Increase in serum hyaluronidase levels in rats given hydrocortisone or prednisolone

Intraperitoneal injection of 5 mg hydrocortisone to rats was found to cause a considerable increase in serum hyaluronidase activity above the normal level within 12 h, with the maximum response occurring about 18 h after injection. The response at 18 or 24 h increased up to a dose of about 10 mg per rat.Daily injections of 5 mg hydrocortisone or 1.25 mg prednisolone into each of a group of six rats maintained a mean level of serum hyaluronidase which was significantly higher than that of a control group over a period of 6 days. Peaks of activity were found at 1 and 6 days which were almost double the normal mean levels found in both groups on day zero before injections were begun. When the hormone injections were stopped, the hyaluronidase level fell to normal within 24 h.Administration of 20 000 – 50 000 I.U. vitamin A acetate to rats failed to produce an increase in the serum hyaluronidase level even after 13 daily injections. These amounts are known to cause breakdown of cartilage matrix in vivo and disruption of lysosomes in vitro.The absence of any effect of actinomycin D indicated that enzyme induction was not the cause of the increased hyaluronidase activity.