Mechanisms of luteolysis during the oestrus cycle of cows

Luteolysis starts between days 16-17 post oestrus in the cow. Bovine luteal tissue is usually not responsive to PGF2-alpha until after day 4 post oestrus.

Two major mechanisms of luteolysis have been suggested:

  1. Reduction of the blood flow in the corpus luteum (CL)
    A rapid decrease in luteal blood flow has been recently proposed as one of the main luteolytic actions of PGF2-alpha. It was demonstrated that the reduction in luteal blood supply 8 hours after prostaglandin injection was coincident with the onset of structural luteolysis, the first significant decrease in CL volume was seen.
  2. Direct action on luteal cells
    A direct action of prostaglandin on the luteal cells, resulting from both the decrease in cAMP synthesis normally produced in response to LH and the inhibition of the steroidogenic action of cAMP. These effects would be further amplified by a reduction in the number of receptors for LH.
    This theory is further supported by the result of a study that demonstrated that a prostaglandin-induced decrease in plasma progesterone concentrations occurs before a detectable decrease in both the volume of the CL and the luteal blood flow.
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