for several symptoms of inflammatory stress induced during neurotoxemia. In fact, we found that this particular PLA2-related SV is able to stimulate both HPA axis and immune functions during the acute phase response of the inflammatory processes.

Gender-dependent characteristics of the hypothalamo-corticotrope axis function in glucocorticoid-replete and glucocorticoid-depleted rats.

The aim of the present study was to determine the role of the endogenous sex steroid environment in the hypothalamo-corticotrope (HC) function in both sham-operated (SHAM) and bilaterally adrenalectomized (ADX) rats. For this purpose adult rats of both sexes were used 3 and 6 weeks after either SHAM or ADX. The results indicate that: a) in SHAM animals, basal plasma ACTH levels were significantly higher in females than in males, and this sexual dimorphism was overridden by ADX, regardless of the time post-surgery; b) although basal anterior pituitary (AP) ACTH content was similar in SHAM animals of both sexes, 3- and 6-week ADX induced higher AP ACTH in males than in females; c) at 3- and 6-weeks, ADX rats of hoth sexes had an AVP:CRH ratio (r), in the median eminence (ME) and medial basal hypothalamus (MBH), increased several fold over the respective SHAM-value and, although no sexual dimorphism was found at week 3 post-ADX, by 6-weeks post ADX, these ratios were significantly higher in both brain tissues of females than in those of males; and d) the in vitro ME CRH and AVP output in response to high potassium concentrations (hK+; 28 and 56 mmol/I), was concentration-related, regardless of sex and surgery, and was characterized by enhanced secretion of neuropeptides by MEs from ADX in comparison to SHAM rats of both sexes, and a sexual dimorphism was found in this parameter, consisting in general, in greater neuropeptide output from tissues of female than of male animals. Our results indicate that: 1) there is a gender-dependent characteristic of the HC axis function in glucocorticoid-replete rats and 2) the absence of the glucocorticoid negative feedback mechanism is responsible for either the expression or for the override of the sexual dimorphism in different parameters, a phenomenon which dependent on the time elapsed after ADX.

Participation of the central serotonergic pathway in the endotoxin-stimulated hypothalamo-pituitary-adrenal axis function.

The aim of the present study was to determine whether the central serotoninergic pathway (5HT) plays any stimulatory/inhibitory role in endotoxin-stimulated hypothalamo-pituitary-adrenal (HPA) axis function in the male rat. For this purpose, animals inhibited or not of central 5HT synthesis were injected with vehicle alone or containing endotoxin (LPS) and killed 2 h later. The results indicate that the inhibition of the 5HT pathway did not modify the LPS-induced hypoglycemia but that it significantly reduced ACTH release in plasma. Although the inhibition of 5HT did not modify the CRH-ergic system, it diminished hypothalamic vasopressin (AVP) content in basal condition. After LPS injection, rats inhibited of 5HT synthesis showed a significant activation of the hypothalamic AVP-ergic system whereas control rats did not. These data clearly indicate that decreased HPA axis function after 5HT inhibition could be partially compensated by the facilitation of the AVP neuronal activity.

Decreased hypothalamo-pituitary-adrenal axis response to neuroendocrine challenge under repeated endotoxemia.

It has been established that in vivo administration of bacterial lipopolysaccharide (LPS) enhances hypothalamo-pituitary-adrenal (HPA) axis function by a mechanism involving endotoxin-stimulated cytokine release. Since under chronic LPS treatment a tolerance of the HPA axis response takes place, the aim of the present study was to determine whether mice submitted to repeated LPS administration could present an impairment in the HPA response to insulin (INS) administration, a pure neuroendocrine challenge. For this purpose, adult female BALB/c mice were injected with 200 microliters i.p. of sterile saline solution (VEH) containing 25 micrograms of LPS in a single or repeated (at 24-hour intervals, during 5 consecutive days) fashion. Animals were then killed at either 45 min after INS (0.3 IU/mouse, i.p.) or 2 h after LPS (25 micrograms/mouse) administration on experimental day 1 (D1; without any previous LPS injection), 3 (D3; mice having received 2 previous LPS injections) or 5 (D5; mice having received 4 previous LPS administrations). Control groups were injected a similar volume of VEH alone on experimental day 1 (D1; without any previous LPS injection), 3 (D3; mice having received 2 previous LPS injections) or 5 (D5; mice having received 4 previous LPS administrations); in each group, mice were killed at either 45 min or 2 h after VEH injection. Immediately after decapitation, trunk blood was collected. Plasma tumor necrosis factor alpha (TNF), ACTH and corticosterone (B) levels were determined by specific assays. Plasma TNF, ACTH and B levels were significantly increased 2 h after the first LPS treatment (D1). Although no significant increase in plasma TNF concentration was found 2 h after the third LPS injection (D3), the corticotrope response was still significant and induced a full effect on adrenal B output. Two hours after the fifth LPS administration (D5) TNF output was minimal and the HPA axis response was significantly diminished. Finally, the pattern of the HPA axis response to INS-induced hypoglycemia was similar to that elicited after LPS challenge although somewhat delayed. Our results indicate that: (1) TNF seems to play an important role in stimulating HPA axis function after single but not after repeated endotoxin administration; and (2) an impairment in the HPA axis response to both immuneneuroendocrine (LPS) and neuroendocrine (INS) stimuli takes place after repeated LPS administration. This study further suggests that the tolerance of the HPA axis response under recurrent endotoxemia could be, at least partially, due to an impairment in both immune (TNF output) and neuroendocrine functions.