Ultrasensitive new immunoassays for gonadotropins in the evaluation of puberty.

The increased sensitivity and specificity of new immunometric gonadotropin assays make them particularly useful to study the ontogenesis of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion in normal and abnormal puberty. The results show that the gonadotropin-releasing hormone pulse generator is functionally active even in prepubertal children with selective occurrence of LH and FSH pulses after the onset of sleep. The onset of puberty is associated with a major increase in pulse amplitude and a small increase in pulse frequency, expressed as a progressive increase in day-time pulsatility, and a gradual reduction of sleep-entrained amplification. Daytime gonadotropin measurements may better distinguish pubertal stages than nighttime sampling because of less overlapping. As the changes are greater with the sensitive assays, the diagnosis of pubertal disturbances is improved. It is easier to differentiate constitutionally delayed puberty and hypogonadotropic hypogonadism, but biologically overlapping phenomena cannot be separated by even sensitive assays. The augmentation of LH secretion after onset of sleep might be missing in hypogonadotropic hypogonadism and is proposed as a new, somewhat complicated, diagnostic approach. As serum concentrations of FSH in prepubertal children are much higher than those of LH, the measurement of FSH in this age group is particularly useful, and lower-than-normal levels can be found in gonadotropin-releasing hormone-independent precocious puberty as well as in pituitary defects.