Pituitary–gonadal axis and secondary sex characters in the spontaneously masculinized pintail, Anas acuta (Anatidae, Aves), with special regard to the gonadotrophs

Abstract This paper describes some aspects of the pituitary gland, gonads, and secondary sex characters of unusual pintails, Anas acuta , found in the wild. They were demonstrated to be females with partially masculinized plumage; i.e., their plumage showed various degrees of intersex, but the genital organs, syrinx, and electrophoretic pattern of sex-specific DNA were of the female type. Their left ovary underwent a marked involution and was associated with the mesonephros (the Wolffian body), as was the degenerated right ovary. Neither testicular tissue nor ovotestis was found in the gonad of either side. The oviduct was anatomically normal and comparable to that of the control adult. The plasma concentration of estradiol-17β (E2) was shown to be 5.7 ± 0.5 (mean ± SE) pg/ml in the masculinized birds, 7.0 ± 0.7 pg/ml in control males, and 22.5 ± 6.1 pg/ml in control females, whereas plasma testosterone (T) was below the detection level in all of the samples. As to the pituitary gland, hypertrophy and/or deformity of the pars distalis was evident in the majority of the masculinized birds. Among others, hyperactive gonadotrophs, mainly luteinizing hormone (LH)- and LH/follicle-stimulating hormone (FSH)-immunoreactive cells, were prominent in the entire gland; and typical signet ring cells (castration cells) or giant gonadotrophs were frequently observed. These changes in the gonadotrophs may have been caused by a feedback response to the physiologically ovariectomized condition in the masculinized birds. Causal factor(s) of the ovarian degeneration remain to be further investigated.