The effects of human leptin fragment(126-140) on pituitary functions in man

Hanew Endocrine Clinic, Sendai 980-0824, and Division of Nephrology, Endocrinology, and Vascular Medicine, Department of Medicine, Tohoku University School of Medicine, Sendai 980-8574, Japan. hanew-endo-clinic@juno.ocn.ne.jp

OBJECTIVE: The effects of human leptin fragment(126-140) on pituitary function in eight healthy, non-obese men were studied. METHODS AND DESIGN: The effects of the fragment on spontaneous secretion of pituitary hormones and endogenous leptin, as well as on GHRH-induced GH secretion were examined. RESULTS: After the administration of the fragment (50 microg i.v. for 150 min), the mean nadir value and 45 min value were significantly lower than that of the control study. Endogenous leptin levels did not decrease significantly following the administration of the leptin fragment. Other pituitary hormones were not affected by the fragment. The area under the curve of the GH response to GHRH(1-44)NH(2) (10 microg, i.v. from 0 to 75 min) was also significantly inhibited by the combined administration of the leptin fragment (100 microg i.v. from -30 to 75 min) (P<0.001). Three subjects were re-examined with larger doses of the leptin fragment (200-400 microg), and even greater GH suppression was observed. CONCLUSIONS: These results indicate that human leptin fragment(126-140) has an inhibitory role in GH secretion, since when administered exogenously this fragment significantly suppressed spontaneous and, in a dose-response manner, GHRH-induced GH secretion. Clear effects of the fragment on other pituitary hormones and an inhibitory effect on endogenous leptin secretion were not observed in this study.