KIDNEY CHANGES IN MULTIPAROUS, NULLIPAROUS AND OVARIECTOMIZED MICE FED EITHER A NUTRIENT-SUFFICIENT OR NUTRIENT-DEFICIENT DIET CONTAINING CADMIUM

As a simulation of the etiological factors known for Itai-Itai disease , a syndrome characterized by renal dysfunction and osteomalacia in it s Japanese victims, female mice were subjected to the individual and c ombined stresses of dietary Cd, nutrient-deficient diet, multiparity a nd ovariectomy. Renal function as affected by the etiological factors was periodically evaluated by determination of protein, amino acid, gl ucose and Cd concentrations in urine; periodic changes in skeletal Ca status were assessed relative to current renal function. Renal metabol ism of Cd, Zn and Cu was also examined. At age 68 days, female mice we re given nutrient-sufficient (+) or -deficient (-), purified diets con taining either 0.25 (environmental), 5, or 50 ppm Cd as CdCl2; the nut ritional composition of (-)diet simulated that of food consumed by Jap anese victims of Itai-Itai disease. At age 70 days, half of the female s began a breeding regimen of six consecutive, 42-day rounds of pregna ncy/lactation (PL mice); the remainder were maintained as virgin, non- pregnant controls (NP mice). Limited numbers of PL and NP mice were sa crificed at the end of each reproductive round. PL(+) mice taken in a given round had successively borne litters in that round and all prece ding ones. PL(-) females taken at the end of round (R)-1, -2 and -3 ha d successively borne litters through there rounds; those taken at the end of R-5 or R-6 had nonsuccessively borne litters in four of five or three of six rounds, respectively. At the conclusion of the 252-day r eproductive period, remaining females entered the 392-day, post-reprod uctive phase of the experiment. At age 546 days (mid-R-12), PL Females having successfully borne at least three litters were ovariectomized (OV) to mimic human menopause; at the same time, NP females were eithe r ovariectomized or sham-operated (SO). After surgery, all females wer e maintained to age 714 days (mid-R-16), then sacrificed. Spot urine s amples were taken from individual mice at the end of most reproductive rounds (R-2 --> 6), prior to surgery (mid-R-10), and prior to final s acrifice (late-R-15); samples were also collected via metabolism cages at the ned of R-10. Food consumption, monitored on a weekly basis ove r the first nine rounds, was generally not significantly affected by d ietary Cd level of nutrient deficiencies in females of the same reprod uctive status; consumption was increased about 2.5-fold in PL versus N P groups during the reproductive period and about 1.4-fold during the post-reproductive period. At each of the three dietary Cd levels and a fter all reproductive rounds, mean renal Cd concentrations were 1.2- t o 5.6-fold higher in PL than NP mice. After six reproductive rounds, r enal Cd concentrations in PL(+) and (-) groups exposed to 50 ppm Cd ha d reached 155 and 179 mu g Cd/g kidney, respectively. Although these l evels fell within a concentration range (145-200 mu g Cd/g) where cadm ium-induced renal dysfunction could be anticipated, no significant. Cd -dependent changes in mean urinary amino acid or protein concentration s were found. Moreover, among the same population, a 12% incidence of elevated urinary Cd (greater than or equal to 250 ng/ml) was noted, ho wever none of the affected individuals exhibited depressed total calci um content (TCa) or calcium:dry weight ratios (Ca:DW) for femur.Such r esults suggested that the Cd-induced, skeletal demineralization observ ed in mice during the reproductive period (Bhattacharyya et al., Toxic ology 1988a; 50: 193-204; Whelton et al., Toxicology 1994; 91: 235-251 ) likely occurred in the general absence of cadmium-induced renal dysf unction. By the end of the post-reproductive period, the incidence of elevated urinary Cd increased to 26% among ovariectomized females; of these, 89% with urinary Cd greater than or equal to 345 ng/ml exhibite d decreases in TCa and/or Ca:DW values for femur or lumbar vertebrae t hat exceeded one S.D. of their group mean. Such results suggested that skeletal demineralization observed at this time (Whelton et al., Toxi cology 1997a; 119: 103-121) likely occurred, for at least a portion of the population, in the presence of an ovariectomy-enhanced, cadmium-i nduced nephrotoxicity. During the reproductive period, small increases in Zn and Cu concentrations (ca. 1.8- and 1.5-fold, respectively) wer e observed for kidneys of (-) diet mice with very large increases in r enal Cd concentrations (ca. 7700-fold) analogous to results previously found for (+) diet mice (Bhattacharyya et al., Toxicology 1988b; 50: 205-215). A threshold Cd concentration below which the concentration o f Zn was relatively constant and independent of Cd concentration was i dentified (13.6 mu g Cd/g kidney); no similar threshold could be obser ved for Cu. At the end of six rounds, less Zn was found in the kidneys of PL(-) mice exposed to Cd at the 50 than 5 ppm level, however more Cu was found in the kidneys of both NP and PL(-) mice. (C) 1997 Elsevi er Science Ireland Ltd.