Effect of acarbose on acute acidosis.

A challenge model was used to evaluate a new approach to controlling acute acidosis. Acute acidosis reduces performance in both dairy and beef cattle and most often occurs as a consequence of ingestion of large amounts of readily fermentable starch, resulting in increased production of volatile fatty acids (VFA) and lactic acid and a reduction in ruminal pH. Acarbose is an alpha-amylase and glucosidase inhibitor that slows the rate of degradation of starch to glucose, thereby reducing the rate of VFA production and maintaining rumen pH at a more stable level. It is commercially available (Glucobay, Bayer, Wuppertal, Germany) and indicated for the control of blood glucose in diabetic patients. The ability of acarbose to reduce the incidence of acidosis and the comparative efficacies of acarbose, sodium bicarbonate, and monensin were tested in 3 acute acidosis challenge experiments in cattle. Rumen-cannulated Holstein steers were challenged with a mixture of 48.4% cornstarch, 48.4% ground corn, 2.1% sodium caseinate, and 1.1% urea with or without test substance. The challenge was administered at a rate of 12.5 g/kg of body weight (BW) as a slurry through the cannula directly into the rumen. Ruminal pH was monitored at 10-min intervals throughout the study. Animals were removed from study and rumen contents replaced if they exhibited acute acidosis as defined as pH <4.5. If acidosis was not observed within 24 h, animals were subjected to a second challenge. Ruminal fluid samples were taken for measurement of VFA and lactate concentrations at various intervals after the challenge. In experiment 1, the carbohydrate challenge induced acidosis in 4 of 4 control animals and 0 of 4 animals treated with 2.14 or 21.4 mg of acarbose/kg of BW in the challenge based on the criterion of pH <4.5. In experiment 2, the carbohydrate challenge induced acidosis in 4 of 7 control animals and 1 of 7 animals when 1.07 mg of acarbose/kg of BW was included in the challenge. In experiment 3, acidosis was induced in 7 of 7 animals in the control, 1% sodium bicarbonate, and 12 mg of monensin/kg of dry matter intake groups and in 3 of 8 steers administered 1.07 mg of acarbose/kg of BW in the challenge. Increases in lactate concentrations and decreases in total VFA associated with acute acidosis were mitigated by acarbose. Thus, acarbose, an amylase and glucosidase inhibitor, prevented or reduced the incidence of acidosis in an acute challenge model in steers and was more effective than monensin or sodium bicarbonate.

Circadian rhythm of feeding induced changes in hypothalamic Met-enkephalin concentrations.

Accumulating evidence suggests that opioid peptides play an important role in the hunger component of the control of food intake. The enkephalins, one of the opioid peptide families, stimulate feeding when injected into specific hypothalamic areas and endogenous concentrations change with the fed/fasted condition of rats and sheep and with phase of circadian cycle. To demonstrate a possible circadian rhythm in feeding-induced changes in Met-enkephalin (MEK), 54 male rats initially weighing 255 +/- 3 g were adapted to a 12-hr fast during the light (light-fasted) or dark (dark-fasted) phase of the circadian cycle, then sacrificed before (non-fed) or after (fed) being allowed to eat a meal. In non-fed compared with fed rats, MEK concentrations were higher in the paraventricular nucleus (PVN, 170 vs. 109 pg/mg tissue, p less than 0.05) and ventromedial hypothalamus (VMH, 209 vs. 161 pg/mg tissue, p less than 0.05) in the dark (light-fasted) but not light (dark-fasted), even though rats ate a larger meal in the light (8.6 vs. 5.0 g, p less than 0.01). In rats fed the same amount of food in the light (dark-fasted) as ad lib fed rats in the dark (light-fasted), MEK concentrations did not differ in the PVN or VMH, suggesting that circadian rhythm is more important than meal size. Rats gavaged with an amount of milk equal in calories to dark ad lib-fed rats (light-fasted) had MEK concentrations not different from light-fasted non-fed rats (216 vs. 209 pg/mg tissue, NS) suggesting that feeding behavior, pregastric stimuli and/or form of diet is important for influencing MEK concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Opioid peptides and the control of feeding in sheep.

Opioid peptides, particularly beta-endorphin, methionine- (MEK) and leucine-enkephalin, and dynorphin, are involved in the regulation of food intake in mammals. The precursor molecules of these peptides undergo differential processing in brain areas producing regional concentration differences in opioids. Intraregional concentration changes also accompany alterations in feeding states. For example, MEK concentrations decrease in the basomedial hypothalamus, amygdala, and olfactory bulb in fed sheep compared with fasted sheep. Moreover, these changes are species specific. In sheep, beta-endorphin decreases in the dorsomedial and posterior hypothalami after feeding, but in the rat it is increased in the ventromedial hypothalamus and decreased in the posterior hypothalamus. In addition, immunohistochemical localization of cell bodies shows interspecies differences in concentrations. For example, dynorphin is found predominantly in the suprachiasmatic area in sheep, but in the paraventricular nucleus in the rat. These observations indicate that regulation of food intake may be differentially controlled in these species. In sheep, kappa agonists increase food intake, whereas stimulation of delta receptors inhibits feeding. Further clarification of the receptors involved in food intake will necessitate studies with more specific agonists.

Weight gain and food intake in corticotropin releasing factor immunized Zucker rats.

In Zucker obese rats (fa/fa) there are disturbances in the regulation of ACTH and corticosterone. In addition, beta-endorphin concentrations are higher in the pituitary and hypothalamus in obese than in lean rats. Since ACTH and beta-endorphin are thought to be controlled by corticotropin releasing factor (CRF), these effects may be due to abnormalities in CRF regulation. This possibility was investigated by immunizing rats against CRF. Obese rats immunized against CRF developed higher titer antibodies than lean rats. Hypothalamic CRF concentrations were higher in CRF-immunized obese but not lean rats compared with those of control rats, suggesting that compensation for sequestration of peripheral CRF developed in obese rats. In obese, but not lean rats, immunization against CRF decreased weight gains during weeks 1-4 and increased gains during weeks 9-12 and food intakes were decreased during weeks 5-8 compared with those for obese rats immunized against bovine serum albumin (BSA). Adrenal glands weighed 30% less in both obese and lean rats immunized against CRF compared with those immunized against BSA. These responses to immunization against CRF occurred even though plasma, hypothalamic and pituitary concentrations of ACTH and beta-endorphin were unaffected at the end of the study.

Changes in brain CCK concentrations with peripheral CCK injections in Zucker rats.

Evidence suggests that the satiety responses to peripherally administered CCK are mediated by a CNS component(s). Since CCK concentrations in the hypothalamus can change with degree of hunger, they may also be involved in the feeding response to peripherally administered CCK. Six-hr fasted rats were administered saline or 2 micrograms/kg CCK-8 and half were allowed to eat a meal. They were sacrificed after a meal or after the fast and hypothalamic content of CCK was measured by RIA. In rats injected with CCK, compared with those injected with saline, CCK concentrations were decreased in the ventromedial hypothalamus (VMH, 39 vs. 47 pg/mg tissue, p less than 0.004) and dorsomedial hypothalamus (17 vs. 21 pg/mg, p less than 0.009) and increased in the lateral hypothalamus (28 vs. 19 pg/mg, p less than 0.01). CCK concentrations in fed compared with fasted rats were higher in the VMH (47 vs. 39 pg/mg, p less than 0.002) and in obese compared with lean rats CCK concentrations were higher in the paraventricular nucleus (48 vs. 38 pg/mg, p less than 0.05), suprachiasmatic nucleus (46 vs. 34 pg/mg, p less than 0.008) and VMH (52 vs. 34 pg/mg, p less than 0.001). Since peripheral injections of CCK influenced concentrations of CCK in hypothalamic areas associated with feeding, these results provide evidence that the feeding response to peripherally injected CCK may be mediated by changes in CCK content of specific brain areas.

Changes in brain met-enkephalin concentrations with peripheral CCK injections in Zucker rats.

There is increasing evidence that peptides in the brain are important in the control of food intake. Administration of opioid and CCK peptides have elicited hunger and satiety, respectively. To evaluate the interaction of these peptides and their role in the central nervous system, concentrations of met-enkephalin were measured in the hypothalamus of rats following peripheral administration of CCK; in addition, effects of feeding and fasting and obesity were studied. In CCK- vs. saline-injected rats met-enkephalin concentrations were decreased in the paraventricular nucleus (PVN), suprachiasmatic nucleus (SC), supraoptic nucleus (SON), dorsomedial hypothalamus (DMH) and ventromedial hypothalamus (VMH). In fed compared with fasted rats met-enkephalin concentrations were higher in the anterior hypothalamus (AH) and lower in the SC; in obese compared with lean rats, concentrations were higher in the AH, PVN, SC, SON, DMH, lateral hypothalamus and VMH. These results show that peripheral injections of CCK can decrease concentrations of met-enkephalin in the brain and suggest a mechanism by which these peptides may interact to influence behavior. In addition, the findings support the hypothesis that the hyperphagia which is typical of obese rats may be due to increased concentrations of met-enkephalin.

Meal-stimulated increased concentrations of beta-endorphin in the hypothalamus of Zucker obese and lean rats.

Increased opiate peptide concentrations in brain and plasma have been associated with increased feeding. The role of beta-endorphin in the control of food intake and obesity was examined by measuring concentrations in hypothalamus, pituitary and plasma of hungry (6-hr fasted) and satiated (5 min after a meal) Zucker obese and lean rats. beta-Endorphin concentrations (1) in satiated vs. hungry rats were increased in the VMH (90 vs. 79 pg/mg tissue, p less than 0.05) and decreased in the supraoptic nucleus (65 vs. 78 pg/mg tissue, p less than 0.05), (2) in obese vs. lean rats were decreased in the VMH (79 vs. 90 pg/mg tissue, p less than 0.05) and (3) in female vs. male rats were increased in the anterior hypothalamus (123 vs. 59 pg/mg tissue, p less than 0.01) and VMH (90 vs. 79 pg/mg tissue, p less than 0.05). Analysis of a phenotype by feeding condition interaction revealed that obese but not lean rats had higher beta-endorphin concentrations in the satiated vs. hunger condition. However, plasma beta-endorphin concentrations did not differ with feeding condition, phenotype or sex. Intermediate and posterior but not anterior pituitary beta-endorphin concentrations were lower in obese than lean rats. Thus, there is some evidence for a relationship between beta-endorphin concentration and feeding in the hypothalamus, but beta-endorphin concentrations in plasma do not appear to be influenced by feeding condition or obesity.

Autoimmunization against beta-endorphin increases food intakes and body weights of obese rats.

Opioid peptides in the brain are postulated to mediate the hunger component of the control of food intake and regulation of body weight and concentrations are increased in the pituitaries of genetically obese rodents. However, systemic increases in opioids have been associated with satiety. Thus a chronic decrease in systemic concentrations of the opioid beta-endorphin induced by autoimmunization was predicted to increase food intake and body weight. Zucker obese (n = 20, 568 +/- 13 g) and lean (n = 20, 299 +/- 16 g) rats were autoimmunized against bovine serum albumin (BSA) or BSA conjugated to beta-endorphin (BSA-BE). Eight weeks after immunization serum from BSA-BE rats bound at least 7 times the circulating concentration of beta-endorphin. Food intakes were greater in BSA-BE obese (31.7 vs. 30.4 g/day, p less than 0.001) and lean rats (21.4 vs. 21.0 g/day, p less than 0.007) during weeks 5-8 and only obese rats, weeks 9-12 (31.8 vs. 30.3 g/day, p less than 0.009). Body weight gains were greater for BSA-BE than BSA obese rats during weeks 1-4 (1.34 vs. 0.92 g/day, p less than 0.05) and 9-12 (0.95 vs. 0.43 g/day, p less than 0.01). At 8 weeks the plasma concentrations of "free" beta-endorphin were decreased 78% (34 vs. 154 pmol/l, p less than 0.001) and "total" ("free" plus antibody-bound) beta-endorphin were increased (427 vs. 101 pmol/l, p less than 0.001). These results suggest that systemic concentrations of beta-endorphin may play an important role in the control of food intake and regulation of energy balance.

Meal-stimulated increased concentrations of CCK in the hypothalamus of Zucker obese and lean rats.

CCK is a putative satiety peptide found to be active when administered peripherally and centrally. Concentrations of CCK have been measured in the brains of fed and fasted animals, but as yet no clear correlation with feeding has been found. In the present experiment rats were sacrificed after a 6-hr fast or 5 min after a meal. Areas of the hypothalamus were removed from these rats and assayed for CCK content. The relationship between obesity and CCK content in specific areas of the brain was also investigated by using Zucker obese and lean rats. In fed rats the CCK concentrations were higher than in fasted rats in the ventromedial hypothalamus (VMH) (56 vs. 42 pg/mg tissue, p less than 0.005), lateral hypothalamus (38 vs. 27 pg/mg, p less than 0.01) and supraoptic nucleus (48 vs. 39 pg/mg, p less than 0.01). In obese rats the concentrations were higher than in lean rats in the VMH (56 vs. 41 pg/mg, p less than 0.003), dorsal medial hypothalamus (37 vs. 30 pg/mg, p less than 0.04) and anterior hypothalamus (61 vs. 37 pg/mg, p less than 0.001). Average concentrations of CCK in all hypothalamic areas were higher in females than males (50 vs. 40 pg/mg, p less than 0.001). Thus, CCK concentrations in specific areas of the hypothalamus increased with feeding, supporting the potential role of CCK in the central nervous system as a satiety peptide. Further, although the concentrations of CCK in obese rats were higher than those in lean rats, the changes in CCK concentration with feeding were the same, showing that obesity is not a consequence of decreased concentrations or concentration changes of CCK in brain.

Effect of CCK antibodies on food intake and weight gain in Zucker rats.

While exogenous administration of cholecystokinin (CCK) decreases food intake in many species, it has not been demonstrated conclusively that CCK is necessary for satiety to occur. In these experiments the role of CCK in eliciting satiety was further investigated by using endogenously produced and exogenously administered antibodies to CCK which were hypothesized to sequester circulating CCK. In the first experiment Zucker obese (n = 12, 192 +/- 16 g) and lean (n = 12, 152 +/- 11 g) male rats were administered CCK-8 conjugated to bovine serum albumin or bovine serum albumin by subcutaneous administration in Freund's adjuvant. Average percent binding of 125I-gastrin-17 by serum taken 4, 8 and 12 weeks after treatment initiation was increased (19.9 vs. 2.1, p less than 0.001) in rats treated with CCK conjugate than controls, and the increase was greater in lean (27.5 vs. 1.9) than in obese (12.2 vs. 2.2, p less than 0.001) rats. In lean, but not obese rats, average daily food intake and weight gain were increased (9 and 17% p less than 0.04 and p less than 0.02 respectively) in rats with CCK-AB compared with rats with no CCK-AB during the three months. Development of CCK-AB did not affect food intake response to exogenously administered CCK-8 or pancreas weight relative to body weight. In Experiment 2 increased food intakes of obese and lean rats 30 min after intraperitoneal injection of rabbit serum with CCK-AB were greater than those after intraperitoneal injection of rabbit serum without CCK-AB (1.92 vs. 1.41, g, p less than 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)

Feeding following intrahypothalamic injections of calcium and magnesium ions in sheep.

To study ionic effects on hypothalamic control of feeding, seven sheep were each prepared with six bilateral medial-hypothalamic guides. Hypothalamic loci were identified where feeding resulted following 1 mu 1 injections of calcium chloride and/or magnesium chloride. Doses of 1 and 2 mumol were most effective to induce feeding, and potassium chloride was not effective. Injections of phentolamine, LB-46, carbachol, atropine, or prostaglandin E1 did not inhibit the feeding responses following magnesium chloride injections into magnesium ion responsive loci. Feeding following calcium chloride injections into calcium ion responsive loci was blocked by atropine and reduced by phentolamine. Carbachol and prostaglandin E1 elicited feeding when injected into magnesium but not calcium ion responsive loci. Injections of carbachol followed by magnesium chloride resulted in greater feeding than when either chemical was injected alone. Calcium and/or magnesium ion bound feeding loci were in the anterior, ventromedial, dorsomedial, posterior and lateral hypothalamus, and the mammillary bodies. These ions elicited feeding in sheep perhaps by decreasing excitability of feeding-inhibitory neural pathways in the hypothalamus.