Retinoic acid stimulates growth hormone synthesis in human somatotropic adenoma cells: characterization of its nuclear receptors.

In order to gain a better understanding on the possible role of retinoic acid (RA) on human GH secretion, we have characterized the expression of its nuclear receptors in somatotropic adenoma cell extracts. By immunoblotting with rabbit polyclonal antibodies directed against RAR alpha, beta, and gamma and RXR alpha and beta, we could only detect the presence of RAR alpha and RXR alpha proteins. The predominant expression of RXR alpha was confirmed at the mRNA level by Northern and slot-blot analysis.

[Paracrine regulation of anterior pituitary hormones by neuropeptides].

The hypothalamus is the source of neuropeptides which, being secreted into the portal system, control the synthesis and the secretion of the anterior pituitary hormones. Besides the well characterized hypothalamic central control and the hormonal peripheral control, recent studies have shown, in the anterior pituitary, the expression, among many other regulatory factors, of neuropeptides that are identical to those produced by the hypothalamus and that seem involved in the local control of anterior pituitary functions through autocrine or paracrine mechanisms. The presence of the neuropeptide mRNAs, precursors and mature forms of the peptides in anterior pituitary tissues as well as the secretion of the mature peptides argue in favor of the intrinsic ability of the normal and tumoral anterior pituitary to express neuropeptides.

Evidence of thyrotropin-releasing hormone (TRH) gene expression in rat anterior pituitaries and modulation by estrogens of TRH-like immunoreactivity and TRH-elongated peptide contents.

TRH gene expression in the anterior pituitary has previously been reported in the human in vivo and in the rat in vitro. Until now, modulation of this synthesis with glucocorticoids and thyroid hormones has been observed in rats. The present study demonstrates for the first time that the TRH gene is also expressed, in vivo, in the rat anterior pituitary and that anterior pituitary TRH-like immunoreactivity (TRH-LI) and elongated forms of the immediate TRH progenitor sequence (TRH-elongated peptide) contents are also modulated by estrogens (E2).

Vitamin A and retinoic acid stimulate within minutes cAMP release and growth hormone secretion in human pituitary cells.

In order to gain a better understanding on the possible role of vitamin A (VA) and retinoic acid (RA) on human growth hormone (GH) secretion, we used the physiological model of pituitary cells perifusion. In perifused cells from pituitary somatotropic adenomas, RA induced within minutes a peak of GH secretion. This effect was dose dependent, maximal effect being observed with 100 nM.