Effect of Neonatal Thyroidectomy on Growth Hormone Secretion in the Rat
Total Page：16
File Type：pdf, Size：1020Kb
245 Effect of neonatal thyroidectomy on growth hormone secretion in the rat S Kitauchi, H Yamanouchi, N Hirano, S Tone´ 1 and M Shiino Department of Anatomy, Wakayama Medical College, Wakayama 640-8155, Japan and 1Department of Radiation Research, Tokyo Metropolitan Institute of Medical Science, Tokyo 133-0021, Japan (Requests for offprints should be addressed to S Kitauchi, Department of Anatomy, Wakayama Medical College, 27-kyubancho, Wakayama-shi, 640, Japan) Abstract The influence of neonatal thyroidectomy (Tx) on GH pituitary GH cells were significantly decreased in number production was investigated by means of Northern blot 15 and 20 days after Tx. These data suggest that GH analysis. Tx resulted in a significant decrease in pituitary mRNA is transcribed, independent of thyroid hormone, GH mRNA levels after 10, 15 and 20 days. The changes in the rat anterior pituitary gland during early neonatal life. of pituitary GH mRNA were soon reflected in pituitary In addition, the present study ascertained that GH depen- GH content. There was, however, no significant differ- dence on thyroid hormone is acquired between the 5th ence in pituitary GH mRNA levels and GH content and 10th day of neonatal life. between Tx and sham-operated rats at 5 days old. The Journal of Endocrinology (1998) 157, 245–250 Introduction Materials and Methods It is known that thyroid hormone is an important regulator Animals of growth hormone (GH) production in the rat somato- Sprague–Dawley derived rats were bred in our animal troph (Peake et al. 1973). Recent work suggests that quarters. Female and male neonatal rats were used in this thyroid hormone directly induces the transcription of the experiment. Tx was performed under anesthesia induced GH gene (Evans et al. 1982, Spindler et al. 1982, Casanova by cold temperature within 24 h of birth. After the et al. 1985, Brent et al. 1991). On the other hand, operation the animals were warmed under a tungsten lamp previous studies demonstrated that GH dependence on until they began to move actively, and then returned to thyroid hormone was not clear during the early neonatal their mothers. Controls were sham operated by only period (Coulombe et al. 1980, Seo et al. 1981). However, cutting the skin and exposing the gland. The mothers and the quantitative aspects of GH gene expression their pups were housed in individual cages under con- during neonatal hypothyroidism have not been well trolled illumination (ratio of 14 h light:10 h darkness) and investigated. In the rat, serum thyroid hormone concen- temperature (26 C). They were fed Purina Laboratory tration is low at birth and increases to adult values in ) chow with water freely available. On days 5, 10, 15 and the weaning stage (Dussault & Labrie 1975). The 20, the pups were weighed and killed by decapitation. thyroid hormone system is still immature in the neonatal Immediately after exsanguination pituitary glands were period. Is thyroid hormone really essential for GH produc- removed, and stored at 80 C until RIA and Northern tion in the neonatal rat, as in older animals? To answer " ) blot analysis. For immunocytochemistry and electron this question, we investigated the influence of neonatal microscopy, pituitary glands were fixed immediately. The thyroidectomy (Tx) on GH gene expression in the rat blood was centrifuged, and the serum was collected and by using Northern blot analysis. We also evaluated stored at 20 C. In all experiments, rats were killed the amount of pituitary GH content to compare with " ) between 1400 and 1600 h. The absence of the thyroid GH mRNA levels. Additionally, we performed a gland in Tx rats was verified at autopsy. morphometrical analysis of pituitary GH cells in parallel with the biochemical examinations using immuno- cytochemistry. Finally, we observed immunoelectron RNA extraction and Northern blot analysis microscopic profiles of GH cells at all experimental stages in order to confirm the effects of Tx on GH cells Total RNA was prepared by homogenization of pituitary morphologically. glands in guanidinium isothiocyanate followed by acid Journal of Endocrinology (1998) 157, 245–250 1998 Society for Endocrinology Printed in Great Britain 0022–0795/98/0157–0245 $08.00/0 Downloaded from Bioscientifica.com at 09/28/2021 01:33:31AM via free access 246 S KITAUCHI and others · Neonatal thyroidectomy and GH phenol–chloroform extraction (Chomczynski & Sacchi were rinsed in PBS and stained by the streptavidin–biotin 1987). RNA was ethanol precipitated, redissolved in method using a HISTOFINE SABPO Kit (Nichirei Corp. sterile water and quantified by absorbance at 260 nm. Tokyo, Japan) with diaminobenzidine as a chromogen. Two µg of total RNA from one pituitary were separated Rabbit antibody against rat GH was provided by Dr K on a l% agarose gel containing formalin and trans- Wakabayashi of the Institute for Molecular and Cellular ferred onto a nylon membrane (Hybond N, Amersham Regulation, Gunma University. International plc, Amersham, Bucks, UK) by capillary The sections were visualized with a microscope action (Sambrook et al. 1989). The blot was hybridized equipped with a CCD TV camera. Ten images were with 32P-labeled rat GH cDNA. The rat GH cDNA insert captured at random for each pituitary and analyzed with a (pRGH-1, 0·8 kb (Seeburg et al. 1977)) was excised from Macintosh computer using Image 1·5 (NIH, USA; public the pBR322/Hind III site and radiolabeled with 32Pby domain). Background density points were removed by nick translation (Rigby et al. 1977) to about 108 c.p.m./µg thresholding the image. The number of the cells that DNA using a commercial kit (Takara Shuzo Co. Ltd, reacted with anti-GH antibody was counted. Kyoto, Japan). The GH cDNA probe was removed, and For immunoelectron microscopic examination, pitu- the filters were rehybridized with human ribosomal DNA itary tissues were cut into small pieces and fixed in a (5* portion, pHr21Ab (Safrany et al. 1989)) to hybridize solution consisting of 3% paraformaldehyde and 3% with 18S rRNA for the comparison of the amount of glutaraldehyde in 0·1 M cacodylate buffer (pH 7·4) for 2 h RNA in samples loaded on the gel between experimental at room temperature and then post-fixed in 0·1% osmium groups. The human ribosomal DNA was excised from tetroxide dissolved in 0·1 M cacodylate buffer for 1 h at the pUC13/EcoRI site and radiolabeled as GH cDNA. 0 )C. After routine dehydration, the tissues were em- Radioactivity on the filters was quantified using a Bio bedded in Epon-Araldyde mixture. The thin sections were Imaging Analyzer BAS 2000 (Fujix, Tokyo, Japan). The reacted by the protein A-gold method described pre- ratio of the intensity of the GH mRNA band to that of the viously (Bendayan & Zollinger 1983). Control immuno- 18S rRNA band was used to express the relative amounts cytochemical tests were carried out by substituting normal of mRNA present. Rat GH cDNA was provided by Dr rabbit serum or PBS for specific antiserum. Electron J D Baxter of the University of California, USA. Human microscopic observations were made with a Hitachi 7000 ribosomal DNA was provided by Health Science electron microscope. Research Resources Bank (Osaka, Japan). Data analysis RIA For Northern blot analysis and RIA, experiments were The pituitary glands were homogenized in 0·05 M reproduced six times. For immunocytochemistry and NaHCO3–Na2CO3 buffer (pH 10·0) and diluted with immunoelectron microscopic examination, experiments BSA-PBS. Pituitary GH content was measured by the were reproduced four times. Data are expressed as double-antibody RIA using reagents provided by the mean&.. Statistical analyses were performed by the National Hormone and Pituitary Program, Rockville, Mann–Whitney U test. We considered differences signifi- MD, USA (rat GH RIA kit, reference standard NIDDK- cant at P<0·05. rGH-RP2) and Biosignal Research Center, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan (second antisera, HAC-MKA2–02GTP88). Results The intraassay and interassay coefficients of variation were 3·15 and 3·80% respectively. Serum thyroxine (T4)con- Serum T concentrations centration was measured using a commercial kit (Eiken 4 Co., Tokyo, Japan). Serum T4 concentrations were significantly decreased: 0·35&0·11 vs 1·75&0·78, 0·44&0·15 vs 4·29&1·99, 0·98&0·49 vs 8·24&2·98, 1·58&0·92 vs 5·72& Immunocytochemistry and morphometry 1·24 µg/dl (n=6, P<0·005) at 5, 10, 15 and 20 days after Pituitaries were fixed in Bouin’s fluid for 24 h at 4 )C, Tx respectively. dehydrated and embedded in paraffin. Serial frontal sec- tions (2 µm) were mounted on glass slides and deparaffin- GH mRNA levels of Tx and sham-operated rats in the ated. They were incubated in ethanol with 3% H O to 2 2 neonatal period inactivate endogenous peroxidase activity, and immersed in 10% normal goat serum in 0·9% NaCl–0·01 M phos- In the early neonatal period, pituitary GH mRNA content phate buffer, pH 7·5, at room temperature for 30 min. was not affected by Tx. As shown in Fig. 1, no significant Then, rabbit antibody against rat GH was applied to the differences were found between Tx and sham-operated sections. After overnight incubation at 37 )C, the sections pups in the amount of pituitary GH mRNA at the 5th day. Journal of Endocrinology (1998) 157, 245–250 Downloaded from Bioscientifica.com at 09/28/2021 01:33:31AM via free access Neonatal thyroidectomy and GH · S KITAUCHI and others 247 Figure 1 Effect of Tx on the expression of pituitary GH mRNA. Pituitary GH mRNA and 18S rRNA in Tx and sham-operated (S) neonatal rats on days 5, 10, 15 and 20 were detected by Northern blot analysis as described in Materials and Methods.