A microdialysis system was used to monitor LH-RH patterns in the extracellular fluid of the adenohypophysis of testes-intact and short-term castrate rats. Male rats received guide cannulae implants fitted with stylets that extended into the anterior pole of the anterior pituitary gland. At the same time, animals were either castrated or received sham surgeries. On day 4 following surgeries, microdialysis probes were inserted into the guide cannulae and artificial CSF was pumped through the system at a flow rate of 2.5 microliters/min. Continuous samples were obtained from each animal over 5- or 10-min intervals throughout 4-7 sessions. Placements of probe tips were verified by histological examination of stained tissue sections. In vitro tests of microdialysis probe performance revealed an exchange rate of 4% at the 2.5 microliters/min flow rate. In vivo patterns of LH-RH in microdialysates obtained from sham-operated and castrate rats were pulsatile, as determined by the computer algorithm ULTRA. Pulses of LH-RH occurred at a higher frequency (P less than 0.05) in the castrates (1.30 +/- 0.26 pulses/h, n = 6) versus the sham-castrates (0.87 +/- 0.06 pulses/h, n = 11). Mean LH-RH pulse amplitude (castrates delta 0.24 +/- 0.03 pg, testes-intact delta 0.42 +/- 0.06 pg) and mean LH-RH levels (castrate 0.37 +/- 0.04 pg/10 min, intact 0.48 +/- 0.06 pg/10 min), however, were not significantly changed by castration (delta = difference between trough and peak LH-RH value of an LH-RH pulse).(ABSTRACT TRUNCATED AT 250 WORDS)