β-Mercaptoethanol Differentially Acts on the Rat Somatotrophs and Lactotrophs in Primary Culture to Suppress the Secretion of Immunoreactive Hormones

Summary

We previously reported that β-mercaptoethanol (ME) reduced the content of immunoreactive prolactin (iPRL) within the adenohypophyseal cells, primarily through its direct effect on the disulfide bonding of the PRL molecule. Because of the structural similarities between PRL and growth hormone (GH), the effects of ME on the hormonal dynamics of iGH were compared to those of iPRL. ME reduced secretion and intracellular content of both iGH and iPRL in the cultured rat adenohypophyseal cells. However, iGH was more resistant to the suppressive effects of ME than iPRL. This was particularly so with regard to the intracellular hormonal contents. While 0.01% ME caused approximately 90% reduction in the iPRL content of the lactotrophic cells, the highest tested dose of ME, i.e. 0.1%, showed only 20% reduction in the iGH content of the somatotrophic cells. Also, the minimum effective dose of ME to suppress iGH secretion was 10-fold higher than that required for the suppression of iPRL secretion. Significant suppression of iGH secretion was not observed until 120 min after the onset of ME incubation as opposed to 2-9 min for the suppression of iPRL. These findings, together with the lack of any direct effects of ME on the iGH molecule itself, strongly suggested that ME acted via different mechanisms and/or pathways in the somatotrophs and lactotrophs to suppress respective hormonal dynamics. It was also noteworthy that there was a striking difference with regard to the reversibility of the ME effects, depending on whether the cells were under the stimulation of GH-releasing hormone (GH-RH); the suppressive effects of ME were more pronounced, yet completely reversible with GH-RH stimulation, which was not the case without GH-RH. This suggested differential actions of ME on two secretory components of iGH, basal and GH-RH-stimulated secretion.

Key words

Mercaptoethanol - Growth Hormone - Prolactin - GH-RH