Abnormalities of the hypothalamo‐pituitary‐gonadal axis after head injury

OBJECTIVE We aimed to investigate the mechanisms of hypogonadism which develops after head Injury. DESIGN Pulsatile secretion of LH was studied in subjects 6–10 days after major head Injury. PATIENTS We studied five male subjects admitted with major head injuries and six healthy age-matched control subjects. MEASUREMENTS During the pulsatility study, LH was measured at 5-minute intervals for 4 hours and 15-minute intervals for a further 2 hours. In addition, testosterone and LH were measured on Days 1–5, 14 and after 3–6 months. RESULTS The analysis of pulsatile secretion of LH demonstrated an LH pulse frequency similar to control subjects, but a significantly reduced LH pulse amplitude (P < 0.001, fixed threshold method; P<0.02, Detect method). Both testosterone and LH levels were reduced after injury with the nadir occurring on Day 4. CONCLUSIONS Hypogonadism after head Injury is due to defective LH secretion, with normal pulse frequency but a reduced pulse amplitude.