LUTEINIZING-HORMONE (LH)-RELEASING HORMONE IN 3RD VENTRICULAR CEREBROSPINAL-FLUID OF THE EWE - CORRELATION WITH LH PULSES AND THE LH SURGE

Morphological evidence suggests that LHRH may be secreted into cerebro spinal fluid (CSF), but only in the rhesus monkey has CSF LHRH been fo und to reflect changes occurring in the LHRH neuroendocrine system. Th is 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 thread ed through a stainless steel guide cannula previously implanted into t he third ventricle of an ovariectomized ewe, which enabled continuous CSF withdrawal on repeated occasions. The first experiment (n = 3) sho wed that peripheral LH concentrations were unaffected by CSF removal a t rates of 12, 30, 50, and 100 mu l/min, and the second (n = 4) establ ished that CSF LHRH secretion was pulsatile, with considerable variati on in pulse amplitude (6.3 +/- 1.8 pg/ml; range, 1.3-18.7 pg/ml). In t he 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 o ccurred simultaneously, CSF LHRH concentrations were greater than half -maximal levels for longer (11.0 +/- 0.6 h; P < 0.005) than LH concent rations (6.0 +/- 0.4 h). This is the first study in sheep to reveal th e presence of LHRH in CSF and show that it expresses dynamic and longe r term changes coincident with peripheral LH fluctuations. CSF LHRH an alysis also permits repeated sampling from individuals and, therefore, long term within individual comparisons.