The female rat as a model describing patterns of pulsatile LH secretion during puberty and their control by melatonin

A characteristic of the advent of final stages of sexual maturation in the rat, the equivalent of puberty in the human, is the development of a specific pattern of pulsatile GnRH secretion, reflected by an equivalent pattern of LH secretion. Many hypotheses have been put forward to explain these last changes, including a change at the hypothalamic level and a modification of the ovary. These models are developed to include melatonin, an indoleamine produced by the pineal gland, which appears to play a role in the establishment of the final pattern of LH secretion, thus affecting both vaginal opening and subsequent estrous cycles. Prior to first ovulation, pulsatile release of LH acquires at least two types of patterns, one with low-amplitude, high-frequency pulses, announcing a pattern observed in the follicular phase of primates, and one with high-amplitude, low-frequency pulses, mimicking what is seen in the luteal phase of primates. From the results presented, it is postulated that chronic melatonin administration increases the number of patterns typical of luteal phases, and reduces those of the follicular type, resulting in a decrease frequency of LH pulses and longer intervals between estrous cycles.