Luteinizing hormone (LH)-releasing hormone in third ventricular cerebrospinal fluid of the ewe: correlation with LH pulses and the LH surge.

Morphological evidence suggests that LHRH may be secreted into cerebrospinal fluid (CSF), but only in the rhesus monkey has CSF LHRH been found to reflect changes occurring in the LHRH neuroendocrine system. This study investigated whether LHRH is detectable in ovine CSF and, if so, whether its release profile correlates with peripheral LH profiles during pulse and surge conditions. A polyethylene catheter was threaded through a stainless steel guide cannula previously implanted into the third ventricle of an ovariectomized ewe, which enabled continuous CSF withdrawal on repeated occasions. The first experiment (n = 3) showed that peripheral LH concentrations were unaffected by CSF removal at rates of 12, 30, 50, and 100 microliters/min, and the second (n = 4) established that CSF LHRH secretion was pulsatile, with considerable variation in pulse amplitude (6.3 +/- 1.8 pg/ml; range, 1.3-18.7 pg/ml). In the third experiment (n = 6), an endogenous LH surge was induced after progesterone withdrawal and 17 beta-estradiol administration. Although CSF LHRH (15.3 +/- 1.3 h) and peripheral LH (14.8 +/- 1.0 h) surges occurred simultaneously, CSF LHRH concentrations were greater than half-maximal levels for longer (11.0 +/- 0.6 h; P < 0.005) than LH concentrations (6.0 +/- 0.4 h). This is the first study in sheep to reveal the presence of LHRH in CSF and show that it expresses dynamic and longer term changes coincident with peripheral LH fluctuations. CSF LHRH analysis also permits repeated sampling from individuals and, therefore, long term within-individual comparisons.