1991 Volume 38 Issue 1 Pages 15-21
The effects of intranasal and iv administration of His-D-Trp-Ala-Trp-D-Phe-Lys NH2 (GHRP) on plasma GH, PRL, LH, FSH, TSH, cortisol, insulin, IGF-I as well as GHRH-like immunoreactivity (LI) levels were examined in 6 healthy male subjects. An iv bolus injection of GHRP (lμg/kg BW) caused a remarkable increase in plasma GH levels with a mean (±SE) peak of 54.9±4.2μg/L. In addition an intranasal administration of GHRP resulted in a significant, dose-related increase in plasma GH with peaks of 39.6±15.3μg/L at a dose of 30μg/kg BW, 14.1±5.0μg/L at 15μEg/kg BW and 7.5±5.7μg/L at 5μg/kg BW. Plasma PRL and cortisol levels were slightly but significantly increased after iv administration of GHRP, whereas GHRP totally failed to affect plasma TSH, LH, FSH, insulin, blood sugar and GHRH-LI levels. Seven consecutive, intranasal administrations of 15μg/kg BW GHRP every 8h were well tolerated in all subjects examined. During this treatment, GH responsiveness to GHRP was not attenuated by desensitization and plasma IGF-I was increased from 94.5±5.8μg/L before GHRP to 125.8±6.0μg/L after repeated GHRP administration.
These findings indicate that intranasal administration of GHRP stimulates GH secretion and consequently enhances IGF-I production in normal subjects. If GHRP is demonstrated to be beneficial in the treatment of some patients with GH deficiency, the intranasal route of administration may be more useful than the painful injections because a prolonged period is required for the treatment.