Chronic heat stress and prenatal development in sheep: II. Placental cellularity and metabolism.
Aspects of placental protein and energy metabolism were examined in pregnant ewes subjected to either thermoneutral (TN, 18 to 20 degrees C, 30% humidity, n = 7) or hot (H, 30 to 40 degrees C, 40% humidity, n = 5) temperatures through mid and late gestation. Fetal and placental weights and total content of protein, RNA, and DNA were reduced (P less than .001) in H ewes. Placental protein and RNA concentrations (mg/g) were not different, and DNA concentrations were slightly greater (P less than .1), in H vs TN ewes. Thus, heat seemed to greatly reduce total cell number and placentome size and only slightly decrease cell size. Ratios of RNA to DNA indicated a reduced capacity for protein synthesis in H placenta. However, in vitro fractional rates of protein synthesis in tissue slices from the fetal and maternal placenta and from the myoendometrium were not different between TN and H ewes. The H ewes had greater placental protein concentrations of hydroxyproline and glycine, perhaps suggesting a greater collagen content. In vitro oxygen consumption of fetal placenta, but not of maternal placenta or myoendometrium, was lower in H than in TN ewes. This lower oxygen consumption was partially due to a lower Na+,K+ ATPase-dependent oxygen consumption.
Early
R J
RJ
Dept. of Anim. Poult. Sci., University of Guelph, Ontario, Canada.
McBride
B W
BW
Vatnick
I
I
Bell
A W
AW
D000818:Animals; D002455:Cell Division; D004247:DNA / Q000032:analysis; D005314:Embryonic and Fetal Development; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D009929:Organ Size; D010101:Oxygen Consumption; D010920:Placenta / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism; D011247:Pregnancy; D011248:Pregnancy Complications / Q000378:metabolism / Q000662:veterinary*; D011257:Pregnancy Proteins / Q000032:analysis / Q000096:biosynthesis; D012313:RNA / Q000032:analysis; D012756:Sheep; D012757:Sheep Diseases / Q000378:metabolism*; D013312:Stress, Physiological / Q000378:metabolism / Q000662:veterinary*
D011257:Pregnancy Proteins; D012313:RNA; D004247:DNA