Immunocytochemical differences in adenohypophyseal cells among adult Mongolian pony mares, stallions, and geldings.

OBJECTIVE

To analyze the sex difference in 6 kinds of adenohypophyseal cells of Mongolian ponies and the effect of prepubertal orchidectomy on adenohypophyseal cells.

SAMPLE POPULATION

Pituitary glands collected from 15 adult Mongolian ponies, 5 to 10 years old: 5 stallions, 5 mares, and 5 geldings, orchidectomized between the ages of 1 and 2 years.

PROCEDURE

Morphologic comparison of 6 kinds of adenohypophyseal cells among mares, stallions, and geldings was done, using immunocytochemistry and morphometry.

RESULTS

A sex difference was evident in the percentage of somatotrophs, gonadotrophs (follicle-stimulating hormone [FSH] and luteinizing hormone [LH] cells), and lactotrophs in adult ponies: somatotrophs were more numerous (P = 0.0003) in stallions (approx 40%) than in mares (approx 25%), whereas FSH and LH cells and lactotrophs were more numerous (P = 0.0116, P = 0.0044, P = 0.0085, respectively) in mares (approx 10, 20, and 24%, respectively) than in stallions (approx 6, 15, and 15%, respectively). Prepubertal orchidectomy markedly reduced the proportion of somatotrophs (approx 28%; P = 0.0016) and increased that of lactotrophs (approx 22%; P = 0.0318) in geldings, compared with stallions. The LH cell area was larger in mares than stallions (P < 0.0001). Prepubertal orchidectomy increased FSH (P = 0.0005) and LH (P < 0.0001) cell areas in adult geldings, compared with stallions.

CONCLUSIONS

A sex difference exists in adenohypophyseal cells of adult ponies: somatotrophs are more abundant in stallions; FSH and LH cells and lactotrophs are more abundant in mares. Our data indicate that equine testes during postnatal life may stimulate development of GH cells while suppressing development of FSH and LH cells and lactotrophs. The effects of prepubertal orchidectomy on pony somatotrophs and lactotrophs differ greatly from effects on those cells in mice.