Changes in organ weights and blood parameters in ageing Brattleboro rats with hereditary diabetes insipidus

Organ weights and blood parameters were measured in male and female Brattleboro rats with hereditary diabetes insipidus (DI) and in normal rats of the same strain, between 37 and 138 weeks old. Although differences in body weight between the homozygous DI and heterozygous normal rats accounted for differences in the weights of the heart and gonads, the weights of the spleen, liver and kidney were not solely body-weight dependent; there were significant sex and genotype differences in the mean weights of these organs. The liver, heart and gonads were the only organs showing age-dependent changes. No genotype-dependent differences were observed in the haematocrit and haemoglobin concentration, although there was a sex difference; the mean values of these parameters were higher in males. Plasma glucose concentrations were significantly lower in homozygous than in heterozygous rats; in the latter, plasma glucose concentration decreased with age. No significant changes occurred in the mean plasma concentrations of sodium or potassium with age or genotype. Total plasma lipids of heterozygous female rats showed both age- and genotype-dependent changes; this parameter reached a plateau at 90-100 weeks old, and was significantly higher in heterozygous females than in all other groups. Plasma proteins showed no age-dependent changes, but were of higher mean value in heterozygous than in homozygous rats and were greater in females than in males. Differences in blood parameters of homozygous and heterozygous Brattleboro rats are discussed in terms of differences in hormone concentrations.