Influence of Different-Frequency Glucocorticoid Induction on Morphological Structures of Humeri Soft Tissues and Immune System in Rats

Objective: To explore the influence of different-frequency glucocorticoid ((GC) induction on morphological structures of humeri and soft tissues as well as immune system in rats. Methods: A total of 32 specific pathogen-free (SPF) SD rats at the age of 3 months were selected and randomly divided into 4 groups, 8 cases in each group. The rats in control group were not given any treatment, while those in low-, moderate- and high-frequency groups were treated with intramuscular injection of dexamethasone 1 mg/kg per time for twice, 4 times and 6 times per week, respectively. All the rats were sacrificed on d30 to measure their body mass and qualities of soft tissues and immune organs, and bone histomorphometry was applied to analyze humeral bone mass and bone structural changes. Results: Compared with control group, there was no change in cancellous bone mass and bone structures of upper humeri in low-frequency group, but serious loss of bone mass, significantly degenerated bone structure, markedly reduced trabecular thickness and number as well as notably increased trabecular separation was all observed in moderate- and high-frequency groups. The size of cortical bones, total size of bone structure, thickness of cortical bones and size percentage of cortical bones in middle humeri reduced apparently, while the size percentage of medullary cavity increased dramatically in high-frequency group. Growth plate thickness of upper humeri decreased in low-, moderate- and high-frequency groups, and the diameters of mastocytes diminished in moderate- and high-frequency groups. Compared with control group, body mass decreased obviously, qualities and indexes of spleen and thymus showed decreasing tendency along with the increase of drug administration frequency in low-, moderate- and high-frequency groups. Conclusion: Low-frequency GC cannot change humeral morphology. The higher the frequency of drug administration is, the more the loss of cancellous bone mass is. When the frequency reaches to 6 times per week, the loss of cortical and cancellous bones is much severer. However, with the increase of drug administration frequency, thymic degeneration, splenic atrophy and immunosuppression can be induced. Therefore, the influence of different-frequency drug administration on bones and soft tissues in different locations as well as immune function should be fully considered and reasonable drug administration protocols should be designed for the establishment of SD rat models with osteoporosis.