Objective:We investigated whether GnRH has the properties of a growth hormone-releasing factor in vivo in a mammalian species.
Methods:Sexually mature female Sprague-Dawley rats were prepared for in vivo dynamic hormone testing. The rats were assigned to one of four groups: I) GnRH, II) apomorphine and GnRH, III) somatostatin and GnRH, or IV) saline control. Blood samples were drawn at 0, 30, 60, 90, and 120 minutes after treatment. Growth hormone (GH) and LH were measured by radioimmunoassay. Results were analyzed using repeated-measures analysis of variance, Student t test, and comparisons of the area under the curve where appropriate.
Results:Gonadotropin-releasing hormone caused a marked rise in both GH and LH levels as a function of time. Apomorphine caused a significant blunting of the LH response to GnRH but did not blunt 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 controls, neither the GH nor LH levels exhibited a statistically significant variance over the 2-hour test period.
Conclusions:Gonadotropin-releasing hormone appears to have the properties of a growth hormone-releasing factor.
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