LHRH or hypothalamic gonadotropin (GNRH), is a hormone secreted in neuroendocrine cells or neurons of the hypothalamus, it is a peptide of 10 amino acids that is released in a pulsatile manner, regulated by kisspeptins which are in turn regulated by sex hormones.
It allows to appreciate the pituitary reserve in gonadotropins. After intravenous injection of 100 μg of LH-RH, variations in plasma FSH and LH are studied at baseline and at 30 ‘, 60, 90, t and 120.
An answer is positive if the baseline FSH level is multiplied by 1.5 to 2 and the LH level by 3 to 4.
It is required to know the interpretation of the basic doses, the principle of the tests, their usefulness and their interpretation. Figures are given for guidance only.
Pituitary secretions are part of a whole: they are subject to the action of the hypothalamus, whose neuro-secretory system directs its activity (hypothalamic releasing hormone, R.H = releasing hormone).
Base rates vary by gender and age: (before puberty, adulthood, menopause) and the progress of the menstrual cycle.
The value of the gonadotropic hormones should always be compared with the corresponding values of the target hormones (estradiol, progesterone, testosterone).
When the level is very high and the corresponding steroids are low, the measurement of the basal level of FSH and LH allows to identify a deficit in the target glands (gonadal dysgenesis, early menopause).
This test is used in the evaluation of early or late onset puberty. The timing of puberty is controlled by the pituitary gland located just below the base of the brain behind the bridge of the nose. It is very small, about the size of a pea.
LHRH can be substituted for an analog such as decapeptyl (triptorelin) 1mg x mt2 (+ -0.6 ml) and a new measurement at 3 or 4 hours, the expected normal values are FSH> 3mU / ml and LH> 10 mU / ml.
The next day in the morning, testosterone> 7ng / ml will be measured in men and estradiol> 100 pg / ml in women, if the hypothalamic-pituitary-gonadal axis is intact.
Low levels of estradiol in women or testosterone in men in the presence of non-elevated gonadotropins (normal or low) are indicative of gonadotropic failure.
However, testosterone levels can fluctuate and several measurements are sometimes needed to diagnose gonadotropic insufficiency. The GnRH test can assess the partial or complete nature of this insufficiency.
The answer varies by age: before puberty in boys, the increase is very limited for both gonadotropins.
In girls an LH response is observed that does not appear until puberty. In regulated women, the FSH response is weak in the follicular phase and that of LH is very marked during the immediate ovulatory period (peak of 80 to 100 mU / ml), it is reduced in the post-ovulatory period.
High basal rate and very strong response without overlap with normal subjects in cases of ovarian dysgenesis (Turner syndrome).
Low basal rate and very poor LH-RH response in pituitary insufficiency (Sheehan’s S.), or even hypothalamic insufficiency.
An almost normal response: can be seen with hypothalamic or pituitary disease of moderate intensity, psychogenic amenorrhea, anorexia nervosa.
A dissociated response: with a more marked LH response can be seen in polycystic ovaries.
These stimulus tests are used to differentiate a central precocious puberty from a thelarche or peripheral pubarche and are also essential to establish the indemnity of the pituitary in cases of hypogonadism of central origin (decreased LH and FSH).
-Sultan C, Gaspari L, Maimoun L, Kalfa N, Paris F. Disorders of puberty. Best Pract Res Clin Obstet Gynaecol. 2018 Apr;48:62-89.
– Lee PA. Central precocious puberty. An overview of diagnosis, treatment, and outcome. Endocrinol Metab Clin North Am. 1999 Dec; 28(4):901-918. PubMed 10609126
keywords: LHRH stimulation, LHRH stimulation, decapeptyl stimulation, precocious puberty, precocious puberty, telarche, puberty, gonadal dysgenesis, kisspeptin and gonadotropins, central hypogonadism, secondary hypogonadism, decreased LH and FSH, pituitary insufficiency, hypothalamic insufficiency.