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Functional Heterogeneity in Somatotrophs Isolated from the Rat Anterior Pituitary¹

Department of Biochemistry and Biophysics, The Pennsylvania State University University Park, Pennsylvania 16802

Abstract

Somatotrophs in suspensions of anterior pituitary cells from adult male rats can be separated into 2 fractions by density gradient centrifugation. In addition to their different densities, somatotrophs in these 2 fractions can be distinguished morphologically by their staining characteristics and ultrastructure. Somatotrophs of lesser density (type I; 1.068 g/cm³) have fewer secretory granules and a more extensive Golgi apparatus than the somatotrophs of greater density (type II; 1.073 g/cm³).

Responsiveness of type I and type II cells to secretory agents (i.e., dibutyryl cyclic adenosine monophosphate, somatostatin, thyroxine, and hydrocortisone) was evaluated by GH radioimmunoassay. Type I cells were consistently more responsive (% GH release) than type II cells. During 7 days in culture, type I cells produced more (200%) GH than they initially contained, whereas type II cells did not show evidence of increased GH production. Hydrocortisone significantly stimulated GH production in type I, but not type II cells. These results support the hypothesis that at least 2 functionally distinct populations of somatotrophs are present in the anterior pituitary gland of the adult male rat.

Footnotes

¹ Supported by NSF Grant BMS 71-01568 A02.

² Current address: Southwestern Medical School, Department of Physiology, Dallas, Texas 75235.

³ To whom reprint requests should be sent.

⁴ Current address: Southwestern Medical School, Department of Biochemistry, Dallas, Texas 75235.

Received November 8, 1976.

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