Effect of an oral contraceptive on NaCl appetite and preference threshold in rats

Abstract

Dietary administration of the oral contraceptive, Envoid R, to male rats at 7.5 mg/kg of food for 25 days was accompanied by a spontaneous appetite for salt solution when the rats were given choice between distilled water and 0.15 M. NaCl solution to drink. Administration of the progestational component of Enovoid R, norethynodrel, at 7.5 and 15.0 mg/kg of food for two weeks induced a spontaneous NaCl appetite in other male rats. The estrogenic compound, ethynyl estradiol, administered in food at 1.0 and 2.0 mg/kg for two weeks, was also accompanied by an appetite for NaCl solution in male rats. Thus, the NaCl appetite induced by Enovid R may be associated with both its estrogenic and progestational components. Other studies have been conducted to determine the effect of chronic administration of Enovid R at 7.5 mg/kg of food on preference (detection) threshold of female rats for NaCl solution. Drug treatment was accompanied by a significant reduction in preference threshold (0.015 M) compared to controls (0.030 M). The volume of NaCl solution ingested by treated rats was greater than that of control rats at all concentrations tested above threshold, including hypertonic concentrations. Thus, the results suggest that Enovid R not only induces an appetite for NaCl solution but also reduces the preference threshold for this salt.