Variations in peripheral levels of LH and testosterone in adult male rabbits.

Seasonal, diurnal and episodic patterns of LH and tests-sterone secretion in sexually mature male New Zealand rabbits were studied. Blood samples were obtained from the central ear artery by puncture or through an indwelling catheter, and were assayed for hormones using radioimmunoassay. Testosterone values appeared to be lower in the summer months while LH showed no seasonal cyclicity. There were no significant fluctuations when samples were taken at 10-min intervals, but specimens taken every hour for 24 or 36 hr revealed an episodic pattern of release. Peaks of both hormones occurred every 4 to 5 hr in most animals. Testosterone levels ranged from 0.5 to 10 ng/ml and LH from 15 to 200 ng/ml of WP360A standard. In general, a rise in LH preceded or coincided with an increase in testosterone. No specific diurnal rhythm could be demonstrated and the patterns appeared to be unrelated to external stimuli.