role of zinc in the endocrine system

Zinc is essential in the regulation of a variety of physiological and biochemical events in the organism. It plays a critical role in maintaining the cell membrane integrity, protein-carbohydrate-lipid metabolism, immune system, wound injury and in the regulation of a number of other biological processes associated with normal growth and development. Physiological and biochemical levels of many hormones are affected by zinc metabolism. Therefore, growth impairment, hypogonadism, and some endocrine diseases are associated with the deficiency of zinc. These effects of zinc are considered versatile. Zinc increases the synthesis of the growth hormone and its number of receptors; thus, it is an important mediator in the binding of this hormone to its receptor. Found in a large quantity in the pancreas tissue, zinc has a part in the regulation of the effect of insulin. Zinc is involved to much more thyroid hormone metabolism such as hormone synthesis, receptor activity, conversion of T4 to T3, and production of carrier proteins. The low levels of zinc and high levels of leptin in obese individuals point to a critical relationship between zinc and leptin. Zinc is related to enzyme activity to melatonin synthesis. Melatonin has regulatory activity for zinc absorption from gastrointestinal system. Zinc particularly affects the conversion of testosterone to dihydrotestosterone, as 5?-reductase that is involved in this conversion is a zinc-dependent enzyme. In consideration of these relations, zinc is accepted to play critical roles in the endocrine system. The aim of the current review is to draw attention to the effects of zinc on the endocrine system

effect of zinc supplementation on the urinary excretion of elements in female athletes

This study was carried out to find out how oral zinc supplementation to elite athletes affects the element changes in the urine. The study registered 10 female athletes who were on the women's volleyball team of Gazi University Sports Club and whose mean age, weight, and height were 14.2 +/- 0.42 years, 59.8 +/- 7.79kg and 173.6 +/- 6.15 cm. The study protocol was approved by the local ethics committee. The athletes who continued their daily routine training sessions [6 days/week] were supplemented with 220mg/day oral zinc sulfate for 4 weeks. In order to induce exhaustion, the subjects were put to a 20-meter shuttle run test before and after supplementation. A total, 7 times urine samples were collected follows as pre and post exercise before the start of the experiment and at the end [4 times], at the end of first, second and third week [3 times]. Urinary levels of magnesium, phosphorus, and calcium [mg/dl], as well as zinc, copper, and selenium [micro g/dl] were analyzed in the atomic emission device [ICP-MS]. Arithmetic means and standard errors of the data were calculated. Kruskal Wallis test was used to determine differences between weeks. Values for which p<0,05 were considered significant. When compared to resting values, urinary excretion of copper and selenium decreased in exercise [p<0,05], but increased with zinc supplementation [p<0,05]. Pre- and post-supplementation exercise resulted in reduced urinary zinc excretion [p<0,05]. Zinc supplementation increased urinary zinc excretion in one-week intervals over the course of 4 weeks [p<0,05], and reduced selenium levels [p<0,05]. When zinc is supplemented to athletes, the relation between the duration and dose of supplementation is important. The results of the study indicated that zinc does not have any negative effect on the urinary excretion of the concerned elements. It can thus be concluded that athletes may benefit from zinc support

Effect of vitamin A administration on free radicals and lactate levels in individuals exercised to exhaustion

This study was performed to explore the effect of vitamin A administration on Free Radicals production and antioxidant system activity and lactate levels in individuals exercised to exhaustion The study registered 10 healthy sedentary males their mean age was 22,85+/-0,26 years. The subjects were orally administrated with 300 mg vitamin A [retinol] for 4 weeks and engaged in strenuous exercise [using the Bruce protocol] once a week. Blood samples were collected from the subjects at four different times, before and after the supplementation and before and after exercise to analyze Malondialdehyde [MDA], Nitric oxide [NO], Glutathione [GSH], Glutathione peroxidase [GSH-Px], Catalase [CAT], Superoxide dismutase [SOD] levels using colorimetric ELISA test kits and plasma lactate levels using an autoanalyzer. Exhaustion exercise leaded to an increase in both MDA, NO, and lactate, and GSH, GSH-Px, CAT and SOD levels compared to resting levels both before and after supplementation [p<0.05]. Increased NO levels found in pre-supplementation exhaustion showed a significant decrease after the supplementation of vitamin A [p<0.05], but the other parameters were not changed after vitamin A administration. The results of our study demonstrate that the increase caused by 4-week strenuous exercise in the levels of the free radical NO was offset by vitamin A supplementation. It can be suggested that supplementation of vitamin A at physiological doses has a limited effect on lipid peroxidation caused by strenuous exercise

Selenium: Its metabolism and relation to exercise

Selenium [Se], which is commonly found in nature, is one of the essential trace elements necessary for the normal development of human and animal organisms. Selenium was first defined in 1818 by the Swedish chemist Berzelius in sulfuric acid residues. At the end of 1960s, the role of selenium in human health began to attract attention and human diseases that resembled animal diseases responding to selenium was started to be investigated. Selenium, which is highly important for human health, is necessary for a variety of metabolic processes, including thyroid hormone metabolism, protection against oxidative stress and immunity functions. Selenium is a molecule that activates glutathione peroxidase, and thus, it is involved in the antioxidant mechanisms that prevent oxidant damage. Exhaustive physical exercise is known to cause oxidant damage, probably by promoting free radical production in many tissues, including muscle, liver, heart and lungs in animals. The increase in oxidative stress during exercise and recognition of selenium's stimulation of antioxidant activity inevitably suggest a relation between selenium and exercise. The present review aims to provide information on selenium metabolism and the relation between selenium and exercise

Effect of melatonin supplementation on plasma glucose and liver glycogen levels in rats subjected to acute swimming exercise

The aim of the present study is to examine how melatonin supplementation affects plasma glucose and liver glycogen levels in rats subjected to acute swimming exercise. Spraque-Dawley species thirty adult male rats were allocated to 3 groups with equal number of animals: general control group which was not subjected to any procedure [Group 1], the group subjected to a 30-minute acute swimming exercise [Group 2], and the group subjected to a 30-minute acute swimming exercise after intraperitoneal [i.p.] melatonin supplementation [3 mg/kg/day] for 4 weeks [Group 3]. Blood samples collected from the experimental animals by decapitation method were analyzed in terms of plasma glucose, and glycogen levels were determined in liver tissue samples by histological method. The highest plasma glucose levels were obtained in group 2 [p<0,05]. Plasma glucose levels in groups 1 and 3 were not different. Mean liver glycogen level in group 3 was significantly higher than those in the other groups [p<0,01], while there was no significant difference between group 1 and group 2 in terms of this parameter. Results of the study demonstrate that melatonin supplementation can have a protective effect on liver glycogen reserves in rats subjected to acute swimming exercise

Zinc deficiency and supplementation in ovariectomized rats: their effect on serum estrogen and progesterone levels and their relation to calcium and phosphorus

The aim of this study is to examine how zinc deficiency or supplementation affects estrogen and progesterone and calcium and phosphorus levels in the serum. The study was carried out on 40 adult female rats of Spraque-Dawley species. The rats were allocated to four groups: Group 1: Control, Group 2: Ovariectomized [OVX] control. Group 3: OVX-Zinc-supplemented. Group 4: OVX-Zinc-deficient. Blood samples were taken from the experimental animals by decapitation method and analyzed in terms of estrogen, progesterone, calcium, phosphorus, magnesium and zinc levels. Group 1 had the highest estrogen levels [p < 0.05]. Estrogen levels in group 3 were higher than those in groups 2 and 4 [p < 0.05]. The lowest estrogen levels were found in group 4 [p < 0.05]. Progesterone levels were higher in group 1 than in groups 2, 3 and 4 and the same parameter in group 3 was higher than those in groups 2 and 4. The highest calcium and phosphorus levels were obtained in groups 1 and 3 [p < 0.05]. Calcium and phosphorus levels in group 2 were higher than those in group 4 [p < 0.05]. There was no difference among groups with regard to magnesium levels. Group 3 had the highest serum zinc levels [p < 0.05]. Zinc levels in group 1 were higher than those in groups 2 and 4 and the levels in group 2 were higher than those in group 4. Findings of the study show that zinc deficiency causes a significant decrease in calcium and phosphorus levels and that zinc supplementation prevents these adversities in ovariectomized rats

Effect of exhausting exercise and calcium supplementation on potassium, magnesium, copper, zinc and calcium levels in Athletes

Present study was performed to determine four week calcium supplementation and athleticism exercise on plasma potassium, calcium, magnesium, cupper and zinc levels in resting and exhaustion. Research was carried out on 30 healthy male people. Group 1; Exercise, Group 2; Exercise + Calcium supplementation, Group 3; Sedentary+Calcium supplemented. All elements levels increased by exhausting exercise [P<0.05]. Plasma K and Ca levels increased in exercise group after supplementation [P<0.05]. Ca levels increased in exercise + supplemented group [P<0.05]. This increase was much more in group three [P<0.05]. Plasma Cu levels increased by Ca supplementation in sedentary [P<0.05]. Exhausting exercise increased Zn levels in sedentary after supplementation [P<0.05]. The results of present study show that calcium supplementation for 4 week does not have clear affect on potassium and Mg. However, calcium levels were increased by supplementation and Cu after the supplementation. It was also exhausting exercise that caused increase in all parameters

effect of magnesium supplementation on glucose and insulin levels of Tae-Kwan-Do sportsmen and sedentary subjects

This study was performed to determine how the magnesium supplementation for a 4-week period affects the glucose and insulin levels at rest and at exhaustion in sportsmen. This is a 4 week study performed on 30 healthy male subjects varying between 18-22 ages. Subjects were separated into 3 groups. 1st group; group supplemented with magnesium, 2nd group; Magnesium supplementations +exercise group, 3rd group; training group. Glucose and insulin parameters of the groups were measured 4 times; at rest and exhaustion in the beginning of the research and at rest and exhaustion after the end of 4 weeks application period. Glucose levels in exhaustion measurements both before and after the supplementation significantly increased compared to resting levels [p < 0.05]. Significant difference was determined in the glucose values of 1st and 2nd groups supplemented with magnesium in comparison to their first measurements [p < 0.05]. Insulin values a decrease in all of the 3 groups occurred with exercise both before and after the supplementation [p < 0.05]. Magnesium supplementation has an important effect on glucose levels whereas it has no effect on insulin levels