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Notes: We recently reported that galanin gene expression is markedly increased in the hyperplastic anterior pituitary gland of the human growth hormone-releasing hormone (hGHRH) transgenic mouse. To determine if another pituitary peptide hormone with putative growth-promoting activity is similarly affected, or if this effect is specific to the peptide galanin, we examined vasoactive intestinal polypeptide (VIP) gene expression in the hypothalamic-pituitary axis of male hGHRH transgenic and non-transgenic mice. The objectives were to: 1) assess VIP peptide concentrations, 2) estimate relative differences in VIP mRNA levels, 3) determine the effects of acute treatment with 17(3-estradiol on VIP peptide and mRNA levels, and 4) quantify the density of immunoreactive VIP pituitary cells by immunohistochemistry. Four to five month old male hGHRH transgenic mice and their non-transgenic siblings were identified by PCR. Immunoreactive VIP concentrations were decreased by 50% in the anterior pituitary glands of hGHRH transgenic mice as compared to non-transgenic siblings. In contrast, no differences in immunoreactive VIP concentrations were observed in the hypothalamus or frontal cerebral cortex of transgenic and non-transgenic mice. Treatment with 17β-estradiol significantly increased VIP concentrations in the anterior pituitary gland of both transgenic and non-transgenic mice; however, VIP peptide concentrations in the anterior pituitary glands of hGHRH transgenic mice remained 50% lower. Relative differences in VIP mRNA levels were estimated by RT-PCR, and were found to be 2.5-fold higher in the anterior pituitary glands of non-transgenic mice. In contrast, no differences in VIP mRNA levels in the cerebral cortex were detected between transgenic and non-transgenic mice. Treatment with 17(3-estradiol increased VIP mRNA levels in the anterior pituitary, but not in the cerebral cortex. In concert with the changes in VIP peptide and mRNA, the density of immunoreactive VIP pituitary cells was decreased approximately 50% in hGHRH transgenic mice. In conclusion, unlike galanin gene expression, VIP peptide and mRNA levels are significantly decreased in the anterior pituitary gland of hGHRH transgenic mice. Moreover, these changes appear to be tissue-specific and are likely due, in part, to the decrease in the density of VIP-containing pituitary cells in the hyperplastic pituitary. Although the pituitary cell type(s) synthesizing VIP remains unclear, these data suggest that VIP in the anterior pituitary is not stimulating pituitary tumor development in hGHRH transgenic mice.

Notes: Estrogen dramatically increases galanin mRNA and peptide levels in the rat anterior pituitary gland. We recently reported that galanin secretion in vitro from estrogen-exposed anterior pituitary cells is regulated by hypothalamic factors; dopamine and somatostatin inhibit galanin secretion, and thyrotrophin-releasing hormone stimulates galanin release. To determine whether galanin is regulated by a dopaminergic mechanism in vivo, we used ovariectomized Fischer 344 rats treated with 17ß-estradiol-containing or empty Silastic capsules. Rats were also administered bromocriptine, a dopamine receptor agonist, haloperidol, a dopamine receptor antagonist, or placebo for 2 weeks. Galanin peptide levels were measured in the anterior pituitary, neurointermediate lobe, medial basal hypothalamus, and plasma by radioimmunoassay. Plasma and pituitary prolactin levels were also determined. Bromocriptine decreased gaianin peptide levels in the anterior pituitary gland of ovariectomized rats by 30%, but had no effect on galanin in the neurointermediate lobe or medial basal hypothalamus. In contrast, haloperidol had no effect on galanin in the anterior pituitary or medial basal hypothalamus of ovariectomized rats, but decreased galanin peptide levels in the neurointermediate lobe. In the anterior pituitary gland of estrogen-treated rats, bromocriptine increased and haloperidol decreased both galanin and prolactin levels. Galanin mRNA levels were quantified in the anterior pituitary gland by solution hybridization. Bromocriptine increased galanin mRNA levels 3-fold in the anterior pituitary, whereas haloperidol had no effect. Galanin mRNA levels in the anterior pituitary were elevated 10-fold by estrogen. Bromocriptine reduced galanin mRNA levels in the pituitary by 50% in estrogen-treated rats, where again haloperidol had no effect. Estrogen increased plasma galanin levels 4-fold compared to ovariectomized rats and this effect was reduced 60% by bromocriptine and increased 20% by haloperidol.We conclude 1) galanin synthesis and release from the estrogen-exposed anterior pituitary gland is inhibited by a dopaminergic mechanism in vivo, 2) dopamine regulates galanin gene expression in the ovariectomized rat, 3) the changes in galanin peptide levels in the anterior pituitary of rats treated with estrogen and dopamine receptor ligands are primarily due to alterations in peptide secretion, and 4) galanin release from the neurointermediate lobe may also be regulated by a dopaminergic mechanism in vivo. These data, in conjunction with previous studies, provide evidence for the co-regulation of galanin and prolactin in estrogen-treated rats, and further discriminate between the regulation of galanin in the hypothalamus and pituitary gland.

Notes: Abstract. Transgenic mice in which overexpression of the transforming growth factor alpha (TGF-α) gene was directed by the keratin-14 promoter were used to study the regulation of cell cycle progression and proliferation in vivo in the olfactory epithelium. The level of TGF-α protein was 73% greater in the nasal-olfactory epithelium of the transgenic mice than in that of nontransgenic littermate controls. Increased levels of TGF-α protein were accompanied by a 5.8-fold selective increase in the proliferation of phenotypically characterized horizontal basal cells in the transgenics compared with nontransgenics; in contrast, globose basal cells exhibited a similar low level of proliferation in both transgenics and nontransgenics. The level of expression of epidermal growth factor receptor protein, the receptor for TGF-α, was also upregulated in the transgenics, indicating a role for the ErbB tyrosine kinase receptor family in the response to TGF-α in the olfactory epithelium. TGF-α overexpression was also associated with increased expression of several early cell-cycle-associated proteins, including the growth factor sensor cyclin D1, retinoblastoma, E2F-1 transcription factor, and cyclin E, indicating the progression of relatively quiescent progenitor cells in the G1 phase of the cell cycle toward the G1/S restriction point, after which the cells become refractive to mitogens. These results demonstrate a role for the growth factor TGF-α in the in vivo regulation of cell cycle progression and proliferation in the mitotically active olfactory epithelium in these transgenic mice.