Simultaneous Measurement of Luteinizing Hormone-Releasing Hormone and Luteinizing Hormone Release in Unanesthetized, Ovariectomized Sheep*

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Abstract
The push-pull perfusion technique was used in combination with a sequential bleeding schedule to estimate simultaneously the release patterns of LHRH and LH in unanesthetized oviuriectomized sheep and to determine the temporal relationship between the release of these two hormones. Ovariectomized (>30 days) ewes received unilateral push-pull cannula (PPC) implants (od, 0.85 mm) into the median eminence. After at least 6 days of recovery, each ewe was fitted with an indwelling jugular catheter. For push-pull perfusion, a stylette was removed from the outer PPC, and an inner cannula assembly (od, 0.40 mm) was inserted. Artificial cerebrospinal fluid was pushed through the inner cannula and pulled up between the cannulae at 20 μl/min. Continuous 10-min perfusate fractions were collected, acidified, and stored at -20 C for LHRH RIA. Blood samples were obtained every 10 min via the jugular catheter, each being drawn 5 min after the start of a perfusate collection interval. Plasma LH levels were determined by RIA. The duration of the sampling was 3–7 h. LHRH output was distinctly pulsatile, occurring at a frequency of approximately one pulse every 30–40 min (n – 5 sheep). LHRH pulse amplitude and frequency remained relatively constant throughout each perfusion. Plasma LH values also were pulsatile, and all LH peaks occurred either during the same interval or during the interval after a LHRH pulse. LH pulses always were accompanied or directly preceded by LHRH pulses, but LHRH pulses were not always followed by LH pulses. The amplitudes of LH pulses and corresponding LHRH pulses were highly correlated (r = 0.81; P < 0.01). Histological examination revealed that detection of LHRH in perfusates depended upon the placement of the PPC tip into either the zona externa of the central median eminence or adjacent areas. These experiments demonstrate that 1) hypothalamic LHRH release in the Ovx ewe occurs in discrete pulses, with a mean interpulse interval of 38.7 ± 1.5 min, 2) LH pulses invariably are preceded or accompanied by LHRH pulses, and 3) LH pulse amplitude is highly correlated with LHRH pulse amplitude.

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