Is changing hypothalamic activity important for control of ovulation?

Abstract

The activity of the hypothalamic gonadotrophin releasing hormone pulse generator in women with regular ovulatory and anovulatory menstrual cycles was assessed to see whether changes therein are important determinants of normal and impaired ovarian function. Endogenous gonadotrophin releasing hormone secretion was inferred by measurement of the pituitary luteinising hormone response by characterisation of pulsatile luteinising hormone release over eight hours on three occasions during the course of follicular development and once during the luteal stage of the same cycles.In 13 ovulatory cycles (serum progesterone concentration >25 nmol/l) confirmed by ovarian ultrasonography a pronounced variability in luteinising hormone pulse patterns among subjects was compatible with ovulation. In the luteal stage of ovulatory cycles the luteinising hormone interpeak interval (85 min, range 42-125) was significantly longer than that during the early follicular (64 min, 40-103), mid-follicular (62 min, 37-107), and late follicular (59 min, compared with the mid-follicular stage of the same cycles or when compared with the late follicular stage ofother cycles when no luteinising hormone surge was captured. Though mean luteinising hormone concentrations in luteinising hormone surge series (36 IU/l) were high, the amplitude of luteinising hormone pulses (165%) was only slightly greater than during non-surge late follicular stage studies (145%). Hence no change in hypothalamic gonadotrophin releasing hormone activity is required to generate the preovulatory discharge of luteinising hormone in man, which occurs as a result of the sensitising action of rising oestradiol concentrations on pituitary responsiveness to the same hypothalamic input signal.Luteinising hormone pulse frequency, peak amplitude, and mean serum luteinising hormone concentrations in seven anovulatory cycles (progesterone concentration <10 nmol/l) were not different from those at comparable stages of ovulatory cycles. These data suggest that the primary abnormality in this group of regularly menstruating anovulatory women lies in the ovary rather than in the hypothalamic control of the anterior pituitary.

Physiological Growth Hormone Secretion in Children with Short Stature and Intra-Uterine Growth Retardation

“…The problem of assessment is probably due to the method of pulse analysis. Clayton et al [ 12], when exam ining gonadotrophin pulsatility, commented that it is important that the results of a computerised pulse anal ysis 'look right' when compared to the plot of the raw data. The profiles of the children that we have described as 'fast frequency' appeared abnormal on visual inspec tion.…”

“…Our attempts to analyse the overnight GH profiles illustrated the difficulties in interpreting profiles of phys iological hormone secretion, a problem that has recently been discussed in relation to gonadotropin secretion [12], We used Pulsar, a widely used programme for pulse analysis, but, especially in those children with a fast-fre quency secretion pattern, more valuable information could be obtained by a simple visual inspection of the data.…”

Acute Effects of Progesterone and the Antiprogestin RU 486 on Gonadotropin Secretion in the Follicular Phase of the Menstrual Cycle*

“…Pulses of hormone secretion were detected using the peak detection method of Clayton et al (8). This computer algorithm considers both the preceding and subsequent nadirs in the definition of a pulse.…”

Luteinizing Hormone (LH) Secretory Burst Duration Is Independent from LH, Prolactin, or Gonadal Steroid Plasma Levels in Amenorrheic Women

“…R ECENTLY, LH pulsatile secretion has been extensively studied in both men and women (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). Several researchers have characterized the dynamic changes in LH episodic release during the different phases of the menstrual cycle (1,4,5,9).…”

“…(J Clin Endocrinol Metab 72: 1220-1225,1991 R ECENTLY, LH pulsatile secretion has been extensively studied in both men and women (1-11). Several researchers have characterized the dynamic changes in LH episodic release during the different phases of the menstrual cycle (1,4,5,9). Both the frequency and the amplitude of the pulses are related to changes in the sex steroid milieau during the menstrual cycle (5).…”