Lambs that are born to obese sheep don't experience a peak in a hormone that regulates appetite, according to a new study that could help explain why human children born to obese mothers are at an increased risk for being obese themselves, researchers say.
In lambs born to normal-weight sheep, there was a peak in the hormone leptin, which is produced by fat cells and regulates appetite, during their first six to nine days of life. But the same hormonal peak did not occur in lambs born to the obese ewes, the study said.
Blood samples taken from day-old lambs also revealed that levels of cortisol, a hormone that's released in response to stress, were up to 50 percent higher in obese sheep than normal-weight sheep, the study said.
Exposure to higher levels of cortisol in the womb may prevent the lambs of obese mothers from experiencing the normal peak in leptin, said study researcher Dr. Peter Nathanielsz, a professor in the Center for Pregnancy & Newborn Research at the University of Texas Health Science Center at San Antonio.
"Seeing these hormonal changes in lambs, in addition to what we have already found with rodents, is advancing our understanding of what programs appetite," Nathanielsz said in a statement. "We are getting closer to understanding what causes obesity in humans ."
Rodents have been used in previous research to study maternal obesity and offspring obesity, but it's hard to apply those findings to humans because mouse offspring are often born immature, he said.
"Lambs offer a more similar model to understand the mechanism of human obesity as they are born at a more advanced level of maturity — equivalent to humans," Nathanielsz said.
Nathanielsz and his colleagues followed two groups of sheep for 60 days before conception and throughout their pregnancy, as well as their offspring, for 19 months after birth. One group of mother sheep was fed a normal diet and the other was fed an obesity-promoting diet, the study said.
Researchers took blood samples from the lambs throughout the study to monitor blood levels of hormones known to affect developmental programming, particularly leptin.
"We propose that cortisol prepares fetal adipose tissue to secrete leptin, and that this process seems to be disrupted in lambs born to obese mothers," Nathanielsz said. "The nutrient excess present in the blood of obese mothers throughout gestation seems to inhibit the postnatal leptin peak, which likely has important consequences for the development of the lamb."
The study was published yesterday (March 15) in the Journal of Physiology.
Pass it on: Lambs born to obese ewes lack a peak in an appetite-regulating hormone soon after birth. Scientists say this discovery could shed light on why children born to obese women have an increased risk of becoming obese.
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