Ff. Bartol et al., NEONATAL EXPOSURE TO PROGESTERONE AND ESTRADIOL ALTERS UTERINE MORPHOLOGY AND LUMINAL PROTEIN-CONTENT IN ADULT BEEF HEIFERS, Theriogenology, 43(5), 1995, pp. 835-844
Exposure of the developing urogenital tract to steroids can affect str
ucture and function of adult tissues and compromise reproductive perfo
rmance. This study was conducted to determine 1) if exposure of neonat
al heifer calves to progesterone (P) and estradiol benzoate (E), deliv
ered from a commercial growth-promoting implant, would affect adult ut
erine morphology or uterine luminal protein content; and 2) whether su
ch effects would be related to neonatal age at the first exposure. At
birth (Day 0), 20 crossbred beef heifers were assigned to 1 of 4 treat
ment groups (n = 5 per group), defined by age at implant placement. He
ifers either received an implant on Days 0, 21 or 45, or served as unt
reated controls. The heifers were maintained together and slaughtered
at 15 mo of age, during the luteal phase of an induced estrous cycle,
when reproductive tracts and blood samples were obtained. Peripheral p
lasma P concentrations were determined by RIA. Uterocervical wet weigh
ts were recorded, and uterine luminal flushings (ULF) were assayed for
total protein. Cross-sections of uterine tissues were evaluated histo
morphometrically to determine myometrial and endometrial areas and rel
ative endometrial gland density. Treatment did not affect plasma P con
centrations (3.2+/-0.5 ng/ml). Regardless of age at treatment, neonata
l PE exposure reduced uterocervical wet weight by 35% (112.8 < 173.9+/
-13.9 g; P<0.01), myometrial area by 23% (125.3 < 162.8+/-8.5 mm2; P<0
.02), and endometrial area by 27% (33.3 < 45.4+/-2.7 mm2; P < 0.09) co
mpared with the untreated controls. Endometrial gland density was redu
ced (P<0.01) by 40% in treated heifers. This effect was related to age
at implant placement. Uterine gland density was reduced (P<0.01) by 6
5% in heifers treated at birth, while reductions of 22 and 33% were ob
served for heifers treated on neonatal Day 21 or 45, respectively. Con
sistently, ULF protein content was lower (P<0.01) in the treated heife
rs (2.67 < 4.98+/-.72 mg/ULF). Thus, exposure of newborn calves to PE
can have profound effects on adult uterine morphology and environment,
the extent of which may depend upon the developmental period when exp
osure occurs. The potential of such alterations to affect reproductive
performance in adult beef heifers remains to be investigated.