Effect of exposure to long days on the secretion of oestradiol, oestrone, progesterone, testosterone, androstenedione, cortisol and follicle-stimulating hormone in intact and spayed ferrets.

The changes in concentration of plasma oestradiol, oestrone, progesterone, androstenedione, testosterone, cortisol and FSH were followed in intact female ferrets brought into oestrus by extension of the photoperiod from 8 to 16 h daily. An additional group of spayed females was similarly exposed to the extended photoperiod. There was no change in the blood oestrone, androstenedione and testosterone levels in the spayed females; the concentration of oestradiol, progesterone and FSH fell, while that of cortisol rose after 6 weeks. The intact females showed no change in plasma oestrone and cortisol concentrations, a rise in plasma oestradiol associated with the onset of oestrus, and falls in the blood levels of testosterone, androstenedione, progesterone and FSH. These results indicate that the changes in plasma gonadal steroid levels after extension of the photoperiod differ markedly from those in rodents or ruminants.