[Endocrine function of the ovaries of blue foxes (Alopex ladopus) during postnatal ontogenesis].

Progesterone, androgen and estradiol levels in the blood plasma were radioimmunologically studied in female Alopex lagopus aged 2 to 9 months with different weight at birth. The blood sex steroid level showed a sharp elevation at the age of 4 months. The weight gain stops by this time. Thus, by the age of 4 months in females the sexual system becomes mature. From the age of 5 to 8 months there is a fall of the blood sex hormones, corresponding to anestrus, and by the age of 9 months there is a significant rise in the level of sex hormones pointing to activation of the ovarian function by the reproductive season. Large females had a tendency to earlier sexual maturation in comparison with the small ones. Since in the female animals of the species under study two peaks of sexual hormone concentration were revealed in the course of a year it is suggested that at the preceding evolutional stages representatives of the family were capable of reproducing twice a year.