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Abstract

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. (Am J Vet Res 1998;59:262–266)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To analyze and characterize adenoma and hyperplasia of the pars intermedia (PI) of Thoroughbred mares.

Animals

165 Thoroughbred mares, without clinical signs of hyperadrenocorticism that had been euthanatized or had died, of causes such as sudden death, colic, pneumonia, or trauma, and were necropsied. Five of those horses, 17 to 25 years old, had a large pituitary gland at necropsy. Eight mares, 5 to 15 years old with normal-size pituitary gland, were selected at random for comparison.

Procedure

A morphologic comparison of the pituitary gland between horses with and without tumors of the PI was conducted by use of immunocytochemistry and morphometry.

Results

In horses with normal pituitary gland, the PI was supplied by a vast capillary or sinusoidal plexus, which connected that in the pars distalis (PD) with that in the pars nervosa (PN). Cells of the PI stained slightly with ACTH antiserum, but some cells in the border region, which is contiguous to the PD, were strongly ACTH immunoreactive. At necrospy, horses with an enlarged pituitary gland also had adenoma of the pituitary gland involving the PI. Cells of the border region were hypertrophied and stained strongly with ACTH antiserum. The area and number of individual tumor cells of the border region of the PI of horses with adenoma were significantly increased, compared with those in horses with normal pituitary gland.

Conclusions

Cells of the PI-PD border region may secrete substantial quantities of ACTH, owing to stimulation by corticotropin-releasing factor. Adenoma and hyperplasia of the PI in Thoroughbred mares may be associated with hyperadrenocorticism. (Am J Vet Res 1997;58:920–924)

Free access
in American Journal of Veterinary Research