RESUMEN
Glutamine is the major fuel for enterocytes and promotes the growth of intestinal mucosa. Although oral glutamine exerts a positive effect on intestinal villus height in very old rats, how glutamine is used by enterocytes is unclear. Adult (8 months) and very old (27 months) female rats were exposed to intermittent glutamine supplementation for 50% of their age lifetime. Treated rats received glutamine added to their drinking water, and control rats received water alone. Jejunal epithelial cells (~300×10(6) cells) were incubated in oxygenated Krebs-Henseleit buffer for 30 min containing [1-(13)C] glutamine (~17 M) for analysis of glutamine metabolites by (13)C nuclear magnetic resonance ((13)C NMR). An aliquot fraction was incubated in the presence of [U-(14)C] glutamine to measure produced CO2. Glutamine pretreatment increased glutamate production and decreased CO2 production in very old rats. The ratio CO2/glutamate, which was very high in control very old rats, was similar at both ages after glutamine pretreatment, as if enterocytes from very old rats recovered the metabolic abilities of enterocytes from adult rats. Our results suggest that long-term treatment with glutamine started before advanced age (a) prevented the loss of rat body weight without limiting sarcopenia and (b) had a beneficial effect on enterocytes from very old rats probably by favoring the role of glutamate as a precursor for glutathione, arginine and proline biosynthesis, which was not detected in (13)C NMR spectra in our experimental conditions.
Asunto(s)
Envejecimiento/metabolismo , Dióxido de Carbono/metabolismo , Enterocitos/metabolismo , Ácido Glutámico/biosíntesis , Glutamina/metabolismo , Animales , Ratas , Ratas WistarRESUMEN
BACKGROUND: Glutamine is known to have a specific role in very old rats (>25 months of age). For this reason, we have orally supplemented female rats with glutamine (20% of diet protein) intermittently. The treatment started before animals became very old and lasted 5 months. Very old rats were studied in fed state or after 5-day fasting after the last glutamine cure. The aim of this study was to determine whether this in vivo pretreatment improves the well-being of very old rats (muscle sarcopenia decrease, gut integrity improvement, decrease of the known up-regulated glutamine synthetase observed regardless of nutrition state). METHODS: Protein turnover was measured in epitrochlearis muscle, whereas glutamine synthetase (GS) activities were assessed in tibialis anterior muscle from fed and 5-days-fasted female Wistar adult (6 months) and very old (27 months) rats, pretreated or not with glutamine. Furthermore, gut was dissected and weighed. RESULTS: Long-term treatment with glutamine had positive effects on very old rats: (1) it prevented the loss of body weight, but, (2) it did not prevent the inevitable sarcopenia regardless of nutrition state, and (3) it maintained the gut mass. Surprisingly, the muscle up-regulated GS activity observed in fed and fasted very old rats was only decreased in the fed state when rats were supplemented, without change in plasma and muscle glutamine concentrations. CONCLUSIONS: Long-term treatment with glutamine started before advanced age had essentially a beneficial role on the gut. It may play a role in maintaining intestine integrity and intestinal immune function. Further investigations would be warranted to explore these mechanisms.
Asunto(s)
Envejecimiento/efectos de los fármacos , Glutamato-Amoníaco Ligasa/metabolismo , Glutamina/farmacología , Intestinos/efectos de los fármacos , Músculo Esquelético/enzimología , Factores de Edad , Envejecimiento/fisiología , Animales , Suplementos Dietéticos , Modelos Animales de Enfermedad , Ayuno/metabolismo , Femenino , Intestinos/inmunología , Intestinos/fisiología , Músculo Esquelético/patología , Estado Nutricional , Ratas , Ratas WistarRESUMEN
BACKGROUND & AIMS: Glutamine synthetase (GS), a key enzyme in the glutamine synthesis, is thus crucial in glutamine homeostasis. GS is known to be up-regulated by fasting and inhibited by glutamine supplementation. The aim of this study was to determine whether the presence of glucose in glutamine supplementation with refeeding differently affects up-regulation of muscle GS by fasting in vivo in adult female rats than glutamine alone. METHODS: Muscle GS activities were assessed in 5-day-fasted female Wistar adult rats refed and supplemented with glutamine or glycine in the presence or not of glucose. RESULTS: After 5-day-fasting, the up-regulated GS activity was decreased whatever the type of amino acid supplementation (glutamine or glycine), whereas it was more decreased by supplementation with a mixture glutamine/glucose. In glycine/glucose supplemented rats, no effect of glucose supplementation was observed on GS activity. CONCLUSION: These results demonstrated that intramuscular glutamine was spared when glucose was added to glutamine supplementation in adult rats. Consequently, the role of glucose consisted in slowing down the glutamine synthesis. By contrast, glucose has no role when it was associated with glycine whose degradation does not produce energy.
Asunto(s)
Glucosa/farmacología , Glutamato-Amoníaco Ligasa/efectos de los fármacos , Glutamina/farmacología , Músculo Esquelético/enzimología , Animales , Suplementos Dietéticos , Modelos Animales de Enfermedad , Sinergismo Farmacológico , Ayuno/metabolismo , Femenino , Glucosa/metabolismo , Glutamato-Amoníaco Ligasa/metabolismo , Glutamina/metabolismo , Músculo Esquelético/metabolismo , Distribución Aleatoria , Ratas , Ratas Wistar , Regulación hacia ArribaRESUMEN
BACKGROUND: Glutamine synthetase (GS), a key enzyme in the production of glutamine, is preserved in rat skeletal muscle during aging but is increased with advanced age in vivo. The aim of this study was to determine whether glutamine supplementation affects up-regulation of GS by fasting in vivo in adult and very old female rats. METHODS: Muscle GS activities were assessed in 5-day-fasted female Wistar adult (6 months) and very old (27 months) rats refed and supplemented with glutamine or other amino acids (alanine or glycine). Fed rats were used to investigate the possible effect of glutamine supplementation in the fed state. RESULTS: After 5 days' fasting, the up-regulated GS activity was decreased whatever the type of amino acid supplementation (glutamine, alanine, and glycine) in adults, whereas it was only decreased by glutamine supplementation in very old rats). In the fed state, no effect of glutamine supplementation was observed even if GS activity remained up-regulated whatever the age and the period of supplementation. CONCLUSIONS: These results confirm that glutamine has a specific role in very old rats. The up-regulated GS activity was decreased by an exogenous supply of glutamine only if intramuscular glutamine was depleted; this was confirmed by studies in the fed state. The up-regulated GS activity in both fed and fasted rats may be associated with increased glutamine requirements in the whole body.
Asunto(s)
Glutamato-Amoníaco Ligasa/metabolismo , Glutamina/biosíntesis , Glutamina/farmacología , Músculo Esquelético/metabolismo , Necesidades Nutricionales , Envejecimiento/metabolismo , Envejecimiento/fisiología , Animales , Suplementos Dietéticos , Modelos Animales de Enfermedad , Ayuno/metabolismo , Femenino , Músculo Esquelético/enzimología , Ratas , Ratas WistarRESUMEN
OBJECTIVE: Glutamine synthetase (GS), a key enzyme in the production of glutamine, is preserved in skeletal muscle during early aging (<24 mo). Because the effects of advanced age on GS are unknown, we investigated the effect of advanced age (>24 mo) on GS activity in skeletal muscle. We hypothesized that advanced age would enhance muscle GS activity. METHODS: Muscle GS activities were assessed in adult (8 mo), mature adult (15 mo), aged (20-22 mo), advanced age (25-27 mo), or very advanced age (29-32 mo) female Wistar rats. Male Wistar (6-27 mo) were used to investigate the effect of gender on this activity. RESULTS: Glutamine synthetase activity remained low and unaltered in rats from 8 to 22 mo of age, as previously demonstrated. In contrast, GS activity was high ( approximately 75% of individual values were higher than the low value mean) in 25-mo to 27-mo-old rats. In very-old-aged rats (29-32 mo), approximately 55% of GS activity data points exhibited low values. Changes in GS protein content paralleled those in GS activities. In male rats, GS activity was also high ( approximately 80% of individual values were higher than the mean value of 6-mo to 19-mo-old rats) at the upper limit of life expectancy (27 mo). CONCLUSION: There is enhanced GS activity in old female and male rats suggesting a greater need for glutamine. In some very old rats, low GS activity may be associated with longevity or reflect a limitation in glutamine production due to extremely advanced age per se.
Asunto(s)
Envejecimiento/metabolismo , Glutamato-Amoníaco Ligasa/metabolismo , Músculo Esquelético/enzimología , Adenosina Trifosfato/análisis , Animales , Composición Corporal , Metabolismo Energético , Femenino , Ácido Glutámico/análisis , Glutamina/análisis , Ácido Láctico/análisis , Masculino , Músculo Esquelético/química , Fosfocreatina/análisis , Ratas , Ratas Wistar , Caracteres SexualesRESUMEN
BACKGROUND AND AIMS: In earlier studies, skeletal muscle glutamine synthetase (GS) activity was shown to be enhanced by fasting and glucocorticoids, and inhibited by exogenous glutamine (Gln) supplementation. The current study was designed to determine whether phenylbutyrate (PhiB), a Gln-chelating agent in humans, (1) could trap Gln and produce a decline in plasma Gln in rats, as it does in humans, and (2) if so, whether (Phi)B would further enhance the response of muscle GS activity to fasting in rats. METHODS: Adult (6-8 months) and aged (20-21 months) rats were fasted for 5 days and received two doses of 0.5 g(Phi)Bby orogastric route at times 0 and 4 h, and were then sacrificed at 5.5 h. Plasma Gln was measured by enzymatic methods, other amino acids were quantified by amino acid analysis. GS activity was measured in soleus (SO) and tibialis anterior (TA) muscles. RESULTS: (Phi)B treatment was associated with: (1) a 20% decline in plasma Gln concentration from 572+/-54 to 424+/-34 micromol/L (P<0.05) and from 476+/-49 to 360+/-80 micromol/L (P<0.05) in fasted adult and old rats, respectively; and (2) a preservation of GS up-regulation by fasting in TA and SO muscles in both adult and aged rats, with TA muscle GS activities of 198+/-65 vs. 203+/-68 ((Phi)B-treated vs. vehicle-treated, NS), and 244+/-81 vs. 274+/-59 (NS) nmol/h/mg protein in adult and aged rats, respectively. CONCLUSION: These data suggest that: (1) large doses of (Phi)B deplete plasma Gln in fasted rats, regardless of age, (2) Gln depletion induced by Phi)B does not alter GS activity.
Asunto(s)
Ayuno/metabolismo , Glutamato-Amoníaco Ligasa/metabolismo , Glutamina/metabolismo , Músculo Esquelético/metabolismo , Factores de Edad , Animales , Quelantes/farmacología , Ayuno/sangre , Glutamina/análogos & derivados , Glutamina/biosíntesis , Glutamina/sangre , Glutamina/deficiencia , Glutamina/orina , Masculino , Músculo Esquelético/enzimología , Fenilbutiratos/farmacología , Ratas , Ratas WistarRESUMEN
Insulin resistance with aging may be responsible for impaired glycogen synthesis in the skeletal muscle of aged rats and contribute to the well-known decreased ability to respond to stress with aging. For this reason, to assess the ability of the skeletal muscle to utilize glucose for glycogen synthesis during aging, the time course of glycogen synthesis was continuously monitored by 13C nuclear magnetic resonance for 2 h in isolated [13C] glucose-perfused gastrocnemius-plantaris muscles of 5-day food-deprived adult (6-8 months; n=10) or 5-day food-deprived aged (22 months; n=8) rats. [13C] glucose (10 mmol/L) perfusion was carried out in the presence or absence of an excess of insulin (1 micromol/L). Food deprivation only decreased glycogen level in adult rats (8.9+/-2.4 micromol/g in adults vs. 35.6+/-2.4 micromol/g in aged rats; P<.05). In the presence of an excess of insulin, muscle glycogen synthesis was stimulated in both adult and aged muscles, but the onset was delayed with aging (40 min later). In conclusion, this study highlights the important role of glycogen depletion in stimulating glycogen synthesis in muscles. Consequently, the absence of glycogen depletion in response to starvation in aged rats may be the origin of the delay in insulin-stimulated glycogen synthesis in the skeletal muscle. Glycogen synthesis clearly was not impaired with aging.
Asunto(s)
Envejecimiento , Privación de Alimentos , Glucógeno/biosíntesis , Insulina/farmacología , Músculo Esquelético/metabolismo , Animales , Isótopos de Carbono , Resistencia a la Insulina , Cinética , Espectroscopía de Resonancia Magnética , Masculino , Ratas , Ratas WistarRESUMEN
Glutamine synthetase, a key enzyme in the production of glutamine, is known to be induced by glucocorticoids and preserved in skeletal muscle during aging, but the effect of other steroids, such as sex steroids (progesterone, estradiol), is unknown in vivo. The aim of this study was to determine whether progesterone or estradiol plays a role in the regulation of glutamine synthetase (GS) with aging. The effects of glucocorticoids and sex steroids on muscle GS activity and mRNA expression were measured in adult (6-8 mo; n = 7 in each group) and aged (26 mo; n = 10 in each group) female Wistar rats after adrenalectomy (ADX), ovariectomy (OV), or both (ADXOV) and were compared with those in sham-operated (Sham) control rats. In tibialis anterior muscle, ADX noticeably decreased both GS activity and expression irrespective of age (50-60%; P < 0.05), whereas OV had no effect at either age. Progesterone and estradiol replacement had no effect on the recovery of muscle GS response in either ADX or OV rats, regardless of age. In contrast, heart GS activity was decreased by ADX in aged animals only. These results suggest that the reproductive endocrine status of female rats does not affect muscle GS activity either in muscle or in heart, in young or aged animals, and that the heart GS response to steroids may be differently regulated in aged rats.