Inter-relationship between changing patterns of LHRH and gonadotrophins in the menstrual cycle.

Optimum conditions for a sensitive and highly precise radioimmunoassay of LHRH were established. Precipitation and removal of interfering substances and concentration of the resultant LHRH extracts from peripheral plasma were also achieved. Using these methods, daily plasma LHRH levels in females with normal menstrual cycles were measured and correlated with the corresponding LH and FSH levels. The levels of LHRH in the peripheral plasma of postmenopausal females, as well as eugonadal males, were also determined. The LHRH profile in normal cycling women was found to be cyclic but the peak LHRH levels were observed at the beginning of the rise in LH and FSH levels and preceded the midcycle surge of gonadotrophins. The LHRH levels in the luteal phase (19.8 +/- 1.1 pg/ml, mean +/- SEM) were significantly (P less than 0.01) higher than those in the follicular phase (16.5 +/- 0.5 pg/ml) of the menstrual cycle. A high degree of correlation (r = 0.91) was seen between the immunoreactivity and biological activity of the extracted LHRH.