Neural Control of Growth Hormone Secretion in Aged Humans

It is widely accepted that growth hormone (GH) secretion undergoes an age-related decrease in both animals and humans (Dieguez et al. 1988 Muller and Nistico 1989). Twenty-four-hour integrated GH concentrations have been shown to be lower in older versus younger subjects (Zadik et al. 1985). More recently, the study of the 24-h GH profile with frequent sampling techniques demonstrated that both day-time and night-time mean pulse amplitude and duration but not pulse frequency are reduced in aged humans (Vermeulen 1987; Van Coervorden et al. 1991). On the contrary, other authors (Iranmanesh et al. 1991) found significant reductions in GH secretory burst frequency and half-life but not in GH secretory burst half duration, amplitude or mass. Interestingly, though both slow wave sleep and nocturnal GH secretion are drastically reduced in the elderly, the small GH rises during sleep are nevertheless temporally related to slow wave stages (Van Coervorden et al. 1991).