Posthatch ontogeny and sex-related differences in somatotroph numbers in the chicken adenohypophysis.

Adenohypophyseal total cell and somatotroph numbers were determined in male and female chicks over the early (12 wk) growth period. In a first experiment, adenohypophyses from male and female broiler-strain (Hubbard x Hubbard) chicks were harvested at 2 wk intervals from 2 to 12 wk of age. Glands were enzymatically dispersed to yield uniform cell suspensions that were fixed and stained (Herlant's Tetrachrome system) to distinguish somatotrophs. Percentages of somatotrophs in the total adenohypophyseal cell population were similar for both sexes (P greater than .05) and declined with age (P less than .01) from a high of 16.8 +/- .79% (least squares mean +/- SEM) at 2 wk to 6.3 +/- .88% at 12 wk. From 2 to 6 wk of age, total adenohypophyseal cell numbers increased over two-fold (P less than .01) but sexes did not differ significantly. From 8 to 12 wk of age, however, total cell numbers reached a plateau and were higher in males than females (P less than .01). Similarly, the absolute numbers of somatotrophs per adenohypophysis increased from 2 to 6 wk of age, where it reached a plateau. Somatotroph numbers in males were twice those in females over the 8 to 12-wk growth period. In a second experiment, the percentages of somatotrophs in the total adenohypophyseal cell population from males of a slower growing, layer-type breed (White Leghorn) were compared to those of Hubbard males at 4, 8, and 12 wk of age. Leghorn males were higher than Hubbard males over all ages in percentages of somatotrophs (14.9 +/- .87% vs. 10.8 +/- .71%; P less than .01), however, the absolute numbers of somatotrophs per pituitary of the two breeds did not differ.