Experiment on Changes in Serum Levels of Irisin

Experiment on Changes in Serum Levels of Irisin Khaled Abdelfattah Abdelhamid Abulfadle, MD   Serum irisin level changes after propylthiouracil treatment of L-thyroxine induced hyperthyroidism in rats ABSTRACT Background: Thyroid hormones play an essential role in lipid, protein and carbohydrate metabolism; and they regulate thermogenesis and basal metabolic rate. Irisin is a myokine that is secreted as a product of fibronectin type III domain containing 5 (FNDC5) was shown to be present in many tissues, including the thyroid tissue. Objective: To investigate the possible changes in serum levels of irisin that occurred in a rat model of hyperthyroidism and the effects of use of propylthiouracil (PTU) in its treatment. Design: 18 male albino rats were divided into 3 groups. Group I was the intact control. Rats of group II and III received daily 0.3 mg/kg subcutaneous injection of L-thyroxine (LT4) for 12 consecutive days. On the thirteenth day, animals of group III (Hyperthyroid PTU treated) received 5 ml/kg i.p. injection of propylthiouracil (PTU) along with an equivalent amount of LT4 as administered to group II animals for more 15 days. Animals of group II (Hyperthyroid control) continued to receive LT4. On the day of termination (28th day of starting LT4 treatment), overnight (12hrs) fasted animals were sacrificed by decapitation under ether anesthesia. Results: In the hyperthyroid control group, there was a significant decrease in serum level of TSH (P0.05) in serum levels of TSH, T4, T3 irisin, and, BMI in hyperthyroid PTU group in comparison to that in the intact control group. In the hyperthyroid control group, there was a significant increase in the serum level of both glucose (P0.05) in the hyperthyroid PTU treated group in comparison to that in the intact control group. In the hyperthyroid control group, there was a significant decrease in serum levels of both TC (P0.05) in serum levels of both TG and LDL-C in comparison to that in the intact control group. Conclusion: This study showed a significant increase in serum levels of irisin in L-thyroxine induced hyperthyroidism in rats. On using PTU, serum levels of irisin, thyroid hormones, metabolic parameters and BMI were significantly changed in comparison to the hyperthyroid control group. Keywords: Irisin, T3, T4, TSH, Propylthiouracil, Hyperthyroidism. Introduction: Irisin is a myokine that is secreted as a product of fibronectin type III domain containing 5 (FNDC5) in the skeletal muscle (Samy, Ismail et al. 2015, Jin Zhang 2017, Nathan C. Winn 2017). FNDC5, which is the precursor of irisin was shown to be present in many tissues, including the thyroid tissue (Huh, Panagiotou et al. 2012). It is secreted by a peroxisome proliferator-activated receptor ÃŽÂ ³ (PPARÃŽÂ ³) coactivator 1ÃŽÂ ± (PGC1-ÃŽÂ ±) after an exercise (Aydin 2014). Irisin was found to have an anti-obesity effect as it replaces the white fatty tissue with brown fatty tissue by the increase of uncoupling protein-1 (UCP1) resulting in oxygen consumption and stimulation of thermogenesis (Bostrà ¶m, Wu et al. 2012, Castillo-Quan 2012, Roca-Rivada, Castelao et al. 2013, Jin Zhang 2017, Nathan C. Winn 2017). Stengel, Hofmann et al. (2013) found that irisin level was identified to be high in obesity and to be low in anorexia nervosa. On the other hand, thyroid hormones pla y an essential role in lipid, protein and carbohydrate metabolism; and they regulate thermogenesis and basal metabolic rate (Hulbert 2000). Also, hyperfunction of thyroid gland is a common endocrine disorder which is accompanied by metabolic imbalance, oxidative stress and abnormal energy homeostasis (Erdamar, Demirci et al. 2008). There were some controversies in the results of studying the effect of thyroid hormone level changes on serum levels of irisin as Yalcin, Akturk et al. (2016) found an increase in serum irisin levels in hyperthyroidism and they suggested that it might contribute to altered energy metabolism. Also, Samy, Ismail et al. (2015) stated that hyperthyroidism was associated with up-regulation of serum irisin in male rats, probably as a response to myopathy and/or oxidative damage observed in both conditions. Moreover, Ruchala, Zybek et al. (2014) reported a borderline elevation of serum irisin in hyperthyroid versus hypothyroid patients. On the contrary, Panagiot ou, Pazaitou-Panayiotou et al. (2016) stated that changes in thyroid hormone levels did not affect circulating irisin levels in humans. Also, Stengel, Hofmann et al. (2013), Ellefsen, Vikmoen et al. (2014) and Gouni-Berthold, Berthold et al. (2013) reported lack of associations between levels of irisin, TSH and/or thyroid hormones. On the other hand, Zybek-Kocik, Sawicka-Gutaj et al. (2016) stated that irisin concentration was changed during prolonged thyroid function impairment. Also, AteÃ…Å ¸, Altay et al. (2016) found that, in hypothyroidism, there was a positive correlation between serum irisin levels and thyroid stimulating hormone (TSH) while a negative correlation was found between irisin levels and thyroxine (T4). Thus, this study was conducted to investigate the possible changes in serum levels of irisin that occurred in a rat model of hyperthyroidism and the effects of use of propylthiouracil (PTU) in its treatment. Materials and Methods: Animals preparations and experimental protocol: In the Department of Physiology, Faculty of Medicine, Zagazig University, this experimental study was done from 6th of November 2016 to 28th of December 2016. 18 adult male albino rats, age and weight matched (170-195 gm), were purchased from the animal house of Zagazig University and were housed at 20-22 °C on a 12-h light-dark cycle and for 5 days, to achieve acclimatization, they were supplied with tap water and a standard chow diet. Rats were divided into 3 groups of 6 each. Group I animals served as the intact control, whereas those of group II and III received daily subcutaneous injection of L-thyroxine (LT4) (Sigma, MO, USA) at a dose of 0.3 mg/kg for 12 consecutive days (Panda and Kar 2007). On the thirteenth day, animals of group III received propylthiouracil (PTU) (Sigma, MO, USA) 10 mg/kg intraperitoneally (Panda and Kar 2007) along with an equivalent amount of LT4 as administered to group II animals. PTU was intraperitoneally (i.p.) injected, in a volume of 5 ml/kg, dis solved in saline (Kim, Kim et al. 2012). Experiment was continued for more 15 consecutive days (from 13th LT4 treatment). Animals of group II continued to receive LT4 and acted as hyperthyroid control. Intact control rats were injected with 5 ml/kg/day subcutaneously with saline. On the day of termination (28th day of starting LT4 treatment), overnight (12hrs) fasted animals were sacrificed by decapitation under ether anesthesia. Blood from each animal was collected and by its centrifugation at 3000 rpm for 15 minutes, serum was separated and stored -20oc till the time of assay of different biochemical parameters (Kumar, Kar et al. 2014). PTU was used to treat hyperthyroidism by decreasing the amount of thyroid hormone produced by the thyroid gland (Nakamura, Noh et al. 2007), and it also inhibited the enzyme 5-deiodinase, which converts thyroxine (T4) to the active form triiodothyronine (T3) (Bahn, Burch et al. 2009). Also, it inhibited LT4-induced hyperthyroidisms in rats (Panda a nd Kar 2007). Body mass index (BMI) changes: BMI in gm/cm2 was calculated in the different groups, just before rats were sacrificed (under ether anesthesia), by dividing Body weight (gm) on Length2 (cm2) (Novelli, Diniz et al. 2007). A graduated (in centimeters) metal ruler was used for measuring the rat length by putting the zero end at the rat anus and recorded the reading which reached by the nose. BMI was used as a measure for the change in body weight of rats (Novelli, Diniz et al. 2007). Figure-1: Experimental design. Rats were divided into 3 groups. Group I was the intact control. Rats of group II and III received daily subcutaneous injection of levothyroxine (LT4) for 12 consecutive days. On the thirteenth day, animals of group III (Hyperthyroid PTU treated) received i.p. injection of propylthiouracil (PTU) along with an equivalent amount of LT4 as administered to group II animals for more 15 days. Animals of group II (Hyperthyroid control) continued to receive LT4. On the day of termination (28th day of starting LT4 treatment), overnight (12hrs) fasted animals were sacrificed by decapitation under ether anesthesia. Measurement of serum parameters: Serum level of irisin was estimated (in ng/ml) using an irisin rat ELISA assay kit following the manufacturers instructions (Catalog# EK-067-52; Phoenix Pharmaceuticals Inc., Burlingame, California, USA) with a detection range of 0.1-1000 ng/ml. Quantitative immunoassaying of T3, T4 and TSH using commercially available kits as recommended by the manufacturer (cat#SE120091, SE120090, SE120135, ELISA Kits, Sigma-Aldrich). Both serum levels of total cholesterol (TC) and triglycerides (TG) were estimated using enzymatic colorimetric methods. Serum high density lipoprotein-cholesterol (HDL-C) was assayed using NS Biotec HDL-precipitating reagent. Serum low density lipoprotein-cholesterol (LDL-C) was calculated using the Friedewald formula: LDL-C (mg/dl) = [(TC) (HDL-C) ( (Friedewald, Levy et al. 1972) Estimation of both serum glucose levels, using an automated analyzer (YSI 2300; YSI Life Sciences, Yellow Springs, OH), and serum insulin levels, using ELISA kits (RD Systems, Minneapolis, MN), were done. For assessing insulin resistance (IR), the homeostasis model assessment-IR (HOMA-IR) index was calculated by: HOMA-IR = (Nayak, Hillemane et al. 2014). There is a direct relation between insulin resistance and the value of HOMA-IR (Bonora, Targher et al. 2000). Statistical analysis: By the use of IBM SPSS Statistics for windows package version (24), data were analyzed and described as Mean ± SEM. For calculation of the statistical significance, One-way ANOVA and Tukey HSD post hoc test for multiple group comparison were used. P†°Ã‚ ¤0.05 indicated significance. Results: Table-1: Changes in serum levels of TSH, T4, T3 irisin, and, BMI among different groups Intact control Hyperthyroid control Hyperthyroid PTU treated TSH (à ¯Ã‚ Ã‚ ­IU/L) 2.82 ±0.12 0.81 ±0.05a 2.68 ±0.14bc T4 (à ¯Ã‚ Ã‚ ­g/dl) 5.33 ±0.14 16.2 ±0.2a 5.36 ±0.18bc T3 (ng/ml) 1.29 ±0.04 3.52 ±0.11a 1.36 ±0.04bc Irisin (ng/ml) 401.67 ±5.65 599.17 ±6.82a 409.5 ±6bc BMI (gm/cm2) 0.54 ±0.01 0.44 ±0.01a 0.51 ±0.01bc Data was expressed as Mean ±SEM. a P0.05 in comparison to the intact control group. c P Table-2: Changes in metabolic parameters among different groups Intact control Hyperthyroid control Hyperthyroid PTU treated Glucose (mg/dl) 91.5 ±0.92 113 ±2.33a 91.33 ±1.2bc Insulin (à ¯Ã‚ Ã‚ ­IU/ml) 2.95 ±0.12 4.86 ±0.16a 2.88 ±0.13bc HOMA-IR 0.67 ±0.02 1.36 ±0.05a 0.65 ±0.03bc TC (mg/dl) 106.5 ±2.51 89.83 ±2.52a 103.33 ±1.63bd TG (mg/dl) 55.17 ±1.22 52.33 ±0.67b 53.17 ±0.95be HDL-C (mg/dl) 54 ±1.15 43.33 ±0.88a 51.33 ±0.99bc LDL-C (mg/dl) 41.47 ±3.27 36.03 ±3.07b 41.37 ±1.92be Data was expressed as Mean ±SEM. a P0.05 in comparison to the intact control group. c P0.05 in comparison to the hyperthyroid control group. HOMA-IR, homeostasis model assessment of insulin resistance index; TC, total cholesterol; TG, triglycerides; HDL-C, high density lipoprotein-cholesterol; LDL-C, low density lipoprotein-cholesterol. Figure-2: Correlations between serum irisin levels and: TSH, T4 T3 in, the intact control group (A), hyperthyroid control group (B) and hyperthyroid PTU treated group (C); glucose in the intact control group (D); insulin HOMA-IR in the intact control group (E); glucose in the hyperthyroid control group (F); insulin HOMA-IR in the hyperthyroid PTU treated group (G); TC HDL-C in the hyperthyroid control group (H). r is the correlation coefficient. Table-1 showed changes in serum levels of TSH, T4, T3 irisin, and, BMI among different groups. In the hyperthyroid control group, there was a significant decrease in serum level of TSH (0.81 ±0.05, P group (2.82 ±0.12), (0.54 ±0.01) (5.33 ±0.14), (1.29 ±0.04) and (401.67 ±5.65) respectively. On the other hand, there were insignificant changes (P>0.05) in serum levels of TSH, T4, T3 irisin, and, BMI in hyperthyroid PTU group in comparison to that in the intact control group. Also, there was a significant increase in both serum level of TSH (2.68 ±0.14, P0.05) in the hyperthyroid PTU treated group in comparison to that in the intact control group. Moreover, there was a significant decrease in the serum levels of both glucose (91.33 ±1.2, P0.05) in serum levels of both TG (52.33 ±0.67) and LDL-C (36.03 ±3.07) in comparison to that in the intact control group (106.5 ±2.51), (54 ±1.15), (55.17 ±1.22) and (41.47 ±3.27) respectively. In the hyperthyroid PTU treated group, there was a significant increase in serum levels of both TC (103.33 ±1.63, P0.05) in serum levels of both TG (53.17 ±0.95) and LDL-C (41.37 ±1.92) in comparison to that in the intact co ntrol group (89.83 ±2.52), (43.33 ±0.88), (52.33 ±0.67) and (36.03 ±3.07) respectively. Also, there were no significant changes (P>0.05) in serum levels of TC, TG, HDL-C and LDL-C in the hyperthyroid PTU treated group in comparison to that in the intact control group. Figure-2A showed a significant positive correlation between serum irisin levels and that of T4 (r=0.97, P Discussion: This study was done to declare changes in irisin serum levels in a rat model of hyperthyroidism and the effect of PTU therapy on it. Also, to identify the association between serum irisin level changes in such conditions and some metabolic parameters including insulin resistance and lipid profile. The results of this study showed a significant decrease in serum level of TSH and BMI, but, a significant increase in serum levels of T4, T3, and irisin in the hyperthyroid control group, in comparison to that in the intact control group. Also, there was a significant positive correlation between serum irisin levels and that of T4 T3 but a significant negative correlation with serum TSH in the hyperthyroid control group. These results were supported by Huh, Panagiotou et al. (2012) who stated that FNDC5, irisin precursor, was present in the thyroid tissue. Also, the present study results were supported by Irrcher, Adhihetty et al. (2003), Ruchala, Zybek et al. (2014), Sanchis-Gomar and Per ez-Quilis (2014), Samy, Ismail et al. (2015) and Yalcin, Akturk et al. (2016) who found an increase in serum irisin levels in hyperthyroidism and they suggested that it might contribute to altered energy metabolism. Moreover, Irrcher, Adhihetty et al. (2003) reported that T3 increased the irisin precursor, PGC-1ÃŽÂ ±, expression in muscle. Furthermore, Sanchis-Gomar and Perez-Quilis (2014) stated that serum irisin was increased in hyperthyroidism as a compensatory response to oxidative stress as it had an antioxidant effect. On the contrary, Gouni-Berthold, Berthold et al. (2013), Stengel, Hofmann et al. (2013) and Panagiotou, Pazaitou-Panayiotou et al. (2016) stated that changes in levels of thyroid hormones did not affect circulating irisin levels in humans. This discrepancy between their results and that of this study could be explained by species difference. Regarding the negative correlation between both irisin and TSH hormones which was present in this study, it was support ed by Ruchala, Zybek et al. (2014). On the contrary, Stengel, Hofmann et al. (2013) and Ellefsen, Vikmoen et al. (2014) reported lack of correlation between serum levels of irisin and that of TSH and thyroid hormones. Regarding body weight changes with hyperthyroidism, the result of this study was supported by Janson, Karlsson et al. (1995), Voldstedlund, Tranum-Jensen et al. (1995) and Loeb (1996) who found a decrease in body weight with hyperthyroidism. Also, this study results were supported by Bostrà ¶m, Wu et al. (2012), Castillo-Quan (2012) and Roca-Rivada, Castelao et al. (2013) who found that irisin had an anti-obesity effect as it replaced the white adipose tissue with brown adipose tissue and increased oxygen consumption and thermogenesis. On the contrary, Stengel, Hofmann et al. (2013) and Saleh, et al. (2014) found that irisin level was high in obesity and low in anorexia nervosa. This discrepancy between their results and that of this study can be explained by species difference. On the other hand, this study results showed insignificant changes in serum levels of TSH, T4, T3 irisin, and, BMI in hyperthyroid PTU group in comparison to that in the intact control group. This indicated the improvement that occurred with PTU therapy in cases of hyperthyroidism which was supported by Nakamura, Noh et al. (2007), Panda and Kar (2007) and Bahn, Burch et al. (2009). Also, the results of this study showed a significant increase in both serum level of TSH and BMI, but, a significant decrease in serum levels of T4, T3, and irisin in the hyperthyroid PTU treated group in comparison to that in the hyperthyroid control group. These results were supported by Park, Lee et al. (2016) who found that PTU administration ameliorated hyperthyroidism, reducing T4 and T3, and, increasing both TSH and BMI. Moreover, the results of this study showed a significant increase in the serum level of both glucose and insulin, and, the value of HOMA-IR in the hyperthyroid contro l group in comparison to that of the intact control group. Also, there was a significant positive correlation between serum irisin levels and that of glucose in the hyperthyroid control group. These results indicated occurrence of insulin resistance with hyperthyroidism which was supported by Loeb (1996). This was supported also by Saleh, et al. (2014) who stated that hyperglycemia gradually up regulated FNDC5/irisin expression in the skeletal muscles non-diabetic persons. Also, this study results were supported by Hee Park, Zaichenko et al. (2013), Liu, Wong et al. (2013) and Mehrabian, Taheri et al. (2016) who found a positive correlation between serum irisin and that of glucose. On the contrary, Mehrabian, Taheri et al. (2016) found that serum irisin was negatively correlated with serum glucose level. Opposite to the results of this study, Huh, Panagiotou et al. (2012), Choi, Kim et al. (2013) and Sanchis-Gomar and Perez-Quilis (2014) found that decreased blood irisin level was a ccompanied by insulin resistance development. Sanchis-Gomar and Perez-Quilis (2014) stated also, that irisin ameliorated insulin resistance by increasing betatrophin hormone expression which stimulated ÃŽÂ ²-cell regeneration. Furthermore, the results of this study showed no significant changes in the serum level of both glucose and insulin, and, the value of HOMA-IR in the hyperthyroid PTU treated group in comparison to that in the intact control group. Also, there was a significant decrease in the serum levels of both glucose and insulin, and, the value of HOMA-IR in the hyperthyroid PTU treated group in comparison to that of the hyperthyroid control group which means improvement of insulin resistance with PTU treatment. On the other hand, Huh, Panagiotou et al. (2012) found that exposure to high blood glucose for a long time was associated with a significant decrease in irisin serum level. The discrepancy between their results and the result of this study could be explained by the difference in species and duration of the study. In the hyperthyroid control group, there was a significant decrease in serum levels of both TC and HDL-C but, there were insignificant changes in serum levels of both TG and LDL-C in comparison to that in the intact control group. Also, there were significant negative correlations between serum irisin levels and that of both TC and HDL-C in the hyperthyroid control group. On the other hand, in the hyperthyroid PTU treated group, there was a significant increase in serum levels of both TC and HDL-C but, there were insignificant changes in serum levels of both TG and LDL-C in comparison to that in the intact control group. Also, there were no significant changes in serum levels of TC, TG, HDL-C and LDL-C in the hyperthyroid PTU treated group in comparison to that in the intact control group. The results of this study was partly supported by Mehrabian, Taheri et al. (2016) found a negative correlation between irisin and TC but, a po sitive correlation with HDL-C in normal weight obesity. On the other hand, Liu, Wong et al. (2013) found a positive correlation between serum irisin level and TC in non- obese, non- diabetic persons. Also, Sanchis-Gomar, Alis et al. (2014) reported insignificant correlation between irisin and TC. Conclusion   Ã‚   This study showed a significant increase in serum levels of irisin in L-thyroxine induced hyperthyroidism in rats and this could be related to changes in thyroid hormones, body weight and metabolic parameters. On using PTU, serum levels of irisin, thyroid hormones, metabolic parameters and BMI were significantly changed in comparison to the hyperthyroid control group and insignificantly changed in comparison to the intact control group which confirmed the improvement of the hyperthyroidism. Future studies are needed to confirm these results and to ensure the possible use of irisin as a biomarker for proper treatment of hyperthyroidism.

Leadership Traits for the New Millennium :: Business Management

Leadership Traits for the New Millennium In reading through the leadership articles assigned, there were several leadership theories that I could identify most readily to what I believe my own leadership style to be. These are Transformational, Servant-Leader, and Chaordic. The readings presented many characteristics of what the authors saw as important to becoming the best leader possible. To evaluate my strengths and weaknesses in questions #1 and #2 I used the characteristics from the Little article, Leadership Traits for the New Millennium as I thought they encompassed many of the traits discussed in the other articles as well as being put forward as key components of leadership’s future directions. I see each of these traits as a continuum so I will address both strengths and weaknesses at the same time. My strengths and weaknesses as a senior level leader interviewing for Chief Information Officer at a higher education institution. I begin my self-evaluation with change readiness. While I have made good strides in learning about change, the need for change, and preparing for change, I do believe that this is one area where I would like to target time for more development. Whether upbringing or lack of experience, I have always known the need for change but have not been quick to implement it. I believe I have the skills to lead change once decisions for changes have been made but I need to work on making that timely decision for change in the first place. Related to change is adaptability. Again, I feel like I am able to lead change once it has been decided but I have a harder time adapting to that initial need for change. My experience has been in steady state environments where the need for adaptability has not been a much-needed commodity, so again, I see a need to be introduced to a more dynamic environment to learn and experience adaptability. With that said however, I do see myself as one that can go with the flow and not being the one who is always in control. I feel that some of the best outcomes have been achieved from leadership from behind and have no trouble facilitating group leadership. I also feel I have a very good sense of keeping vision and mission on course. I think one of my major strengths is sensitivity.

Getting stuff and spending money

The way we absorbed ourselves into the world, we put our powers of mind and soul In getting stuff and spending money. These powers are not satisfying – It Is just a waste. Nature is not Just a bunch of trees and water, but nature is the wilderness and the places where a human can go and replenish but we think nature Is not ours and find ourselves not in touch with It. Our hearts, the center of our emotional life, we have given away instead of holding, treasuring and being connected with nature.We should not be giving away our hearts as It Is not good Idea. The sea Is personified as a woman as she opens her chest to the moon, showing the relationship between the two of them. The winds have been gathered to somewhere and they are sleeping like flowers lay out. We are mammals the beauty of nature, the delights of the sea and the winds with Its up gathered flowers. The nature, the sea and the wind don't touch us. I'd rather be a non-charlatans and raised as a child In a religion t hat is worn out.If I were from one of those religions, I might look out and have glimpses of something that will make me less sad, that would give me some joy. I imagine that if I were born in those religions of the past, I would see the ocean as divine, a place where I might encounter God and as a piece of God. I would look out to the sea and it would not just be a bunch of water lying there, I would also see God and other gods. It is not only the ocean that would be sacred, meaningful and important but also the nature around us.

Interesting Bull Shark Facts (Carcharhinus leucas)

The bull shark (Carcharhinus leucas)  is an aggressive shark found throughout the world in warm, shallow waters along coasts, in estuaries, in lakes, and in rivers. Although bull sharks have been found inland as far as the Mississippi River in Illinois, they arent a true freshwater species. The bull shark is listed as near threatened by the International Union for Conservation of Nature (IUCN). Essential Facts Bull sharks get their common name both from their appearance and their behavior. The shark is large and stocky, with a broad, flat snout and an unpredictable, aggressive nature. Females are larger than males. A typical female bull shark is 2.4 m (7.9 ft) long and weighs 130 kg (290 lb), while a male averages 2.25 m (7.4 ft) and 95 kg (209 lb). The largest recorded bull shark was a 4.0 m (13.1 ft) female. The bite force of a bull shark is 5914 Newtons, which is the highest for any fish, weight for weight.There are 43 elasmobranch species found in freshwater. Sand sharks, sawfish, skates, and stingrays are other species that can enter rivers. Bull sharks are capable of osmoregulation, which means they can control their internal osmotic pressure when external salinity changes. This also makes them euryhaline (able to adapt to different salinities) and diadromous (readily able to swim between fresh and salt water). Bulls sharks give birth to four to ten live young in fresh water. Over ti me, the sharks gain a tolerance for salinity. Newborn or young sharks are usually found in fresh water, while older sharks tend to live in salt water. Young bull sharks flow with the tides to conserve energy needed for movement and osmoregulation. However, bull sharks can live their entire lives in fresh water. Adult life in fresh water is not ideal, as most of the sharks food lives in the sea.Bull sharks mainly eat bony fish and smaller sharks, including bull sharks. As opportunistic predators, they also eat terrestrial mammals, birds, turtles, crustaceans, echinoderms, and dolphins. They use the bump-and-bite strategy to attack prey, typically hunting in murky water. Usually, bull sharks are solitary hunters, although they may hunt in pairs to trick prey. Although bull sharks hunt in murky water, they can see color and use it to seek prey. They can be attracted to bright yellow gear, for example. The sharks hunt both during the day and at night.Adult sharks mate in late summer or early autumn. It takes 10 years for a shark to reach maturity. In the mating ritual, the male bites the females tail until she turns upside down, allowing him to copulate. Mature females often have bite marks and scratches.Bull sharks are apex predators, so their main threat is mankind. However, they may be attacked by great white sharks, tiger sharks, and crocodiles. The average life span of a bull shark is 16 years. How Dangerous Is the Bull Shark? The bull shark is believed to be responsible for most shark attacks in shallow water, even though  the International Shark Attack File  (ISAF) cites the great white shark (Carcharodon carcharias) as  responsible for the largest number of bites to humans. The ISAF notes great white bites are often correctly identified, but its difficult to tell bull sharks apart from other members of the family  Carcharhinidae  (the requiem sharks, which include the blacktip, whitetip, and grey reef shark). In any case, the great white, bull shark, and tiger shark are the big three where shark bites are concerned. All three are found in areas frequented by humans, have teeth designed to shear, and are large and aggressive enough to pose a threat. How to Recognize a Bull Shark If you see a shark in fresh water, chances are good its a bull shark. While the genus Glyphis includes three species of river sharks, they are rare and have only been documented in parts of Southeast Asia, Australia, and New Guinea. Bull sharks are gray on top and white underneath. They have a small, bullish snout. This helps camouflage them so they are harder to see viewed from below and blend in with the riverbed or sea floor when viewed from above. The first dorsal fin is larger than the second one and is angled rearward. The caudal fin is lower and longer than that of other sharks. Tips for Telling Sharks Apart If youre swimming in the surf, its not a smart idea to get close enough to identify a shark, but if you see one from a boat or land, you may want to know what type it is: Sandbar sharks also have rounded snouts, but their dorsal fins are larger and more triangular than those of bull sharks.Blacktip sharks are shaped much like bull sharks, but they have pointed snouts and white anal fins. Note juvenile bull sharks may have black-tipped fins, so coloration is not a good way to distinguish these species.Lemon sharks have blunt snouts, but they are yellow-green to olive-gray in color and both their dorsal fins are about the same size. Lemon shark dorsal fins angle back like those of a bull shark.Spinner sharks have pointed shouts, black tipping on their anal fins, and a band of Z-shaped lines on their sides.Tiger sharks have a dark stripe on their sides.Great white sharks are very large (10-15 ft long), have black eyes, and pointed snouts. Their coloration is similar to the bull shark (gray on top, white underneath).