Abstract:
Cystic ovarian disease (COD) is an anovulatory condition in cattle
that afflicts between 6-18% of all dairy cows in the US. Ovulation is
dependent on the plasminogen activator (PA) family of proteases
and protease inhibitor for proteolysis, culminating in follicular rupture.
Failure of the follicle to ovulate suggests an aberration in proteolysis
in cystic follicles. Polycystic ovarian disease in humans is
phenotypically similar to COD is associated with elevated plasma
PAI-1. PAI-1 regulates the proteolytic activity responsible for
ovulation. Vitamin E supplementation reduces plasma PAI-1 and
reduces the incidence of COD. Four experiments were conducted to
elucidate the role of the plasminogen activator system in the etiology
of COD and the ability of vitamin E supplementation to modulate the
PA system in cattle. In experiment one, blood samples were
collected from lactating dairy cows upon diagnosis of a follicular cyst
at least 3.0 cm in diameter by a licensed veterinarian. Cows were
classified based upon their history of follicular cysts. Tissue-type
plasminogen activator (tPA) and plasminogen activator inhibitor-1
(PAI-1) concentrations and activities were measured using
commercially available ELISA and chromogenic reagents. No
differences were detected between cystic and non-cystic dairy cows.
In experiment two, six non-lactating beef cows were supplemented
with 2750 IU of α-tocopherol every four days for 24 days. Blood
samples were collected every two days and assayed for tPA and
PAI-1 concentrations and activities. Supplementation with α-
tocopherol decreased the ratio of PAI-1 to tPA activities adjusted to
the Day 0 measurement (P=0.097). In experiment three, mRNA was
isolated from follicular cysts and preovulatory follicles and relative
quantitative RT-PCR was performed for tPA, urokinase-type
plasminogen activator (uPA), urokinase-type plasminogen activator
receptor (uPAR), PAI-1, and β-actin. uPA expression was reduced
(P<0.1) and uPAR expression was greater (P<0.1) in follicular cysts
compared to preovulatory follicles. Lastly, in experiment four DNA
was extracted from whole blood obtained from cystic and normal
dairy cows and the promoter region of the PAI-1 gene was
sequenced. More Jersey cows with COD possessed a four basepair
deletion polymorphism than normal cows (P<0.1) and more Jerseys
possessed the deletion polymorphism than Holsteins (P<0.01).
