Simulated shift work disrupts maternal circadian rhythms and metabolism, and increases gestation length in sheep

Abstract

Key points Shift work impairs metabolic health, although its effects during pregnancy are not well understood We evaluated the effects of a simulated shift work protocol for one‐third, two‐thirds or all of pregnancy on maternal and pregnancy outcomes in sheep. Simulated shift work changed the timing of activity, disrupted hormonal and cellular rhythms, and impaired maternal glucose tolerance during early pregnancy. Gestation length was increased in twin pregnancies, whereas singleton lambs were lighter at a given gestational age if mothers were subjected to shift work conditions in the first one‐third of pregnancy. Exposure to rotating night and day shifts, even if only in early pregnancy, may adversely affect maternal metabolic and pregnancy outcomes. Abstract Shift workers are at increased risk of developing type 2 diabetes and obesity; however, the impact during pregnancy on maternal metabolism is unknown. Using a large animal model, we assessed the impact of simulated shift work (SSW) exposure during pregnancy on maternal circadian rhythms, glucose tolerance and pregnancy outcomes. Following mating, ewes were randomly allocated to a control photoperiod (CON 12 h light, 12 h dark) or to SSW, where the timing of light exposure and food presentation was reversed twice each week for one‐third, two‐thirds or all of pregnancy. Maternal behaviour followed SSW cycles with increased activity during light exposure and feeding. Melatonin rhythms resynchronized within 2 days of the photoperiod shift, whereas peripheral circadian rhythms were arrhythmic. SSW impaired glucose tolerance (+29%, P = 0.019) and increased glucose‐stimulated insulin secretion (+32%, P = 0.018) in ewes with a singleton fetus in early but not late gestation. SSW exposure did not alter rates of miscarriage or stillbirth, although it extended gestation length in twin pregnancies (+2.4 days, P = 0.032). Relative to gestational age, birth weight was lower in singleton progeny of SSW than CON ewes (–476 g, P = 0.016). These results have implications for the large number of women currently engaged in shift work, and further studies are required to determine progeny health impacts.

Simulated shift work during pregnancy does not impair progeny metabolic outcomes in sheep

“…Sheep provide an excellent animal model of human pregnancy as a result of their long gestation, similar prenatal timing of development and low rates of multiple births (Morrison et al 2018). To address this knowledge gap, we therefore developed a sheep model of maternal shift work in which we manipulated the timing of light exposure and feeding to mimic weekly rotating shifts for the first one-third, the first two-thirds or the entire duration of pregnancy (Gatford et al 2019). Exposure to this simulated shift work protocol altered maternal activity and melatonin rhythms, disrupted clock gene expression in maternal skeletal muscle during pregnancy, reduced birth weight of singleton fetuses, and increased gestation length of twins (Gatford et al 2019).…”

Shift work and pregnancy: night light, baby not right

“…Interestingly, there is capacity for adaptation of maternal metabolic function to SSW as the glucose challenge test normalized at late gestation, despite the altered circadian function. Up to now, the information available in rats, and in sheep, as reported by Gatford et al 2019 in this issue, points to important effects of chronic phase shifts of the photoperiod on maternal physiology. As mentioned previously, long-term effects in the offspring of rodents have been shown.…”

“…Up to now, the information available in rats, and in sheep, as reported by Gatford et al . in this issue, points to important effects of chronic phase shifts of the photoperiod on maternal physiology. As mentioned previously, long‐term effects in the offspring of rodents have been shown.…”

“…As reported in this issue of The Journal of Physiology , Gatford et al . undertook this challenge by studying maternal effects of chronic photoperiod shifts during pregnancy in the ewe. Sheep have a long pregnancy (about 20 weeks), are diurnal and carry one or two fetuses.…”

Long-Term Effects of Altered Photoperiod During Pregnancy on Liver Gene Expression of the Progeny

“…This field is of great interest because of the potential long-term effects on the adult offspring’s health and disease status (Amaral et al, 2014; Varcoe et al, 2017; Richter et al, 2018). The available evidence has demonstrated different consequences of chronodisruption on maternal physiology (Gatford et al, 2019). In animal model, the maternal exposure to CPS disrupted the biological clocks in the pregnant female, altering physiological parameters throughout gestation such as the circadian profile of plasma hormones, changes in the liver metabolic gene expression and alterations in the clock gene expression profile (Varcoe et al, 2013; Mendez et al, 2016).…”