Behavioural effects of oestradiol in the female rat

Abstract

Using behavioural and physiological measures, this thesis investigates behavioural effects of oestradiol, and of two of its synthetic analogues, mestranol and ethynyl oestradiol, in the female rat. Two types of behaviour receive particular attention, feeding and sexual behaviour. The first chapter describes some physiological and behavioural changes in the female rat over the oestrous cycle. Changes in meal size are seen during oestrus, or in ovariectomlzed rats treated with oestradiol. The effect of oestradiol on the gastric emptying of saline, glucose and fat loads was investigated (Chapter 2) to determine whether changes in stomach emptying were responsible for altered meal size. Only the emptying of fats from the stomachs of oestradiol treated rats was significantly reduced. The role of oestradiol in motivational processes associated with sexual behaviour was also examined (Chapter 3). It was found that the performance of females, running to sexually active or castrate males in a straight runway, depended on their oestrous state, and the gonadal condition of the males. These were independent and additive effects. The characteristics of the potent male that were rewarding to a female were then investigated by varying the odour and sexual activity of male rats (Chapter 4). The results suggest that both the odour and sexual activity of a potent male are rewarding to a female rat. Ethynyl oestradiol and mestranol are synthetic oestrogens nonnally used in oral contraceptives. The experiments presented in Chapter 5 show that in female rats both of these steroids reduced food intake reliably, and more than oestradiol. Ethynyl oestradiol, but not mestranol, stimulated sexual behaviour. Furthermore, there was no interaction between oestrogen and progestogen components of oral contraceptives which influenced, in any way, the behaviours observed in this study. The final chapter reviews the effects of oral contraceptives on mental, somatic and behavioural changes in women.