PHY3181 Lecture Notes - Lecture 4: Cervix, Semen, Antigen
30 Jun 2018
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Lecture 3: Male reproduction 2
The interstitial tissue is made up of the Leydig
cells; steroidogenesis, responsive to LH, 2-way
paracrine interactions with Sertoli cells. The
interstitial tissue is highly vascular, has well
developed lymphatics and loose connective
tissue and macrophages. The LH receptor is on
the Leydig cells.
Control of testicular steroidogenesis
Cholesterol from the blood vessels enters the
leydig cells. Other sources of cholesterol in the
leydig cells are acetate and cholesterol stores.
The cholesterol is converted to pregnenolone
testosterone.
• Can be converted to estrogen via
aromatase
• Can act in a paracrine manner to the
Sertoli
In the Sertoli testosterone can act to concert
ABP to ABPT which is released into the tubule
lumen. Or can be converted via 5alpha
reductase to form 5alpha-dihydrotestosterone
(5aDHT). It can also form estrogen – but this
contribution is minor.
Relationship between LH and testosterone
release from the leydig cells. LH responds to
GNRH pulses is released in a pulsatile
manner acts on the leydig cells
testosterone is made/ released in a pulsatile
manner. Note that the pulsatile activity of
testosterone levels differ between men.
Structure of steroid hormones
• Not contracted out of amino acids
• 4 ring structure typical of all steroids
• Hydrophobic (lipophilic)
• Synthesised by steroidogenic cells
• Synthesis via complex pathway with
cholesterol as a precursor
Common steroid hormones
• Androgens – testosterone, DHT
• Oestrogens – oestradiol, oestrone
• Progestogens – progesterone
• Corticosteroids – glucocorticoids,
mineralocorticoids (these are for
carbohydrate metabolism, stress and
blood pressure)
Processing of steroids
Less potent steroids can be converted to more
potent forms. Testosterone can be converted
to DHT (more potent) by 5alpha reductase.
Note that the type of enzyme present affects
the precursor being converted into androgens,
oestrogens or progestogens. Eg males have
very little aromatase. These enzymes regulate
the type of steroid found in tissue and its
potency. The steroidagenic pathway in males
and females is the same – the differences are
in the enzyme amounts.
Steroidogenesis in the male
• Testosterone estradiol (by
aromatase)
• Androstenedione estrone (by
aromatase)
Steroid hormone receptors
• Intracellular (steroids are lipophilic –
they can get through the extracellular
membrane)
• Often bound to other proteins eh heat
shock protein (bioavailability) – this
will allow receptor to see ligand or not
• Bind to response elements in
promoters of various genes
• Steroid molecules diffuse into cells and
bind to receptor
• Dimerise, phosphorylate and
translocate to the nucleus
• The activity of steroid hormones
occurs in the nucleus of the cell
Actions of testosterone
• Sexual behaviour
• Aggressive behaviour (reproductive
contexts)
• Negative feedback
• Sexual behaviour
