Fluid balance in cycling and ovariectomised rats treated with estradiol benzoate

ABSTRACT

Plasma vasopressin levels have been shown to vary throughout the rat oestrus cycle and following ovariectomy. To determine how the fluctuations in vasopressin are related to fluid balance, studies have been carried out in ovariectomized female Sprague-Dawley rats injected subcutaneously daily with either vehicle or oestradiol benzoate [100 ug/100 g.b.w] for 14 days. The animals were housed in individual metabolism cages under 12 hours light/12 h dark regime, with free access to food and water. Urine samples to determine volume, osmolality, and electrolytes concentration were obtained and food a water intake recorded at 8.00-9.00 and 17.00-18.00 h. Plasma samples for determination of plasma volume, plasma vasopressin levels by radioimmunoassay and haematocrit were taken. In the oestradiol benzoate treated rats, food and water intake were reduced during both dark and light periods compared with vehicle treated rats. However, after about 9 days there was little difference between the two groups Urine output showed a similar pattern of changes and appeared to be related to the vasopressin concentrations. Urine osmolality also correlated with the plasma vasopressin levels. The results of 1 study indicate water and electrolytes retention in oestradiol benzoate treated rats and oestradiol induct increase in vasopressin may play a role in this fluid retention