Growth in rabbits during alternate-day cortisone injections: near normal growth on days without cortisone

Longitudinal bone growth in rabbits during treatment with hydrocortisone was measured by means of Roentgen Stereophotogrammetric Analysis, RSA. This method allows accurate measurement of the distance between metallic markers inserted into long bones. Hydrocortisone was given in i.m. injections as single doses and as repeated doses, daily or every other day. Single injections of hydrocortisone resulted in three types of growth effect, depending on dosage. Low dosage (less than 4 mg/kg b.w.) produced no blunting of growth. Intermediate dosage (4-32 mg/kg b.w.) retarded growth during the first but not the second day after the injection. The effect of high dosage (64-128 mg/kg b.w.) lasted for two days. During daily treatment (4 and 16 mg/kg b.w.), growth decreased to a constant level. During alternate-day steroid injections with a double dose every other day, growth almost normalized during the steroid-free days. Average growth was significantly greater during alternate-day injections than during daily injections. It is concluded that alternate-day treatment has no unfavorable effect on growth so long as the interval between injections exceeds the duration of the growth effect of each single dose.