Hypothyroid offspring replacement with euthyroid wet nurses during lactation improves thyroid programming without modifying metabolic programming

Objective: Determine the milk quality effect during lactation on the metabolic and thyroid programming of hypothyroid offspring. Materials and methods: Ten-week-old female Wistar rats were divided into two groups: Euthyroid and thyroidectomy-caused hypothyroidism. The rats were matted and, one day after birth, the pups were divided into three groups: Euthyroid offspring (EO), hypothyroid offspring (HO) and hypothyroid with a euthyroid replacement wet nurse (HRO). During lactation, the milk quality and offspring body length were evaluated. The body weight and energy intake were determined on a weekly basis, as well as the metabolic profile at the prepubertal (P35-36) and postpubertal (P55-56) ages. At P56, the animals were sacrificed, the adipose tissues were weighed and the thyroid glands were dissected for histological processing. Results: The milk of the hypothyroid wet nurse decreases proteins (16-26%), lipids (22-29%) and lactate (22-37%) with respect to euthyroid. The HO has a lower body weight gain (23-33%), length (11-13%) and energy intake (15-21%). In addition, HO presents impaired fasting glucose and dyslipidemia, as well as a reduction in seric thyroid hormone (18-34%), adipose reserves (26-68%) and thyroid gland weight (25-34%). The HO present thyroid gland cytoarchitecture alteration. The HRO develop the same metabolic alterations as the HO. However, the thyroid gland dysfunction was partially prevented because the HRO improved under about 10% of the serum thyroid hormone concentration, the thyroid gland weight although histological glandular changes presented. Conclusions: The replacement of hypothyroid offspring with a euthyroid wet nurse during lactation can improve the thyroid programming without modifying metabolic programming.