Oophorectomy in young rats impairs calcium balance by increasing intestinal calcium secretion

Calcium balance and its major components (true calcium absorption, urinary calcium excretion and intestinal calcium secretion) were assessed by a 6-d balance technique in young (6-wk-old) rats fed a diet containing 7.2 g Ca/kg diet. Following either oophorectomy (oophx) or sham operation, the balance study was repeated at 9, 12 and 15 wk of age. Calcium balance decreased with age but remained positive in each group [mean (pooled SEM): sham, (6 wk) 0.86 to (15 wk) 0.27 (0.03) mmol/d (P < 0.0001); oophx, (6 wk) 0.91 to (15 wk) 0.22 (0.03) mmol/d (P < 0.0001)]. Analysis of variance of the change in calcium balance indicated that there was a significantly greater reduction in calcium balance in the oophx group compared with the sham-operated group. Intestinal calcium absorption decreased in each group with age [sham: (6 wk) 46.3% to (15 wk) 22.6% (1.5%) (P < 0.0001); oophx: (6 wk) 48.2% to (15 wk) 21.2% (1.5%) (P < 0.0001)]. There was a marked rise in intestinal calcium secretion in the oophx group compared with the sham-operated group at 6 wk post-operation (12 wk of age) [oophx: 0.33 (0.02) mmol/d; sham: 0.23 (0.02) mmol/d (P < 0.01)]. Urinary calcium excretion was not affected by either age or oophorectomy. We conclude that oophorectomy in young rats leads to a reduction in calcium accumulation, which is mainly the result of an increase in intestinal calcium secretion.