Plasma Growth Hormone Concentrations Research Articles

Hormone release, milk production and composition in Murrah buffaloes milked by hand and machine

Lactating Murrah buffaloes selected from the institute herd were categorized as hand and machine milking group. Blood samples were collected before milking, after concentrate feeding and teat message, during milking, and after completion of milking. Plasma prolactin (PRL), growth hormone (GH) and cortisol (CORT) concentrations were measured. Mean milk fat, protein, lactose and SNF content varied non-significantly between the groups. Milk somatic cell count (SCC), plasma glucose and NEFA concentration was more (P< 0.05) in machine milking group than in hand milking group. Both hand and machine milking operation significantly released plasma PRL (P< 0.01), CORT (P< 0.05) and GH (P< 0.01) hormone. Feeding of concentrate mixture resulted in a significant release in PRL and CORT hormone and their concentration increased further after teat message. Plasma PRL, CORT and GH varied significantly (P< 0.01) before, during and after milking (P< 0.01), and levels were normal 20-minutes post-milking in both the groups. It was concluded that feeding of concentrate mixture, teat message and milking operations either by hand or machine significantly stimulate release of plasma PRL, CORT and GH hormone in Murrah buffaloes.

Effects of different dietary intake on mRNA levels of MSTN, IGF-I, and IGF-II in the skeletal muscle of Dorper and Hu sheep hybrid F1 rams.

MSTN, IGF-І(insulin-like growth factor-І) and IGF-II (insulin-like growth factor-II) regulate skeletal muscle growth. This study investigated the effects of different dietary intake levels on skeletal muscles. Sheep was randomly assigned to 3 feeding groups: 1) the maintenance diet (M), 2) 1.4 x the maintenance diet (1.4M), and 3) 2.15 x the maintenance diet (2.15M). Before slaughtering the animals, blood samples were collected to measure plasma urea, growth hormone, and insulin concentrations. After slaughtering, the longissimus dorsi, semitendinosus, semimembranosus, gastrocnemius, soleus, and chest muscle were removed to record various parameters, including the mRNA expression levels of MSTN and IGFs, in addition to skeletal muscle fiber diameter and cross-sectional area. The result showed that as dietary intake improved, the mRNA expression levels of MSTN and IGF-II decreased, whereas IGF-Іexpression increased. The mRNA expression levels of MSTN and IGFs were significantly different in the same skeletal muscle under different dietary intake. The skeletal muscle fiber diameter and cross-sectional area increased with greater dietary intake, as observed for the mRNA expression of IGF-І; however, it contrasted to that observed for the mRNA expression of MSTN and IGF-II. In conclusion, dietary intake levels have a certain influence on MSTN and IGFs mRNA expression levels, in addition to skeletal muscle fiber diameter and cross-sectional area. This study contributes valuable information for enhancing the molecular-based breeding of sheep.

Oral L-Arginine Before Resistance Exercise Blunts Growth Hormone in Strength Trained Males

Acute resistance exercise and L-arginine have both been shown to independently elevate plasma growth hormone (GH) concentrations; however, their combined effect is controversial. The purpose was to investigate the combined effects of resistance exercise and L-arginine supplementation on plasma L-arginine, GH, GH secretagogues, and IGF-1 in strength trained participants. Fourteen strength trained males (age: 25 ± 4 y; body mass: 81.4 ± 9.0 kg; height: 179.4 ± 6.9 cm; and training experience: 6.3 ± 3.4 y) participated in a randomized double-blind crossover design (separated by ~7 days). Subjects reported to the laboratory at 08:00 in a fasted state, consumed L-arginine (ARG; 0.075 g·kg-1 body mass) or a placebo (PLA) before performing an acute bout of resistance exercise (3 sets of 8 exercises, 10 repetitions at ~75% 1RM). Blood samples were collected at rest, before exercise, and at 0, 15, 30, and 60 min of rest-recovery. The ARG condition significantly increased plasma L-arginine concentrations (~120%) while no change was detected in the PLA condition. There were no differences between conditions for GH, GH-releasing hormone, ghrelin, or IGF-1 at any time point. GH-inhibiting hormone was significantly lower in the ARG condition. However, integrated area under the curve for GH was blunted in the ARG condition (L-arginine = 288.4 ± 368.7 vs. placebo = 487.9± 482.0 min·ng·mL1, p < .05). L-arginine ingested before resistance exercise significantly elevated plasma L-arginine concentration but attenuated plasma GH in strength trained individuals despite a lower GHIH. Furthermore our data shows that the GH suppression was not due to a GH or IGF-1 induced autonegative feedback loop.

Involvement of the paraventricular (PVN) and arcuate (ARC) nuclei of the hypothalamus in the central noradrenergic regulation of liver cytochrome P450

The present study was aimed at assessing the influence of noradrenergic innervation of the paraventricular nucleus (PVN) and the arcuate nucleus (ARC) of the brain hypothalamus on cytochrome P450 expression in the liver. DSP-4, a neurotoxin specific to noradrenergic nerve terminals, was administrated locally into the PVN or ARC. One week after neurotoxin injection, the levels of neurotansmitters (noradrenaline/dopamine/serotonin) were measured in the middle part of the hypothalamus, hormone concentrations were estimated in blood plasma, and the activity and the protein levels of CYP isoforms were measured in the liver. A significant decrease in noradrenaline level in the hypothalamus was observed after DSP-4 injection into the PVN or ARC. The levels of dopamine or serotonin remained unchanged or slightly lowered. Simultaneously, significant changes in the plasma concentration of growth hormone were found; its elevation in PVN-lesioned rats and a drop in ARC-lesioned ones. There were no changes in the plasma concentration of the thyroid hormones or corticosterone. The activity and protein levels of isoforms CYP2C11, CYP3A and CYP2A rose in the liver of PVN-lesioned rats, but the activity and protein level of CYP2C11 fell in ARC-lesioned animals such a tendency being also observed in the case of CYP3A. Our study shows that noradrenergic innervation of the PVN and ARC of the hypothalamus exerts an opposite effect on the regulation of cytochrome P450 in the liver. These findings may be important for pharmacological experiments and pharmacotherapy with neuroactive drugs, since cytochrome P450 is responsible for the metabolism of steroids and the majority of drugs.

Physiological changes during feeding and rumination in cows

In this study, we investigated the physiological changes in cattle during feeding and rumination. We collected blood samples every 5 min by using an automated blood sampling system and simultaneously recorded feeding, ruminating, and other behaviors using a video camera. Plasma non-esterified fatty acid (NEFA) concentrations continuously decreased during feeding and decreased temporarily during rumination. Plasma glucose concentration continuously decreased during feeding and remained stable during rumination. During feeding and rumination, there were no characteristic increases and subsequent decreases in plasma insulin and growth hormone (GH) concentrations, although insulin concentrations were positively correlated with glucose concentration. NEFA concentrations were not correlated with GH and insulin concentrations. In terms of chewing behavior, feeding and rumination are similar; therefore, the changes in metabolites such as NEFA might have been the same. Combination of behavioral observations and application of an automated blood sampling system could contribute to new findings on behavioral and physiological changes regarding the temporary decrease in plasma NEFA concentration during rumination in ruminants.

Reduced marine survival of hatchery-reared Atlantic salmon post-smolts exposed to aluminium and moderate acidification in freshwater

Short-term Al-exposure and moderate acidification increased initial marine mortality in migrating post-smolts, and can thereby reduce viability of Atlantic salmon stocks. The delayed impact of short-term aluminium (Al) exposure on hatchery-reared Atlantic salmon smolt in moderately acidified freshwater (pH 5.88–5.98) was investigated during the first 37 km of the marine migration. Smolts were tagged with acoustic tags and exposed to low (28.3 ± 4.6 μg l−1 labile Al, 90 h) or high (48.5 ± 6.4 μg l−1 labile Al, 90 or 48 h) Al concentrations within the hatchery. Thereafter their movements, together with a control group, were monitored throughout the marine fjord. Al-exposure resulted in increased gill-Al and compromised hypoosmoregulatory capacity, as shown by elevated mortality in laboratory seawater challenge tests and reduced Na+, K+-ATPase activity levels. Further, Al-exposure resulted in decreased plasma concentrations of growth hormone (GH), while the insulin-like growth factor (IGF-I) was unaffected. There was a significant mortality in the 90 h high-Al group during exposure, and those surviving until release died during the first 3.6 km of the marine migration. Physiological stress and mortality were not only a result of the Al-concentrations, but also dependent on exposure duration, as shown by results from the 48 h high-Al group. Elevated mortality was not recorded in freshwater or after entering the sea for this group, which highly contrasts to the 100% mortality in the 90 h high-Al group, despite both groups having similarly high gill-Al levels. The low-Al group showed a 20% higher mortality compared to the control group during the first 10 km of the marine migration, but during the next 28 km, mortality rates did not differ. Hence, post-smolts surviving the first 10 km subsequently showed no differences in mortality compared to controls. At least one third of the mortality in both the low-Al and control groups were due to predation by marine fishes, indicating that the proximate cause for elevated mortality due to Al-exposure may have been predation. Migration speeds over 3.6, 9.6 or 37.1 km from the release site was not affected by Al-exposure.

Effects of intravenous ghrelin injection on plasma growth hormone, insulin and glucose concentrations in calves at weaning

Ghrelin action, which stimulates growth hormone (GH) secretion, may alter during the weaning period in calves. Our objective was to compare the effects of intravenous ghrelin injection on plasma GH, insulin and glucose concentrations in calves around the weaning period. Four Holstein bull calves were fed whole milk and allowed free access to solid feeds, and weaned at 7 weeks of age. Measurements were performed at weeks 1, 2, 4, 6, 7, 9, 11 and 13, when calves were intravenously injected with ghrelin (1.0 μg/kg body weight (BW)) through a catheter, and jugular blood samples were obtained temporally relative to the injection time. Estimated digestible energy intake per metabolic BW transiently decreased at week 7 because of low solid intake immediately after weaning, and thereafter gradually increased. Plasma insulin and glucose concentrations were not affected by ghrelin injection at all ages. In contrast, plasma GH concentrations increased with ghrelin injection at all ages. The incremental area of GH at week 7 was greatest and significantly higher compared with weeks 2, 4, 6 and 9. This result suggests that nutrient insufficiency immediately after weaning enhances GH responsiveness to ghrelin.

Short-day and melatonin effects on milking parameters, prolactin profiles and growth-hormone secretion in lactating sheep

We tested the hypothesis that elevated levels of melatonin in lactating sheep, simulated either by short-day conditions or by melatonin implants, would decrease milk yield while disturbing the rhythm of prolactin (PRL) and growth-hormone (GH) secretion. Eight weeks after lambing, lambs were weaned, and the ewes were subsequently used for milking. The ewes were divided into three groups: (i) long-day control group (LDC, n=20); (ii) long-day melatonin-treated group (LDM, n=20) and (iii) artificial short-day group (ASD, n=20). Milk yields were recorded individually at 10-day intervals from day 57 of lactation. Blood samples were drawn from the sheep every 28 days to monitor the changes in PRL and GH secretion. On each sampling date, blood samples were collected at 20-min intervals over a 6-h period beginning at 12:00p.m. The plasma concentrations of PRL and GH were measured using radioimmunoassay. The longest duration of lactation was found in LDC sheep, and the shortest duration was found in LDM and ASD sheep (p<0.05). The highest milk yield was found in the LDC group. Significantly (p≤0.01) less milk was obtained from the ASD group. The highest PRL concentration was found during the long-day period (from May to July) in LDC sheep. Prolactin concentration decreased with increasing duration of lactation and decreasing day length. The use of melatonin implants (LDM group) or artificial short-day conditions (ASD group) significantly (p≤0.01) decreased PRL secretion and reduced milk yield as early as the beginning of milking. Growth-hormone concentrations were significantly (p≤0.001) higher in LDC ewes than in LDM and ASD ewes. In contrast to the temporal profile of PRL secretion, GH concentrations decreased during the long-day period but increased as lactation progressed and day length shortened. Despite the considerable reduction in GH concentrations, the GH-secretion profile retained its characteristic seasonal rhythm. Therefore, we conclude that exogenous melatonin (from implants or induced by artificial photoperiod manipulation) decreases milk yield primarily through its effect on PRL concentrations in lactating ewes.

The Effect of Administration of Rutin on Plasma Levels of Estrogen, Prolactin, Growth Hormone and Gene Expression of Their Receptors in Mammary Glands in Ovariectomized Rats

The development of mammary glands, endocrine hormone concentrations and the gene expression of related receptors were measured in ovariectomized virgin rats after adminstration of an estrogen-like plant extract, rutin. Thirty-two ovariectomized virgin Wistar rats were randomly assigned to 4 treatments with 8 animals each: gastric infusion of 2 mL normal saline per unovariectomized rat per day (Sham), gastric infusion of 2 mL normal saline per ovariectomized rat per day (Ova), gastric infusion of 60 mg rutin kg−1 body weight (BW) per ovariectomized rat per day (Ova+Rut), or intramuscular injection of 60 μg estradiol kg−1 BW per ovariectomized rat weekly (Ova+Est). Samples of blood and mammary glands were harvested to determine the levels of estrogen (E2), prolactin (PRL) and growth hormone (GH), and the gene expression of estrogen receptors (ER), prolactin receptors (PRLR) and growth hormone receptors (GHR) with radioimmunoassy (RIA) and RT-PCR technology, respectively. The E2 concentration in plasma and gland tissues from the rats of Ovx+Rut or Ovx+Est was higher than that of Ovx (P<0.05), but the plasma E2 concentration from the rats of Ovx+Rut was lower than that of Sham (P<0.05). The order of the PRL concentration in plasma and gland tissues was Ovx<Ovx+Rut<Ovx+Est <Sham, and the difference in each treatment (P<0.05). The plasma GH concentration was lower in Ovx than in Ovx+Rut or Ovx+Est, and lower in Ovx+Rut than in Sham (P<0.05). The GH concentration in gland tissues was lower in Ovx than in Ovx+Rut or Ovx+Est (P<0.05), and lower in Ovx+Rut than in Sham (P<0.05). The gene expression of ER in gland tissues was increased in an order as Ovx<Ovx+Rut<Ovx+Est<Sham (P<0.05), and PRLR, GHR showed the same trend. In conclusion, adminstration of rutin increased the E2 concentration in plasma and mammary glands, promoted pituitary PRL and GH release, up-regulated the gene expression of ER, PRLR and GHR, and stimulated mammary development in ovariectomized virgin rats.

Suppression in growth hormone during overeating ameliorates the increase in insulin resistance and cardiovascular disease risk

Previously, we reported that overeating for only a few days markedly suppressed the secretion of growth hormone (GH). The purpose of the present study was to determine the role of this reduction in GH concentration on key metabolic adaptations that occur during 2 wk of overeating. Nine nonobese, healthy adults were admitted to the hospital for 2 wk, during which time they ate ∼4,000 kcal/day (70 kcal·kg fat-free mass(-1)·day(-1); 50% carbohydrate, 35% fat, and 15% protein), and their plasma GH concentration was allowed to decline naturally (control). An additional eight subjects underwent the same overeating intervention and received exogenous GH treatment (GHT) administered in four daily injections to mimic physiological GH secretion throughout the 2-wk overeating period. We measured plasma insulin and glucose concentrations in the fasting and postprandial state as well as fasting lipolytic rate, proteolytic rate, and fractional synthetic rate (FSR) using stable-isotope tracer methods. GHT prevented the fall in plasma GH concentration, maintaining plasma GH concentration at baseline levels (1.2 ± 0.2 ng/ml), which increased fasting and postprandial assessments of insulin resistance (P < 0.05) and increased fasting lipidemia (all P < 0.05 vs. control). In addition, preventing the suppression in GH with overeating also blunted the increase in systemic proteolysis (P < 0.05 GHT vs. control). However, GHT did not alter lipolysis or FSR in response to overeating. In conclusion, our main findings suggest that the suppression in GH secretion that naturally occurs during the early stages of overeating may help attenuate the insulin resistance and hyperlipidemia that typically accompany overeating.

Circulating hormone and cytokine response to low-load resistance training with blood flow restriction in older men

It has been suggested that circulating hormones and cytokines are important in the adaptive response to low-load resistance training (LLRT) with blood flow restriction (BFR); however, their response following this type of training in older men is unclear. Seven healthy older men (age 71.0 ± 6.5 year, height 1.77 ± 0.05 m, body mass 80.0 ± 7.5 kg; mean ± SD) performed five sets of unilateral LLRT knee extensions (20 % 1-RM) of both limbs, with or without BFR in a counterbalanced order. For the BFR condition, a pressure cuff was applied on the upper thigh and inflated to ~110 mmHg. Venous blood samples were taken at rest and 30-, 60- and 120-min post-exercise and measured for plasma concentrations of growth hormone (GH), insulin-like growth factor 1 (IGF-1), vascular endothelial growth factor (VEGF), cortisol and interleukin-6 (IL-6). GH increased (P < 0.05) from rest to 30-min post-exercise and was greater (P < 0.05) during LLRT with BFR than without. VEGF was significantly (P < 0.05) elevated from resting levels at 30-, 60- and 120-min post-exercise following LLRT with BFR with no change seen following LLRT without BFR. IL-6 increased (P < 0.05) from 30- to 60-min post-exercise and remained elevated at 120-min post-exercise in both conditions. Cortisol and IGF-1 were unaffected following exercise. In conclusion, a single bout of LLRT with BFR increases the circulating concentrations of GH and VEGF in older men and may explain the skeletal muscle and peripheral vascular adaptations observed following training with BFR.

A high-protein diet induces dissociation between plasma concentrations of growth hormone and ghrelin in wethers1

High-carbohydrate or high-fat diets have been demonstrated to change ghrelin concentrations in plasma; however, there remains a need to clarify the effects of dietary protein on the interaction between circulating GH and ghrelin concentrations in the ruminant. In this study, we investigated the postprandial changes in plasma concentrations of GH and ghrelin and their interactions when wethers were fed either a high-protein (HP; 40% CP) or a low-protein (LP; 10% CP) diet for 2 wk. The wethers were divided into 2 groups and fed once a day for 2 wk in a randomized crossover design. Each diet contained the same level of ME. Blood was collected from the animals at specific times over 24 h to measure hormones and metabolites. Feeding once a day caused a prompt reduction in the GH and ghrelin concentrations regardless of the type of diet that the wethers consumed. The preprandial concentrations (P = 0.04), area under the curve (AUC; P = 0.04), and incremental AUC (iAUC; P = 0.06) for ghrelin in HP-fed wethers were or tended to be greater than those in LP-fed wethers although concentrations for GH were the same for both diets (P = 0.23). In addition, the time it took for the postprandial ghrelin concentrations to recover to the preprandial concentrations was greater in HP-fed wethers than in LP-fed wethers although this was not true for GH concentrations. Similarly, as for ghrelin, postprandial increase (P < 0.001) and AUC (P = 0.03) for insulin concentration was greater in the HP-fed wethers than in the LP-fed wethers. From these findings, we concluded that dietary proteins (or some other derived metabolites) may dissociate the interaction between plasma concentrations of GH and ghrelin in wethers.

Effects of growth hormone gene polymorphism on lipogenic gene expression levels in diaphragm tissues of Japanese black heifers.

Two SNPs, i.e. L127V and T172M, of bovine growth hormone (GH) causing the presence of GH gene haplotypes A, B, and C was previously shown to alter intramuscular fatty acid (FA) composition in Japanese Black (JB) heifers. To determine the SNP effect on somatotropic hormone concentration and lipogenesis, we measured plasma GH, insulin, and insulin-like growth factor-1 (IGF-1) concentrations. We also measured mRNA levels of fatty acid synthase (FASN), stearoyl-coA desaturase (SCD), and sterol regulatory element binding proteins-1 (SREBP-1) and FA composition in diaphragm tissues. Heifers with genotype CC had the lowest plasma insulin concentration and FASN and SCD mRNA levels among genotypes. FASN mRNA levels in haplotype A tended to positively correlate with saturated FA (SFA) content and negatively correlated with C18:2 and unsaturated FA (USFA) contents. SCD mRNA levels in haplotype A positively correlated with monounsaturated FA (MUFA) contents and negatively correlated with C18:0 content. They also tended to positively correlate with C16:1, C18:1, and USFA contents and USFA/SFA ratio and negatively correlate with SFA content. Taken together, GH gene polymorphism affects the lipogenic genes expression levels and their relationships with fatty acid compositions in diaphragm tissues of JB heifers at 31 months of age.

Effect of Dietary Ornithine on the Brain Protein Synthesis Rate in Hypophysectomized Aged Rats

The purpose of this study was to determine whether the regulation of brain protein synthesis is mediated through changes in the plasma concentration of growth hormone (GH) when dietary ornithine treatment is manipulated in the hypophysectomized or sham-operated aged rats. Experiments were done on four groups of hypophysectomized and sham-operated (24-wk-old) male rats given 0% or 0.7% ornithine-HCl added to a 20% casein diet. The concentrations of plasma GH and fractional rates of protein synthesis in the brains increased significantly with the 20% casein+0.7% ornithine compared with the 20% casein diet alone in the sham-operated rats. However ornithine supplementation to the basal diet did not affect the rates of protein synthesis in the hypophysectomized rats. In the cerebral cortex and cerebellum, the RNA activity [g protein synthesized/(g RNA•d)] significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was also related to the fractional rate of protein synthesis in these organs. The results suggest that the treatment with ornithine is likely to increase the concentration of GH and the rate of brain protein synthesis in the sham-operated rats only, not in the hypophysectomized rats, and that the ornithine-induced increase in the concentration of GH may be primarily responsible for changes in the brain protein synthesis. The RNA activity is at least partly related to the fractional rate of brain protein synthesis.

Dietary Ornithine Affects the Tissue Protein Synthesis Rate in Young Rats

The purpose of this study was to determine whether ornithine affects the rate of tissue protein synthesis in male rats. Two experiments were done on five or two groups of young rats (5 wk) given diets containing 0.15, 0.3, 0.5 or 0.7% ornithine-HCl added to a 20% casein diet for 1 d (only one 3 h period) (Experiment 1), and given a diet containing 0 or 0.7% ornithine-HCl added to a 20% casein diet for 10 d (Experiment 2). The plasma concentration of growth hormone (GH) was the highest in rats fed 0.5 and 0.7% ornithine added to the 20% casein diet. The fractional rates of protein synthesis in brain regions, liver and gastrocnemius muscle increased significantly with the 20% casein+0.7% ornithine diet compared with the 20% casein diet. In brain regions, liver and gastrocnemius muscle, the RNA activity [g protein synthesized/(g RNA·d)] significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was not related to the fractional rate of protein synthesis in any organ. The present results suggest that the treatment of young rats with ornithine is likely to increase the concentration of plasma GH and the rate of protein synthesis in the tissues, and that RNA activity is at least partly related to the fractional rate of tissue protein synthesis.

Nutritional Factors That Regulate Ovulation of the Dominant Follicle During the First Follicular Wave Postpartum in High-producing Dairy Cows

During recent decades, milk production per cow has increased drastically due to improved management, nutrition, and genetic selection; however, the reproductive performance of high-producing dairy cows has been declining. One of the factors responsible for this low reproductive performance is negative energy balance (NEB). NEB affects the onset of first ovulation in early postpartum cows. It is generally accepted that early first ovulation positively relates to the resumption of normal ovarian function, first service, and conception rate in dairy cows. Hence, delayed first ovulation has a negative impact on subsequent fertility. The metabolic condition of cows in NEB shifts to catabolic metabolism, which in turn causes increased plasma growth hormone and non-esterified fatty acid concentrations and decreased plasma insulin-like growth factor-1, insulin, and glucose concentrations. On the other hand, plasma β-carotene concentrations decrease throughout the dry period and reach their nadir in about the first week postpartum, and this change reflects energy balance during the peripartum period. β-Carotene plays a role independently of vitamin A in the reproductive performance of dairy cows, and the positive relationship between supplemental β-carotene and reproductive function has been demonstrated in many studies during the past decades. However, β-carotene content in corn silage, which is a popular main feed in high-producing dairy cows, is very low. This review describes nutritional factors related to ovulation during the first follicular wave postpartum in dairy cows.

Existe-t-il une relation entre la dose d'hormone de croissance et d'éventuelles complications tumorales ou cardiovasculaires ?

Growth hormone (GH) affects protein (anabolism), lipid (lipolysis) and carbohydrate (hyperglycemia) metabolism and stimulates hepatic synthesis of insulin-like growth factor 1 (IGF1). IGF1 is believed to act as a postnatal growth factor. In addition to its effects on growth, IGF1 affects cell proliferation, differentiation and survival, and has anabolic effects on proteins, and also lipogenic and glucose-lowering effects. The increasing availability of biosynthetic pituitary GH has made it feasible to treat GH-deficient children and adults, and patients of short stature due to a variety of other causes (Turner's syndrome, anomalies of SHOX, intrauterine growth retardation (IUGR), chronic renal failure, Prader-Willi syndrome, or idiopathic short stature). The therapeutic dose has been increased in some situations in which the response is inadequate, particularly in patients with certain conditions such as IUGR. However, it has been reported that cancers and cardiovascular diseases are associated with high plasma concentrations of GH and IGF1, particularly in patients with acromegaly but also in large epidemiological studies of apparently healthy populations. These findings raise questions as to the safety of GH treatment. Some long-term follow-up studies have shown an increase in the risk of some kinds of cancer or cerebrovascular disease, but these findings have not been replicated by others. The results of these studies remain debatable, due to their small sample sizes, methodological weaknesses, nonexhaustive data collection and problems involved in comparing these patients with an appropriate control group. Finally, GH and IGF1 deficiencies are themselves associated with an increased risk of cardiovascular diseases, as is small stature/low weight at birth (due to IUGR). Recent studies have demonstrated a higher risk of cardiovascular disease in patients with both low and high plasma concentrations of GH and IGF1, these risks disappearing at average values. These findings suggest that the GH dose should be adjusted during treatment to ensure that plasma IGF1 concentrations remain within the physiological range.

Regulation of Growth Hormone Secretion in Nursing Ewes: An Involvement of μ‐Receptor Subtype

Suckling by newborns induces a surge of lactogenic hormones, that is prolactin and growth hormone (GH), in mother's body, with endogenous opioid peptide (EOP) participating in generation of this surge. The aim of the current study was to investigate which types of opioid receptors are involved in generation of the GH surge in ewes during suckling. A series of intracerebroventricular infusions of opioid receptors antagonists: naloxone (for all types of receptors), naloxonazine (specific for μ receptor) and 5'-guanidinonaltrindole (GNTI--specific for κ receptor) and the vehicle (control) were performed in nursing sheep during the fifth week of lactation. All infusions were carried out in a serial manner: five 30-min infusions (60 μg/60 μl) from 10:00 to 15:00, at 30-min intervals. The period of the experiment consisted of the non-suckling (10:00-12:30) and suckling (12:30-15:00) periods. Simultaneously, blood samples were collected at 10-min intervals to determine plasma GH concentration by radioimmunoassay. Suckling evoked a rapid increase in GH concentration in control ewes. Naloxone and naloxonazine significantly decreased both the basal GH release in the non-suckling period and the suckling-induced GH surge. Specifically, the suppressive effect concerned either the duration or the amplitude of the GH surge. In contrast, GNTI did not significantly affect the GH release. In conclusion, the EOPs may affect the regulatory process of GH secretion in lactating sheep, especially through μ opioid receptor.

Temporal changes in plasma concentrations of hormones and metabolites in pasture-fed dairy cows during extended lactation

This experiment measured variations in plasma concentrations of metabolic hormones and metabolites in cows undergoing extended lactations of up to 670 d at 2 planes of nutrition. Thirty-seven Holstein-Friesian cows that calved in late winter were selected for varying milk yield and then managed for a lactation of 670 d by delaying breeding until approximately 450 d in milk (DIM). Cows grazed fresh pasture supplemented with pasture silage or hay and crushed wheat or triticale grain. Dietary intake was reduced by approximately 1.8kg (dry matter) grain/cow per day for 19 of the cows from 300 DIM until the end of lactation to assess the effect of restricted energy intake on the persistency of milk production. Samples of blood were collected monthly from each cow to measure plasma concentrations of selected hormones and metabolites. Dietary restriction beyond 300 DIM reduced yields of milk, protein, and fat, but did not alter the proportion of cows reaching the 670-d lactation target. Dietary restriction had no effect on cow BW or plasma concentrations of any hormones or metabolites. Overall, blood plasma concentrations of insulin-like growth factor-I, leptin, and glucose were elevated from 301 to 600 DIM compared with 0 to 300 DIM, whereas concentrations of growth hormone and nonesterified fatty acids were lower after 300 DIM. Plasma concentrations of insulin and prolactin were unaffected by stage of lactation, but prolactin concentrations increased during summer. These changes were consistent with a decrease in milk yield and an increase in the partitioning of nutrients to body tissue gain, primarily adipose tissue, throughout the later stages of the extended lactation. Cows that continued milking beyond 600 DIM had increased plasma concentrations of growth hormone and decreased concentrations of glucose and leptin compared with cows that milked <600 DIM. These differences, coupled with reduced body weight gain, indicated an increased priority for nutrient partitioning to milk production at the expense of body tissue gain throughout the extended lactation period in cows with greater lactation persistency.

The effect of lighting conditions on the rhythmicity of growth hormone secretion in Holstein steers

Growth hormone (GH) secretion regularity and the effects of lighting condition and GH-releasing hormone (GHRH) on GH release were determined in steers. First, steers were kept under 12:12 L : D conditions (light: 06.00-18.00 hours). The animals were then subjected to a 1-h advancement in lighting on/off conditions (05.00 and 17.00 hours, respectively). Blood was sampled for 24 h at 1-h interval on the seventh day of each condition. Second, GHRH was injected intravenously (IV) at 12.00 and 00.00 hours under 12:12 L : D and blood was sampled at 15-min interval for 4-h (1 h before and 3 h after the injection). Plasma GH concentrations were measured by a radioimmunoassay. Periodicity of GH secretory profile was calculated by power spectrum analysis using the maximum entropy method. Plasma GH concentrations showed a characteristic pattern consisting of four distinct peaks. Mean periodicity of GH secretory profile was 5.7 h, and it was not altered by any change in lighting conditions. IV injection of GHRH increased GH secretion during the day and night. The increase in GH secretory volume after GHRH injection during the night was equal to that during the day. The present results suggest that GH secreted from the anterior pituitary have regularity in steers.