Growth hormone and the heart

Influence of puberty on relationships between body composition and blood pressure: a cross-sectional study

BACKGROUND

Fat mass (FM) and fat-free mass (FFM) are positively associated with blood pressure (BP) in youth. Yet, how puberty, independent of age, affects these relationships remains unclear. Given puberty may be a crucial period for cardiometabolic health, we examined how pubertal development moderates the associations of FM/FFM with BP.

METHODS

Pubertal development, resting BP, and body composition were assessed in a convenience sample of youth (5.5-17 years). General linear models were conducted to assess if pubertal development moderated the relationships between FM/FFM and systolic/diastolic BP standardized for age, sex, and height (SBPz/DBPz).

RESULTS

Among participants (N = 1405; age: M = 13.3 ± 2.9 years; 65.4% female; 53.2% racial/ethnic minority), FM/FFM were positively associated with SBPz and DBPz (ps ≤ 0.02). Pubertal development moderated the associations between FFM and BPz (ps ≤ 0.01), but not FM (ps > 0.43). For early/mid and late pubertal participants, there were positive associations between FFM and BP (DBPz: βs = 0.10-0.18, ps ≤ 0.01; SBPz: βs = 0.33-0.43, ps < 0.001); however, these relationships were attenuated, especially for prepubertal DBPz (DBPz: β = 0.01, p = 0.91; SBPz: β = 0.24, p = 0.001).

CONCLUSIONS

Puberty moderated the relationships between FFM and SBPz/DBPz in analyses that separately modeled the contributions of age and sex. These data suggest that the FFM-DBPz association may potentially be impacted by increasing sex hormone concentrations during puberty.

IMPACT

Fat mass (FM) and blood pressure (BP) were positively associated throughout puberty. Fat-free mass (FFM) and BP were positively associated throughout puberty; however, puberty moderated the FFM-BP relationship, such that there was a positive relationship in early/mid and late puberty, but the relationship was attenuated for prepubertal children. These findings contribute further insight into physiological and cardiometabolic changes occurring during puberty. Changes in hormone concentrations may explain the impact puberty has on the FFM-BP relationship. Understanding predictors of BP are important as childhood BP is associated with future cardiometabolic outcomes.

Short-term efficacy of recombinant human GH therapy in cured acromegaly patients with GH deficiency: a single-center experience

The effectiveness and short-term safety of recombinant human GH (r-hGH) in acromegaly patients with GH deficiency (GHD) after treatment are not well established. The study includes ten subjects with acromegaly who had GHD treated with r-hGH for 6 months. Control groups consisted of ten age-, gender-, and BMI-matched healthy subjects and ten active acromegaly patients who were treatment naïve. Body composition, quality of life (QoL), muscle strength, lipid profile, and cardiovascular risk factors were assessed in all subjects at baseline, and the same parameters were reassessed after 6 months of therapy with r-hGH in acromegaly with GHD. Repeat magnetic resonance imaging of the sella was performed in treated subjects. Optical colonoscopy was done and biopsies were taken from multiple sites for proliferation indices (Ki67). The median duration of GHD was 17.8 months and dose of r-hGH administered was 5.7±1.5 μg/kg per day. There was improvement in bone mineral content (P=0.01), bone mineral density (P=0.04), muscle strength (P<0.001), total cholesterol (P=0.003), high-density cholesterol (P<0.001), and QoL - score (P=0.005), and reduction in low-density cholesterol (P=0.003) and triglyceride (P=0.004) after treatment. There was no change in lean body mass, total body fat, hsCRP, lipoprotein (a), and fibrinogen levels. There was a modest increase in plasminogen activator inhibitor 1 (P=0.002), but it was lower compared with healthy controls and treatment naïve acromegalics (P=0.007). Six month-r-hGH therapy improves body composition, atherogenic lipid profile, QoL, and muscle strength in GHD patients who had acromegaly. Long-term prospective studies are needed to evaluate the effect of r-hGH therapy in these patients.

Growth hormone and insulin-like growth factor-I alter hippocampal excitatory synaptic transmission in young and old rats

In rats, as in humans, normal aging is characterized by a decline in hippocampal-dependent learning and memory, as well as in glutamatergic function. Both growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels have been reported to decrease with age, and treatment with either GH or IGF-I can ameliorate age-related cognitive decline. Interestingly, acute GH and IGF-I treatments enhance glutamatergic synaptic transmission in the rat hippocampus of juvenile animals. However, whether this enhancement also occurs in old rats, when cognitive impairment is ameliorated by GH and IGF-I (des-IGF-I), remains to be determined. To address this issue, we used an in vitro CA1 hippocampal slice preparation and extracellular recording techniques to study the effects of acute application of GH and IGF-I on compound field excitatory postsynaptic potentials (fEPSPs), as well as AMPA- and NMDA-dependent fEPSPs, in young adult (10 months) and old (28 months) rats. The results indicated that both GH and IGF-I increased compound-, AMPA-, and NMDA-dependent fEPSPs to a similar extent in slices from both age groups and that this augmentation was likely mediated via a postsynaptic mechanism. Initial characterization of the signaling cascades underlying these effects revealed that the GH-induced enhancement was not mediated by the JAK2 signaling element in either young adult or old rats but that the IGF-I-induced enhancement involved a PI3K-mediated mechanism in old, but not young adults. The present findings are consistent with a role for a GH- or IGF-I-induced enhancement of glutamatergic transmission in mitigating age-related cognitive impairment in old rats.

Expressional reprogramming of survival pathways in rat cardiocytes by neuregulin-1beta

Neuregulin/ErbB2-induced kinase signaling provides essential survival and protection clues for functional integrity of the adult heart and skeletal muscle. To define the regulatory pathways involved in neuregulin-dependent muscle cell survival, we set out to map the largely unknown transcript targets of this growth/differentiation factor in cardiocytes. Freshly isolated adult primary rat cardiocytes were treated for 24 h with recombinant human neuregulin-1beta (NRG-1beta, 30 ng/ml). Transcript level alterations in NRG-1beta-treated and control cardiocytes (n = 6) were identified with Atlas Rat Toxicology 1.2 cDNA arrays (BD Clontech) and established permutation L1 regression analysis. Selected transcriptional adjustments were confirmed by RT-PCR and Western blotting. Involvement of MAPK pathways was verified with the inhibitor PD-98059. Application of the single dose of NRG-1beta to quiescent cardiocytes induced expressional reprogramming of distinct cellular processes. This response included a prominent 50-100% increase in transcripts of multiple redox systems. It also involved a comparable mRNA augmentation of protein synthetic and folding factors together with augmented message for the trigger of cardiac hypertrophy, cyclin D1 (CCND1). First evidence for a role of neuregulin in promotion of mitochondrial turnover, voltage-gated ion channel expression, and the suppression of fatty acid transporter mRNAs was revealed. Subsequent analysis confirmed a corresponding upregulation of redox factor proteins thioredoxin and the thioredoxin reductase 1, GSTP-1, and CCND1 and demonstrated downregulation of the related transcripts by PD-98059 in neuregulin-stimulated cultures. These MAPK-dependent expressional adjustments point to novel oxidative defense and hypertrophy pathways being involved in the longer lasting protective function of neuregulin in the heart.

Cardiac IGF-I manipulation by growth hormone following myocardial infarction

Evidence of a role for growth hormone (GH) in cardiac structure and function has been derived from studies of patients suffering either GH excess or deficiency, both of which may lead to reduced life expectancy. The role of GH in the ischaemic heart, however, is less than clear. We therefore investigated the effect of 30 days GH treatment in sheep with myocardial infarction. GH treatment significantly increased circulating IGF-I levels (P<0.01), heart weight (P<0.01), and cardiomyocyte cross-sectional area (P<0.001). IGF-I mRNA in peri-infarct cardiac tissue also increased significantly (P<0.05). We conclude that post-infarct GH treatment increases circulating and cardiac IGF-I levels, resulting in significant cardiomyocyte hypertrophy. This increase in cardiomyocyte size appears to correlate with local IGF-I expression rather than plasma IGF-I levels.

Effects of somatotropin and training on indices of exercise capacity in Standardbreds

The recent availability of recombinant equine somatotropin (eST) has led to concern about its use as an ergogenic aid in racehorses. This study was undertaken to investigate the changes in exercise capacity in maturing horses in a training programme, and to assess whether eST is an ergogenic aid to this group. We tested the hypothesis that the combination of training and eST, compared to training alone, would further improve exercise capacity in maturing Standardbreds, by virtue of ST's anabolic effects and potential to enhance cardiac function, circulating fluid volume and red cell mass. Twelve, untrained Standardbreds (mean +/- s.d. 20.7 +/- 1.1 months) were paired according to similar bodyweight and then assigned randomly to treatment or control group. The horses underwent a 12 week treadmill training programme. Methionyl eST (10 microg/kg for the first 7 days, then 20 microg/kg) was administered once daily, i.m., for 42 consecutive days (Weeks 4 to 9 inclusive) to 6 horses in the treatment group. All horses performed a standardised maximal exercise test to fatigue at Weeks 0, 3, 6, 9, and 12. During each exercise test VO2, VCO2, plasma lactate concentrations ([La]), heart rates, blood volume and total run time were measured. There was no significant effect of eST administration on VO2max, V200, V(LA4), LA9, red cell volume (RCV), plasma volume (PV), or run time to fatigue. Combining the data for all horses, training significantly altered the VO2max (mean +/- s.d. 98.2 +/- 11.1 ml/kg/min in Week 0 to 117.6 +/- 4.8 ml/kg/min in Week 12), V(LA4) (5.1 +/- 0.8 m/s to 7.4 +/- 1.0 m/s), LA9 (12.7 +/- 3.9 mmol/l to 7.1 +/- 1.9 mmol/l), RCV (46.3 +/- 4.7 ml/kg to 63.5 +/- 5.0 ml/kg), PV (46.0 +/- 4.8 ml/kg to 57.0 +/- 6.3 ml/kg), and run time to fatigue (431.8 +/- 30.9 to 490.2 +/- 30.5 s), but not V200 (5.0 +/- 0.5 m/s to 5.2 +/- 1.1 m/s). The administration of eST to young Standardbred horses in training did not significantly improve their exercise capacity or indices of fitness. However, these maturing horses demonstrated a rapid physiological response to training exercise. Further research is required to determine the relationship between exercise capacity and ST in the horse.

Effects of early treatment with growth hormone on infarct size, survival, and cardiac gene expression after acute myocardial infarction

OBJECTIVE

This study examined the effects of growth hormone (GH) on infarct size, survival, and cardiac gene expression in rats with acute myocardial infarction.

DESIGN

Animals randomly received sc injection of either saline vehicle (n = 98) or GH (2mg/kg/day, n = 105) for 14 days commencing the day of left coronary artery ligation. Infarct size was determined by morphometric analysis at the time of death or at 52 weeks post-surgery. Gene expression was analyzed by real-time RT-PCR after 2-week treatment.

RESULTS

GH decreased infarct size by 18% (P < 0.01) and increased survival by 36% at 52 weeks. GH also significantly reduced cardiac expression of atrial natriuretic factor, beta-myosin heavy chain, alpha-smooth muscle actin, collagen I, collagen III, fibronectin, and pro-inflammatory cytokines.

CONCLUSIONS

Treatment with GH for 2 weeks beginning on the day of myocardial infarction produced beneficial effects that were associated with reductions in cardiac gene expression symptomatic of pathological remodeling.

Effects of rhIGF-I and insulin-induced hypoglycaemia on cardiovascular parameters recorded with telemetry in the conscious dog

Using telemetry, the effects on cardiovascular parameters after single intravenous administration (0.5 mg/kg) of recombinant human insulin-like growth factor-I (rhIGF-I) were studied in conscious and unrestrained dogs. Insulin (1.1 IU/kg) was used as a reference compound. Telemetry transmitters were implanted subcutaneously with a pressure catheter in the femoral artery and electrodes for ECG subcutaneously. Cardiovascular effects and changes in blood glucose levels induced with rhlGF-I were similar to those induced with insulin. Heart rate increased continuously for about 90 min. after treatment, regardless of compound. Thereafter, heart rate slowly decreased but did not fully reach predose values 4 hr after treatment. Both systolic and diastolic blood pressure decreased continuously for about 90 min. and remained low for up to 4 hr after treatment. Treatment with rhIGF-I or insulin did not influence dp/dt values. Treatment with glucose intravenously to abolish the rhIGF-I-induced hypoglycaemia reduced the heart rate, but caused a substantial increase in dp/dt and a slight increase in blood pressure. RhIGF-I and insulin induced an almost identical onset and degree of hypoglycaemia. Blood glucose reached a minimum level 1 hr after treatment and was almost returned to normal 4 hr after treatment. There was an increase in the amplitude of the T-waves, though this effect occurred earlier and was longer lasting with insulin than with rhIGF-I. After 4 hr, the T-wave amplitude was normal with rhIGF-I but remained high with insulin. These T-wave effects were probably due to an increase in the transport of potassium or calcium since they decreased in plasma. This suggests that the effects of rhIGF-I and insulin are highly comparable and that the cardiovascular changes induced by rhIGF-I are likely caused by its insulin-like activity. As shown by the recorded cardiovascular responses induced by rhIGF-1 and insulin, the telemetric recording system makes it possible to evaluate the effects of different drugs in a continuous way that is not possible with conventional techniques. This new telemetric technique can be of significant importance in the process of future drug development.

Microarray analysis of the in vivo effects of hypophysectomy and growth hormone treatment on gene expression in the rat

Complementary DNA microarrays containing 3000 different rat genes were used to study the consequences of severe hormonal deficiency (hypophysectomy) on the gene expression patterns in heart, liver, and kidney. Hybridization signals were seen from a majority of the arrayed complementary DNAs; nonetheless, tissue-specific expression patterns could be delineated. Hypophysectomy affected the expression of genes involved in a variety of cellular functions. Between 16-29% of the detected transcripts from each tissue changed expression level as a reaction to this condition. Chronic treatment of hypophysectomized animals with human GH also caused significant changes in gene expression patterns. The study confirms previous knowledge concerning certain gene expression changes in the above-mentioned situations and provides new information regarding hypophysectomy and chronic human GH effects in the rat. Furthermore, we have identified several new genes that respond to GH treatment. Our results represent a first step toward a more global understanding of gene expression changes in states of hormonal deficiency.

Echocardiographic assessment of cardiac morphology and function in mutant dwarf rats

Although the mutant dwarf rat has been proposed as a model of growth hormone (GH) deficiency, few studies have addressed its cardiovascular abnormalities. Therefore, the aim of the present study was to investigate cardiac structure and function in mutant dwarf rats in vivo before and after chronic GH administration, by means of transthoracic Doppler echocardiography. To this purpose, forty 90-day-old female dwarf rats were randomized to receive either GH treatment or placebo. Twenty age-and sex-matched Lewis rats (200-250 g) served as the control group. All rats underwent echocardiograms before receiving any drug and after 3 weeks of therapy. Echocardiographically detected left ventricular mass indexed to tibial length was reduced by 41% in dwarf rats compared to the control group. Such relative cardiac atrophy was also evident at the myocyte level, and was fully reversible after GH therapy. In contrast to the control group, dwarf rats also showed a reduction of left ventricular diastolic volumes normalized to tibial length and impaired cardiac performance as suggested by the reduction of cardiac index, abnormal stress-shortening relations, and a significant elevation of total peripheral vascular resistance. All these abnormalities were reversible upon GH therapy for 3 weeks. In conclusion, GH plays an important role in maintaining a normal cardiac structure and function. Since the observed changes are similar to those seen in GH-deficient men, the mutant dwarf rat represents a faithful animal model of GH deficiency.