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      Thyroid Hormones Regulate the Expression of Somatostatin Receptor Subtypes in the Rat Pituitary

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          Circulating TSH levels are increased in hypothyroidism and suppressed in hyperthyroidism. On the other hand, the hypothalamic hormone somatostatin suppresses basal and TRH-induced TSH release, an effect which is enhanced by thyroid hormones. To investigate whether the effects of thyroid hormones on TSH secretion may be mediated in part through alterations in the gene expression of pituitary somatostatin receptors (SSTR), 3-week-old male Sprague-Dawley rats were rendered hypothyroid with antithyroid drugs for 3 weeks. Total RNA extracted from anterior pituitaries were analysed for SSTR mRNA levels, using Northern blot hybridization. Compared to controls, hypothyroid rats had significantly lower pituitary mRNA levels of SSTR1 and SSTR2 (p < 0.0001 for both, n = 16); the reductions could be prevented by T<sub>4</sub> supplementation (3 µg/100 g body weight/day i.p.). In vitro studies using GH<sub>4</sub>C<sub>1</sub> rat pituitary cells showed that the addition of T<sub>3</sub> 10<sup>–8</sup>  M to cells cultured in charcoal-stripped bovine calf serum resulted in significant increases in mRNA levels of SSTR1 (p < 0.0001; n = 7) and the two transcripts of SSTR2 (p < 0.0005; n = 7). The increase for SSTR1 showed no further increase with higher doses of T<sub>3</sub>, but was time-dependent and could be seen consistently after 8 h of incubation. We conclude that thyroid hormones regulate the gene expression of SSTR subtypes in the pituitary, via a direct action on anterior pituitary cells. Changes in SSTR gene expression may contribute to the increase in circulating TSH levels in hypothyroidism.

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          Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.

          A new method of total RNA isolation by a single extraction with an acid guanidinium thiocyanate-phenol-chloroform mixture is described. The method provides a pure preparation of undegraded RNA in high yield and can be completed within 4 h. It is particularly useful for processing large numbers of samples and for isolation of RNA from minute quantities of cells or tissue samples.
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            Sequence analysis of the promoter region of the rat somatostatin receptor subtype 1 gene

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              Sex-related differences and thyroid hormone regulation of vasoactive intestinal peptide gene expression in the rat brain and pituitary

              To determine the effects of hypothyroidism and sexual dimorphism on the gene expression of vasoactive intestinal peptide (VIP) in the rat brain, VIP mRNA levels were measured in the cerebral cortex, hypothalamus and anterior pituitary of control and hypothyroid (thionamide-treated) rats. A tissue-specific increase in VIP mRNA level was observed in the hypothyroid pituitary. In addition, higher levels of VIP mRNA were found in the pituitaries of male rats suggesting a sex-related difference in VIP gene expression. Similar differences were not observed in the cortex or hypothalamus.

                Author and article information

                S. Karger AG
                June 1999
                14 June 1999
                : 69
                : 6
                : 460-464
                Department of Medicine, University of Hong Kong, Hong Kong, China
                54450 Neuroendocrinology 1999;69:460–464
                © 1999 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 3, References: 20, Pages: 5
                Thyroid Hormone Feedback on Brain and Pituitary


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