Effects of Cloxacillin, Doxycycline, Fusidic Acid and Lincomycin on Mineralization and Solubility of Collagen in Young Rats

Abstract

The antibiotics doxycycline, fusidic acid and lincomycin have recently been shown to reduce growth of bones and tensile strength of skin in young rats. Such adverse effects were not found in rats receiving cloxacillin. The present investigation deals with the influences of these four antibiotics on the mineralization of bones and on the solubility of collagen in skin. In rats receiving doxycycline the content of calcium and phosphorus in bones and the concentration of albumin in serum were reduced. None of the antibiotics had a detectable effect on the solubility of collagen. In a previous study (Engesaeter & Skar 1979) the antibiotics doxycycline, fusidic acid and lincomycin were found to cause reduced growth of bones and reduced tensile strength of intact skin in young rats. Such unwanted effects were, however, not detected in a group of rats receiving cloxacillin.T h e purpose of the present investigation was t o examine the effects of these four antibiotics on the solubility (cross-linking) of collagen and on t h e mineralization of bones. These t w o parameters are of particular i n t e r e s t since a n o t h e r a n t i b i o t i c , o x ytetracyline, has been found to impair both collagen solubility and bone mineralization (Engesaeter e t al. 1980 a, b). M A T E R I A L S AND METHODSFifty male Wistar rats, initially weighing 39-44 g, were used. The animals were divided into five groups of 10 rats. The fist group received cloxacillin, the second doxycycline, the third fusidic acid, and the fourth lincomycin. The fifth group of animals served as control, receiving only isotonic sodium chloride solution. The antibiotics were administered as intraperitoneal injections every 12th hour for 14 days. Fusidic acid, however, was given by a stomach tube, as intraperitoneal injections in a pilot study caused massive abdominal adhesions. The doses of the drugs in mg/kg/day were 2-12 times higher than the recommended human doses. Plasma concentrations of the antibiotics were, however, comparable with the therapeutic levels in humans. Further information about the animals and the medication was reported in a previous paper dealing with the mechanical properties of bone and skin of these rats (Engesaeter & Skar 1979).At the end of the l 4 d a y medication period the rats were anaesthetized with ether and blood was collected by puncture of the aorta, death followed by exsanguination. Bones and skin were immediately removed and after mechanical testing stored at -2OoC until biochemical examination. Bone analyses were performed on the left femur after the soft tissues, the cartilages and the epiphyses had been removed. The bones were hydrolyzed in 6M HCl at 125OC for 18 hours, and the content of calcium, phosphorus and collagen was measured, as described below.Skin analyses were performed on skin from the back of the animals, i.e. the most cranial of the three intact skin specimens used in the mechanical testing. The fraction of collagen soluble in saline solution was determined by modifications of the methods of Kivirikko...