The effects of submaximal endurance exercise upon LH pulsatility.
The acute effects of submaximal endurance exercise (three consecutive 20-min runs on a treadmill at 50, 60 and 70% of the subjects' maximum oxygen uptake) upon the pulsatile release of LH were compared with those accompanying leisurely strolling for a similar period in seven normally menstruating young women. All trials were conducted during the early to mid-luteal phase, as determined by body temperature patterns, ultrasonic scans of the ovaries, detection of the LH surge in first morning urine specimens, and serial measurements of plasma progesterone. Blood was sampled every 10 min via an indwelling cannula for 8 h before and 12 h after exercise and serum LH measured by radioimmunoassay. LH pulsations were analysed by a time series method. Following cannulation, mean LH levels declined but then rose to reach a maximum 2 h before the beginning of the exercise bout. LH concentrations remained virtually unchanged during exercise itself, and exhibited a declining trend throughout the post-exercise period. The findings in the two groups were similar in all respects, except that in the control study the rate of LH pulsatility was significantly diminished (P less than 0.05) during the first 2 h of sampling as compared with the subsequent 2-h period. The approximate half-life of LH varied from 27 to 57 min, with a mean of 41 min.