Pattern Of Growth Hormone Research Articles

EXAMINATION OF THE PHYSIOLOGICAL AND BIOCHEMICAL CHANGES AFFECTING NUTRITIONAL REQUIREMENTS THAT OCCUR IN DIFFERENT LIFE STAGES OF FISH

Fish undergo many physiological and biochemical changes throughout life, each demanding distinct nutritional consideration. This study explores the nuanced relationship between physiological and biochemical changes influencing nutritional requirements in different life stages of fish. The research involved an ethical and comprehensive investigation into various fish species' embryonic, larval, juvenile, and adult phases. Results demonstrated significant variations in growth rates, emphasizing rapid larval growth and unique reproductive hormone patterns during adulthood. Enzymatic activities reflected stage-specific digestive and metabolic demands, with larval stages exhibiting elevated digestive enzyme activities. Proximate composition analyses showcased protein, lipid, and carbohydrate content fluctuations, illustrating the evolving nutritional needs.

Effect of Feeding Pattern and Salivary Level of Growth Hormone on the Stage of Primary Tooth Eruption

Introduction: We aimed to evaluate the effect of feeding pattern and salivary level of growth hormone on the stage of primary tooth eruption among infants aged 6 to 18 months. Methods: The sample size of this analytical cross-sectional study was 300 healthy infants from Karbala, Iraq. Feeding pattern answered by the parents, stage of dental eruption assessed according to criteria described by Damodar P. Swami, and level of salivary growth hormone determined using an ELISA assay. Data were analyzed via a linear regression model using R software. Results: The model (adjusted R 2: 0.668) showed the feeding pattern (beast, bottle, or mix), gender, and salivary level of growth hormone were not significant predicators for the stage of primary tooth eruption (p > 0.05). Yet, age was a significant predicator (p < 0.001). Conclusion: The infant’s feeding pattern and salivary level of growth hormone did not affect the timing of the eruption of primary teeth.

Interplay Between GH-regulated, Sex-biased Liver Transcriptome and Hepatic Zonation Revealed by Single-Nucleus RNA Sequencing.

The zonation of liver metabolic processes is well-characterized; however, little is known about the cell type-specificity and zonation of sexually dimorphic gene expression or its growth hormone (GH)-dependent transcriptional regulators. We address these issues using single-nucleus RNA-sequencing of 32 000 nuclei representing 9 major liver cell types. Nuclei were extracted from livers from adult male and female mice; from males infused with GH continuously, mimicking the female plasma GH pattern; and from mice exposed to TCPOBOP, a xenobiotic agonist ligand of the nuclear receptor CAR that perturbs sex-biased gene expression. Analysis of these rich transcriptomic datasets revealed the following: 1) expression of sex-biased genes and their GH-dependent transcriptional regulators is primarily restricted to hepatocytes and is not a feature of liver nonparenchymal cells; 2) many sex-biased transcripts show sex-dependent zonation within the liver lobule; 3) gene expression is substantially feminized both in periportal and pericentral hepatocytes when male mice are infused with GH continuously; 4) sequencing nuclei increases the sensitivity for detecting thousands of nuclear-enriched long-noncoding RNAs (lncRNAs) and enables determination of their liver cell type-specificity, sex-bias and hepatocyte zonation profiles; 5) the periportal to pericentral hepatocyte cell ratio is significantly higher in male than female liver; and 6) TCPOBOP exposure disrupts both sex-specific gene expression and hepatocyte zonation within the liver lobule. These findings highlight the complex interconnections between hepatic sexual dimorphism and zonation at the single-cell level and reveal how endogenous hormones and foreign chemical exposure can alter these interactions across the liver lobule with large effects both on protein-coding genes and lncRNAs.

Ghrelin Gene Deletion Alters Pulsatile Growth Hormone Secretion in Adult Female Mice.

Using preproghrelin-deficient mice (Ghrl-/-), we previously observed that preproghrelin modulates pulsatile growth hormone (GH) secretion in post-pubertal male mice. However, the role of ghrelin and its derived peptides in the regulation of growth parameters or feeding in females is unknown. We measured pulsatile GH secretion, growth, metabolic parameters and feeding behavior in adult Ghrl-/- and Ghrl+/+ male and female mice. We also assessed GH release from pituitary explants and hypothalamic growth hormone-releasing hormone (GHRH) expression and immunoreactivity. Body weight and body fat mass, linear growth, spontaneous food intake and food intake following a 48-h fast, GH pituitary contents and GH release from pituitary explants ex vivo, fasting glucose and glucose tolerance were not different among adult Ghrl-/- and Ghrl+/+ male or female mice. In vivo, pulsatile GH secretion was decreased, while approximate entropy, that quantified orderliness of secretion, was increased in adult Ghrl-/- females only, defining more irregular GH pattern. The number of neurons immunoreactive for GHRH visualized in the hypothalamic arcuate nucleus was increased in adult Ghrl-/- females, as compared to Ghrl+/+ females, whereas the expression of GHRH was not different amongst groups. Thus, these results point to sex-specific effects of preproghrelin gene deletion on pulsatile GH secretion, but not feeding, growth or metabolic parameters, in adult mice.

Sepsis as a Pan-Endocrine Illness-Endocrine Disorders in Septic Patients.

Sepsis is defined as “life-threatening organ dysfunction caused by a dysregulated host response to infection”. One of the elements of dysregulated host response is an endocrine system disorder. Changes in its functioning in the course of sepsis affect almost all hormonal axes. In sepsis, a function disturbance of the hypothalamic–pituitary–adrenal axis has been described, in the range of which the most important seems to be hypercortisolemia in the acute phase. Imbalance in the hypothalamic–pituitary–thyroid axis is also described. The most typical manifestation is a triiodothyronine concentration decrease and reverse triiodothyronine concentration increase. In the somatotropic axis, a change in the secretion pattern of growth hormone and peripheral resistance to this hormone has been described. In the hypothalamic–pituitary–gonadal axis, the reduction in testosterone concentration in men and the stress-induced “hypothalamic amenorrhea” in women have been described. Catecholamine and β-adrenergic stimulation disorders have also been reported. Disorders in the endocrine system are part of the “dysregulated host response to infection”. They may also affect other components of this dysregulated response, such as metabolism. Hormonal changes occurring in the course of sepsis require further research, not only in order to explore their potential significance in therapy, but also due to their promising prognostic value.

Growth Hormone Pulses and Liver Gene Expression Are Differentially Regulated by the Circadian Clock Gene Bmal1.

In this study, we found that loss of the circadian clock gene Bmal1 causes disruptions throughout the growth hormone (GH) axis, from hepatic gene expression to production of urinary pheromones and pheromone-dependent behavior. First, we show that Bmal1 knockout (KO) males elicit reduced aggressive responses from wild-type (WT) males and secrete lower levels of major urinary proteins (MUPs); however, we also found that a liver-specific KO of Bmal1 (liver-Bmal1-KO) produces a similar reduction in MUP secretion without a defect in aggressive behavior, indicating that the decrease in elicited aggression arises from another factor. We then shifted our investigation to determine the cause of MUP dysregulation in Bmal1 KO animals. Because the pulse pattern of GH drives sexually dimorphic expression of hepatic genes including MUPs, we examined GH pulsatility. We found that Bmal1 KO males have a female-like pattern of GH release, whereas liver-Bmal1-KO mice are not significantly different from either WT or Bmal1 KO. Since differential patterns of GH release regulate the transcription of many sexually dimorphic genes in the liver, we then examined hepatic gene transcription in Bmal1 KO and liver-Bmal1-KO mice. We found that while some female-predominant genes increase in the Bmal1 KO, there was no decrease in male-predominant genes, and little change in the liver-Bmal1-KO. We also found disrupted serum insulin growth factor 1 (IGF-1) and liver Igf1 messenger RNA in the Bmal1 KO mice, which may underlie the disrupted GH release. Overall, our findings differentiate between GH-pulse-driven and circadian-driven effects on hepatic genes, and the functional consequences of altered GH pulsatility.

Dose-Effect of Zearalenone on the Localization and Expression of Growth Hormone, Growth Hormone Receptor, and Heat Shock Protein 70 in the Ovaries of Post-weaning Gilts.

Zearalenone (ZEA) has an estrogen-like effect, which can injure the reproductive system of animals, causing infertility, and abortion in sows. However, the underlying mechanisms are still not clear. The objective of this study was to assess the effects of ZEA on the localization and expression of growth hormone (GH), growth hormone receptor (GHR), and heat shock protein 70 (Hsp70) in the ovaries of post-weaning gilts. Forty healthy post-weaning gilts were randomly provided one of four diets: normal basal diet supplemented with 0 (control), 0.5 (ZEA0.5), 1.0 (ZEA1.0), and 1.5 (ZEA1.5) mg ZEA/kg. Gilts were housed and fed individually for 35 days; the ovaries were collected after euthanasia for antioxidant index, relative mRNA and protein expression, and immunohistochemical analyses of GH, GHR, and Hsp70. The results revealed that the glutathione peroxidase and total superoxide dismutase levels decreased (p < 0.05), whereas the malondialdehyde level increased (p < 0.05) with increasing ZEA content. The localization pattern of GH, GHR, and Hsp70 in ZEA-treated gilts was the same as that in the control; however, the localization of yellow and brown immunoreactive substances of GH, GHR, and Hsp70 was stronger in the ZEA groups than in the control. The relative mRNA and protein expression of GHR and Hsp70 was the highest in the ZEA1.0 group (p < 0.05), whereas that of GH was the highest in the ZEA0.5 group (p < 0.05). The mRNA and protein expression of GH was lower in the ZEA1.5 group than in the control (p < 0.05). Hsp70 results showed adverse responses to increasing ZEA levels in gilt ovaries, suggesting that Hsp70 played an important role in alleviating ZEA-induced oxidative stress.

Molecular identification and developmental expression patterns of growth hormone and its receptors in yellowtail kingfish (Seriola lalandi)

In fish and other vertebrates, growth hormone (GH) is an essential polypeptide required for normal growth and development. In an attempt to understand growth regulation in yellowtail kingfish (YTK), the full-length cDNA sequences encoding gh and its receptors (ghr1 and ghr2) were cloned, characterized and the expression profiles of these three genes were investigated during embryonic development. The full-length cDNA sequences of GH and its receptors were obtained by RT-PCR combined with RACE methord. YTK gh cDNA sequence was 852 base pairs (bp) that comprised an open reading frame (ORF) of 615bp encoding a 204-amino acids (aa) precursor. The preprohormone compassed a signal peptide (17 aa) and the mature peptide (187 aa). YTK GHR1 protein consisted of a signal peptide (28 aa), an extracellular domain (222 aa), a single transmembrane domain (23 aa) and an intracellular domain (361 aa). GHR2 protein included 18 aa, 223 aa, 23 aa, and 321 aa, respectively. Tissue distribution analysis showed that the maximal level of gh expression was observed in the pituitary, and ghr1 mRNA was mainly detected in the liver, while ghr2 transcripts were most abundant in the gonad. Moreover, both ghr1 and ghr2 mRNAs were expressed in all embryonic stages and displayed different gene expression profiles. Overall, these results provide initial evidences for the involvement of the GH/GHR system in the early ontogeny of yellowtail kingfish.

Radiomics model predicts granulation pattern in growth hormone-secreting pituitary adenomas.

To investigate whether radiomic features from magnetic resonance image (MRI) can predict the granulation pattern of growth hormone (GH)-secreting pituitary adenoma patients. Sixty-nine pathologically proven acromegaly patients (densely granulated [DG] = 50, sparsely granulated [SG] = 19) were included. Radiomic features (n = 214) were extracted from contrast-enhancing and total tumor portions from T2-weighted (T2) MRIs. Imaging features were selected using a least absolute shrinkage and selection operator (LASSO) logistic regression model with fivefold cross-validation. Diagnostic performance for predicting granulation pattern was compared with that for qualitative T2 signal intensity assessment and T2 relative signal intensity (rSI) using the area under the receiver operating characteristics curve (AUC). Four significant radiomic features from the contrast-enhancing tumor (1 from shape, 1 from first order feature, and 2 from second order features) were selected by LASSO for model construction. The radiomics model showed an AUC, accuracy, sensitivity, and specificity of 0.834 (95% confidence interval [CI] 0.738-0.930), 73.7%, 74.0%, and 73.9%, respectively. The radiomics model showed significantly better performance than the model using qualitative T2 signal intensity assessment (AUC 0.597 [95% CI 0.447-0.747], P = 0.009) and T2 rSI (AUC 0.647 [95% CI 0.523-0.759], P = 0.037). Radiomic features may be useful biomarkers to differentiate granulation pattern of GH-secreting pituitary adenoma patients, and showed better performance than qualitative assessment or rSI evaluation.

Tyrosine Hydroxylase Neurons Regulate Growth Hormone Secretion via Short-Loop Negative Feedback.

Classical studies suggest that growth hormone (GH) secretion is controlled by negative-feedback loops mediated by GH-releasing hormone (GHRH)- or somatostatin-expressing neurons. Catecholamines are known to alter GH secretion and neurons expressing TH are located in several brain areas containing GH-responsive cells. However, whether TH-expressing neurons are required to regulate GH secretion via negative-feedback mechanisms is unknown. In the present study, we showed that between 50% and 90% of TH-expressing neurons in the periventricular, paraventricular, and arcuate hypothalamic nuclei and locus ceruleus of mice exhibited STAT5 phosphorylation (pSTAT5) after an acute GH injection. Ablation of GH receptor (GHR) from TH cells or in the entire brain markedly increased GH pulse secretion and body growth in both male and female mice. In contrast, GHR ablation in cells that express the dopamine transporter (DAT) or dopamine β-hydroxylase (DBH; marker of noradrenergic/adrenergic cells) did not affect body growth. Nevertheless, less than 50% of TH-expressing neurons in the hypothalamus were found to express DAT. Ablation of GHR in TH cells increased the hypothalamic expression of Ghrh mRNA, although very few GHRH neurons were found to coexpress TH- and GH-induced pSTAT5. In summary, TH neurons that do not express DAT or DBH are required for the autoregulation of GH secretion via a negative-feedback loop. Our findings revealed a critical and previously unidentified group of catecholaminergic interneurons that are apt to sense changes in GH levels and regulate the somatotropic axis in mice.SIGNIFICANCE STATEMENT Textbooks indicate until now that the pulsatile pattern of growth hormone (GH) secretion is primarily controlled by GH-releasing hormone and somatostatin neurons. The regulation of GH secretion relies on the ability of these cells to sense changes in circulating GH levels to adjust pituitary GH secretion within a narrow physiological range. However, our study identifies a specific population of tyrosine hydroxylase-expressing neurons that is critical to autoregulate GH secretion via a negative-feedback loop. The lack of this mechanism in transgenic mice results in aberrant GH secretion and body growth. Since GH plays a key role in cell proliferation, body growth, and metabolism, our findings provide a major advance to understand how the brain regulates the somatotropic axis.

Growth hormone activates X-box binding protein 1 in a sexually dimorphic manner through the extracellular signal-regulated protein kinase and CCAAT/enhancer-binding protein β pathway in rat liver.

Growth hormone (GH) has multiple physiological roles, acting on many organs. In order to investigate its roles in rat liver, we tried to identify novel genes whose transcription was regulated by GH. We identified X-box binding protein 1 (Xbp1) as a candidate gene. XBP1 is a key transcription factor activated in response to endoplasmic reticulum (ER) stress. The purpose of this study was to investigate the mode of action of GH on XBP1, including the relation with ER stress, sex-dependent expression of the mRNA, and the signaling pathway. Intravenous administration of GH rapidly and transiently increased Xbp1 mRNA in hypophysectomized rat livers. Neither phosphorylated inositol-requiring-1α (IRE1α) nor phosphorylated PKR-like ER kinase (PERK) increased, suggesting that Xbp1 expression is induced by an ER stress-independent mechanism. The active form of XBP1(S) protein was increased by GH administration and was followed by an increased ER-associated dnaJ protein 4 (ERdj4) mRNA level. XBP1(S) protein levels were predominantly identified in male rat livers with variations among individuals similar to those of phosphorylated signal transducer and activator of transcription 5B (STAT5B), suggesting that XBP1(S) protein levels are regulated by the sex-dependent secretary pattern of GH. The GH signaling pathway to induce Xbp1 mRNA was examined in rat hepatoma H4IIE cells. GH induced the phosphorylation of CCAAT/enhancer-binding protein β (C/EBPβ) following extracellular signal-regulated protein kinase (ERK) phosphorylation. Taken together, the results indicated that XBP1 is activated by GH in rat liver in a sexually dimorphic manner via ERK and C/EBPβ pathway.

Differential expression patterns of candidate genes pertaining to productive and immune functions in hepatic tissue of heat-stressed Salem Black goats

ABSTRACT A study was conducted with the primary objective to assess the impact of heat stress on the expression patterns of different candidate genes pertaining to productive and immunological functions in Salem Black goats. The study was conducted for a period of 45 days in 12, 10-month to 1-year-old female Salem Black breed goats randomly allocated into 2 groups of 6 animals each, C (n = 6; Salem Black control) and HS (n = 6; Salem Black heat stress). The expression pattern of growth hormone receptor,insulin-like growth factor 1 gene, interleukin-2 (IL-2),IL-6, IL-18, tumour necrosis factor α and interferon β (IFN-β) in hepatic tissue was significantly (P < 0.05) lower in HS group as compared to C group. The results generated from this study point towards the compromised growth and immune status of Salem Black breed probably to support life-sustaining activities to adapt to heat stress challenges. Abbreviations: IL: Interleukin; GHR: growth hormone receptor; IGF-1: insulin-like growth factor 1; TNFα: tumour necrosis factor α; IFN-β: interferon β; TLRs: toll-like receptors; HPA: hypothalamo–pituitary–adrenal axis; HSF 1: heat shock factor; NK: natural killer cell; THI: temperature humidity index; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; HPRT1: hypoxanthine phosphoribosyl transferase 1; SDHA: succinate dehydrogenase

Smooth Muscle-Specific BCL6+/- Knockout Abrogates Sex Bias in Chronic Hypoxia-Induced Pulmonary Arterial Hypertension in Mice.

The “estrogen paradox” in pulmonary arterial hypertension (PAH) refers to observations that while there is a higher incidence of idiopathic PAH in women, rodent models of PAH show male dominance and estrogens are protective. To explain these differences, we previously proposed the neuroendocrine-STAT5-BCL6 hypothesis anchored in the sex-biased and species-specific patterns of growth hormone (GH) secretion by the pituitary, the targeting of the hypothalamus by estrogens to feminize GH secretion patterns, and the role of the transcription factors STAT5a/b and BCL6 as downstream mediators of this patterned GH-driven sex bias. As a test of this hypothesis, we previously reported that vascular smooth muscle cell- (SMC-) specific deletion of the STAT5a/b locus abrogated the male-dominant sex bias in the chronic hypoxia model of PAH in mice. In the present study, we confirmed reduced BCL6 expression in pulmonary arterial (PA) segments in both male and female SMC:STAT5a/b−/− mice. In order to test the proposed contribution of BCL6 to sex bias in PAH, we developed mice with SMC-specific deletion of BCL6+/− by crossing SM22α-Cre mice with BCL6-floxed mice and investigated sex bias in these mutant mice in the chronic hypoxia model of PAH. We observed that the male-bias observed in wild-type- (wt-) SM22α-Cre-positive mice was abrogated in the SMC:BCL6+/− knockouts—both males and females showed equivalent enhancement of indices of PAH. The new data confirm BCL6 as a contributor to the sex-bias phenotype observed in hypoxic PAH in mice and support the neuroendocrine-STAT5-BCL6 hypothesis of sex bias in this experimental model of vascular disease.

Functional Roles of Sex-Biased, Growth Hormone-Regulated MicroRNAs miR-1948 and miR-802 in Young Adult Mouse Liver.

Sex-specific temporal patterns of pituitary growth hormone (GH) secretion determine the sex-biased transcription of hundreds of genes in the liver and impart important sex differences in liver physiology, metabolism, and disease. Sex differences in hepatic gene expression vary widely, ranging from less than twofold to >1000-fold in the mouse. Here, we use small RNA sequencing to discover 24 sex-biased mouse liver microRNAs (miRNAs), and then investigate the roles of two of these miRNAs in GH-regulated liver sex differences. Studies in prepubertal and young adult mice, and in mice in which pituitary hormones are ablated or where sex-specific hepatic GH signaling is dysregulated, demonstrated that the male-biased miR-1948 and the female-biased miR-802 are both regulated by sex-specific pituitary GH secretory patterns, acquire sex specificity at puberty, and are dependent on the GH-activated transcription factor STAT5 for their sex-specific expression. Both miRNAs are within genomic regions characterized by sex-biased chromatin accessibility. miR-1948, an uncharacterized miRNA, has essential features for correct Drosha/Dicer processing, generates a bona fide mature miRNA with strong strand bias for the 5p arm, and is bound by Argonaute in liver tissue, as is miR-802. In vivo studies using inhibitory locked nucleic acid sequences revealed that miR-1948-5p preferentially represses female-biased messenger RNAs (mRNAs) and induces male-biased mRNAs in male liver; conversely, miR-802-5p preferentially represses male-biased mRNAs and increases levels of female-biased mRNAs in female liver. Cytochrome P450 mRNAs were strongly enriched as targets of both miRNAs. Thus, miR-1948-5p and miR-802-5p are functional components of the GH regulatory network that shapes sex-differential gene expression in mouse liver.

The key role of targeted betacarotene supplementation on endocrine and reproductive outcomes in goats: Follicular development, ovulation rate and the GH-IGF-1 axis

The possible effects of betacarotene (BC) supplementation on the secretion pattern of growth hormone (GH) and insulin-like growth factor-1 (IGF-1), and their possible relationship with total ovarian activity (TOA), was evaluated in adult goats during the breeding season. In October, goats [n=22, 3.5y. old, 7/8 Sannen-Alpine] were randomly assigned to: a) Betacarotene group [BC, n=10; 45.9±1.97kg live weight (LW), 3.04±0.08 units, body condition score (BCS), supplemented with 50mg of BC goat day−1], and b) Control group [CONT, n=12; 46.2±2.04kg LW, 3.0±0.08 units, BCS]. An ultrasonographic scan was performed to evaluate corpus luteum number (OR) and antral follicle number (AF); TOA=OR+AF. Average LW and BCS did not differ (p>0.05) during the experimental period, yet BC-goats reflected an increased OR (3.4±0.2 vs. 2.8±0.2), AF (5.0±0.6 vs. 3.4±0.6) and TOA (8.4±0.5 vs. 6.2±0.6). Regarding the endocrine profile, the lowest (p<0.05) serum GH average concentrations (10.0 vs. 14.3±1.0ngmL−1; p=0.01) and GH-AUC (3670.4 vs. 5235.7±369.8 units; p=0.01), were observed in the BC-supplemented group. Neither serum IGF-1 concentrations (254.6±28.9ngmL−1 p>0.05) nor GH-PULSE (1.4±0.5 pulses 6h−1 p>0.05) differed between treatments. We document a potential role of BC as modulator of somatotrophic function, decreasing mean serum concentration and the area under the curve of GH, while also noting a positive action upon ovarian function with increases in ovulation rate and antral follicular development; such outcomes may embrace not only physiologic significance but also potential translational applications.

The stability of the transcriptome during the estrous cycle in four regions of the mouse brain.

We analyzed the transcriptome of the C57BL/6J mouse hypothalamus, hippocampus, neocortex, and cerebellum to determine estrous cycle-specific changes in these four brain regions. We found almost 16,000 genes are present in one or more of the brain areas but only 210 genes, ∼1.3%, are significantly changed as a result of the estrous cycle. The hippocampus has the largest number of differentially expressed genes (DEGs) (82), followed by the neocortex (76), hypothalamus (63), and cerebellum (26). Most of these DEGs (186/210) are differentially expressed in only one of the four brain regions. A key finding is the unique expression pattern of growth hormone (Gh) and prolactin (Prl). Gh and Prl are the only DEGs to be expressed during only one stage of the estrous cycle (metestrus). To gain insight into the function of the DEGs, we examined gene ontology and phenotype enrichment and found significant enrichment for genes associated with myelination, hormone stimulus, and abnormal hormone levels. Additionally, 61 of the 210 DEGs are known to change in response to estrogen in the brain. 50 of the 210 genes differentially expressed as a result of the estrous cycle are related to myelin and oligodendrocytes and 12 of the 63 DEGs in the hypothalamus are oligodendrocyte- and myelin-specific genes. This transcriptomic analysis reveals that gene expression in the female mouse brain is remarkably stable during the estrous cycle and demonstrates that the genes that do fluctuate are functionally related.

Secretory pattern and regulatory mechanism of growth hormone in cattle.

The ultradian rhythm of growth hormone (GH) secretion has been known in several animal species for years and has recently been observed in cattle. Although the physiological significance of the rhythm is not yet fully understood, it appears essential for normal growth. In this review, previous studies concerning the GH secretory pattern in cattle, including its ultradian rhythm, are introduced and the regulatory mechanism is discussed on the basis of recent findings.

Twenty-Hour Growth Hormone Secretory Profiles after Aerobic and Resistance Exercise

The pulsatile secretion pattern of growth hormone (GH) is an important parameter of GH action at peripheral tissues, and more information is needed on how exercise impacts GH secretion. This study hypothesized that both aerobic and resistance exercise would exhibit dose-response relationships with respect to exercise duration and 20-h postexercise GH secretion. Eight healthy men randomly completed five separate conditions: 1) control (no exercise; CON), 2) a moderate-duration (1-h) aerobic exercise session (MA), 3) a long-duration (2-h) aerobic exercise session (LA), 4) a moderate-duration (1-h) resistance exercise session (MR), and 5) a long-duration (2-h) resistance exercise session (LR). Exercise intensity, diet, sleep, and physical activity were strictly controlled during each condition, and blood was sampled postexercise every 20 min for 20 h, and GH secretion parameters were analyzed via cluster and deconvolution analyses. Only the 2-h aerobic exercise bout resulted in a significant amplification of GH secretion as evidenced by increases in GH burst peak amplitude (∼100%), basal GH secretion rate (∼127%), total GH basal secretion (∼120%), total pulsatile secretion (∼88%), and total GH secretion (∼89%) over the control (i.e., no exercise) condition. GH secretions for the resistance exercise conditions were not different from control. The fact that the 2-h aerobic exercise condition resulted in higher energy expenditure than the other exercise conditions could offer a partial explanation for the greater GH amplification because of the metabolic effects that GH exerts in stimulating postexercise lipolysis. We conclude that extending the duration of aerobic exercise, but not resistance exercise, from 1- to 2-h significantly amplifies GH secretion during a 20-h period.

Effects of photoperiod on secretory patterns of growth hormone in adult male goats

The aim of the present study was to clarify the effect of photoperiod on secretory patterns of growth hormone (GH) in male goats. Adult male goats were kept at 20°C with an 8-h or 16-h light photoperiod, and secretory patterns of GH secretion were compared. In addition, plasma profiles of prolactin (PRL), insulin-like growth factor-I (IGF-I) and testosterone (T) were also examined to characterize GH secretion. GH was secreted in a pulsatile manner. There was no significant difference in pulse frequency between the 8-h and 16-h photoperiods. However, GH pulse amplitude tended to be greater in the group with the 16-h photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the 16-h photoperiod (P < 0.05). The GH-releasing response to GH releasing hormone was greater in the 16-h than 8-h photoperiod (P < 0.05). Plasma PRL and IGF-I levels were higher in the 16-h than 8-h photoperiod (P < 0.05). In contrast, plasma T levels were lower in the 16-h photoperiod (P < 0.05). These results show that a long light photoperiod enhances the secretion of GH as well as PRL and IGF-I, but reduces plasma T concentrations in male goats.

Performing Resistance Exercise Prior to Aerobic Exercise Results in Higher Growth Hormone Levels during Exercise in Physically Active Individuals with Well‐Controlled Type 1 Diabetes

BackgroundPerforming resistance exercise before aerobic exercise (rather than the reverse) can protect against exercise‐induced hypoglycemia in physically active well‐controlled individuals with type 1 diabetes (T1D). Growth hormone (GH) is a potential mediator of this phenomenon as it promotes lipolysis, thereby sparing blood glucose.PurposeThis research aimed to determine whether GH secretion is affected by the order in which resistance (R) and aerobic (A) exercise are performed in people with T1D.MethodsOn separate days, 6 physically active participants with T1D (HbA1c 7.0±1.0%) either ran on a treadmill for 45‐min prior to performing 45‐min of weight lifting (AR) or performed the resistance exercise before running (RA).ResultsGH (mean±SE) rose only transiently in AR, but the rise was larger and more sustained in RA. Differences between sessions were statistically significant for the last 30‐min of exercise (mean at 60 minutes: AR = 2.86±1.03 vs RA = 5.86±1.91 μg/L; at 75 minutes: AR = 1.98±0.78 vs RA = 7.17±2.54 μg/L; at 90 minutes: AR = 1.98±0.82 vs RA = 6.67±2.51 μg/L.ConclusionGH patterns are consistent with this hormone being a mediator in the stabilization of blood glucose levels when aerobic exercise is performed subsequent to resistance exercise in habitually active individuals with T1D. Supported by the Canadian Diabetes Association and the Ottawa Hospital Research Institute.