[Free fatty acid responses to growth hormone (GH)-releasing factor and the GH-GH receptor axis]

The functional assessment of GH receptor has been previously performed by GH-induced somatomedin (SM) generation test. There is a specific GH receptor on adipocytes, and GH induces lipolysis with an increment of plasma free fatty acid (FFA). In this report, we examined GH and FFA responses to GRF loading tests and GH-binding protein, which reflects the tissue GH-receptor concentration, in 30 short children, and we evaluated the lipolysis mediated by GH and GH-receptor axis. Following GRF administration, there was a definite increase in plasma FFA levels, which mainly consisted of palmitic acid and oleic acid on HPLC analysis. In the group of GH high responders, peak GH levels more than 30 ng/ml, the increments of FFA were apparently more than those in the GH low responders, peak GH levels less than 30 ng/ml. There was a significant correlation between the integrated GH secretion and the integrated FFA net-increments. In the GH low responders, the integrated FFA net-increments significantly correlated with their serum GH-binding protein activities. The net increments of FFA were also correlated with basal SM-C levels. In a case of GH-resistant dwarfism, in which GH-binding protein activity was markedly reduced, the patient's GH secretion to GRF as high as 51 ng/ml did not induce any increment of FFA levels. These results suggest that FFA responses to GRF loading depend on the integrated GH secretion and tissue GH-receptor content. FFA measurements in GRF test samples may be a simple and useful method for the functional assessment of GH and GH-receptor axis.