Increased GH response to GHRH in normal tall men

The importance of growth hormone secretion to the growth of an individual raises the question of the role that the secretory capacity of this hormone may play in defining the variations of height within the population. To investigate this problem we studied the response of GH to GHRH in 20 normal tall (mean +/- SD height 190.8 +/- 2.4 cm, range 187-196 cm) adult males of the third decade and in 17 age-matched controls of average height (mean +/- SD height 173.8 +/- 1.6 cm, range 171-177 cm). Synthetic GHRH (1-29) NH2 (Kabi, Vitrum, Sweden) was administered at 0800 h after an overnight fast and blood was drawn for GH assay. In the tall subjects basal GH concentrations at -15 and 0 min were not significantly different from those of the controls. However, the tendency to higher basal GH levels and spontaneous peaks was evident in tall individuals. Only three basal GH values were below 1 micrograms/l (0.8-0.9 micrograms/l; 1 microgram/l = 2mU/l) in the tall individuals while 24 of 33 basal GH values in the controls ranged between 0.25 and 0.87 micrograms/l. At +15 and +30 min after GHRH the rise in GH was significantly greater in the tall subjects. Moreover, the integrated area under the response curves was significantly greater in the tall subjects than the controls (P less than 0.01). No differences in the mean serum testosterone and prolactin levels were found in the two groups. It is postulated that if this enhanced pituitary responsiveness is constant and chronic in tall individuals a definite relation of their stature to the GH secretion is to be anticipated.