Effects of melatonin implants on insulin-like growth factor 1 in male red deer (Cervus elaphus)

Hormones as adaptive control systems in juvenile fish

Growth is an important theme in biology. Physiologists often relate growth rates to hormonal control of essential processes. Ecologists often study growth as a function of gradients or combinations of environmental factors. Fewer studies have investigated the combined effects of environmental and hormonal control on growth. Here, we present an evolutionary optimization model of fish growth that combines internal regulation of growth by hormone levels with the external influence of food availability and predation risk. The model finds a dynamic hormone profile that optimizes fish growth and survival up to 30 cm, and we use the probability of reaching this milestone as a proxy for fitness. The complex web of interrelated hormones and other signalling molecules is simplified to three functions represented by growth hormone, thyroid hormone and orexin. By studying a range from poor to rich environments, we find that the level of food availability in the environment results in different evolutionarily optimal strategies of hormone levels. With more food available, higher levels of hormones are optimal, resulting in higher food intake, standard metabolism and growth. By using this fitness-based approach we also find a consequence of evolutionary optimization of survival on optimal hormone use. Where foraging is risky, the thyroid hormone can be used strategically to increase metabolic potential and the chance of escaping from predators. By comparing model results to empirical observations, many mechanisms can be recognized, for instance a change in pace-of-life due to resource availability, and reduced emphasis on reserves in more stable environments.This article has an associated First Person interview with the first author of the paper.

Relationship between insulin-like growth factor-1 (IGF-1) concentrations and body trait measurements and climatic factors in prepubertal goat kids

This study aimed to investigate relations between insulin-like growth factor-1 (IGF-1) concentrations and some body trait measurements (body weight, withers height, rump height, body length, chest depth, chest width, chest girth and cannon bone circumference) and climatic factors in prepubertal male and female White (75 % Saanen and 25 % Kilis goat) and Angora goat kids. For this purpose, blood samples were regularly taken from the vena jugularis, and body trait measurements were regularly carried out (every 15 d for 5 months) on each kid. The IGF-1 analysis on the blood serum was performed using the enzyme immunoassay (EIA) method. Climatic values and the length of the photoperiod were obtained from the Turkish State Meteorological Service for the experimental period, and the temperature-humidity index (THI) was calculated using these values. Statistical analysis showed that the IGF-1 concentrations were higher ( P < 0.05 ) in female White goat kids. Furthermore, differences in IGF-1 concentrations were found ( P < 0.05 ) between periods and between the gender groups for both the White and the Angora goat kids. Moreover, the difference between the IGF-1 concentrations between genders was higher ( P < 0.05 ) in White goat kids. Additionally, positive and significant correlations were found between IGF-1 concentrations and some body trait measurements in prepubertal kids, except for in female White goat kids. In summary, it was found that there was a significant relationship between IGF-1 concentrations and growth characteristics of the goat kids. Furthermore, IGF-1 concentrations in the goat kids were significantly influenced by climatic factors such as photoperiod, temperature and the temperature-humidity index, with the release of IGF-1 increasing due to increases in the photoperiod and the environmental temperature.

The Regulatory Mechanism of MLT/MT1 Signaling on the Growth of Antler Mesenchymal Cells

Melatonin (MLT) plays an important role in regulating the physiological cycle of seasonal breeding animals. Melatonin receptor I (MT1) is effectively expressed in the cambium layer of deer antler. However, the function and metabolic mechanism of MLT/MT1 signaling in the mesenchymal cells of sika deer remain to be further elucidated. In this work, we detected the effects of MLT/MT1 signaling on mesenchymal cells proliferation and the interaction between MLT/MT1 and IGF1/IGF1-R signaling. The results show that (1) deer antler mesenchymal cells actually express MT1; (2) exogenous melatonin significantly promotes mesenchymal cells proliferation, while MT1 knock-down significantly impairs the positive effects of melatonin; and (3) melatonin significantly enhanced IGF1/IGF1-R signaling, as both the expression of IGF1 and IGF-1R increased, while MT1 knock-down significantly decreased IGF1-R expression and IGF1 synthesis. In summary, these data verified that MLT/MT1 signaling plays a crucial role in antler mesenchymal proliferation, which may be mediated by IGF1/IGF1-R.

Melatonin promotes sheep Leydig cell testosterone secretion in a co-culture with Sertoli cells

Leydig cells synthesize and secrete testosterone, and are regulated by Sertoli cells. These two cell types may work together to regulate testicular androgen production. Studies have shown that Leydig cell androgen synthesis can be dramatically enhanced by Sertoli cells in the presence of melatonin, which can regulate the secretory function of Leydig and Sertoli cells. However, the molecular mechanism of melatonin-regulated Leydig cell androgen production via Sertoli cells remains unclear. Here, we found that 10^-7 M melatonin increased testosterone production in co-cultured Leydig and Sertoli cells isolated from sheep. Melatonin increased the expression of stem cell factor and insulin-like growth factor-1 and decreased estrogen synthesis in Sertoli cells. Melatonin promoted insulin-like growth factor-1 and decreased estrogen content via the membrane melatonin receptor 1. It also enhanced stem cell factor expression via the retinoic acid receptor-related orphan receptor alpha. Addition of PD98059, a MEK inhibitor, to Sertoli cell culture demonstrated that the melatonin upregulation of insulin-like growth factor-1 and downregulation of estrogen may be through the MEK/extracellular signal-regulated kinase pathway. Together, these results suggest that melatonin may function through modulating melatonin receptor 1-regulated insulin-like growth factor-1 expression, as well as melatonin receptor 1-induced suppression of estrogen synthesis to increase androgen production in co-cultured Leydig and Sertoli cells.

Study on the Changes in Enzyme and Insulin-like Growth Factor-1 Concentrations in Blood Serum and Growth Characteristics of Velvet Antler during the Antler Growth Period in Sika Deer (Cervus nippon)

This study was conducted to investigate changes in blood enzyme parameters and to evaluate the relationship between insulin-like growth factor-1 (IGF-1), antler growth and body weight during the antler growth of sika deer (Cervus nippon). Serum enzyme activity and IGF-1 concentrations were measured in blood samples collected from the jugular and femoral veins at regular intervals during the antler growth period. Blood samples were taken in the morning from fasted stags (n = 12) which were healthy and showed no clinical signs of disease. Alfalfa was available ad libitum and concentrates were given at 1% of body weight to all stags. The experimental diet was provided at 9 am with water available at all times. There were no significant differences in alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase during antler growth, but alkaline phosphatase concentrations increased with antler growth progression, and the highest alkaline phosphatase concentration was obtained 55 days after antler casting. Serum IGF-1 concentrations measured from blood samples taken from the jugular vein during antler growth, determined that levels of IGF-1 was associated with body weight and antler growth patterns. Serum IGF-1 concentrations were higher at the antler cutting date than other sampling dates. Antler length increased significantly during antler growth (p<0.001), and there was a similar trend to between right and left beams. Body weight increased with antler growth but was not significant. Consequently it appeared that serum alkaline phosphatase concentration was related to antler growth and both antler growth and body weight were associated positively with IGF-1 concentrations during antler growth.

Morphogenetic mechanisms in the cyclic regeneration of hair follicles and deer antlers from stem cells

We have made comparisons between hair follicles (HFs) and antler units (AUs)—two seemingly unrelated mammalian organs. HFs are tiny and concealed within skin, whereas AUs are gigantic and grown externally for visual display. However, these two organs share some striking similarities. Both consist of permanent and cyclic/temporary components and undergo stem-cell-based organogenesis and cyclic regeneration. Stem cells of both organs reside in the permanent part and the growth centres are located in the temporary part of each respective organ. Organogenesis and regeneration of both organs depend on epithelial-mesenchymal interactions. Establishment of these interactions requires stem cells and reactive/niche cells (dermal papilla cells for HFs and epidermal cells for AUs) to be juxtaposed, which is achieved through destruction of the cyclic part to bring the reactive cells into close proximity to the respective stem cell niche. Developments of HFs and AUs are regulated by similar endocrine (particularly testosterone) and paracrine (particularly IGF1) factors. Interestingly, these two organs come to interplay during antlerogenesis. In conclusion, we believe that investigators from the fields of both HF and AU biology could greatly benefit from a comprehensive comparison between these two organs.

Melatonin, endocrine pancreas and diabetes

Melatonin influences insulin secretion both in vivo and in vitro. (i) The effects are MT(1)-and MT(2)-receptor-mediated. (ii) They are specific, high-affinity, pertussis-toxin-sensitive, G(i)-protein-coupled, leading to inhibition of the cAMP-pathway and decrease of insulin release. [Correction added after online publication 4 December 2007: in the preceding sentence, 'increase of insulin release' was changed to 'decrease of insulin release'.] Furthermore, melatonin inhibits the cGMP-pathway, possibly mediated by MT(2) receptors. In this way, melatonin likely inhibits insulin release. A third system, the IP(3)-pathway, is mediated by G(q)-proteins, phospholipase C and IP(3), which mobilize Ca(2+) from intracellular stores, with a resultant increase in insulin. (iii) Insulin secretion in vivo, as well as from isolated islets, exhibits a circadian rhythm. This rhythm, which is apparently generated within the islets, is influenced by melatonin, which induces a phase shift in insulin secretion. (iv) Observation of the circadian expression of clock genes in the pancreas could possibly be an indication of the generation of circadian rhythms in the pancreatic islets themselves. (v) Melatonin influences diabetes and associated metabolic disturbances. The diabetogens, alloxan and streptozotocin, lead to selective destruction of beta-cells through their accumulation in these cells, where they induce the generation of ROS. Beta-cells are very susceptible to oxidative stress because they possess only low-antioxidative capacity. Results suggest that melatonin in pharmacological doses provides protection against ROS. (vi) Finally, melatonin levels in plasma, as well as the arylalkylamine-N-acetyltransferase (AANAT) activity, are lower in diabetic than in nondiabetic rats and humans. In contrast, in the pineal gland, the AANAT mRNA is increased and the insulin receptor mRNA is decreased, which indicates a close interrelationship between insulin and melatonin.

Effect of electric and magnetic fields (60 Hz) on production, and levels of growth hormone and insulin-like growth factor 1, in lactating, pregnant cows subjected to short days

Electric and magnetic fields (EMF) are generated by the transmission of electricity through high tension lines traversing rural areas. Previous studies showed increased dry matter intake (DMI) and fat corrected milk in dairy cows exposed to EMF. Because EMF exposure has been shown to suppress pineal release of melatonin in some species, it was hypothesized that EMF effects resemble those of exposure to long days. Previous studies have shown that DMI and milk production increase in dairy cattle in response to long day photoperiods, and this has been observed in association with increased circulating insulin-like growth factor 1 (IGF-1), but not growth hormone (GH). The hypothesis that EMF act by modifying the response to photoperiod was tested by subjecting dairy cows to controlled EMF exposure while keeping them under short-day conditions. Sixteen lactating, pregnant Holstein cows were exposed to a vertical electric field of 10 kV/m and a horizontal magnetic field of 30 microT in a crossover design with treatment switchback. Two groups of eight cows each were exposed to EMF for 16 h/d in either oftwo sequences. Each sequence consisted of three consecutive 28-d periods. All animals were maintained under short day conditions (8 h light, 16 h dark) during the trial. DMI and plasma IGF-1 were increased (P < 0.01) during EMF exposure (17.03 vs.16.04 kg/d, SE = 0.4; 137 +/- 6 ng/ml vs 126 +/- 6, respectively). The mean GH concentration was not affected, but a treatment x hour interaction was detected, with GH lower for the EMF exposed animals during the first 16 h of the sampling period, and higher for the last 8 h. Overall, the yield of milk or its components was not affected by EMF exposure, but milk yield was significantly higher for the exposed animals during wk 4 of treatment.

Photoperiodic effects on dairy cattle: a review

Since the initial report in 1978 of galactopoietic effects of a photoperiod of 16 h of light:8 h of darkness, numerous studies have confirmed long-day stimulation of milk yield. The endocrine factor(s) responsible for increased milk yield, however, has eluded identification. Recent studies suggest that insulin-like growth factor-I (IGF-I) may mediate the galactopoietic response to long day photoperiod. Indeed, long days increase IGF-I in heifers and lactating cows; in the latter case, the response preceded an increase in milk yield. In heifers and cows, the increase in IGF-I is independent of changes in circulating growth hormone. Melatonin feeding to mimic a short-day photoperiod suppressed the increase of IGF-I in heifers induced by long days. However, melatonin feeding had no effect on milk yield in cows. Despite lack of resolution of the endocrine mechanism, dairy producers are interested in how photoperiod management can be integrated with current practices throughout the lactation cycle. There is strong evidence that milk yield responses to long days persist through an entire lactation. Also, long days can be combined with bovine somatotropin (bST) to produce additive increases in milk yield. During the dry period, long days increase the periparturient surge of prolactin. However, relative to long days, short-day treatment during the dry period produces the largest magnitude of response in milk yield during the subsequent lactation. The response to short days during the dry period may be due to a priming effect on the photoperiodic response system. In summary, IGF-I has emerged as a possible mediator of the increase of milk yield in response to long-day photoperiod. Photoperiod can be combined effectively with other management techniques such as bST. Consideration of photoperiod management during the dry period is essential to maximize responses during the subsequent lactation.

Effects of photoperiod on the cessation of growth during autumn in male red deer and growth hormone and insulin-like growth factor-I secretion

Male red deer undergo seasonal cycles of food intake and growth rate, which are high during spring and low during winter, despite high quality food ad libitum. Hormonal profiles during the cessation of growth in autumn and the potential role of photoperiod in the timing of the observed changes have been investigated. Whether this seasonal decrease in growth affected the response of GH and IGF-I to fasting was also examined. Two groups of six male 1-year-old red deer were exposed to different photoperiods after the summer solstice. One group (C) was given a simulated natural photoperiod while the other group (SS) was maintained on a summer solstice photoperiod (16L:8D). GH was measured in blood collected continuously and divided into pools every 5 min for 24 h in the fed state and after a 48-h fast on two occasions; the first was in November before photoperiod manipulation began and the second was in April approximately 16 weeks after initiating treatments. IGF-I, prolactin, and testosterone were measured in weekly samples. Individual live weight and group food intake were also measured each week. The normal growth pattern seen in the C group was delayed in the SS group. Thus, from 7 March until the second GH sampling on 11 April the live weight of deer in group C fell; in contrast, deer in group SS continued to grow (-43 vs 186 g/day s.e.d. = 65.5, P < 0. 01). Food intake changes reflected the pattern of growth in both groups. Mean GH (P < 0.05), GH pulse amplitude (P < 0.01), and IGF-I (P < 0.001) declined in both groups from November to April. This decline was more marked in group C and in April these parameters were all lower in group C than in group SS (GH, P < 0.05; IGF-1, P < 0.01). Prolactin levels in April were also lower in group C than in group SS (P < 0.01); testosterone was not affected by treatment. Fasting increased mean GH and GH pulse amplitude in both groups in November (P < 0.05). In April, the fasting response differed between the groups. In group C, mean GH, pulse amplitude, and pulse frequency were all greater in the fasted state than in the fed state (P < 0.05), while in group SS there were no significant differences (P > 0.05). IGF-I was lower in the fasted state than in the fed state at both sampling dates (P < 0.001). The seasonal decline in food intake and growth is associated with decreased GH, IGF-I, and prolactin concentrations, and increased testosterone and the GH response associated with fasting. All these changes except those of testosterone were delayed or reduced by continued exposure to a summer solstice photoperiod in autumn. The decreased photoperiod in autumn may thus influence the normal timing of the seasonal growth cycle.

Seasonal levels of metabolic hormones and substrates in male and female reindeer (Rangifer tarandus)

Seasonal levels of cortisol, growth hormone (GH), insulin like growth factor 1 (IGF-1), glucose, triiodothyronine (T3), free T3, thyroxine and free fatty acids (FFA) were measured every 3 weeks for 54 weeks in the plasma of five adult bulls, and four barren and five pregnant Alaskan reindeer (Rangifer tarandus) cows. Three consecutive samples were taken from each animal. Cortisol levels exhibited wide seasonal variation (9-45 ng/ml) [corrected] without any peak or difference in levels among groups. Rising levels were detected between the 3 consequent samples. Peak GH levels, detected during January and February, were higher in the non-pregnant group (54 ng/ml) than the pregnant (26 ng ml-1) and the male (27 ng ml-1) groups. Low GH levels (2-10 ng ml-1) were recorded between May and September. IGF-1 reached peak levels (715 ng ml-1) in males in August, in non-pregnant females in September (677 ng ml-1), and in the pregnant females in October (505 ng ml-1). Seasonal minima (404 in males, 172 and 93 in pregnant and non-pregnant groups) were detected in February. Glucose was fairly stable throughout the year (100-200 mg/100 ml). A rising levels were found between the three consecutive samples. Triiodothyronine (T3) (2.16-2.30 ng ml-1) peaked in all three groups during the spring and early summer, and minimal levels (0.61-0.97 ng ml-1) were detected from October to January. Conversely, thyroxine or free T3 did not exhibit seasonal variation. FFA fluctuated widely (97-1076 nmol l-1) throughout the year. Only in pregnant females were concentrations more stable (150-460 nmol l-1). Perhaps, because of ad libitum supply of food in captive reindeer, only T3 and GH exhibited pronounced seasonal fluctuations which could be related to the metabolic changes expected during the annual cycle.

Melatonin and farm animals: endogenous rhythms and exogenous applications

Studies on farm animals have contributed significantly to our increased understanding of basic melatonin-related physiological mechanisms, as well as to the regulation of reproduction and pelage in individual domestic species. This review concentrates on recent work on the role of melatonin in the regulation of porcine reproduction, cervine endocrine, and behavioral cycles and wool and cashmere production which has added to this knowledge base. Early studies of the domestic pig indicated that melatonin secretion in this species differed markedly from that in other domestic and laboratory animals. There is now clear evidence that this is not the case and that the domestic pig uses a circadian rhythm of melatonin release for the transduction of photoperiodic information. Apparent inconsistencies among reports may be due, in part, to differences in the conditions under which the experiments were performed and to the assay systems employed to measure circulating melatonin, the concentrations of which are much lower than in other domestic species. Appropriately administered exogenous melatonin advances the onset of puberty in gilts, and may prove to be effective in overcoming seasonal infertility in female pigs. Appropriately timed melatonin and/or photoperiod treatments, administered to ruminants in utero, influence the reproductive physiology of the offspring, indicating that even in species which don't develop an endogenous melatonin rhythm till some weeks postnatally, awareness of photoenvironment, presumably via maternal melatonin, predates birth. Pre- or early postnatal melatonin-related treatments also influence the development/cycle frequency of pelage. Areas requiring further investigation include the hormonal/growth factors involved, reasons for the transient nature of the effects in sheep and goats, and the reason for similar effects on pelage of augmenting or inactivating melatonin. Aspects of endogenous melatonin rhythms in farm species which require further study include: the significance of the abolition of the nocturnal melatonin peak in the sheep by prolonged short day exposure; the increased pineal bloodflow in sheep bred to produce high wool yields; the presence of high daytime melatonin levels immediately prior to the rut in the fallow buck; and the low amplitude of the rhythm in the domestic pig.

Threshold photoperiods for the induction of short day traits in collared lemmings (Dicrostonyx groenlandicus)

When exposed to short photoperiod collared lemmings undergo a number of physiological and morphological changes including an increase in body weight, a change in body composition, development and enlargement of the bifid "digging" claw, and a molt to a white winter pelage. We investigated the threshold photoperiods for the induction of these traits in male and female lemmings born and raised under a 22L:2D photoperiod and transferred at weaning (19 days of age) to various other photoperiods. Male lemmings showed the characteristic increase in body weight when exposed to 16 hr of light or less per day whereas females required a photoperiod of 14 hr of light or less per day to elicit an increase in body weight. The threshold photoperiods for the increase in bifid claw size were 16 and 18 hr of light per day in male and female lemmings, respectively. The molt to the white winter pelage began under a longer photoperiod in females (16L:8D) than in males (14L:10D). Testes and seminal vesicles were significantly inhibited by photoperiods of 22L:2D and 20L:4D. Likewise, uterine weights were inhibited by maintenance on a photoperiod of 22L:2D. Taken together, these data show that the threshold photoperiods for the induction of the short day traits in collared lemmings are both trait- and sex-dependent. These observations also suggest that under some conditions, exposure to long photoperiods can inhibit sexual maturation.