Effect of aging on human plasma growth hormone response to clonidine

The effect of the oral administration of 0.150 mg/m2 clonidine on the plasma level of human growth hormone (hGH) was studied in 53 adults (25 males and 28 females) aged from 28 to 68 years, of which 15 were healthy volunteers and 38 were hypertensive. Both the normal and hypertensive subjects of both sexes showed an age-related responsiveness of hGH to clonidine, with a normal or partial response in the younger subjects and blunting or lack of response in the more elderly subjects. In the females the blunting of the hGH response appeared at an earlier age than in the males. It is speculated that an alteration in the sensitivity of the central alpha-adrenergic receptors and a decrease in the sex steroid hormones may account for the progressive reduction in hGH secretion with advancing age.