Effects of activin on hormone secretion by single female rat pituitary cells: analysis by cell immunoblot assay

Abstract

We investigated the effect of activin A on secretion of LH, FSH, and prolactin (PRL) by female cultured rat pituitary cells at the single-cell level by means of the cell immunoblot assay. Anterior pituitary cells from 8-week-old female rats were preincubated with or without activin A for 24 h, after which they were monodispersed and immediately used for cell immunoblot assay.The percentages of LH-, FSH-and PRLimmunoreactive cell blots detected were 5·5, 5·3 and 43·1%, respectively, of all pituitary cells applied to the transfer membrane. The percentage of LH-secreting cells and mean LH secretion per cell did not change after treatment with activin. In contrast, activin significantly increased the percentage of FSH-secreting cells and mean FSH secretion per cell to 136·0 and 114·5% respectively. In addition, activin significantly decreased the percentage of PRL-secreting cells and mean PRL secretion per cell to 52·2 and 72·0% respectively.These results suggest that (1) activin A has effects on female rat pituitary cells that increase not only the amount of FSH secretion per cell but also the number of FSHsecreting cells, and (2) activin A decreases both the amount of PRL secretion per cell and the number of PRL-secreting cells.

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“…In the pituitary gland, inhibin activity seems to be specifically directed to regulate gonadotroph functions, and no other functional role has been identified for this regulatory factor to date [15,17,19]; thus, the exclusive localization of inhibins in FSH-producing cells is not surprising. On the contrary, activins have been reported to modulate GH and PRL synthesis and secretion [17,18,29], and to influence the proliferation rate of GH-cells and PRLcells [18,19] and these data are in agreement with our results showing that most GH-cells and a few PRLcells express bA subunit which is indicative of the presence of activin A in these cell-types.…”

“…Recent studies, have provided further details about this FSH-secretagogue activity, demonstrating that inhibins are able to reduce transcription of FSH gene and to down-regulate GnRH receptors [16]. Further investigations, however, have pointed out that these proteins, and particularly activin, play also a role in the regulation of synthesis and release of growth hormone (GH) [17] and prolactin [18]; in addition, they are able to modulate the proliferation of GH-and PRLcells [18,19]. It has also been suggested that activin may influence the phenotype of pituitary cells, intervening in the temporary conversion from somatotrophs to gonadosomatotrophs during proestrus and diestrous of female rats [20].…”

Myostatin regulates pituitary development and hepatic IGF1

“…Differences in cell number between wild-type and Jekyll mice were independently replicated in both sexes and are complemented by myostatin's direct actions on GH3 cells. They are also consistent with the known actions of activin in GH3 cells and in the pituitary as it suppresses expression of Pit-1, a transcription factor that drives somato-trope and lactotrope development (14,19,23,38,49,64). Myostatin circulates at physiologically relevant levels that greatly exceed other ActRIIb ligands (54).…”

“…Activin A shares homology with myostatin and binds the same ActRIIb receptors. It also inhibits PRL secretion from primary rat lactotropes whereas in GH3 cells, it stimulates GH and inhibits PRL secretion at concentrations similar to those used in the current study (49,64).…”