Fluid regulation and A.D.H. in rat oestrus cycle; the effect of difluoromethyl ornithine [demo] and oestradiol

ABSTRACT

Plasma ADH concentration have been shown to fluctuate during the oestrus cycle of the rat and following ovariectomy. Oestradiol is also known to participate in the regulation of fluid and electrolyte balance. To determine how these variations in ADH and oestradiol concentrations are related to fluid balance, studies have been carried out in the overiectomized female rats injected subcutaneously daily with oestradiol benzoate [50 [micro]g/rat] and specific inhibitor of ornithine decarboxylase [ODC]; difuormethylorithine [DEMO 20 mg/100 g.b.w] for 7 days. The animals were housed in individual metabolism cages under 12 hr dark regimen with free excess to food and water. Urine samples to determine volume were obtained and food and water intake recorded at 800-900 and 1700-1800 hr. Plasma samples for determination of ADH levels by radioimmunoassay were taken. In DFMO and cestradiol benzoate treated rats, food and water intake were reduced during both dark and light periods compared with vehicle treated rats. But more urine output was observed in these animals. The result of this study indicate decreased water retention in the drug treated animals as compared to the controls. The observations of this study have shown that the underlying cause of fluid retention in the cycling rat during pro-oestrus may the oestradiol dependent elevation of the ADH levels. Furthermore, this increase in ODC activity in the hypothalamic neurons is part of mechanism underlying the oestradiol induced ADH release