Impermeability of the Rat Blood-Brain Barrier to Exogenously Administered Gonadotropin-Releasing Hormone

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Abstract
To assess the permeability of the blood-brain barrier (BBB) to exogenously administered gonadotropin-releasing hormone (GnRH), a study was performed in male rats using the double isotope, intracarotid, single injection technique of Oldendrof. The mean (.+-. SEM [standard error of the mean]) brain uptake indices (BUI) of 3H-GnRH in comparison to a freely diffusible reference compound, 14C-butanol, were 1.1 .+-. 0.2, 3.5 .+-. 0.7 and 3.0 .+-. 0.6 when the injection vehicles were Ringer''s lactate, rat serum and human serum, respectively. The BUI of 3H-GnRH was similar to that of 3H-inulin, a nondiffusible compound. With different concentrations, the BUI of 3H-GnRH did not change significantly. The BBB of the male rat is impermeable to exogenously administered GnRH.