Short-term effects of recombinant human growth hormone and feeding on gluconeogenesis in humans

Glycemia and Gluconeogenesis With Metformin and Liraglutide: A Randomized Trial in Youth-onset Type 2 Diabetes

OBJECTIVE

Elevated rates of gluconeogenesis are an early pathogenic feature of youth-onset type 2 diabetes (Y-T2D), but targeted first-line therapies are suboptimal, especially in African American (AA) youth. We evaluated glucose-lowering mechanisms of metformin and liraglutide by measuring rates of gluconeogenesis and β-cell function after therapy in AA Y-T2D.

METHODS

In this parallel randomized clinical trial, 22 youth with Y-T2D-age 15.3 ± 2.1 years (mean ± SD), 68% female, body mass index (BMI) 40.1 ± 7.9 kg/m2, duration of diagnosis 1.8 ± 1.3 years-were randomized to metformin alone (Met) or metformin + liraglutide (Lira) (Met + Lira) and evaluated before and after 12 weeks. Stable isotope tracers were used to measure gluconeogenesis [2H2O] and glucose production [6,6-2H2]glucose after an overnight fast and during a continuous meal. β-cell function (sigma) and whole-body insulin sensitivity (mSI) were assessed during a frequently sampled 2-hour oral glucose tolerance test.

RESULTS

At baseline, gluconeogenesis, glucose production, and fasting and 2-hour glucose were comparable in both groups, though Met + Lira had higher hemoglobin A1C. Met + Lira had a greater decrease from baseline in fasting glucose (-2.0 ± 1.3 vs -0.6 ± 0.9 mmol/L, P = .008) and a greater increase in sigma (0.72 ± 0.68 vs -0.05 ± 0.71, P = .03). The change in fractional gluconeogenesis was similar between groups (Met + Lira: -0.36 ± 9.4 vs Met: 0.04 ± 12.3%, P = .9), and there were no changes in prandial gluconeogenesis or mSI. Increased glucose clearance in both groups was related to sigma (r = 0.63, P = .003) but not gluconeogenesis or mSI.

CONCLUSION

Among Y-T2D, metformin with or without liraglutide improved glycemia but did not suppress high rates of gluconeogenesis. Novel therapies that will enhance β-cell function and target the elevated rates of gluconeogenesis in Y-T2D are needed.

Growth Hormone Mediators and Glycemic Control in Youths With Type 2 Diabetes: A Secondary Analysis of a Randomized Clinical Trial

Importance

Youth-onset type 2 diabetes (T2D) has a more aggressive phenotype than adult-onset T2D, including rapid loss of glycemic control and increased complication risk.

Objective

To identify associations of growth hormone mediators with glycemic failure, beta cell function, and insulin sensitivity in youth-onset T2D.

Design, Setting, and Participants

This post hoc secondary analysis of the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) randomized clinical trial, which enrolled participants from July 2004 to February 2009, included 398 participants from 15 university-affiliated medical centers with available plasma samples from baseline and 36 months. Participants were youths aged 10 to 17 years with a duration of T2D of less than 2 years who were randomized to metformin, metformin plus lifestyle intervention, or metformin plus rosiglitazone. Participants were followed up for a mean (SD) of 3.9 (1.5) years during the trial, ending in 2011. Statistical analysis was performed from August 2022 to November 2023.

Exposure

Plasma insulin-like growth factor-1 (IGF-1), growth hormone receptor (GHR), and insulin-like growth factor binding protein 1 (IGFBP-1).

Main Outcomes and Measures

Main outcomes were (1) loss of glycemic control during the TODAY study, defined as hemoglobin A1c (HbA1c) level of 8% or more for 6 months or inability to wean from insulin therapy, and (2) baseline and 36-month measures of glycemia (fasting glucose, HbA1c), insulin sensitivity (1/fasting C-peptide), high-molecular-weight adiponectin, and beta cell function (C-peptide index, C-peptide oral disposition index).

Results

This analysis included 398 participants (mean [SD] age, 13.9 [2.0] years; 248 girls [62%]; 166 Hispanic participants [42%]; 134 non-Hispanic Black participants [34%], and 84 non-Hispanic White participants [21%]). A greater increase in IGF-1 level between baseline and 36 months was associated with lower odds of glycemic failure (odds ratio [OR], 0.995 [95% CI, 0.991-0.997]; P < .001) and higher C-peptide index per 100-ng/mL increase in IGF-1 (β [SE], 0.015 [0.003]; P < .001). A greater increase in log2 GHR level between baseline and 36 months was associated with higher odds of glycemic failure (OR, 1.75 [95% CI, 1.05-2.99]; P = .04) and lower C-peptide index (β [SE], -0.02 [0.006]; P < .001). A greater increase in log2 IGFBP-1 level between baseline and 36 months was associated with higher odds of glycemic failure (OR, 1.37 [95% CI, 1.09-1.74]; P = .007) and higher high-molecular-weight adiponectin (β [SE], 431 [156]; P = .007).

Conclusions and Relevance

This study suggests that changes in plasma growth hormone mediators are associated with loss of glycemic control in youth-onset T2D, with IGF-1 associated with lower risk and GHR and IGFBP-1 associated with increased risk.

Trial Registration

ClinicalTrials.gov Identifier: NCT00081328.

Gluconeogenesis Flux in Metabolic Disease

Gluconeogenesis is a critical biosynthetic process that helps maintain whole-body glucose homeostasis and becomes altered in certain medical diseases. We review gluconeogenic flux in various medical diseases, including common metabolic disorders, hormonal imbalances, specific inborn genetic errors, and cancer. We discuss how the altered gluconeogenic activity contributes to disease pathogenesis using data from experiments using isotopic tracer and spectroscopy methodologies. These in vitro, animal, and human studies provide insights into the changes in circulating levels of available gluconeogenesis substrates and the efficiency of converting those substrates to glucose by gluconeogenic organs. We highlight ongoing knowledge gaps, discuss emerging research areas, and suggest future investigations. A better understanding of altered gluconeogenesis flux may ultimately identify novel and targeted treatment strategies for such diseases.

A glucose-insulin-glucagon coupled model of the isoglycemic intravenous glucose infusion experiment

Type 2 diabetes (T2D) is a pathophysiology that is characterized by insulin resistance, beta- and alpha-cell dysfunction. Mathematical models of various glucose challenge experiments have been developed to quantify the contribution of insulin and beta-cell dysfunction to the pathophysiology of T2D. There is a need for effective extended models that also capture the impact of alpha-cell dysregulation on T2D. In this paper a delay differential equation-based model is developed to describe the coupled glucose-insulin-glucagon dynamics in the isoglycemic intravenous glucose infusion (IIGI) experiment. As the glucose profile in IIGI is tailored to match that of a corresponding oral glucose tolerance test (OGTT), it provides a perfect method for studying hormone responses that are in the normal physiological domain and without the confounding effect of incretins and other gut mediated factors. The model was fit to IIGI data from individuals with and without T2D. Parameters related to glucagon action, suppression, and secretion as well as measures of insulin sensitivity, and glucose stimulated response were determined simultaneously. Significant impairment in glucose dependent glucagon suppression was observed in patients with T2D (duration of T2D: 8 (6–36) months) relative to weight matched control subjects (CS) without diabetes (k1 (mM)−1: 0.16 ± 0.015 (T2D, n = 7); 0.26 ± 0.047 (CS, n = 7)). Insulin action was significantly lower in patients with T2D (a1 (10 pM min)−1: 0.000084 ± 0.0000075 (T2D); 0.00052 ± 0.00015 (CS)) and the Hill coefficient in the equation for glucose dependent insulin response was found to be significantly different in T2D patients relative to CS (h: 1.4 ± 0.15; 1.9 ± 0.14). Trends in parameters with respect to fasting plasma glucose, HbA1c and 2-h glucose values are also presented. Significantly, a negative linear relationship is observed between the glucagon suppression parameter, k1, and the three markers for diabetes and is thus indicative of the role of glucagon in exacerbating the pathophysiology of diabetes (Spearman Rank Correlation: (n = 12; (−0.79, 0.002), (−0.73,.007), (−0.86,.0003)) respectively).

Intensive lactation among women with recent gestational diabetes significantly alters the early postpartum circulating lipid profile: the SWIFT study

BACKGROUND

Women with a history of gestational diabetes mellitus (GDM) have a 7-fold higher risk of developing type 2 diabetes (T2D). It is estimated that 20-50% of women with GDM history will progress to T2D within 10 years after delivery. Intensive lactation could be negatively associated with this risk, but the mechanisms behind a protective effect remain unknown.

METHODS

In this study, we utilized a prospective GDM cohort of 1010 women without T2D at 6-9 weeks postpartum (study baseline) and tested for T2D onset up to 8 years post-baseline (n=980). Targeted metabolic profiling was performed on fasting plasma samples collected at both baseline and follow-up (1-2 years post-baseline) during research exams in a subset of 350 women (216 intensive breastfeeding, IBF vs. 134 intensive formula feeding or mixed feeding, IFF/Mixed). The relationship between lactation intensity and circulating metabolites at both baseline and follow-up were evaluated to discover underlying metabolic responses of lactation and to explore the link between these metabolites and T2D risk.

RESULTS

We observed that lactation intensity was strongly associated with decreased glycerolipids (TAGs/DAGs) and increased phospholipids/sphingolipids at baseline. This lipid profile suggested decreased lipogenesis caused by a shift away from the glycerolipid metabolism pathway towards the phospholipid/sphingolipid metabolism pathway as a component of the mechanism underlying the benefits of lactation. Longitudinal analysis demonstrated that this favorable lipid profile was transient and diminished at 1-2 years postpartum, coinciding with the cessation of lactation. Importantly, when stratifying these 350 women by future T2D status during the follow-up (171 future T2D vs. 179 no T2D), we discovered that lactation induced robust lipid changes only in women who did not develop incident T2D. Subsequently, we identified a cluster of metabolites that strongly associated with future T2D risk from which we developed a predictive metabolic signature with a discriminating power (AUC) of 0.78, superior to common clinical variables (i.e., fasting glucose, AUC 0.56 or 2-h glucose, AUC 0.62).

CONCLUSIONS

In this study, we show that intensive lactation significantly alters the circulating lipid profile at early postpartum and that women who do not respond metabolically to lactation are more likely to develop T2D. We also discovered a 10-analyte metabolic signature capable of predicting future onset of T2D in IBF women. Our findings provide novel insight into how lactation affects maternal metabolism and its link to future diabetes onset.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01967030 .

In Vivo and In Vitro Quantification of Glucose Kinetics: From Bedside to Bench

Like other substrates, plasma glucose is in a dynamic state of constant turnover (i.e., rates of glucose appearance [Ra glucose] into and disappearance [Rd glucose] from the plasma) while staying within a narrow range of normal concentrations, a physiological priority. Persistent imbalance of glucose turnover leads to elevations (i.e., hyperglycemia, Ra>Rd) or falls (i.e., hypoglycemia, Ra Collapse

Key Words

• Diabetes mellitus
• Insulin resistance
• Metabolic fluxomics
• Stable isotope tracers

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MESH Headings

• Animals
• Diabetes Mellitus/metabolism
• Gluconeogenesis
• Glucose/biosynthesis
• Glycogenolysis
• Humans
• Hyperglycemia/metabolism
• Hypoglycemia/metabolism
• Insulin Resistance
• Isotopes/administration & dosage
• Isotopes/metabolism
• Kinetics
• Liver/metabolism
• Metabolic Flux Analysis

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Grants

• 2018R1D1A1B07051053 National Research Foundation of Korea
• 2019H1D3A1A01071043 National Research Foundation of Korea
• 2020R1I1A1A01074380 National Research Foundation of Korea
• 2014M3A9D5A01073886 National Research Foundation of Korea
• 2017R1D1A1B03032988 National Research Foundation of Korea
• Ministry of Education
• Ministry of Sciences and ICT

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Affiliation(s)

Il-Young Kim Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Seoul, Korea Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Seoul, Korea
Sanghee Park Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Seoul, Korea Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Seoul, Korea
Yeongmin Kim Department of Health Sciences and Technology, Gachon Advanced Institute for Health Sciences & Technology (GAIHST), Gachon University, Incheon, Seoul, Korea
Yewon Chang Department of Health Sciences and Technology, Gachon Advanced Institute for Health Sciences & Technology (GAIHST), Gachon University, Incheon, Seoul, Korea
Cheol Soo Choi Department of Molecular Medicine, College of Medicine, Gachon University, Incheon, Seoul, Korea Korea Mouse Metabolic Phenotyping Center, Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Seoul, Korea
Sang-Hoon Suh Department of Physical Education, Yonsei University, Seoul, Korea
Robert R. Wolfe Department of Geriatrics, the Center for Translational Research in Aging & Longevity, Donald W. Reynolds Institute on Aging, University of Arkansas for Medical Sciences, Little Rock, AR, USA

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Juvenile hyposomatotropism in a Somali cat presenting with seizures due to intermittent hypoglycaemia

Case summary

A 3-month-old intact male Somali cat was evaluated for a history of seizures, hypoglycaemia and mental dullness 4 weeks after being bitten in the head by a dog. The cat’s body size and weight were approximately half that of his littermates and its haircoat was woolly, with fewer guard hairs. Multiple hypoglycaemic episodes were documented over a period of 4 weeks, which resolved rapidly after correction of the hypoglycaemia. Juvenile hyposomatotropism was presumptively diagnosed by demonstrating low circulating levels of insulin-like growth factor 1 and after exclusion of other endocrine and non-endocrine causes of small stature and hypoglycaemia. The cat’s intermittent hypoglycaemia resolved spontaneously within 1 month and the cat never showed any more neurological signs. Nevertheless, the physical retardation and the coat abnormalities remained unchanged. A year later, the cat was diagnosed with chronic kidney disease IRIS stage 2.

Relevance and novel information

Hyposomatotropism is an extremely rare feline endocrinopathy. This is the second case reported in the veterinary literature, and the only one to describe hypoglycaemic events associated with growth hormone deficiency. Although hypoglycaemia is one of the most common disease manifestations in children with pituitary dwarfism, this has not yet been reported in veterinary medicine.

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

Measurements of Gluconeogenesis and Glycogenolysis: A Methodological Review

Gluconeogenesis is a complex metabolic process that involves multiple enzymatic steps regulated by myriad factors, including substrate concentrations, the redox state, activation and inhibition of specific enzyme steps, and hormonal modulation. At present, the most widely accepted technique to determine gluconeogenesis is by measuring the incorporation of deuterium from the body water pool into newly formed glucose. However, several techniques using radioactive and stable-labeled isotopes have been used to quantitate the contribution and regulation of gluconeogenesis in humans. Each method has its advantages, methodological assumptions, and set of propagated errors. In this review, we examine the strengths and weaknesses of the most commonly used stable isotopes methods to measure gluconeogenesis in vivo. We discuss the advantages and limitations of each method and summarize the applicability of these measurements in understanding normal and pathophysiological conditions.

Precursors of hexoneogenesis within the human mammary gland

The human mammary gland is capable of de novo synthesis of glucose and galactose (hexoneogenesis); however, the carbon source is incompletely understood. In this study, we investigated the role of acetate, glutamine, lactate and glycerol as potential carbon sources for hexoneogenesis. Healthy breastfeeding women were studied following a 24-h fast on two occasions separated by 1-3 wk. Five women were infused with [U-¹³C]lactate or [1,2-¹³C₂]glutamine and five women with [U-¹³C]glycerol or [1,2-¹³C₂]acetate. Enrichments of ¹³C in plasma and milk substrates were analyzed using GC-MS. Infusion of labeled lactate, glycerol, glutamine, and acetate resulted in plasma glucose being 22.0±3.7, 11.2±1.0, 2.5±0.5, and 1.3±0.2% labeled, respectively. Lactate, glutamine, or acetate did not contribute to milk glucose or galactose (0-2%). In milk, ¹³C-free glycerol enrichment was one-fourth that in plasma but free glycerol concentration in milk was fourfold higher than in plasma. Using [U-¹³C]glycerol and by accounting for tracer dilution, glycerol alone contributed to 10±2 and 69±11% of the hexoneogenesis of milk glucose and galactose, respectively. During [U-¹³C]glycerol infusion, the ratio of M₃ enrichment on 4-6 carbons/M₃ on 1-3 carbons of galactose was higher (P<0.05, 1.22±0.05) than those of glucose in plasma (1.05±0.03) and milk (1.07±0.02). Reanalysis of samples from a previous study involving [U-¹³C]glucose infusion alone suggested labeling a portion of galactose consistent with pentose phosphate pathway (PPP) activity. We conclude that, although lactate contributed significantly to gluconeogenesis, glycerol alone provides the vast majority of substrate for hexoneogenesis. The relative contribution of the PPP vs. the reversal Embden-Meyerhof pathway to hexoneogenesis within the human mammary gland remains to be determined.

Increased gluconeogenesis in youth with newly diagnosed type 2 diabetes

AIMS/HYPOTHESIS

The role of increased gluconeogenesis as an important contributor to fasting hyperglycaemia at diabetes onset is not known. We evaluated the contribution of gluconeogenesis and glycogenolysis to fasting hyperglycaemia in newly diagnosed youths with type 2 diabetes following an overnight fast.

METHODS

Basal rates (μmol kg(FFM) (-1) min(-1)) of gluconeogenesis ((2)H2O), glycogenolysis and glycerol production ([(2)H5] glycerol) were measured in 18 adolescents (nine treatment naive diabetic and nine normal-glucose-tolerant obese adolescents).

RESULTS

Type 2 diabetes was associated with higher gluconeogenesis (9.2 ± 0.6 vs 7.0 ± 0.3 μmol kg(FFM) (-1) min(-1), p < 0.01), plasma fasting glucose (7.0 ± 0.6 vs 5.0 ± 0.2 mmol/l, p = 0.004) and insulin (300 ± 30 vs 126 ± 31 pmol/l, p = 0.001). Glucose production and glycogenolysis were similar between the groups (15.4 ± 0.3 vs 12.4 ± 1.4 μmol kg(FFM) (-1) min(-1), p = 0.06; and 6.2 ± 0.8 vs 5.3 ± 0.7 μmol kg(FFM) (-1) min(-1), p = 0.5, respectively). After controlling for differences in adiposity, gluconeogenesis, glycogenolysis and glucose production were higher in diabetic youth (p ≤ 0.02). Glycerol concentration (84 ± 6 vs 57 ± 6 μmol/l, p = 0.01) and glycerol production (5.0 ± 0.3 vs 3.6 ± 0.5 μmol kg(FFM) (-1) min(-1), p = 0.03) were 40% higher in youth with diabetes. The increased glycerol production could account for only ~1/3 of substrate needed for the increased gluconeogenesis in diabetic youth.

CONCLUSION/INTERPRETATIONS

Increased gluconeogenesis was a major contributor to fasting hyperglycaemia and hepatic insulin resistance in newly diagnosed untreated adolescents and was an early pathological feature of type 2 diabetes. Increased glycerol availability may represent a significant source of new carbon substrates for increased gluconeogenesis but would not account for all the carbons required to sustain the increased rates.

Minimizing morbidity of hypoglycemia in diabetes: a review of mini-dose glucagon

Type 1 diabetes is a common chronic disease of childhood and one of the most difficult conditions to manage. Advances in insulin formulations and insulin delivery devices have markedly improved the ability to achieve normal glucose homeostasis. However, hypoglycemia remains the primary limiting factor in achieving normoglycemia and is a frequent complication in children with acute gastroenteritis and/or poor oral intake. In situations of impaired carbohydrate intake or absorption, glucagon therapy is the only out-of-hospital treatment option available to families and caregivers. Glucagon is recommended for the treatment of severe hypoglycemia and rapidly increases blood glucose by increasing hepatic glucose production from glycogenolysis. Mini-dose glucagon is a widely utilized off-label treatment for managing mild or impending hypoglycemia and is administered as a small subcutaneous injection. It was initially described for use in children who were unable to tolerate or absorb oral carbohydrates but not in need of advanced medical care. Yet, mini-dose glucagon may be useful in any individual with relative insulin excess. The regimen aims to prevent severe hypoglycemic episodes and is safe, effective, and easily administered by patients and caregivers in the out-of-hospital setting. By empowering patients and their families, this important tool could help to alleviate the physical, psychosocial, and financial burden evolving from impending hypoglycemia.

Regional body composition changes during lactation in Indian women from the low-income group and their relationship to the growth of their infants

BACKGROUND

Increased energy requirement during lactation may lead to maternal tissue depletion in women from poor subsistence communities.

OBJECTIVES

To examine the regional body composition changes in undernourished lactating women and to assess the relationship of maternal body composition changes with weight gain of the infants.

SUBJECTS AND METHODS

Body composition was assessed using dual energy x-ray absorptiometry in 35 lactating women at 4 time points: within 1 month after delivery (baseline) and at 6, 12, and 18 months postpartum.

RESULTS

The mean age, height, and body mass index of the women were 23.5 years, 150.7 cm, and 20.0 kg/m(2), respectively. There were no significant differences in body weight or whole-body lean as well as fat mass at 4 time points, but the percentage fat decreased significantly during lactation. There was selective mobilization of fat mass from the leg region, whereas the appendicular skeletal mass (ASM) increased significantly. When the growth of the infants in the first 6 months (proxy for the lactation performance) was assessed in relation to the maternal body composition changes during that period, it was observed that the change in fat mass had a negative relationship to the weight gain of the infant. Change in the ASM during this period, however, had a significant positive relationship with the weight gain of the infants.

CONCLUSION

There were important differences in the lactation-related changes in the regional body composition parameters of these undernourished women. Regional body composition changes may be related to the weight gain of the breast-fed infants.

ABM Clinical Protocol #9: Use of galactogogues in initiating or augmenting the rate of maternal milk secretion (First Revision January 2011)

A central goal of The Academy of Breastfeeding Medicine is the development of clinical protocols for managing common medical problems that may impact breastfeeding success. These protocols serve only as guidelines for the care of breastfeeding mothers and infants and do not delineate an exclusive course of treatment or serve as standards of medical care. Variations in treatment may be appropriate according to the needs of an individual patient. These guidelines are not intended to be all-inclusive, but to provide a basic framework for physician education regarding breastfeeding.

Short-term administration of rhGH increases markers of cellular proliferation but not milk protein gene expression in normal lactating women

Growth hormone is one of few pharmacologic agents known to augment milk production in humans. We hypothesized that recombinant human GH (rhGH) increases the expression of cell proliferation and milk protein synthesis genes. Sequential milk and blood samples collected over four days were obtained from five normal lactating women. Following 24 h of baseline milk and blood sampling, rhGH (0.1 mg/kg/day) was administered subcutaneously once daily for 3 days. Gene expression changes were determined by microarray studies utilizing milk fat globule RNA isolated from each milk sample. Following rhGH administration, DNA synthesis and cell cycle genes were induced, while no significant changes were observed in the expression of milk synthesis genes. Expression of glycolysis and citric acid cycle genes were increased by day 4 compared with day 1, while lipid synthesis genes displayed a circadian-like pattern. Cell cycle gene upregulation occurred after a lag of ∼2 days, likely explaining the failure to increase milk production after only 3 days of rhGH treatment. We conclude that rhGH induces expression of cellular proliferation and metabolism genes but does not induce milk protein gene expression, as potential mechanisms for increasing milk production and could account for the known effect of rhGH to increase milk production following 7-10 days.

The intricate role of growth hormone in metabolism

Growth hormone (GH), a master regulator of somatic growth, also regulates carbohydrate and lipid metabolism via complex interactions with insulin and insulin-like growth factor-1 (IGF-1). Data from human and rodent studies reveal the importance of GH in insulin synthesis and secretion, lipid metabolism and body fat remodeling. In this review, we will summarize the tissue-specific metabolic effects of GH, with emphasis on recent targets identified to mediate these effects. Furthermore, we will discuss what role GH plays in obesity and present possible mechanisms by which this may occur.

Biological effects of growth hormone on carbohydrate and lipid metabolism

This review will summarize the metabolic effects of growth hormone (GH) on the adipose tissue, liver, and skeletal muscle with focus on lipid and carbohydrate metabolism. The metabolic effects of GH predominantly involve the stimulation of lipolysis in the adipose tissue resulting in an increased flux of free fatty acids (FFAs) into the circulation. In the muscle and liver, GH stimulates triglyceride (TG) uptake, by enhancing lipoprotein lipase (LPL) expression, and its subsequent storage. The effects of GH on carbohydrate metabolism are more complicated and may be mediated indirectly via the antagonism of insulin action. Furthermore, GH has a net anabolic effect on protein metabolism although the molecular mechanisms of its actions are not completely understood. The major questions that still remain to be answered are (i) What are the molecular mechanisms by which GH regulates substrate metabolism? (ii) Does GH affect substrate metabolism directly or indirectly via IGF-1 or antagonism of insulin action?

Mechanisms to conserve glucose in lactating women during a 42-h fast

Little is known about how lactating women accommodate for their increased glucose demands during fasting to avoid maternal hypoglycemia. The objective of this study was to determine whether lactating women conserve plasma glucose by reducing maternal glucose utilization by increasing utilization of FFA and ketone bodies and/or increasing gluconeogenesis and mammary gland hexoneogenesis. Six healthy exclusively breastfeeding women and six nonlactating controls were studied during 42 h of fasting and 6 h of refeeding. Glucose and protein kinetic parameters were measured using stable isotopes and GCMS and energy expenditure and substrate oxidation using indirect calorimetry. After 42 h of fasting, milk production decreased by 16% but remained within normal range. Glucose, insulin, and C-peptide concentrations decreased with the duration of fasting in both groups but were lower (P < 0.05) in lactating women. Glucagon, FFA, and beta-hydroxybutyrate concentrations increased with fasting time (P < 0.001) and were higher (P < 0.0001) in lactating women during both fasting and refeeding. During 42 h of fasting, gluconeogenesis was higher in lactating women compared with nonlactating controls (7.7 +/- 0.4 vs. 6.5 +/- 0.2 micromol kg(-1) min(-1), P < 0.05), whereas glycogenolysis was suppressed to similar values (0.4 +/- 0.1 vs. 0.9 +/- 0.2 micromol kg(-1) min(-1), respectively). Mammary hexoneogenesis did not increase with the duration of fasting. Carbohydrate oxidation was lower and fat and protein oxidations higher (P < 0.05) in lactating women. In summary, lactating women are at risk for hypoglycemia if fasting is extended beyond 30 h. The extra glucose demands of extended fasting during lactation appear to be compensated by increasing gluconeogenesis associated with ketosis, decreasing carbohydrate oxidation, and increasing protein and FFA oxidations.