Androgen negative feedback on LH and FSH in males
In males, rising androgens (male sex hormones) lower their own production by negative feedback, mainly by inhibiting luteinising hormone (LH), a hormone from the anterior pituitary gland.
Remember
Testosterone, made by the Leydig cells of the testes, feeds back mainly on gonadotrophin-releasing hormone (GnRH, which the hypothalamus releases to drive the release of LH and follicle-stimulating hormone, FSH) and on LH. Inhibin, a hormone made by the Sertoli cells (the cells that support developing sperm), is the main brake on FSH.
Memory aid
each testicular cell brakes its own driver, so Leydig cell testosterone brakes LH and Sertoli cell inhibin brakes FSH
Leydig cells go with LH and Sertoli cells with FSH, because each cell's product mainly brakes that same driver.
In a man, the testes are controlled by the hypothalamic-pituitary-gonadal axis, the chain of command running from the hypothalamus (the part of the brain just above the pituitary) to the anterior pituitary (the front part of the pituitary gland) and on to the testes. The hypothalamus releases GnRH, which makes the anterior pituitary release two gonadotrophins (hormones that act on the testes), LH and FSH. LH acts on the Leydig cells to make testosterone, an androgen. FSH acts on the Sertoli cells, the supporting cells of the seminiferous tubules (the coiled tubes where sperm are made).
The loop runs on negative feedback: the product of a pathway turns down the signal that drives it. When testosterone reaches a threshold, it binds androgen receptors in the hypothalamus and the anterior pituitary, which inhibits the release of GnRH and LH. Because LH acts on the Leydig cells to make testosterone, lowering LH stops hormone production becoming excessive.
The brake turns gonadotrophin output down, but it does not switch it off. LH and FSH are still needed for testosterone and sperm production, so a steady, lowered output is expected.
FSH has its own main brake, inhibin, a hormone made by the Sertoli cells. Testosterone also reduces FSH secretion, partly through conversion to oestradiol (a form of oestrogen that the body makes from testosterone), a step called aromatisation. In men given testosterone replacement, both FSH and LH levels fell.
Key facts
- Feedback direction
- androgen feedback is negative, not positive.
- Where testosterone acts
- it binds androgen receptors in the hypothalamus and the anterior pituitary, inhibiting the release of GnRH and LH.
- Main brake on FSH
- inhibin from the Sertoli cells, with testosterone also lowering FSH, partly through conversion to oestradiol.
- Not complete suppression
- negative feedback turns gonadotrophin output down, but it does not switch it off.
- Other pituitary hormones
- prolactin (linked with lactation) is held down mainly by dopamine, and ACTH (adrenocorticotrophic hormone, the pituitary signal to the adrenal glands) by cortisol, so neither is switched off by androgens.
Exam traps
- LH stimulates the testes to make androgens, yet rising androgens do not stimulate LH release, because they restrain GnRH and LH.
- Androgen feedback does not bring about complete suppression of LH and FSH, because both are still needed for testosterone and sperm production.
- Selective inhibition of FSH is the role of inhibin from the Sertoli cells; androgen feedback acts mainly on GnRH and LH, and also lowers FSH, partly through conversion to oestradiol.
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