Effects of growth hormone on growth performance, haematology, metabolites and hormones in iron-deficient veal calves

A Large Proportion of the Neonatal Iron Pool Is Acquired from the Gestational Diet in a Murine Model

BACKGROUND

Iron is crucial for growth and development, but excess iron is harmful. Neonatal mice have elevated concentrations of circulating iron, but the source of this iron is unclear. This lack of understanding makes it difficult to optimize early life iron balance.

OBJECTIVES

Identify the origins of neonatal tissue-specific iron pools using dietary manipulation and cross-fostering murine models.

METHODS

To determine whether tissue-specific neonatal iron was primarily acquired during gestation or after birth, pups born to iron-sufficient or iron-deficient dams were cross-fostered, and tissues were harvested at postnatal days 3-5 to measure iron content. A separate set of female mice were fed a diet enriched with the stable iron isotope 57 (57Fe) for 4 generations to replace naturally abundant liver iron isotope 56 (56Fe) stores with 57Fe. To quantify the proportions of neonatal iron acquired during gestation, pups born to dams with 56Fe or 57Fe stores were cross-fostered, and tissues were harvested at postnatal day 3-5 to determine 56Fe:57Fe ratios by inductively coupled plasma mass spectrometry. Finally, to quantify the proportion of neonatal iron acquired from the maternal diet, female mice with 56Fe or 57Fe stores switched diets upon mating, and pup tissues were harvested on P0 to determine 56Fe:57Fe ratios by inductively coupled plasma mass spectrometry.

RESULTS

Perinatal iron deficiency resulted in smaller pups, and gestational iron deficiency resulted in lower neonatal serum and liver iron. Cross-fostering between dams with 56Fe and 57Fe stores demonstrated that ≤70% of neonatal serum, liver, and brain iron were acquired during gestation. Dietary manipulation experiments using dams with 56Fe and 57Fe stores showed that over half of neonatal serum, liver, and brain iron were from the dam's gestational diet rather than preconception iron stores.

CONCLUSIONS

This study provides quantitative values for the sources of neonatal iron, which may inform approaches to optimize neonatal iron status.

Milk Supplemented with Organic Iron Improves Performance, Blood Hematology, Iron Metabolism Parameters, Biochemical and Immunological Parameters in Suckling Dalagh Lambs

This study was conducted to investigate the effect of milk supplemented with organic iron on performance, blood hematology, iron metabolism parameters, biochemical and immunological parameters in suckling lambs. Thirty-six newborn Dalagh lambs were randomly divided into three groups with 12 replications. The control group was fed with milk without organic iron. The other two groups were fed milk supplemented with 25 and 50 mg/d organic iron, respectively. During the experiment, increased daily weight gain and total body weight were observed in the iron-supplemented groups. An increase in the levels of red blood cell, hemoglobin, hematocrit, mean corpuscular hemoglobin, and mean corpuscular concentration in iron supplemented groups was indicated. Consumption of organic iron caused a significant decrease in plasma copper concentration. Total antioxidant status level was lower, but levels of glutathione peroxidase, superoxide dismutase, and catalase were higher in iron supplemented groups. In organic iron supplemented groups, insulin and thyroid hormones levels were significantly increased, and glucose level was significantly decreased. In organic iron supplemented groups, alkaline phosphatase level significantly increased, and aminotransferase level significantly decreased. Overall, the use of organic iron in the milk improved the performance and health in suckling lambs, and since a lower level of supplementation is naturally preferable, supplementation of milk with 25 mg/d organic iron is recommended.

Ironing out mechanisms of iron homeostasis and disorders of iron deficiency

Iron plays an important role in mammalian physiological processes. It is a critical component for the function of many proteins, including enzymes that require heme and iron-sulfur clusters. However, excess iron is also detrimental because of its ability to catalyze the formation of reactive oxygen species. As a result, cellular and systemic iron levels are tightly regulated to prevent oxidative damage. Iron deficiency can lead to a number of pathological conditions, the most prominent being anemia. Iron deficiency should be corrected to improve adult patients' symptoms and to facilitate normal growth during fetal development and childhood. However, inappropriate use of intravenous iron in chronic conditions, such as cancer and heart failure, in the absence of clear iron deficiency can lead to unwanted side effects. Thus, this form of therapy should be reserved for certain patients who cannot tolerate oral iron and need rapid iron replenishment. Here, we will review cellular and systemic iron homeostasis and will discuss complications of iron deficiency.

The Effects of Parenteral Iron Administration on Thyroid Hormones, Hematology, Oxidative Stress Characteristics, Performance, and Health in Neonatal Holstein Calves

The present study investigated the effect of iron supplementation on thyroid hormones concentrations, oxidative stress characteristics, complete blood count (CBC) and serum biochemistry, and performance and health in calves of two groups: test group (n = 17, intramuscular injection of 500 mg iron-dextran on the 2nd day of life) and control group (n = 17, intramuscular injection of normal saline at the same time). Blood samples were taken from all of the calves instantly after birth and at 7, 14, 21, 28, and 90 days of age. Duration of treatment for diseases, body weight, height, and length were measured at each sampling time to evaluate growth and health. The results indicated that age (sampling time) had a significant effect (p ≤ 0.05) on the values of all measured variables except for ferric reducing ability of plasma (FRAP) amount and band neutrophil number. The treatment (group) had no significant effect on the amount of measured variables. Significant interactions between sampling time and group were found for white blood cell count (WBC), adult neutrophil, and bilirubin amounts (p ≤ 0.05). Significant higher amounts of hematocrit (HCT) and hemoglobin (Hb) at day 28 and mean corpuscular volume (MCV) at day 7 were seen in the test group compared with control group. Test group in comparison with control group had significantly lower amount of WBC at day 7; mean corpuscular hemoglobin concentration (MCHC), band neutrophils, and lymphocytes at day 14; and number of platelets at day 28. Growth and total weight gain and mean daily gain had no significant differences between the two groups. The duration of treatment for pneumonia and diarrhea was not significantly different between trial groups. The results show that parenterally administration of iron to newborn calves had no effect on improving erythropoiesis, performance, thyroid metabolism, oxidative/antioxidative situation, and health of dairy calves.

Association Between Hemoglobin and Growth Hormone Peak in Chinese Children and Adolescents with Short Stature: A Cross-Sectional Study

Objective

This research aimed to investigate the relationship between hemoglobin (Hb) and growth hormone (GH) peak in children and adolescents with short stature.

Design

This cross-sectional study included a total of 787 children and adolescents with short stature. Anthropometric and biochemical indicators were measured at baseline. All patients underwent GH provocation tests with L-dopa and insulin to assess GH peak levels.

Results

The univariate analysis results showed that Hb was positively associated with GH peak (β 0.07, P=0.001). Furthermore, a non-linear relationship was detected between Hb and GH peaks through smooth curve fitting, and the inflection point was 123 g/L after multivariate piecewise linear regression analysis. GH peak increased with Hb elevation when the Hb level was greater than 123 g/L (β 0.08, 95% CI 0.01, 0.14; P=0.0207).

Conclusion

In children and adolescents with short stature, we found GH peak was positively associated with the Hb level when the Hb level reached the inflection point.

Cross talk between mineral metabolism and meat quality: a systems biology overview

Meat quality has an inherent complexity because of the multiple interrelated causative factors and layers of feedback regulation. Understanding the key factors and their interactions has been challenging, despite the availability of remarkable high-throughput tools and techniques that have provided insights on muscle metabolism and the genetic basis of meat quality. Likewise, we have deepened our knowledge about mineral metabolism and its role in cell functioning. Regardless of these facts, complex traits like mineral content and meat quality have been studied under reductionist approaches. However, as these phenotypes arise from complex interactions among different biological layers (genome, transcriptome, proteome, epigenome, etc.), along with environmental effects, a holistic view and systemic-level understanding of the genetic basis of complex phenotypes are in demand. Based on the state of the art, we addressed some of the questions regarding the interdependence of meat quality traits and mineral content. Furthermore, we sought to highlight potential regulatory mechanisms arising from the genes, miRNAs, and mineral interactions, as well as the pathways modulated by this interplay affecting muscle, mineral metabolism, and meat quality. By answering these questions, we did not intend to give an exhaustive review but to identify the key biological points, the challenges, and benefits of integrative genomic approaches.

The Unexplored Crossroads of the Female Athlete Triad and Iron Deficiency: A Narrative Review

Despite the severity and prevalence of iron deficiency in exercising women, few published reports have explored how iron deficiency interacts with another prevalent and severe condition in exercising women: the 'female athlete triad.' This review aims to describe how iron deficiency may interact with each component of the female athlete triad, that is, energy status, reproductive function, and bone health. The effects of iron deficiency on energy status are discussed in regards to thyroid function, metabolic fuel availability, eating behaviors, and energy expenditure. The interactions between iron deficiency and reproductive function are explored by discussing the potentially impaired fertility and hyperprolactinemia due to iron deficiency and the alterations in iron metabolism due to menstrual blood loss and estrogen exposure. The interaction of iron deficiency with bone health may occur via dysregulation of the growth hormone/insulin-like growth factor-1 axis, hypoxia, and hypothyroidism. Based on these discussions, several future directions for research are presented.

Growth and Growth hormone - Insulin Like Growth Factor -I (GH-IGF-I) Axis in Chronic Anemias

Anaemia is a global public health problem affecting both developing and developed countries with major consequences for human health as well as social and economic development. It occurs at all stages of the life cycle, but is more prevalent in pregnant women and young children. Iron deficiency anaemia (IDA) was considered to be among the most important contributing factors to the global burden of disease. Prolonged and/or chronic anemia has a negative effect on linear growth especially during the rapid phases (infancy and puberty). Additionally infants with chronic IDA have delayed cognitive, motor, and affective development that may be long-lasting. In view of the significant impact of chronic anemias on growth, pediatricians endocrinologists and hematologists should advocate primary prevention and screening for growth disturbance in these forms of anemias. The extent of the negative effect of different forms of chronic anemias on linear growth and its possible reversibilty is addressed in this review. The possible mechanisms that may impair growth in the different forms of anemias are addressed with special attention to their effect on the growth hormone (GH) – insulin like growth factor -I (IGF-I). (www.actabiomedica.it)

Relationship between serum iron and insulin-like growth factor-I concentrations in 10-day-old calves

Newborn calves are often deficient in iron and progressive reduction in blood iron concentration occurs over the first weeks of life. Some reports indicate the importance of interactions among iron and components of the insulin-like growth factor system. The aim of the study was to determine if there is a relationship between serum iron and insulin-like growth factor-I concentrations in neonatal calves. Blood samples were collected from 16 female Holstein-Friesian calves on day 10 of age. Erythrogram determination and measurements of serum iron, total protein, albumin, total iron binding capacity and serum insulin-like growth factor-I concentrations were performed. Haematological values were measured using an automatic analyzer, biochemical properties were determined spectrophotometrically, insulin-like growth factor-I concentration was measured by radioimmunoassay. Calves were divided into 2 groups according to iron concentrations; the first group of iron-deficient calves (n = 8, Fe < 10 μmol/l) and the second group of calves with optimal iron concentration (n = 8, Fe > 18 μmol/l). Blood indicators in all calves from the first group followed a pattern typically observed in anaemic calves. Insulin-like growth factor-I concentrations were significantly (P < 0.01) lower in the first group compared to the second group. However, insulin-like growth factor-I very strongly correlated with iron in calves from the second group compared to iron-deficient calves (r = 0.624; P < 0.01 and r = 0.478; P > 0.05, respectively). Based on our results, iron seems to have an important relationship to secretion of insulin-like growth factor-I in 10-day-old calves. This is the first report about such relationship in this age group of animals.

Energy metabolism in the newborn farm animal with emphasis on the calf: endocrine changes and responses to milk-born and systemic hormones

Neonatal mammals need adaption to changes in nutrient supply because energy intake shifts from continuous parenteral supply of nutrients (mainly glucose, lactate, and amino acids) via the placenta to discontinuous colostrum and milk intake with lactose and fat as main energy sources. Besides ingested lactose, endogenous glucose production is essential in the neonate to assure sufficient glucose availability. Fetal endogenous glucose production is low, but endocrine changes (especially the prenatal rise of glucocorticoid production) promote maturation of metabolic pathways that enable marked glycogen synthesis before and enhanced gluconeogenesis after birth to establish an adequate glucose status during postnatal maturation. In preterm born farm animals gluconeogenic activity is low, mainly because of a low glucocorticoid and thyroid status. In full-term neonates, endogenous glucose production increases with age. Colostral bioactive components (such as growth factors, hormones, bioactive peptides, and cytokines) do not have a direct effect on endogenous glucose production. However, colostrum feeding stimulates intestinal growth and development, an effect at least in part mediated by bioactive substances. Increased nutrient and glucose absorption thus allows increased glucose supply and hepatic glycogen storage, which improves the glucose status. The improved energetic status of colostrum-fed neonates is reflected by an accelerated maturation of the somatotropic axis, leading especially to enhanced production of IGF-I in the neonate. Secretion and production of hormones involved in the regulation of glucose and fat metabolism in neonates depend on the developmental stage and the response to feeding. In addition, many such hormones have actions in the neonate that differ from adult animals. Endocrine action to support endogenous energy supply in neonates is probably not fully established, and therefore, needs postnatal maturation. Therefore, our knowledge on energy metabolism in the neonate needs to be extended to better understand the function and the failure and to assess endocrine responses during the neonatal period.

Scientific Opinion on the welfare of cattle kept for beef production and the welfare in intensive calf farming systems

Information given in previous Opinions "Welfare of cattle kept for beef production" (SCAHAW, 2001) and "The risks of poor welfare in intensive calf farming systems" (EFSA, 2006) is updated and recent scientific evidence on the topics reviewed. Risks of poor welfare are identified using a structured analysis, and issues not identified in the SCAHAW (2001) beef Opinion, especially effects of housing and management on enteric and respiratory diseases are reviewed. The Opinion covers all systems of beef production, although the welfare of suckler cows or breeding bulls is not considered. The Chapter on beef cattle presents new evidence and recommendations in relation to heat and cold stress, mutilations and pain management, digestive disorders linked to high concentrate feeds and respiratory disorders linked to overstocking, inadequate ventilation, mixing of animals and failure of early diagnosis and treatment. Major welfare problems in cattle kept for beef production, as identified by risk assessment, were respiratory diseases linked to overstocking, inadequate ventilation, mixing of animals and failure of early diagnosis and treatment, digestive disorders linked to intensive concentrate feeding, lack of physically effective fibre in the diet, and behavioural disorders linked to inadequate floor space, and co-mingling in the feedlot. Major hazards for white veal calves were considered to be iron-deficiency anaemia, a direct consequence of dietary iron restriction, enteric diseases linked to high intakes of liquid feed and inadequate intake of physically effective fibre, discomfort and behavioural disorders linked to inadequate floors and floor space.

Effects of parenteral supply of iron on RBC parameters, performance, and health in neonatal dairy calves

The present study was designed to evaluate the effects of parenteral iron on red blood cell parameters, performance, and health in dairy Holstein calves. Twenty neonatal calves were equally divided at random into two groups, one of which served as controls. Care was taken to ensure homogeneity of sex, age, and general health status of the animals. The controls received a normal diet and water ad libitum, while the study animals were injected with 1 g iron as Fe-dextran 2 days after birth. A daily record was kept of the calves' weight and growth parameters. At periods of 24-48 h after birth and at 14, 28, and 42 days of age, jugular blood was drawn from all the experimental and control animals to measure the packed cell volume, red blood count, hemoglobin, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and iron levels. At the start of the experiments, there were no significant differences between these parameters between the two study groups (p > 0.05). With time, significant differences were seen between most of the values measured (p < 0.05) except for the mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and iron level. Significant differences were seen for total weight gain and mean daily weight gain, which were higher in the iron-supplemented group (p < 0.05).

Insulin-like growth factors (IGFs), IGF binding proteins, and other endocrine factors in milk: role in the newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Endocrine and metabolic aspects in milk-fed calves

In neonatal calves besides adaptations in organ function there are marked metabolic and endocrine changes. The growth hormone (GH)-insulin-like growth factor (IGF) axis is basically functioning, but needs maturation. Various metabolic and endocrine traits do not exhibit marked ontogenetic changes after the first week of life, but others remain different from the adult stage. Thus, plasma oxytocin or an oxytocin-like substance and nitrate concentrations are elevated for months. The ability to digest colostrum (C) and milk involves great alterations in structure and function of the gastrointestinal (GI) tract. C intake is important for passive immunity, provision of nutrients, minerals and vitamins, and contains biologically active substances. IGF-I, present in C in high amounts, appears to enhance GI tract development and function. For sufficient absorption not only of immunoglobulins, but also of fatty acids and fat-soluble vitamins, C should be ingested immediately after birth. The amino acid pattern and the glutamine/glutamate ratio depends greatly on whether C is fed or not. Effects on insulin, IGF-I, and IGF binding proteins depend on time-point and amounts of C fed. After the colostral period calves are almost exclusively fed milk and milk substitutes or weaned. Low iron intake, required for the production of pale meat, besides anemia causes metabolic and endocrine adaptations, such as enhanced insulin-dependent glucose utilization and appears to reduce IGF-I responses to GH. Metabolic and endocrine changes, such as insulin resistance and disturbed glucose metabolism, can be observed in part in association with high feeding intensity in veal calves.

Long-term effects of feeding gossypol and vitamin E to dairy calves

Male Holstein calves were used to test the effect of feeding 400 mg of free gossypol/kg of diet and to determine whether vitamin E could counteract gossypol toxicity. Fifty-two calves were allotted to treatments as follows: 1) soybean meal-based starter; 2) cottonseed meal-based starter; 3) cottonseed meal-based starter + 2000 IU of vitamin E/d per calf, and 4) cottonseed meal-based starter + 4000 IU of vitamin E/d per calf. Vitamin E supplementation (treatments 3 and 4) improved weight gain and feed intake over calves on treatment 1. Gossypol concentrations in plasma were higher in calves on treatments 2, 3, and 4 than in calves on treatment 1; however, no differences were observed among animals receiving the three cottonseed meal diets. Hemoglobin and hematocrit were decreased in calves receiving treatment 2, and vitamin E supplementation counteracted this effect (treatments 3 and 4). Plasma alpha-tocopherol concentrations were not affected by gossypol intake and followed the vitamin E supplementation pattern During the experimental period, 10 calves died, six from treatment 2 and two each from treatments 3 and 4. Necropsy findings from 4 of 10 calves were suggestive of gossypol toxicity. Histopathological examination revealed centrilobular necrosis in the liver and atrophy and vacuolation of cardiocytes. Feeding cottonseed meal caused death of some calves with gossypol related toxicity signs, but did not decrease plasma alpha-tocopherol; however, vitamin E supplementation increased performance and may have conferred some protection against gossypol toxicity.

Long-term effects of gossypol and vitamin E in the diets of dairy bulls

Long-term effects of the inclusion of cottonseed meal in the diet on hematological and tissue parameters of Holstein bulls were investigated. Twenty-four Holstein bulls that were approximately 6 mo of age received the following treatments for 10 mo: 1) soybean meal plus 30 IU of vitamin E/kg, 2) cottonseed meal plus 30 IU of vitamin E/kg, and 3) cottonseed meal plus 4000 IU of vitamin E/d per bull. Treatments 2 and 3 were formulated to supply 14 mg of free gossypol/kg of body weight per d. Average daily gain, total gain, and final body weights were not affected by treatment. The osmotic fragility of erythrocytes was greater during all collection periods for bulls on treatments 2 and 3 than for bulls on treatment 1. The inclusion of 4000 IU of vitamin E/d per bull did not reduce the increase in the osmotic fragility of erythrocytes that was caused by gossypol. Bulls on treatment 3 had higher plasma alpha-tocopherol concentrations than did bulls on treatments 1 and 2. Vitamin E supplementation did not affect gossypol concentrations in plasma or tissue. The highest gossypol concentrations were found in the liver followed by the heart and testis. In vitro lipid peroxidation of tissue indicated that gossypol acts as an antioxidant in lipid peroxidation systems, and its role as an antioxidant may be dependent on dose or tissue. Cottonseed meal in the diets of bulls did not affect growth or vitamin E status.

Clinical, haematological, metabolic and endocrine traits during the first three months of life of suckling simmentaler calves held in a cow-calf operation

Newborn suckling Simmentaler calves (10 males and 9 females) in a cow-calf operation were examined from birth up to the age of 3 months. The average daily gain from 47 to 120 kg was 0.86 kg. Except for higher average daily weight gains and insulin-like growth factor-I concentrations and lower thyroid hormone levels in male than female calves, there were no significant sex differences. Plasma glucose, total protein and immunoglobulin G concentrations increased on day 1 of life, thrombocyte number and plasma triglyceride concentrations rose during the first 7 days, whereas lymphocyte and monocyte percentage and plasma inorganic phosphorus, phospholipid, cholesterol and albumin concentrations increased during the first 14 or 21 days and then remained elevated. Eosinophil percentage increased after 3 weeks and insulin-like growth factor-I concentrations increased over the whole growth period. There were transient elevations of plasma glucagon concentrations up to day 14, of the activity of alkaline phosphatase transiently up to day 7 and of gamma-glutamyltransferase, aspartate aminotransferase and lactate dehydrogenase activities on day 1 of life. Plasma iron concentration transiently decreased up to day 28 and creatine kinase activity up to day 7. Total white blood cell number, neutrophil percentage, packed cell volume and concentrations of haemoglobin, calcium, magnesium (after a transient rise on day 1), non-esterified fatty acids, bilirubin, creatinine, triiodothyronine and thyroxine decreased from birth up to days 42, 56, 28, 28, 21, 84, 14, 14, 7, 14 and 7, respectively. Basophil percentage and concentrations of beta-hydroxybutyrate, urea and insulin did not exhibit significant age-dependent changes. The behaviour of most traits in the first weeks was the same in suckling calves under study as in non-suckling pre-ruminant calves. However, packed cell volume, red blood cell number, haemoglobin and plasma iron concentrations were higher, whereas glucose and insulin concentrations were lower than normally found in veal calves. On the other hand, concentrations of glucose, insulin and insulin-like growth factor-I in suckling calves in the third month of age were higher than can normally be measured in breeding calves.

Blood metabolites and hormones--especially glucose and insulin--in veal calves: effects of age and nutrition

Veal calves often develop insulin resistance, hyperglycaemia and glucosuria. We have studied effects of age and nutrition on blood metabolites and hormones, with major emphasis on glucose and insulin, in four groups of veal calves from 66-69 kg until slaughter at 175-196 kg. Calves were fed milk replacers which differed with respect to lactose, total sugar, protein and fat content. Mean intakes in groups 1, 2, 3 and 4 of lactose (1.24, 1.08, 0.95 and 0.66 kg/d), total sugar (1.27, 1.10, 1.01 and 96 kg/d), crude protein (0.40, 0.48, 0.65 and 0.49 kg/d) and crude fat (0.32, 0.31, 0.37 and 0.46 kg/d) were different. Average daily gains were 1.46-1.49 kg and feed/gain ratios were 1.49-1.61 kg/kg. Glucose and insulin concentrations were not associated with protein and fat intakes, but followed lactose and total sugar intakes, albeit differently at the start and end of the growth trial. Thus, insulin concentrations were higher (P < 0.05) at the end than at start of the growth trial in all 4 groups, whereas glucose concentrations increased (P < 0.05) with increasing age in only group 2. In conclusion, lactose and total sugar intakes affected the degree of hyperglycaemia and modified hyperinsulinemia at a given age, but the age-dependent rise of insulin concentrations could not be explained by hyperglycaemia alone.