Failure to detect luteinizing hormone-releasing hormone in third ventricle cerebral spinal fluid under a variety of experimental conditions

Abstract

Cerebral spinal fluid (CSF) was examined for the presence of luteinizing hormone-releasing hormone (LH-RH) at times when copious amounts of LH were being secreted by the adenohypophysis. A "push-pull" apparatus was designed which permitted the perfusion of artificial CSF through the 3rd ventricle from the region of the medial preoptic area (MPOA) to the site of recollection adjacent to the median eminence (ME). It was observed on radioimmunoassay that LH-RH concentrations were low in CSF and peripheral plasma of Nembutal-blocked proestrous rats. Intraarterial injections of LH-RH did not increase CSF concentrations of this decapeptide, although a significant release of pituitary LH occurred. Further, electrochemical stimulation of the MPOA also elevated plasma LH without altering CSF-LH-RH levels. When synthetic LH-RH, dissolved in artificial CSF, was perfused through the 3rd ventricle, plasma LH levels rose dramatically, and a significant decrease in the concentration of LH-RH in the CSF efflux was observed on collection and assay. CSF collected from MPOA-stimulated rats also was tested for biologically active LH-RH by its reinjection into Nembutal-blocked proestrous recipients. While such injections failed to induce pituitary LH release, it was observed that LH-RH, when mixed with artificial CSF, and allowed to stand at room temperature (24 C), also lost all biological potency even though immunoreactivity was retained. The results suggest that CSF does not serve as a vehicle for transport of LH-RH to the median eminence under physiological conditions.