Oral administration of the growth hormone secretagogue NN703 in adult patients with growth hormone deficiency.

OBJECTIVE: Little is known of the usefulness of GH secretagogues (GHSs) in GH-deficient (GHD) adults. The objective of this study was to determine the number of responders to treatment with NN703 in GHD adults. DESIGN: A multicentre, randomized, double-blind, and placebo-controlled study. PATIENTS: Ninety-seven GHD adults were included. MEASUREMENTS: The GH response before and after 1 week of oral treatment with NN703 (n = 83) or placebo (n = 14) was determined. The first and last dose of NN703 was 3 mg/kg, whereas the dose of NN703 was 1.5 mg/kg/day during the 6 days between the first and last doses. Furthermore, all 97 patients received 1 micro g/kg GH-releasing hormone (GHRH) 3 weeks after the last dose of NN703. RESULTS: Serum GH peak and area under curve (AUC) values after the first NN703 administration were greater than those after placebo administration (P < 0.05). However, after correction for the lower body mass index (BMI) in the NN703 group, this difference lost statistical significance. After 1 week of therapy, GH peak and AUC values were similar following the final doses of NN703 and placebo. Serum peak and AUC values of other anterior pituitary hormones were similar between the NN703 and placebo groups both after the first and last administration of study drug. Nine of the 83 patients (11%) responded with a serum peak GH concentration >or= 5 micro g/l after the first and/or last NN703 administration, whereas no patient responded after placebo administration. Serum IGF-I was unaffected by 1-week NN703 treatment, whereas serum IGFBP-3 was increased (P < 0.05 vs. placebo) also after correction for BMI. Mean serum peak GH concentration after GHRH administration was 2.1 micro g/l (+/-0.3, SEM), which was higher than that after the first NN703 administration (1.32 +/- 0.3, P < 0.05). CONCLUSION: NN703 administration was generally well tolerated. Eleven per cent of the GHD adult patients responded with a peak GH response >or= 5 micro g/l after the first and/or last administration of oral NN703. Although a majority of GHD adults will not respond to NN703, the present results suggest that oral NN703 treatment could be useful in some adult patients with moderately severe GHD. These patients may be identified by a test dose of GHS.

Growth hormone - hormone replacement for the somatopause?

Twenty-four-hour growth hormone (GH) secretion reaches a peak at around puberty and by the age of 21 has begun to decrease. Thereafter the fall in GH secretion is progressive such that by the age of 60 most adults have total 24-hour secretion rates indistinguishable from those of hypopituitary patients with organic lesions in the pituitary gland. Patterns of GH secretion are similar to those in younger people but GH pulses are markedly reduced in amplitude. Sleep and exercise remain the major stimuli for GH secretion. The fall in GH secretion seen with ageing coincides with changes in body composition and lipid metabolism that are similar to those seen in adults with GH deficiency. In elderly subjects, although GH secretion is markedly reduced, remaining GH secretion correlates closely with body composition (particularly with lean body mass and inversely with central abdominal fat). Pioneering studies carried out by Rudman showed that GH administration to elderly subjects with low insulin-like growth factor-I levels resulted in reversal of many of the changes associated with GH deficiency, namely an increase in lean body mass and bone mineral density and a reduction in body fat and plasma cholesterol. These changes were remarkably similar to those shown a year earlier in adults with GH deficiency given GH replacement. Subsequent studies of GH replacement in elderly adults have confirmed Rudman's initial observations but have been dominated by side effects which have led to a high number of dropouts. It is now clear that the elderly are very sensitive to GH and the doses used need to be very low, increased very slowly and tailored to the individual needs of each patient. Using this more cautious approach, recent studies have been very positive. A series of papers from Blackman's group, presented at the US endocrine meeting in San Diego in 1999, investigated the effects of GH with or without testosterone supplements (in men) and oestrogen supplements (in women). Their results showed positive effects of GH on lean body mass, central fat, low-density lipoprotein cholesterol and aerobic capacity. In many instances there was a positive interaction between GH and hormone replacement with testosterone and oestrogen, but it appeared that GH showed the most potent anabolic effects. Clearly more studies are needed before GH replacement for the elderly becomes established. Safety issues will require close scrutiny, but the data available so far are sufficiently positive to undertake large multicentre, placebo-controlled trials, particularly looking at endpoints associated with prevention of frailty and loss of independence.

Is the somatopause an indication for growth hormone replacement?

In the normal population, a gradual and progressive fall in spontaneous growth hormone (GH) secretion occurs with increasing age and is reflected in a parallel fall in circulating insulin-like growth factor (IGF)-I, reduction in lean body mass, increase in body fat and rise in low-density lipoprotein (LDL) cholesterol. Aging is also associated with a progressive failure of body functions and particularly with an increasing lack of physical strength and mobility. Many problems of aging are attributable to the progressive loss of lean tissues and to catabolic events. This can be and often is associated with a progressive decline in independence and quality of life, leading eventually to a prolonged dependence on others, followed by a distressing process of death. By analogy with the fall in ovarian function that inevitably eventually occurs in women with increasing age, this fall in GH secretion has been termed the somatopause. In cross-sectional studies on elderly people, the amount of GH secreted spontaneously correlates well with "good risk factors" such as body composition, mobility, lipid profiles and blood pressure. The important question that these scientific facts raises is whether this fall in GH secretion with increasing years is an important physiological safety event of the normal aging process, or whether it marks the development of GH deficiency which would benefit from GH replacement. It is established that a number of the clinical features of the somatopause are shared with the syndrome of adult-onset GH deficiency and Rudman first proposed the importance of GH in maintaining health and vitality with increasing age many years ago. In 1989, GH replacement was shown to be beneficial in adults with GH deficiency, and in 1990 Rudman showed remarkably similar beneficial effects in a group of elderly men with low plasma IGF-I values, but no underlying pituitary pathology, who were administered GH. In these adults, low doses of GH increased lean body mass and bone mineral density, decreased body fat and lowered LDL cholesterol. Sleep and exercise are the two major stimuli for secretion of GH in normal people and there is evidence to indicate that the GH response to exercise is essential for developing and maintaining physical fitness. There is also some evidence to suggest that adults who continue to exercise with increasing age better maintain lean body mass and physiological GH secretion. So, is the somatopause due to lifestyle changes consequent upon indolence, too much TV and modern living? Is it better to chase our patients (and colleagues?) down to the gym three times a week or should we give them an injection of GH before they sit down with a can of lager to watch the World Cup? Should the fact that elite athletes in virtually all sports have decided from their own "clinical trials" that GH is a performance-enhancing drug, when combined with exercise, have any influence on our strategy? The long-term safety of GH replacement is clearly a matter for concern but we do now know that life without GH is poor both in quantity and quality. Is there a safe therapeutic window that allows GH replacement in the somatopause to add years to life, quality to these years, and maybe even improves the quality of death?