PRELIMINARY EVIDENCE THAT GNRH HAS THE PROPERTIES OF A GROWTH HORMONE-RELEASING FACTOR IN-VIVO IN THE RAT

OBJECTIVE: We investigated whether GnRH has the properties of a growth hormone-releasing factor in vivo in a mammalian species. METHODS: Sex ually mature female Sprague-Dawley rats weve prepared for in vivo dyna mic hormone testing. The vats were assigned to one of four groups: I) GnRH, II) apomorphine and GnRH, III) somatostatin and GnRH, or IV) sal ine control. Blood samples were drawn at 0, 30, 60, 90, and 120 minute s after treatment. Growth hormone (GH) and LH were measured by radioim munoassay. Results weve analyzed using repeated-measures analysis of v ariance, Student t test, and comparisons of the area under the curve w here appropriate. RESULTS: Gonadotropin-releasing hormone caused a mar ked rise in both GH and LH levels as a function of time. Apomorphine c aused a significant blunting of the LH response to GnRH but did not bl unt the GnRH-induced rise in GH. Somatostatin blocked the GnRH-induced rise in GH but did not block the increase in LH. In saline-treated co ntrols, neither the GH nor LH levels exhibited a statistically signifi cant variance over the 2-hour test period. CONCLUSIONS: Gonadotropin-r eleasing hormone appears to have the properties of a growth harmone-re leasing factor.