Objective—To macroscopically, histomorphologically,
and morphometrically compare uterine tissues
obtained from nulliparous and multiparous dogs.
Animals—12 dogs constituting 2 homogenous
groups (7 nulliparous Beagles and 5 multiparous
Beagles, each of which had at least 7 pregnancies).
Procedure—Serum concentrations of progesterone
and estradiol-17β were determined. Samples of uterine
tissues were fixed, embedded in paraffin, and cut
into serial cross sections. Morphometric analysis was
performed on systematically selected trichromestained
Results—Mean absolute volume of the uterine wall
did not differ between groups. Volume of blood vessels
was significantly higher and relative mean value
for myometrial connective tissue was significantly
lower in the multiparous dogs. Arteries in the
myometrium of multiparous dogs had pronounced
thickening of the intima (ie, pregnancy sclerosis) and
a concomitant thinning of the smooth muscle layer
(tunica media). Furthermore, the elastica interna of
these arteries appeared to be disintegrating and was
highly and irregularly folded. Adventitia of the myometrial
veins in multiparous dogs contained numerous
layers of elastic fibers; however, only a few layers
were observed in the adventitia of corresponding
veins in nulliparous dogs.
Conclusions and Clinical Relevance—In this study,
we documented that in contrast to other species, the
uterus of nonpregnant dogs does not increase in size
and volume even after at least 7 pregnancies.
Furthermore, sclerotic alterations of uterine arteries
are proof of at least 1 pregnancy. Results of this study
may be useful in the evaluation of uterine diseases.
( Am J Vet Res 2004;65:552–558)