Gonadal steroids and bone metabolism in young castrated male rats

At 45 days of age, 40 male Wistar rats were castrated, then randomly divide d into four groups, S.C. injected for 60 days after surgery either with 17 beta-estradiol (E) 10 mu g/kg BW/48 hours, progesterone (P) 140 mu g/kg BW/ 48 hours, dihydrotestosterone (D) 2 mu g/kg BW/48 hours, E + P + D same dos es, or solvent alone (CX). Ten other rats were sham-operated (SH) and used as controls. Animals were put in balance to determine Ca and phosphorus (Pi ) intestinal apparent absorption (IA Ca, IA Pi) and urinary pyridinium cros slinks excretion. Plasma was collected for measurement of intact-parathyroi d hormone (PTH), calcitonin (CT), insulin-like growth factor I (IGF-I), 1,2 5 dihydroxyvitamin D (1,25(OH)(2)D), Ca, and Pi. Orchidectomy induced marke d seminal vesicles atrophy and increased plasma CT, PTH, and Ca concentrati ons. IA Ca was significantly higher in P rats, however, neither castration nor any other treatment had significant effects. Orchidectomy decreased fem oral length, dry weight, and Ca content, whereas E or D given alone or toge ther with P improved endochondral growth and enhanced femoral Ca content. A gain, bone mineral density was lowered by orchidectomy and reestablished by both E and EPD, even above SH values, this effect being more important at the metaphyseal levels. Urinary pyridinium cross-links excretion and plasma osteocalcin concentrations were higher in the CX animals than in the contr ols. Although E and D given alone did reduce both biochemical turnover mark ers, they showed additive effect when given together (EPD). In conclusion, in the young castrated male rat, E was more efficient than D for preventing bone loss, the most important effect being induced by a combination of E P + D.