Release of lh by lrf injected into the CSF: A transport role for the median eminence

At time zero, 0.15M NaCl (2 μl) was injected into the third ventricle of anesthetized male rats. LH release was unaffected by such treatment as judged by the constancy of the concentration of this hormone in the plasma of these rats during the succeeding 2 hr. In contrast to 0.15M NaCl, synthetic LRF (1, 10, or 100 ng in 2 μl 0.1 5M NaCl) when injected into the third ventricle, caused significant increases in the plasma concentration of LH indicating increased LH release. The increased release was evident 10 min after the injection of LRF. One or 10 ng LRF injected into the cisterna magna had no effect on LH release during the first hour after the injection. However, 90 and 120 min after 10 ng LRF was administered via the cisterna magna, the plasma LH level rose slightly. When 100 ng LRF was given by way of the cisterna magna, LH release was stimulated markedly. However, the interval between the time of injection of LRF into the cisterna magna and the release of LH was prolonged when compared to that seen in animals given 100 ng LRF via the third ventricle. The results are consistent with the interpretation that LRF in the CSF of the third ventricle reaches the hypophysial portal vasculature by direct passage across the median eminence. In contrast, LRF in the CSF of the cisterna magna reaches the hypophysial portal vasculature via arterial blood; hence, the response is delayed. The results suggest that the median eminence transports substances, e.g., hypophysiotropic agents, from the CSF in the third ventricle to hypophysial portal blood.