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Effect of carbetocin, oxytocin and prostaglandin E2 and F2α on intrauterine pressure in cows in dioestrus and oestrus.

OBJECTIVE
To describe the physiological activity of the myometrium in oestrus and dioestrus and the induced activity after medication in cows with particular reference to segmental differences.


MATERIAL AND METHODS
Six cows were given the pharmaceuticals carbetocin, oxytocin and prostaglandin (PG) F2α (dinoprost) intramuscularly and PGE2 intravenously. The physiological myometrial activity was recorded for 15 minutes and the induced activity for 105 minutes by using a transcervically attached pressure probe containing six pressure microtransducers.


RESULTS
Lower pressures were measured in dioestrus compared to oestrus before (dioestrus 3.2±8.88 mmHg, oestrus 12.4±13.23 mmHg, p<0.0001) and after the drug administration. Carbetocin provoked the longest lasting effect (60 minutes in dioestrus, 75 minutes in oestrus) followed by PGE2 (45 minutes in dioestrus, 60 minutes in oestrus), PGF2α (30 minutes each) and oxytocin (15 minutes in oestrus only). In contrast to the other drugs carbetocin did not cause any pressure decrease beneath the base level after the primary pressure increase in dioestrus. In dioestrus the pressure before drug administration was significantly higher in the cervix (3.6±19.40 mmHg) and the uterine body (7.1±36.10 mmHg) than in the uterine horn (1.1±7.21 mmHg). Conversely, in oestrus the pressure in the uterine horn (16.6±17.73 mmHg) was significantly higher than in the uterine body (6.2±16.59 mmHg) and the cervix (10.4±17.91 mmHg). Drug administration in dioestrus caused a cornual pressure increase and the pressure in the uterine body decreased, whereas in oestrus the pressure increased in all uterine segments. The physiological frequency of the pressure waves in dioestrus was 5.2±3.02 in 15 minutes compared to 7.5±2.89 in 15 minutes in oestrus. No traceable changes of the contraction frequency were found after medication.


CONCLUSION AND CLINICAL RELEVANCE
Carbetocin caused the most enduring increase in intrauterine pressure in dioestrus and oestrus and may therefore be indicated best for therapeutic use. The tested drugs had the same effects on the various uterine segments and no effect on the contraction frequency.