Download Energy Metabolism of spermatozoa

6th lect. 2nd semester
Male Fertility and AI
dr. Abbas F. Daham
Energy Metabolism of spermatozoa
Energy metabolism is the means by which spermatozoa convert energy
substrates in to usable forms of energy . Enzymes for this conversion are
in the mitochondrial sheath .
The principal energy substrates in semen are ;fructose(simple sugar)
,sorbitol(sugar alcohol) and Glycerylphosphorylcholine(GPC).
Notes 1-fructose and sorbitol are produced by seminal vesicle while GPC
is produced by in the epididymis .
2-Fructose can be used by spermatozoa as an energy substrate under the
anaerobic (oxygenless) conditions of storage and the aerobic
(oxygenated) conditions found in the female tract , while sorbitol and
GPC can be utilized only aerobically .
3-GPC must be acted on by enzyme found in the female tract before it
can be utilized .This enzyme split the choline from the molecule , forming
glycerylphosphate , which can be metabolized as energy substrate .Lactic
acid , a byproduct of anaerobic metabolism of fructose builds up in semen
that is being stored and theoretically can be used as an energy substrate
when placed in aerobic conditions .
4-Fructose is found in high concentrations in bull and ram semen , but is
much lower in both boar and stallion semen .The low concentrations of
fructose in boar and stallion semen may contribute to the problems of
storing semen from these species.
5-Plasmlogen a lipid found within the spermatozoon, is an energy reserve
that can used when other substrates are limiting.
6-Adinosine triphosphate +(ATP), a high - energy compound, is the form
of energy that can be used by spermatozoa. ATP is converted to ADP
yielding 7000 calories per mole of energy by the following reaction:
ATP +H2O
ADP +H3PO4+7000 calories/ mole.
If there were no means of regenerating ATP, the spermatozoa would not
survive due to lack of energy. Energy substrates provide a means by
which ATP can be regenerated from ADP +inorganic phosphorus(pi).
Fructose serves as a good example, since it can be utilized anaerobically
and aerobically.
The anaerobic reaction is as follow:
No O2
Fructose
2 Lactic Acid +2ATP (net yield).
14000 calories
The aerobic reaction of fructose metabolism is as follow:
O2
Fructose
CO2+H2O +38ATP (net yield).
266000 calories
The anaerobic reaction provide energy to maintain the viability of
spermatozoa during storage.
Factors affecting rate of sperm metabolism:
1-Temperature: Metabolic rate increases and the life span of spermatozoa
decreases as the temperature of the semen rises.
2-PH: A PH of about 7.0(6.9-7.5 for different species)falls in optimum
activity range of most of the enzymes in spermatozoa. Therefore, a higher
metabolic rate is expected when the PH of semen is maintained near
neutrality (7.0).
3-Osmotic pressure: Semen maintain maximum metabolic activity when
diluted with an isotonic diluter. Either hypotonic or hypertonic diluters
will reduce metabolic rate, but neither will extend the life of the semen.
4-Concentration of the spermatozoa:
Increasing concentration of spermatozoa above that in the normal
ejaculate (Polyzoospermia) will decrease metabolic rate due to increase
potassium to sodium ratio in the semen . (Potassium is natural metabolic
inhibitor) .Generally , moderate dilution of semen in a buffered , isotonic
medium containing fructose will not greatly alter metabolic rate .
5-Hormones ;
Testosterone and other androgen depress metabolic rate . fluids from the
female tract increase the metabolic activity of spermatozoa .
6-Gasses ;
Low concentration of carbon dioxide (CO2) stimulate aerobic metabolism
of spermatozoa . Too high a level of O2 is toxic and will depress
metabolic rate .
7-Light ; The harmful effect of light is observed only if semen is in
contact with O2 .
8-Antimicribial agents ;
Gentamycin , Tylocin , and Linco-Spectin are added to semen during
processing to control bacterial growth . None have a demonstrated effect
on metabolic rate .