Anterior pituitary morphology and hormone production during sustained critical illness in a rabbit model

Prolonged critical illness is hallmarked by striking alterations in the somatrope, thyrotrope, and lactotrope axes, the severity of which is associated with the risk of morbidity and mortality. The exact role of the pituitary gland in these alterations is unknown. We studied the impact of sustained critical illness on pituitary morphology and hormone production in a standardized rabbit model of prolonged (7 days) burn injury-induced critical illness. In healthy and prolonged critically ill rabbits, we determined pituitary weight, size, morphology and orientation of the somatrope, lactotrope and thyrotrope cells and the pituitary expression of GH, PRL, and TSH at gene and protein level. The weight of the pituitary gland was unaltered by 7 days of critical illness. Also, spatial orientation and morphology of the GH, PRL, and TSH producing cells remained normal. In prolonged critically ill rabbits GH mRNA levels were higher and PRL mRNA levels were lower than in healthy controls, whereas TSH mRNA was not affected. The sizes of GH, PRL, or TSH producing cells and the pituitary content of GH, PRL, and TSH proteins were unaltered. In conclusion, in this rabbit model of prolonged critical illness, the morphology of the pituitary gland and the pituitary GH, PRL, and TSH content was normal. The alterations in pituitary hormone mRNA levels with sustained critical illness are compatible with altered hypothalamic and peripheral regulation of pituitary hormone release as previously suggested indirectly by responses to exogenous releasing factors.