Interactions between thyroxine, hydrocortisone and cyclophosphamide in their effects on the eruption of the rat mandibular incisor.

The effects on the unimpeded eruption rates of the rat mandibular incisor of daily doses of thyroxine (0.5 mg/kg) and hydrocortisone (12.5 mg/kg) and of a single injection of cyclophosphamide (40 mg/kg), either alone or in combination, were studied over approximately 15 days. Both the thyroxine and hydrocortisone alone produced increases in eruption, whereas a decrease was recorded with cyclophosphamide alone. When thyroxine was combined with hydrocortisone, the increase in eruption rate was greater than that with thyroxine or hydrocortisone alone. When cyclophosphamide was combined with hydrocortisone, there was no difference compared with cyclophosphamide alone. These results obtained with drug combinations are consistent with eruption having a multifactorial basis.