Long-term effect of prolactin treatment on glucose-induced insulin secretion in cultured neonatal rat islets

Insulin secretion and 45SCa2+ uptake and efflux were studied in neonatal rat islets maintained in culture for 7 or 19 days in the absence or presence of prolactin (PRL). Insulin secretion in response to glucose (G), leucine (Leu), arginine (Arg) and carbachol (Cch) was augmented after 7 and 19 days in culture, compared to basal secretion (G 2.8 mM), in both PRL- treated and control islets. However, the increase in insulin secretion induced by the above secretagogues was higher in islets cultured in the presence of PRL for 19 days. In PRL-treated islets, the 45Ca2+ content after a 5 min incubation in the presence of G, Leu, Arg and Cch was significantly higher than the control only in islets cultured for 19 days. Except with Arg, the 45Ca2+ uptake in PRL-treated islets after a 90 min incubation was also significantly higher than the control only in islets cultured for 19 days. Finally, Leu-induced alterations in the 45Ca2+ efflux were higher in PRL-treated than in control islets cultured for 7 or 19 days. In the absence of external Ca2+, the reduction in 45Ca2+ efflux induced by glucose was also significantly higher in PRL-treated than in control islets. This effect was slightly potentiated after 19 days in culture. These data further support the hypothesis that PRL treatment enhances maturation of the secretory mechanism in neonatal islets. This effect can be potentiated even more if the treatment is prolonged.

Protein deficiency and nutritional recovery modulate insulin secretion and the early steps of insulin action in rats

Maternal malnutrition was shown to affect early growth and leads to permanent alterations in insulin secretion and sensitivity of offspring. In addition, epidemiological studies showed an association between low birth weight and glucose intolerance in adult life. To understand these interactions better, we investigated the insulin secretion by isolated islets and the early events related to insulin action in the hind-limb muscle of adult rats fed a diet of 17% protein (control) or 6% protein [low (LP) protein] during fetal life, suckling and after weaning, and in rats receiving 6% protein during fetal life and suckling followed by a 17% protein diet after weaning (recovered). The basal and maximal insulin secretion by islets from rats fed LP diet and the basal release by islets from recovered rats were significantly lower than that of control rats. The dose-response curves to glucose of islets from LP and recovered groups were shifted to the right compared to control islets, with the half-maximal response (EC 50) occurring at 16.9 ± 1.3, 12.4 ± 0.5 and 8.4 ± 0.1 mmol/L, respectively. The levels of insulin receptor, as well as insulin receptor substrate-1 and phosphorylation and the association between insulin receptor substrate-1 and phosphatidylinositol 3-kinase were greater in rats fed a LP diet than in control rats. In recovered rats, these variables were not significantly different from those of the other two groups. These results suggest that glucose homeostasis is maintained in LP and recovered rats by an increased sensitivity to insulin as a result of alterations in the early steps of the insulin signal transduction pathway.

Protein Deficiency Attenuates the Effects of Alloxan on Insulin Secretion and Glucose Homeostasis in Rats

We have investigated the effect of alloxan on insulin secretion and glucose homeostasis in rats maintained on a 17% protein (normal protein, NP) or 6% protein (low protein, LP) diet from weaning (21 days old) to adulthood (90 days old). The incidence of alloxan diabetes was higher in the NP (3.5 times) than in the LP group. During an oral glucose tolerance test, the area under serum glucose curve was lower in LP (57%) than in NP rats while there were no differences between the two groups in the area under serum insulin curve. The serum glucose disappearance rate (Kitt) after exogenous insulin administration was higher in LP (50%) than in NP rats. In pancreatic islets isolated from rats not injected with alloxan, acute exposure to alloxan (0.05 mmol/L) reduced the glucose- or arginine-stimulated insulin secretion of NP islets by 78% and 56%, respectively, whereas for islets from LP rats, the reduction was 47% and 17% in the presence of glucose and arginine, respectively. Alloxan treatment reduced the glucose oxidation in islets from LP rats to a lesser extent than in NP islets (23% vs. 56%). In conclusion, alloxan was less effective in producing hyperglycemia in rats fed a low protein diet than in normal diet rats. This effect is attributable to an increased peripheral sensivity to insulin in addition to a better preservation of glucose oxidation and insulin secretion in islets from rats fed a low protein diet.

Insulin secretion in monosodium glutamate (MSG) obese rats submitted to aerobic exercise training

The present study was designed to evaluate the effects of aerobic exercise training on glucose tolerance and insulin secretion of obese male Wistar rats (monosodium glutamate [MSG] administration, 4mg/g-body weight, each other day, from birth to the 14th day). Fourteen weeks after the drug administration, the rats were separated into two groups: MSG-S (sedentary) and MSG-T (T = swimming, 1 h/day, 5 days/week, with an overload of 5% body weight for 10 weeks). Rats of the same age and strain injected with saline were used as control (C) and subdivided into two groups: C-S and C-T. Insulin and glucose responses during an oral glucose tolerance test (GTT) were evaluated by the estimation of the total areas under serum insulin (AI) and glucose (AG) curves. Glucose-induced insulin secretion by isolated pancreatic islets was also evaluated. MSG-S rats showed higher AI than C-rats while MSG-T rats presented lower AI than MSG-S rats. No differences in AG were observed among the 4 groups. Pancreatic islets from MSG-rats showed higher insulin secretion in response to low (2.8) and moderate (8.3 mM) concentrations of glucose than those from their control counterparts and no differences were observed between MSG-S and MSG-T rats. These results provide evidences that the hyperinsulinemia at low or moderate glucose concentrations observed in MSG-obese rats is, at least in part, a consequence of direct hypersecretion of the B cells and that chronic aerobic exercise is able to partially counteract the hyperinsulinemic state of these animals without disrupting glucose homeostasis.

Secretion of tumor necrosis factor-alpha by mouse peritoneal macrophages in the presence of dental sealers, sealapex and endomethasone

After filling root canals, the healing process depends on the chemical composition or physical-chemical properties of the material used, among other factors. All root canal sealers, whether solid or plastic, are foreign matter for the body if they remain in permanent contact with apical and periapical tissues. As a result, the first organic reaction that occurs is an attempt to phagocytize the material. During phagocytosis, macrophages release a large number of cell mediators into the area, among which are cytokines that are essential in intercellular communication and in many physiological and pathophysiological processes. One of these cytokines is tumor necrosis factor-alfa (TNF-α), which acts through links to specific receptors on the cell membrane initiating a cascade of events leading to induction, activation, or inhibition of numerous cytokine-regulated genes in the cell nucleus. The release of TNF-α in a cell culture of mouse peritoneal macrophages incubated with three concentrations (25, 50, and 100 mg/ml) of two endodontic sealers was measured. The solutions containing the calcium hydroxide-based root canal sealer (Sealapex) released fewer units of TNF-α than solutions containing the zinc oxide and eugenol-based sealer (Endomethasone).

Chemical composition of the dufour gland secretion in queens of Melipona bicolor (Hymenoptera, Meliponini)

We describe differences in the chemical composition of the Dufour gland secretion of virgin and physogastric queens of Melipona bicolor through gas chromatography and mass spectrometry. The Dufour gland secretion of virgin queens consists only of hydrocarbons, while that of physogastric queens contains, besides these, a variety of other compounds, such as isobutyrate and acetate esters. Such differences may indicate the queen fecundity condition and the oxygenated compounds of the physogastrics secretion may help to increase their attractiveness.

The chemical composition of the mandibular gland secretion of Melipona bicolor lepeletier, 1836 (Hymenoptera, Apidae, Meliponini): A comparative study among castes and sexes

The mandibular gland secretions of newly emerged, nurse and forager workers, virgin and physogastric queens and males of Melipona bicolor were analyzed by gas chromatography-mass spectrometry. The secretion is composed of a blend of hydrocarbons, alcohols, esters, and acids. The secretion is caste-sex specific and also differs with the tasks performed by the workers and the physiological reproductive condition of the queens.

Macromolecular array patterns of silk gland secretion in social Hymenoptera larvae

The cocoon, produced by most holometabolous insects, is built with silk that is usually produced by the larval salivary gland. Although this silk has been widely studied in the Lepidoptera, its composition and macromolecular arrangement remains unknown in the Hymenoptera. The macromolecular array patterns of the silk in the larval salivary gland of some meliponids, wasps, and ants were analyzed with polarized-light microscopy, and they were compared with those of Bombyx mori (Lepidoptera). There is a birefringent secretion in the glandular lumen of all larvae, due to filamentous structural proteins that display anisotropy. The silk in the distal, middle and proximal regions of the secretory portion of Formicidae and Vespidae glands presented a lattice optical pattern. We found a different pattern in the middle secretory portion of the Meliponini, with a zigzag rather than a lattice pattern. This indicates that the biopolymer fibers begin their macromolecular reorganization at this glandular region, different from the Formicidae and the Vespidae, in which the zigzag optical pattern was only found at the lateral duct. Probably, the mechanism of silk production in the Hymenoptera is a characteristic inherited from a common ancestor of Vespoidea and Sphecoidea; the alterations in the pattern observed in the Meliponini could be a derived characteristic in the Hymenoptera. We found no similarity in the macromolecular reorganization patterns of the silk between the Hymenoptera species and the silkworm.

Secretion of middle ear in infants - Occurrence, recurrence and related factors

Objective: The present study aimed at evaluating the occurrence and recurrence of middle ear effusion and possible associated factors in the first two years of life of 190 newborns and infants, participants in the interdisciplinary prevention, detection, and intervention program at the Clínica de Educação para Saúde of Universidade do Sagrado Coração, Methods: Newborns and infants were monthly submitted to anamneses, otoscopy, behavioral hearing assessment using sound instruments and pure tones (pediatric audiometry) and tympanometry. Results: The results revealed that 68.4% of infants presented one or more episodes of middle ear effusion during their two first years, with more recurrence among males. Peak occurrence was between four and 12 months of age and, the earlier the first episode, the higher the probability of recurrence. Greatest incidence was during May and August. It was found that, of the variables investigated, the period of exclusive breastfeeding actuated as a protector factor. With respect of risk factors, it was observed that passive smoking, gastro-esophageal reflux and respiratory allergy were related with the recurrences of effusion. Conclusion: Findings revealed the importance of periodic auditory follow-up for infants during their first two years of life, considered to be the critical period of auditory system maturation, during which sensory deprivation can be responsible for damage to the development of speech, language and other auditory abilities. Copyright © 2005 by Sociedade Brasileira de Pediatria.

Lack of inhibitory effect of zinc on prolactin secretion induced by cimetidine

The dopaminergic, serotoninergic and GABA-ergic systems are closely involved in PRL secretion, as well as thyrotropin-releasing hormone. There is some evidence that zinc interacts with some of these neuroamines and neuropeptides. The histamine H2-receptor cimetidine stimulates PRL secretion rapidly following an intravenous injection in man. In this sense, we investigated probable inhibitory effect of zinc on prolactin secretion following cimetidine injection (300 mg). Therefore, we studied five healthy adult men, before and after oral zinc administration (25 mg elemental zinc) during three consecutive months. The results did not demonstrate any inhibitory effect of zinc on prolactin secretion. So, we originally concluded that zinc did not interact with dopamine, serotonine, gamma-aminobutyric acid and the thyrotropin-releasing hormone in humans. In addition, the intravenous administration of cimetidine did not change the serum zinc profile. © 2005 Dustri-Vertag Dr. K. Feistle.

Zinc does not inhibit prolactin secretion during insulin-induced hypoglycemia in normal men

Zinc (Zn ++) has been shown as an important physiological inhibitor of pituitary PRL release, and Zn ++ and PRL could be involved in a negative feedback regulatory loop. However, this inhibitory effect has not been detected in humans with regard to thyrotropin releasing hormone (TRH), dopamine (DA) and histamine (HA) neurotransmitters. In order to investigate this topic, Zn ++ was acutely and chronically administered to five healthy men to observe the probable inhibitory effect on PRL release during insulin-induced hypoglycemia. The positive PRL response to hypoglycemia has generally been considered to be mediated via the hypothalamus by adrenergic, serotoninergic, histaminergic, opioid-peptidergic and TRH neurotransmitters. The results showed that Zn ++ was not able to inhibit the PRL release during insulin-induced hypoglycemia. Under these conditions, Zn ++ does not block hypothalamic neurotransmitters stimulated by hypoglycemia, thus excluding its clinical application in human beings. On the other hand, the effect of acute stress, such as hypoglycemia, on the serum Zn ++ profile was not observed. ©2006 Dustri-Verlag Dr. K. Feistle.

The effect of pH on horseradish peroxidase-catalyzed oxidation of melatonin: Production of N1-acetyl-N2-formyl-5- methoxykynuramine versus radical-mediated degradation

There is a growing body of evidence that melatonin and its oxidation product, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), have anti-inflammatory properties. From a nutritional point of view, the discovery of melatonin in plant tissues emphasizes the importance of its relationship with plant peroxidases. Here we found that the pH of the reaction mixture has a profound influence in the reaction rate and products distribution when melatonin is oxidized by the plant enzyme horseradish peroxidase. At pH 5.5, 1 mm of melatonin was almost completely oxidized within 2 min, whereas only about 3% was consumed at pH 7.4. However, the relative yield of AFMK was higher in physiological pH. Radical-mediated oxidation products, including 2-hydroxymelatonin, a dimer of 2-hydroxymelatonin and O-demethylated dimer of melatonin account for the fast consumption of melatonin at pH 5.5. The higher production of AFMK at pH 7.4 was explained by the involvement of compound III of peroxidases as evidenced by spectral studies. On the other hand, the fast oxidative degradation at pH 5.5 was explained by the classic peroxidase cycle. © 2007 The Authors.

Histochemical and ultrastructural evidence of lipid secretion by the silk gland of the sugarcane borer Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae)

The silk gland in Lepidoptera larvae is responsible for the silk production used for shelter or cocoon construction. The secretion of fibroin and sericin by the different silk gland regions are well established. There are few attempts to detect lipid components in the insect silk secretion, although the presence of such element may contribute to the resistance of the shelter to wet environment. This study characterizes the glandular region and detects the presence of lipid components in the secretion of the silk gland of Diatraea saccharalis (Fabricius). The silk gland was submitted to histochemical procedure for lipid detection or conventionally prepared for ultrastructural analyses. Lipid droplets were histochemically detected in both the apical cytoplasm of cell of the anterior region and in the lumen among the microvilli. Ultrastructural analyses of the anterior region showed lipid material, visualized as myelin-like structures within the vesicular Golgi complex and in the apical secretory globules, mixed up with the sericin; similar material was observed into the lumen, adjacent to the microvilli. Lipids were not detected in the cells neither in the lumen of the posterior region. Our results suggest that the silk produced by D. saccharalis has a minor lipid content that is secreted by the anterior region together with the sericin.

Induction and secretion of elastinolytic and proteolytic activity in cultures of Paracoccidioides brasiliensis

P. brasiliensis parasitizes various human tissues and proteinases exported by this fungus may allow it to metabolize and invade host tissues. The influence of the culture medium on the production of proteinases by P. brasiliensis isolates was studied and the export of these enzymes was followed as a function of culture time. The fungus was grown in neopeptone, BSA, elastin or collagen medium. The culture medium was assayed for azocollytic, elastinolytic and caseinolytic activity. Proteolytic activity was also analysed by electrophoresis of the culture medium on gelatin and casein substrate gels. P. brasiliensis expressed relatively high levels of azocoll, elastin and casein degrading activity in all types of medium, except in neopeptone medium. Generally, expression of azocollytic activity peaked during the third week of culture and caseinolytic activity during the fourth week of culture. Azocollytic activity was highest at pH 4.0 and caseinolytic activity at pH 8.0. Elastinolytic activity was also highest at pH 8.0. This activity, as well as the others, may provide the fungus with a source of carbon and nitrogen and may also be responsible for the invasion of host tissues, such as pulmonary elastic fiber, by P. brasiliensis.

Modulation of insulin secretion by physical training during recovery from protein malnutrition in rats

Objective: The purpose of the present study was to examine insulin secretion in rats submitted to protein restriction and nutritional recovery associated or not to physical training. Methods: The experiment was designed in two sets of five weeks each. In the first set the rats were fed a nonnal-protein diet(17%-control group) or a low-protein diet (6%-malnourished group) for five weeks. After this, all animals were fed the 17% protein diet and separated into four groups: sedentary control(SC); trained eontrol(TC); sedentary recovered(SR) and trained recovered(TR). TC and TR rats performed swimming exercise. Results: The results indicated efficiency of the 6% protein diet in producing signs of malnutrition, as reduction in body weight gain and serum albumin levels, as well as liver fat. Serum insulin in the fed state and insulin secretion by isolated pancreatic islets in response to glucose were Keduced,but peripheral sensitivity to insulin was increased and glucose tolerance was not changed in the protein deficient rats, indicating adaptation to malnutrition. Diet protocol for nutritional recovery was efficient in repairing body weight gain, serum albumin and liver fat levels of the previously malnourished rats. Glucose induced insulin release by pancreatic islets remained low after nutritional recovery. Insulin secretion by the islets isolated from rats submitted to exercise training during nutritional recovery was improved when compared with the sedentary animals. Conclusion: This indicates that exercise training may be useful in the treatment of protein calorie malnutrition, concerning to glucose induced insulip secretion.