UNUSUAL HISTOMORPHOMETRIC CHANGES IN THE ILIAC CREST IN OVARIECTOMIZED AND SHAM-OPERATED EWES

A large animal model to study cancellous bone loss and the effect of v arious therapeutic agents-following oestrogen deficiency-related bone loss is needed. Following double fluorochrome labeling at the time of surgery, six and 12 months later, static and dynamic histomorphometry was performed on undecalcified sections of the iliac crests of 16 matu re (4 to 5-year-old) ewes following ovariectomy (OVX; n = 8) or sham-o peration (Sham; n = 8). We found a slight decrease in bone mass associ ated with oestrogen deficiency as indicated by a statistically signifi cant increase in trabecular separation (Tb.Sp: +14%, p <0.05) and decr ease in wall thickness (W.Th: -10%, p <0.05) in the OVX group. However , at six months, we saw evidence of complete cessation of bone formati on in both OVX and Sham animals. At that time there was a statisticall y significant (p <0.05) decline in the following parameters in both th e Sham and OVX animals respectively: osteoid surface (OS: -79%, -77%), osteoid thickness (O.Th: -40%, -30%), flat osteoblasts (Fl.Ob.S: -87% , -94%), cuboidal osteoblasts (Cu.Ob.S: -88%, -65%), osteoid surface a s a percentage of the total cancellous bone perimeter (OS/BS: -82%, -8 0%), osteoblast surface as a percentage of total cancellous bone surfa ce (Ob.S/BS: -94%, -77%), mineralizing surface as a percentage of doub le labels plus half single labels (MS/OS: -44%, -42%), osteoid volume as a percentage of total area of mineralized bone plus osteoid (OV/TV: -88%, -88%), osteoid as a percentage of mineralized bone (OV/BV: -87% , -86%), osteoid maturation time (Omt: -27%, -35%), bone formation rat e, surface referent (BFR/BS: -90%, -87%), bone formation rate, volume referent (BFR/BV: -89%, -86%), and bone formation rate, tissue referen t (BFR/TV: -91%, -88%). The data was compared to static and dynamic hi stomorphometry of three intact ewes (similar age, breed, source) whose biopsies were taken two months after the second biopsies in the prese nt study. The data indicate that there is a slight loss of trabecular bone following OVX but we are unable to explain the dramatic depressio n of bone turnover with little change in bone resorption. The data res embles the response seen when sheep are given daily doses of methylpre dnisolone. We speculate that this phenomenon may be a response to endo genous corticosteroid release in a response to stresses of transport, and surgery. A seasonal effect may be another explanation fro these ch anges, whereas dietary alteration (e. g. poisonous plants), hormonal c hanges or response to changes in physical activity are unlikely causes .