Repetitive growth hormone-releasing hormone administration restores the attenuated growth hormone (GH) response to GH-releasing hormone testing in normal aging.

The plasma GH response to human pituitary GH (hpGH)-releasing hormone-40 (hpGHRH-40; 1 microgram/kg BW) was significantly lower in seven healthy aged men (age range, 65-78 yr) than in seven healthy young men (age range, 18-31 yr) 30, 60, and 90 min after acute hpGHRH-40 administration (P less than 0.0001, by Student's unpaired t test). To verify whether a priming regimen might be able to reverse the reduced GH response to GHRH, elderly subjects underwent repetitive administration of hpGHRH-40 and placebo in a double blind design (100 micrograms hpGHRH-40 or volume-matched saline iv as a single morning dose, every 2 days for 12 days). After the hpGHRH-40-priming regimen, plasma GH values 30, 60, and 90 min after the acute GHRH test were significantly higher than values at the corresponding time points after placebo treatment. These findings suggest that somatotroph cells become less sensitive to GHRH with normal aging and demonstrate that repetitive administration of GHRH restores the attenuated response.