The aim of the study is to evaluate the gender specific effects of physiologic Growth Hormone (GH) replacement in women with GH deficiency on the basis of pituitary/hypothalamic region tumors, radiation, or surgery on cardiovascular risk markers and arterial distensibility. Cardiovascular mortality in growth hormone (GH) deficient adults has been shown to be increased in a number of retrospective studies. Increased arterial intima-media thickness, increased prevalence of atherosclerotic plaques and endothelial dysfunction have been reported in growth hormone deficient adults both in childhood and adulthood onset forms.
The growth hormone deficiency (GHD) syndrome is associated with a cluster of cardiovascular-risk factors such as central adiposity, increased visceral fat, insulin resistance, dyslipoproteinemia and decreased plasma fibrinolytic activity. GH administration has effects on a number of these factors, but it is unknown which mechanisms are implicated in GH action on the process of atherosclerosis. In addition to alterations in atherosclerotic markers, abnormalities in cardiac function and structure have been reported among patients with GHD possibly contributing to the increased cardiovascular mortality. In addition, GHD is associated with cardiac autonomic dysfunction that may also contribute to cardiovascular mortality and improves with GH replacement therapy.
The vast majority of studies have focused primarily on men and the gender-specific effects of GH replacement on cardiovascular risk factors remain unknown. In addition to being of interest in terms of understanding the physiologic effects of GH therapy, there are important therapeutic implications regarding data in women. Cardiovascular disease is the leading cause of mortality in women. Effects of GH replacement on bone density may be less pronounced in women and because specific GH effects on cardiovascular risk factors in women are unknown, many adult women with GHD are untreated.
Long-term GH treatment decreases total body fat including visceral fat. Decreases in central fat as assessed by waist to hip ratio have been reported in some studies, but not in others. Administration of GH causes insulin resistance acutely but long-term therapy may restore glucose sensitivity. GH treatment increases lipoprotein (a) (Lp (a)) levels but its effects on other lipoproteins are still controversial. Some studies have reported decreases in LDL cholesterol with or without increases in HDL cholesterol with GH administration, while others have not. Twelve months of GH replacement improves left ventricular mass and cardiac performance in young adults with GHD. Key factors likely involved in the discrepant findings include heterogeneity of patients studied in terms of age of onset of the GH deficiency (childhood versus adulthood), gender, severity of GHD and methodologic issues such as dose and duration of GH administration. In addition, many of the studies have no control period.
Inflammation plays a central role in the pathophysiology of atherosclerosis. Each atherosclerotic lesion represents a different stage of a chronic inflammatory process in the arterial wall and different markers along the inflammatory cascade have been reported to predict cardiovascular risk \[34\]. Among those, high-sensitivity testing for C-reactive protein (CRP) is one of the best validated. Several prospective studies support a strong link between levels of CRP and future risk of coronary events. CRP adds considerable value to the total and HDL cholesterol measurement in the prediction of cardiovascular risk. Other distal indicators of inflammation such as serum-amyloid polypeptide A (SAA) likewise predict coronary risk. These distal markers reflect the consequences of elevated proinflammatory cytokines like interleukin-6 (IL-6). GH is known to have important immunomodulatory effects. We therefore hypothesized that the effects of GH on the process of atherosclerosis might be mediated through the cytokine-inflammatory pathway. We have recently investigated the effects of physiologic GH replacement in cardiovascular risk markers in men with GHD. In this study we found that CRP and IL-6 levels decreased in GH treated men compared to controls despite no significant change in serum lipid levels. We also recently have investigated levels of inflammatory markers in women with hypopituitarism compared with healthy controls. We found that women with hypopituitarism have increased levels of IL-6 and CRP suggesting that chronic inflammation may be involved in the pathogenesis of atherosclerosis in this population. It will be critical to determine whether physiologic GH replacement has beneficial effects in women, and whether these effects are influenced by estrogen.
We will investigate the effect of long-term physiologic GH administration on IL-6, CRP, SAA as well as other classic cardiovascular risk factors in women with GHD in a randomized, placebo-controlled study. In addition, we will evaluate structural/function correlates in women by measuring arterial wall distensibility and heart rate variability in parallel with cardiovascular risk markers.
We will establish the gender-specific effects of physiologic GH replacement on cardiovascular risk in women with GHD by investigating whether this therapy:
1. has gender-specific effects on cardiovascular risk markers
2. has gender-specific effects on lipid profiles
3. alters heart rate variability and arterial distensibility in parallel with changes in cardiovascular risk markers
4. has different effects depending upon gonadal status
