Effects of periconceptional undernutrition on the initiation of parturition in sheep

Abstract

In sheep, parturition is initiated by increased fetal hypothalamic-pituitary-adrenal axis (HPAA) activity leading to PGE2 and PGF2␣ production and a rise in the 17␤-estradiol-progesterone (E 2/P4) ratio. Uteroplacental PG production can also increase fetal HPAA activity. Periconceptional maternal undernutrition accelerates fetal HPAA maturation resulting in preterm labor. We determined whether preterm labor was preceded by an increase in PG concentrations and E 2/P4 ratio and whether these increases preceded or followed the corresponding rise in cortisol concentrations. Singleton-bearing ewes were nourished ad libitum (N, n ϭ 9) or undernourished (UN, n ϭ 10) to reduce maternal weight by 15% from Ϫ61 days (d) to ϩ30 d after mating with ad libitum intake thereafter. Paired maternal and fetal blood samples were collected from 126 d until delivery. Half the UN group delivered prematurely (Ͼ2 SD below mean gestation for the flock). PG and cortisol concentrations and E 2/P4 ratio increased before delivery in the same way in both groups. However, the increases occurred 7-10 d earlier in UN than in N animals. In both UN and N fetuses cortisol concentrations rose before fetal and maternal PG concentrations and maternal E 2/P4 ratio. Periconceptional maternal undernutrition induces preterm delivery in sheep by advancing the expected prepartum rise in cortisol and PG concentrations and E 2/P4 ratio. The rise in fetal cortisol concentration precedes the rise in fetal and maternal PG concentrations and maternal E 2/P4 ratio, suggesting that the underlying mechanism is likely to be acceleration of fetal HPAA maturation, resulting in initiation of the normal process of parturition.hypothalamic-pituitary-adrenal axis; prostaglandin; cortisol; estrogenprogesterone ratio

Maternal and Fetal Growth, Body Composition, Endocrinology, and Metabolic Status in Undernourished Adolescent Sheep1

“…Gestation length was equivalent in control and undernourished dams (147.3 and 147.5 days) and was, on average, 4 days longer than in overnourished dams (143.0 days; P , 0.001; n ¼ 18 to 22 pregnancies per group; Wallace et al, unpublished data). These results are perhaps surprising in view of reports of extreme premature delivery in adult ewes that were nutrient restricted during the periconceptual period [49,50]. Premature deliveries in these latter pregnancies have been attributed to accelerated maturation of the fetal hypothalamic-pituitary-adrenal axis in late pregnancy [51]; however, neither fetal nor maternal cortisol concentrations were altered by maternal nutrition in the present study.…”

Intrauterine Programming of Physiological Systems: Causes and Consequences

“…Exposure to excess progesterone and metabolites, such as urea, specifically during these periods leads to enhanced birth weight in sheep and pigs (34). In addition, dietary restriction during the periconceptional period has also been shown to shorten gestation and cause hypertension and abnormal HPA function in adult sheep (29). Developmental changes arising before implantation are likely to affect many cell lineages, although adaptations later in gestation, such as upregulation of placental nutrient and O 2 transport, may compensate for the early defects and normalize birth weight.…”

Nutrition maternelle : incidence sur la fertilité de la descendance et importance de la période périconceptionelle pour le long terme

“…S'il a été montré par de nombreuses équipes que l'alimentation maternelle durant la vie foetale pouvait affecter le développe-ment à long terme de la descendance, certains modèles animaux indiquent qu'une restriction alimentaire périconceptionelle affecte le développement de l'axe hypothalamo-hypophysairesurrénalien de la descendance, le développement cardiovasculaire ainsi que d'autres paramètres. Ainsi, les fenêtres de susceptibilité du conceptus à la programmation métabolique s'étendent à la période préimplantatoire [3][4][5][6].…”

“…La sous-nutrition périconceptionnelle induit des modifications des sécrétions endocrines, en particulier du profil plasmatique de IGF1 et IGFBP-3 chez le foetus ovin en cours de gestation, avec des conséquences possibles pour le développe-ment des organes reproductifs [48]. Des naissances prématu-rées et une croissance foetale diminuée ont été décrites après une restriction alimentaire sévère (28 % des besoins) pendant la période périconceptionnelle, avec une activation de l'axe HHS [4,49]. De plus, le poids des surrénales était réduit et accompagné d'une diminution de l'expression des gènes clés de la famille des IGF [50].…”