RESUMEN
BACKGROUND: Iron deficiency results in altered gallbladder and sphincter of Oddi (SO) motility and cholesterol crystal formation. In addition, gallbladder neuronal nitric oxide synthase (nNOS) has been shown to be markedly reduced after 8 weeks on an iron-deficient diet. However, the effects of prolonged iron deficiency on gallbladder and SO nNOS as well as crystal formation have not been determined. Therefore, we tested the hypothesis that iron deficiency would downregulate both gallbladder and SO nNOS expression and that nNOS downregulation and cholesterol crystal formation would progress over time. MATERIALS AND METHODS: Thirty-eight adult female prairie dogs were fed either an ironsupplemented (Fe+) (200 ppm) or an iron-deficient (Fe-) (8 ppm) diet for 8 weeks (Fe+ n = 9, Fe- n = 10) or 16 weeks (Fe+ n = 9, Fe- n = 10). Blood hemoglobin (HbG) was measured; gallbladder cholesterol crystals were counted; and cholesterol saturation indices (CSI) were calculated. Gallbladder and SO nNOS levels were measured by Western blot. RESULTS: The Fe+ prairie dogs had significantly higher HbG than the Fe- animals (16.9 +/- 0.6 g/dl vs 15.2 +/- 0.5 g/dl, respectively, P < 0.05) after 8 weeks. This difference was even greater after 16 weeks (16.1 +/- 0.4 g/dl vs 14.0 +/- 0.5 g/dl, P < 0.01). At 8 weeks, more cholesterol crystals per 10 HPF were observed in the Fe- animals (0.4 +/- 0.3 vs 1.6 +/- 0.4 per 10 HPF, P < 0.05). This difference was even greater after 16 weeks (0.0 +/- 0.0 vs 52.6 +/- 25.3 per 10 HPF, P < 0.01). No difference in the CSI was observed in the four groups. Iron deficiency decreased the nNOS/beta-actin protein levels in the gallbladder and SO at 8 weeks (57.0 +/- 29.6 vs 7.4 +/- 2.6, gallbladder, P < 0.05) (98.4 +/- 39.7 vs 29.9 +/- 11.0, SO, P = 0.09), but these levels returned to baseline at 16 weeks. CONCLUSIONS: We conclude that iron deficiency acutely suppresses gallbladder and SO nNOS, and that compensatory mechanisms return nNOS to baseline levels while cholesterol crystal formation increases over time.
Asunto(s)
Anemia Ferropénica/metabolismo , Vesícula Biliar/enzimología , Óxido Nítrico Sintasa/metabolismo , Esfínter de la Ampolla Hepatopancreática/enzimología , Animales , Bilis/química , Western Blotting , Peso Corporal , Colelitiasis/metabolismo , Colesterol/química , Colesterol/metabolismo , Cristalización , Regulación hacia Abajo , Femenino , Hemoglobinas , Hierro de la Dieta/farmacología , Óxido Nítrico Sintasa/análisis , Óxido Nítrico Sintasa de Tipo I , SciuridaeRESUMEN
Intestinal motility disorders are more common in women of childbearing age who are prone to iron deficiency anemia. The neurotransmitters nitric oxide (NO) and acetylcholine (ACh) play a key role in ileal smooth muscle relaxation and contraction, respectively. Iron-containing heme is known to be a cofactor for nitric oxide synthase (NOS), the enzyme responsible for NO production. Therefore we tested the hypothesis that iron deficiency would downregulate ileal NOS activity without affecting the ileum's response to ACh. Twelve adult female prairie dogs were fed either an iron-supplemented (Fe+) (200 ppm) (n = 6) or an iron-deficient (Fe-) (8 ppm) (n = 6) diet for 8 weeks. Ileal circular muscle strips were harvested to measure responses to ACh and electrical field stimulation. Under nonadrenergic noncholinergic (NANC) conditions, Nomega-nitro-L-arginine (L-NNA), an NOS inhibitor, and VIP(10-28), a vasoactive intestinal peptide (VIP) inhibitor, were added prior to electrical field stimulation. NANC inhibitory responses are expressed as a percentage of optimal relaxation from EDTA. The excitatory response to ACh was similar in both groups (1.1 +/- 0.3 N/cm(2) vs. 1.5 +/- 0.3 N/cm(2), P = 0.45). The inhibitory response to electrical field stimulation under NANC conditions was greater in the Fe+ group (34.7 +/- 2.9%) compared to the Fe- group (23.9 +/- 3.2%; P<0.01). L-NNA eliminated the inhibitory response in the Fe+ group (0.02 +/- 0.02%) but not in the Fe- group (8.38 +/- 2.15%; P <0.01). VIP(10-28) led to greater relaxation in the Fe+ animals (45.8 +/- 6.6%) than in the Fe- animals (23.4 +/- 5.8%; P <0.05). Both L-NNA and VIP(10-28) had no inhibitory response (0.02 +/- 0.02%) in the Fe+ animals, whereas the Fe- animals had some residual inhibition (2.54 +/- 1.04%; P <0.05). These data suggest that ileal NANC relaxation is due to NOS and that iron deficiency results in (1) decreased NANC relaxation, (2) a compensatory relaxation due to a non-NOS, non-VIP mechanism, and (3) a normal excitatory response. We conclude that iron deficiency suppresses ileal NOS activity.
Asunto(s)
Anemia Ferropénica/metabolismo , Íleon/enzimología , Óxido Nítrico Sintasa/metabolismo , Acetilcolina/farmacología , Animales , Western Blotting , Regulación hacia Abajo , Estimulación Eléctrica , Inhibidores Enzimáticos/farmacología , Femenino , Humanos , Íleon/fisiología , Músculo Liso/enzimología , Músculo Liso/fisiología , Nitroarginina/farmacología , Fragmentos de Péptidos/farmacología , Receptores de Péptido Intestinal Vasoactivo/antagonistas & inhibidores , Sciuridae , Péptido Intestinal Vasoactivo/farmacologíaRESUMEN
BACKGROUND: Intestinal adaptation after loss of functional small bowel surface area is characterized by cellular hyperplasia and increased absorptive function. Interventions to enhance the adaptive response are needed to decrease the morbidity and mortality associated with short bowel syndrome. Retinoic acid was shown to stimulate crypt cell proliferation in the adapting remnant rat ileum by 6 hours after resection. Thus, vitamin A, which is required for normal epithelial cell proliferation and differentiation and which can modulate programmed cell death, may play an important role in the adapting intestine. On the basis of these observations, the effects of vitamin A deficiency on intestinal morphology, epithelial cell proliferation, and apoptosis in the adapting intestine after resection were investigated. METHODS: Weanling male Sprague-Dawley rats fed either a vitamin A-deficient or -sufficient diet for 58 days underwent 70% proximal small bowel resection. The deficient rats were divided into cohorts that were either maintained on the experimental diet after surgery or replenished with vitamin A 20 hours before surgery and switched to the control diet after surgery. RESULTS: Ten days after resection, vitamin A-deficient rats exhibited a markedly blunted adaptive response. The adaptive increase in villus height and crypt depth was absent in the deficient rats. However, adaptive increases in crypt cell proliferation were not attenuated by vitamin A deficiency, and there were no differences in apoptotic indices. CONCLUSIONS: Vitamin A deficiency inhibits the adaptive response to partial small bowel resection, supporting a role for vitamin A in the adaptive process. Changes in cellular proliferation or programmed cell death are not sufficient to account for this inhibition. This model system will be useful for examining the role of other mechanisms, such as changes in cell-cell and cell-extracellular matrix interactions, and rates of epithelial cell migration and cell extrusion.
Asunto(s)
Adaptación Fisiológica , Intestino Delgado/fisiología , Deficiencia de Vitamina A/fisiopatología , Vitamina A/farmacología , Animales , Apoptosis , Peso Corporal , División Celular , Cromatografía Líquida de Alta Presión , Dieta , Ingestión de Alimentos , Intestino Delgado/efectos de los fármacos , Intestino Delgado/cirugía , Hígado/efectos de los fármacos , Hígado/metabolismo , Masculino , Ratas , Ratas Sprague-Dawley , Vitamina A/sangreRESUMEN
BACKGROUND: Iron deficiency has been demonstrated in the prairie dog to result in cholesterol crystal formation and altered biliary motility. Gallbladder filling and emptying are influenced by both inhibitory and excitatory stimuli, with nitric oxide (NO) playing a key role in normal relaxation. Iron is a cofactor for nitric oxide synthase. Therefore, we tested the hypothesis that iron deficiency would result in diminished levels of gallbladder neuronal nitric oxide synthase (nNOS) but would not influence the gallbladder's response to excitatory stimuli. MATERIALS AND METHODS: Twenty adult female prairie dogs were fed either an iron-supplemented (Fe(+)) (200 ppm) control diet (n = 10) or an iron-deficient (Fe-) (8 ppm) diet (n = 10) for 8 weeks. Fasting gallbladder volume was measured. Gallbladder muscle strips were harvested for response to excitatory stimuli and measurement of nNOS protein levels by Western blotting. Muscle strip response to a spectrum of doses of cholecystokinin, acetylcholine, and electrical field stimuli was determined, and the areas under the response curves were calculated. RESULTS: Gallbladder volume increased in the iron-deficient prairie dogs compared with the iron-supplemented group (1.45 +/- 0.27 mL vs 0.80 +/- 0.13 mL, P < 0.05). Iron deficiency diminished the ratio of gallbladder nNOS to beta-actin protein levels (0.05 +/- 0.01 vs 3.48 +/- 1.02, P < 0.05) but resulted in a normal response to excitatory stimuli. CONCLUSIONS: We conclude that diminished gallbladder neuronal nitric oxide synthase contributes to the gallbladder stasis that occurs with iron deficiency. This phenomenon may contribute to the increased incidence of gallstones in premenopausal women.
Asunto(s)
Vesícula Biliar/enzimología , Deficiencias de Hierro , Óxido Nítrico Sintasa/metabolismo , Animales , Western Blotting , Peso Corporal , Colelitiasis/etiología , Colelitiasis/metabolismo , Colesterol/metabolismo , Perros , Femenino , Vesícula Biliar/efectos de los fármacos , Vesícula Biliar/fisiología , Contracción Muscular/efectos de los fármacos , Óxido Nítrico Sintasa de Tipo I , Sincalida/farmacología , Transferrina/metabolismoRESUMEN
Following loss of small bowel surface area, the remnant intestine undergoes a remarkable adaptive response. To define more fully the underlying molecular mechanisms, we have identified genes that are specifically induced in the adapting remnant after partial small bowel resection. Several of these, including cellular retinol binding protein II (CRBP II) and apolipoprotein (apo) AI, participate in vitamin A and lipid trafficking. The CRBP II and apo A-I promoters contain response elements for the nuclear retinoid X receptor RXR-alpha. It is well established that vitamin A is essential for normal cell growth, differentiation and maintenance of epithelial tissues and that CRBP II functions to facilitate intestinal vitamin A absorption and metabolism. On the basis of these considerations, changes in CRBP II and apo A-I mRNA levels could reflect a role for retinoids in modulating the intestinal adaptive response. To explore this hypothesis, we used a rat resection model of intestinal adaptation to examine the temporal patterns of CRBP II, apo A-I and RXR-alpha expression postresection. CRBP II and apo A-I mRNA levels were increased in the remnant intestine in distinct temporal patterns, whereas RXR-alpha expression was unchanged. To address directly the effects of vitamin A in adaptation, retinoic acid or vehicle was administered intravenously to rats immediately after 70% small bowel resection. Compared with vehicle, all-trans-retinoic acid significantly stimulated crypt cell proliferation in the adapting remnant intestine by 6 h after surgery. These data suggest that retinoic acid acts to modulate intestinal proliferation in the adapting small intestine after loss of functional small bowel surface area.