Relationships between short-term variations of LH, FSH, prolactin and testosterone in peripheral plasma of prepubertal bulls.

In 2 prepubertal bulls 10-min blood samples collected during a 24-h period showed that gonadotrophin and testosterone peaks occurred regularly at intervals of 6h in one animal and 8h in the other. There was a clear relationship between the LH, FSH and testosterone peaks. The increase of gonadotrophin levels was followed 20 +/- 6 (s.d.) min later by an increase of testosterone; the interval between the peak values was 61 +/- 9 (s.d.) min. The pattern of prolactin concentration differed; there were two prolonged elevations rather than regular peaks.