Impaired growth hormone response to growth hormone releasing factor and insulin-hypoglycaemia in obesity

We have previously reported an impaired growth hormone (GH) response and abnormal prolactin release to insulin-hypoglycaemia in obesity. We suggested that obese women with an absent prolactin response to hypoglycaemia ('non-responders') have a disorder of hypothalamic function. We have now investigated the GH response to i.v. growth hormone releasing factor, GHRF (1-29)NH2, in 14 obese women and nine age-matched normal-weight women. We found a significantly reduced GH response to GHRF in the obese women as compared with controls (mean peak +/- SEM: obese 8.9 +/- 2 mu/l, controls 28 +/- 2 mu/l; P less than 0.01). When the obese women were divided on the basis of their prolactin response to insulin-hypoglycaemia (seven 'non-responders', mean weight 102 +/- 5 kg; seven responders, mean weight 108 +/- 8 kg) a similar GH response to GHRF was found between the two groups but the GH response to hypoglycaemia was significantly less in the 'non-responder' women (mean peak 'non-responders' 10.5 +/- 3 mu/l, responders 27 +/- 4 mu/l; P less than 0.05). We conclude that obesity may be characterized by an impaired GH response to both i.v. GHRF and insulin-hypoglycaemia, which suggests altered hypothalamic-pituitary function. The finding that the GH response to hypoglycaemia is significantly less in the obese prolactin 'non-responder' women supports the hypothesis for a hypothalamic disorder.