Growth hormone (GH) and atherosclerosis: changes in morphology and function of major arteries during GH treatment

L-arginine as a nutritional prophylaxis against vascular endothelial dysfunction with aging

With advancing age, peripheral conduit and resistance arteries lose the ability to effectively dilate owing to endothelial dysfunction. This vascular senescence contributes to increased risk of cardiovascular disease (CVD) with aging. L-arginine plays a role in numerous physiological processes including nitrogen detoxification, immunocompetence, growth hormone (GH) secretion, and insulin secretion. Recently, a considerable amount of attention has been placed on the ability of this amino acid to affect vascular endothelial function. The purpose of this review will be to examine the use of L-arginine as a novel nutritional strategy to potentially stave progression of vascular dysfunction with aging and CVD. Emphasis will be placed on the ability of L-arginine to modulate the vascular inflammatory and systemic hormonal milieu, which in turn may have a positive effect on vascular endothelial function.

Small vessel remodeling and impaired endothelial-dependent dilatation in subcutaneous resistance arteries from patients with acromegaly

CONTEXT

Patients with acromegaly have increased morbidity and mortality, predominantly from cardiovascular disease. Hypertension and diabetes are more prevalent, and both cause small vessel remodeling and endothelial dysfunction.

OBJECTIVE

To understand the structure and function of small arteries in acromegaly, sc blood vessels from gluteal fat biopsies were harvested from 18 patients with active disease (AD; age, 56 +/- 15 yr; 14 males), 23 patients in remission (CD; age, 55 +/- 12 yr; 15 males), and 20 healthy controls (age, 55 +/- 11 yr; 10 males) and examined in vitro using pressure myography.

DESIGN

Contractile responses to cumulative noradrenaline concentrations were recorded and followed by dose-dependent dilator responses to acetylcholine. The acetylcholine protocol was repeated after incubation with a nitric oxide synthase inhibitor (N-nitro-L-arginine methyl ester) and cyclooxygenase inhibitor (indomethacin). After perfusion with Ca(2+)-free physiological saline solution, structural measurements were recorded at varying intraluminal pressures (3-180 mm Hg).

RESULTS

Wall thickness and wall:lumen ratio were increased in AD, reduced with treatment but remained greater in CD than controls. Wall cross-sectional area was increased in AD vs. controls (P < 0.001), decreased with treatment (AD vs. CD, P < 0.001), but remained higher than controls (CD vs. controls, P = 0.015). Growth index was increased in AD (20%) compared to controls (CD, 9%). Contractility was similar in all groups. Endothelial-dependent dysfunction was evident in AD compared with CD (P < 0.001) and controls (P < 0.01). Dilation did not change after N-nitro-L-arginine methyl ester but was impaired after indomethacin incubation.

CONCLUSION

Active acromegaly is associated with hypertrophic remodeling of the vascular wall and embarrassed endothelial function due to reduced nitric oxide and endothelium-derived hyperpolarizing factor bioavailability, both of which may contribute to the early mortality from cardiovascular disease.

Assessment of flow-mediated vasodilatation (FMD) of the brachial artery: effects of technical aspects of the FMD measurement on the FMD response

AIMS

The ability to assess endothelial function non-invasively with B-mode ultrasound has lead to its widespread application in a variety of studies. However, the absolute values obtained using this approach vary considerably across studies. We studied whether technical aspects of the methodology can explain the wide variety in absolute values across studies.

METHODS AND RESULTS

A literature search was performed to identify published reports on flow-mediated vasodilatation (FMD) of the brachial artery published between 1992 and 2001. Information on type of equipment (wall track/B-mode), location of the measurement (antecubital fossa/upper arm), occlusion site (lower/upper arm), occlusion duration (min), and occlusion pressure was extracted. Patient characteristics were also extracted. For the healthy populations, mean FMD varied from 0.20 to 19.2%; for the coronary heart disease (CHD) patients FMD varied from -1.3 to 14%; for subjects with diabetes mellitus FMD varied from 0.75 to 12%. Compared with occlusion at the upper arm, lower arm occlusion was related to decreased FMD (mean difference in FMD -2.47%; 95% CI 0.55-4.39). An occlusion duration of > or =4.5 min was related to an increased FMD compared with an occlusion time of < or =4 min (mean difference 1.30%; 95% CI 0.35-2.46). These findings were adjusted for other technical aspects of the methodology and for differences in risk factors between populations.

CONCLUSION

Mean FMD differs widely between studies. There is a great overlap between populations (healthy, CHD, diabetics). Our findings suggest that the technical aspects of the measurements, the location, and the duration of the occlusion may explain some of these differences, whereas type of equipment, location of the measurement, and occlusion pressure do not.

A low-fat, whole-food vegan diet, as well as other strategies that down-regulate IGF-I activity, may slow the human aging process

A considerable amount of evidence is consistent with the proposition that systemic IGF-I activity acts as pacesetter in the aging process. A reduction in IGF-I activity is the common characteristic of rodents whose maximal lifespan has been increased by a wide range of genetic or dietary measures, including caloric restriction. The lifespans of breeds of dogs and strains of rats tend to be inversely proportional to their mature weight and IGF-I levels. The link between IGF-I and aging appears to be evolutionarily conserved; in worms and flies, lifespan is increased by reduction-of-function mutations in signaling intermediates homologous to those which mediate insulin/IGF-I activity in mammals. The fact that an increase in IGF-I activity plays a key role in the induction of sexual maturity, is consistent with a broader role for-IGF-I in aging regulation. If down-regulation of IGF-I activity could indeed slow aging in humans, a range of practical measures for achieving this may be at hand. These include a low-fat, whole-food, vegan diet, exercise training, soluble fiber, insulin sensitizers, appetite suppressants, and agents such as flax lignans, oral estrogen, or tamoxifen that decrease hepatic synthesis of IGF-I. Many of these measures would also be expected to decrease risk for common age-related diseases. Regimens combining several of these approaches might have a sufficient impact on IGF-I activity to achieve a useful retardation of the aging process. However, in light of the fact that IGF-I promotes endothelial production of nitric oxide and may be of especial importance to cerebrovascular health, additional measures for stroke prevention-most notably salt restriction-may be advisable when attempting to down-regulate IGF-I activity as a pro-longevity strategy.

Long-term growth hormone replacement therapy in hypopituitary adults

Growth hormone deficiency (GHD) in the adult has now been fully recognised as a clinical entity characterised by abnormal body composition, osteopenia, impaired quality of life, cardiac dysfunction and an adverse lipid profile. While short-term studies of GH replacement have demonstrated irrefutably a favourable effect on all if not most features of GHD, data on long-term administration spanning more than 2 years are still scarce. Experience of GH replacement up to 5 to 10 years indicate that the beneficial effects on body composition, predominantly a decrease in body fat and an increase in lean mass, is maintained during treatment. Long-term GH therapy also increases muscle strength and exercise performance. All data, with one exception, are consistent with a significant increase in bone mass during prolonged GH therapy. The most distinct effect on bone was observed in the worst affected individuals and in males. Improvement in quality of life is documented shortly after initiation of GH replacement and is maintained during long-term studies. This may explain the reduction in days of sick leave seen during GH therapy. The beneficial effect on cardiovascular risk factors is sustained over a prolonged period of time, revealing a reduction in intima wall thickness, and an improvement in serum lipid levels and clotting parameters. The increase in lipoprotein(a) levels with GH therapy in some studies may be disturbing, but difficulties in measuring this parameter and inconsistencies between the different studies makes it difficult to estimate its real impact. No data are yet available to show that GH replacement will normalise or even improve mortality rate and fracture rate. Adverse events associated with GH replacement therapy are mainly secondary to fluid retention as a result of excess dose administration. This can be adequately prevented by monitoring GH replacement according to serum insulin-like growth factor (IGF)-I levels. From what is currently known, GH replacement does not increase the prevalence of diabetes mellitus, and does not induce new neoplasms or recurrence of the primary brain tumour; however, longer follow-up studies are needed to provide definitive answers. In conclusion, it appears not only that long-term GH replacement therapy in adults with GHD is a procedure that can be safely used, but that GH replacement should be considered as a possible life-long therapy in order to maintain its benefits.

Growth hormone deficiency and vascular risk

The importance of growth hormone deficiency (GHD) in adult life has become more apparent over the last decade. As well as a distinct clinical syndrome there is a significant excess risk of cardiovascular disease. Although it is difficult to ascertain what part is played by the original pituitary disorder and the concomitant replacement hormonal therapies, there is clear evidence that GHD is associated with known cardiovascular risk factors such as body shape, lipid profile, insulin resistance, blood pressure, vessel wall morphology and haemostatic factors. Novel means of assessing vascular risk such as pulse wave velocity and flow-mediated dilatation can also estimate the risk without invasive procedures. The role of possible mediators of endothelial function such as nitric oxide and free radicals is being investigated further. Replacement of GH in GH-deficient patients leads to many effects on the above indices, some but not all of which are associated with reduced vascular risk. Long-term follow-up studies of morbidity and mortality are required for an accurate assessment of the beneficial effects of therapy.

Clinical evaluation and management of metabolic and morphologic abnormalities associated with human immunodeficiency virus

In recent years, a spectrum of metabolic and morphologic alterations has emerged among patients infected with human immunodeficiency virus (HIV) receiving antiretroviral treatment. Changes observed include insulin resistance, dyslipidemia, abdominal and dorsocervical fat accumulation, and fat depletion in the extremities and in the face. The health consequences of these changes are not well understood but may include increased risk for diabetes, heart disease, and stroke. Therefore, clinicians that treat patients with HIV need current, practical information on management strategies and interventions for patients with manifestations of HIV-associated lipodystrophy. Literature is reviewed on the health consequences of insulin resistance, dyslipidemia, and alterations in body fat distribution in non-HIV populations to gain perspective on how such abnormalities might affect HIV-infected patients. We also suggest treatments and strategies to manage metabolic and morphologic changes in patients with HIV.

Differential effects of growth hormone and insulin-like growth factor I on human endothelial cell migration

Effects of growth hormone (GH), insulin-like growth factor I (IGF-I), and endothelin-1 (ET-1) on endothelial cell migration and the underlying molecular mechanisms were explored using a human umbilical cord endothelial cell line, ECV304 cells, in vitro. Treatment of the cells with IGF-I or ET-1, but not GH, stimulated the cell migration. Interestingly, however, ET-1-induced, but not IGF-I-induced, migration of the cells was inhibited by GH. Both ET-1 and IGF-I caused activation of mitogen-activated protein kinase (MAPK) in the cells, and GH eliminated the MAPK activation produced by ET-1 but not that produced by IGF-I. On the other hand, migration of the cells was stimulated by protein kinase C (PKC) agonist, phorbol 12-myristate 13-acetate. ET-1 promoted PKC activity, and a PKC inhibitor, GF-109203X, blocked ET-1-induced cell migration. Although GH inhibited ET-1-induced cell migration and MAPK activity, it did not block ET-1-induced PKC activation. Thus ET-1 stimulation of endothelial cell migration appears to be mediated by PKC/MAPK pathway, and GH may inhibit the MAPK activation by ET-1 at the downstream of PKC.

Sporadic pituitary tumours: from epidemiology to use of databases

Pituitary tumours account for 10% of intracranial neoplasms and have an annual incidence of about 25 per million head of population. Prolactinomas and non-functioning tumours are the most common subtypes clinically, as well as in surgical and histopathological series. In pre-pubertal children, corticotrophinomas, although rare, are the most common subtype, prolactinomas being most common in adolescents. In autopsy series, 11% of pituitaries harbour an adenoma. These are usually small (less than 10 mm in diameter), and where examined, about half are prolactinomas. Computed tomography or magnetic resonance imaging examination of normal subjects reveals abnormalities of greater than 3 mm in diameter in 10% of pituitaries. Other cancers in patients with pituitary tumours are confined to acromegalics, in whom colonic lesions are more prevalent than in the general population. Several long-term sequelae of pituitary tumours with respect to morbidity and mortality have been identified from retrospective analyses. However, data on these are not standardized, requiring the development of national databases and registers to collect clinical outcomes from large cohorts according to agreed standard proformas. These registers will provide a sufficient number of cases for statistically valid conclusions on different clinical subgroups. The development of national guidelines for best practice for the management of patients with these tumours provides the basis for an audit of the management process and outcomes between centres. This will inform decisions on the optimum configuration of services for such patients.