Do lactating seals maintain blood glucose levels whilst fasting during lactation?

Weddell seals are well adapted polar animals. They give birth to pups in the Antarctic summer when they haul out onto the ice. While feeding their pups, they have a massive fasting weight loss (and fat mobilisation) and their suckling pup has a correspondingly massive weight gain and fat deposition. This study aimed to investigate how these animals regulate the massive changes in body weight and simultaneously maintain lactation while fasting. To study lactation, milk samples, together with blood samples, from the same animals and their pups were taken. Blood samples were also collected from non-lactating adult females. The milk and plasma samples were analysed for a wide range of parameters related to lipid, carbohydrate, protein, water and mineral homeostasis. One of the metabolic features which has been postulated for lactating and concurrently fasting animals is sparing of glucose. To examine glucose homeostasis, a intravenous glucose tolerance test in 6 lactating and 6 non lactating adult females was conducted by injecting glucose into the seals and then collecting blood samples from 20 minutes before the injection to 180 minutes afterwards. Blood samples were analysed for glucose and insulin concentrations to monitor how quickly these animals take up glucose from the blood.