Delayed Postnatal Growth and Anterior Pituitary Development in Growth-Retarded (grt) Female Mice.

Growth-retarded (grt) mice display primary congenital hypothyroidism due to the hyporesponsiveness of their thyroid glands to thyroid-stimulating hormone (TSH). We examined somatic growth, anterior pituitary development, and hormonal profiles in female grt mice and normal ones. Although growth in grt females was suppressed 2 weeks after birth, the measured growth parameters and organ weights gradually increased and finally reached close to the normal levels. Grt mice exhibited delayed eye and vaginal openings and remained in a state of persistent diestrus thereafter, plasma estrogen levels being lower than those in normal mice. Grt mice that received normal-donor thyroids showed accelerated growth and their body weights increased up to the sham-normal levels, indicating the importance of early thyroid hormone supplementation. In the anterior pituitary, there were fewer growth hormone (GH) and prolactin (PRL) cells in grt mice than in normal mice as examined at 12 weeks after birth, but the numbers of these cells did not differ from those in normal mice after 24 weeks. Grt mice had more TSH cells than normal mice until 48 weeks. Plasma GH levels in grt mice were lower than those in normal mice at 2 weeks, but did not differ substantially after 5 weeks. Compared with normal mice, grt mice had significantly lower plasma PRL and thyroxine levels, but notably higher TSH levels until 48 weeks. These findings indicate that thyroid hormone deficiency in grt mice causes delayed development and growth, and inappropriate development of GH, PRL and TSH cells, followed by the abnormal secretion of hormones by these pituitary cells.

Insights into the Nanobiology of Growth Hormone Secretion.

The fact that partially empty vesicles are generated following cell secretion suggested that secretory vesicles do not collapse at the cell plasma membrane but, rather, transiently dock and fuse at the plasma membrane to expel a portion of their contents before retracting or undergoing endocytosis into the cell. Such a process has also been referred to in the literature as a "kiss-and-run" mechanism. This mechanism of cell secretion was conclusively demonstrated following the discovery of permanent cup-shaped lipoprotein structures at the cell plasma membrane, called "porosomes", where secretory vesicles transiently dock and fuse to expel intravesicular contents from the cell. Porosomes are present in all secretory cells, from the digestive enzyme-secreting pancreatic acinar cells, to the hormone-releasing growth hormone cells, mast cells, chromaffin cells, hair cells of the inner ear, to neurons secreting neurotransmitters. Hence, it can be asserted that porosomes are the universal secretory machinery in the plasma membrane of secretory cells. Therefore, the discovery of the porosome has resulted in a paradigm shift in our understanding of cell secretion. Rapid transport of secretory vesicles containing hormones to the plasma membrane is powered by high-energy molecules such as ATP, GTP or NADH. Immunogold labeled transmission electron microscopy (TEM) was used to determine the total number of secretory vesicles in resting and in GH-stimulated porcine pituitary cells. We identified three categories of vesicles: filled, empty, and partly empty. Resting GH cells contained more than twice as many filled vesicles than did the stimulated ones. However, stimulated cells contained nearly twice as many empty vesicles and 2.5 times more partly empty vesicles than did resting cells. Secretory vesicles in GH cells further revealed the localization of GH only in electron dense vesicles in both resting and stimulated cells. No change in the total number of secretory vesicles following secretion was observed. These results are consistent with a mechanism that, after stimulation of secretion, vesicles transiently dock and fuse at the porosome to establish a fusion pore, through which intravesicular contents are released.

Phosphorylation of BK channels modulates the sensitivity to hydrogen sulfide (H2S).

INTRODUCTION: Gases, such as nitric oxide (NO), carbon monoxide (CO), or hydrogen sulfide (H2S), termed gasotransmitters, play an increasingly important role in understanding of how electrical signaling of cells is modulated. H2S is well-known to act on various ion channels and receptors. In a previous study we reported that H2S increased calcium-activated potassium (BK) channel activity. AIMS: The goal of the present study is to investigate the modulatory effect of BK channel phosphorylation on the action of H2S on the channel as well as to recalculate and determine the H2S concentrations in aqueous sodium hydrogen sulfide (NaHS) solutions. METHODS: Single channel recordings of GH3, GH4, and GH4 STREX cells were used to analyze channel open probability, amplitude, and open dwell times. H2S was measured with an anion selective electrode. RESULTS: The concentration of H2S produced from NaHS was recalculated taking pH, temperature salinity of the perfusate, and evaporation of H2S into account. The results indicate that from a concentration of 300 µM NaHS, only 11-13%, i.e., 34-41 µM is effective as H2S in solution. GH3, GH4, and GH4 STREX cells respond differently to phosphorylation. BK channel open probability (Po) of all cells lines used was increased by H2S in ATP-containing solutions. PKA prevented the action of H2S on channel Po in GH4 and GH4 STREX, but not in GH3 cells. H2S, high significantly increased Po of all PKG pretreated cells. In the presence of PKC, which lowers channel activity, H2S increased channel Po of GH4 and GH4 STREX, but not those of GH3 cells. H2S increased open dwell times of GH3 cells in the absence of ATP significantly. A significant increase of dwell times with H2S was also observed in the presence of okadaic acid. CONCLUSIONS: Our results suggest that phosphorylation by PKG primes the channels for H2S activation and indicate that channel phosphorylation plays an important role in the response to H2S.

Involvement of Polyamine in Growth Hormine Secretion from the GH3 Cells / 대한내분비학회지

BACKGROUNDS: Polyamines are known to be essential for cell growth and differentiation. Recently, possible roles of the polyamine in signal transduction as neurotransmitter, modulator, or second messenger are suggested in many studies. Furthermore, it is widely studied that possible roles of polyamine are involved in the action of hormone. Thus, it was to investigate the effect of polyamines in the cell proliferation and secretion of GH from the GH cells. METHODS: Cells(5*10 cells/mL) were incubated for 3 days in DMEM containing test drugs and labeled with 20pCi/mL of [S]-methionine for 2 hr. Proteins secreted into the medium were separated by 13% SDS-gel electrophoresis, then autoradiography was performed to identify radiolabeled proteins. [S]-methionine labelled GH was identified by radioimmuno-precipitation. Total protein synthesis was determined from the radioactivity of the cell homogenate by liquid scintillation counter. The intracellular polyamine content was determined by HPLC. RESULTS: Externally added polyamines(putrescine, spermidine, spermine) induced cell proliferation in a dose-dependent manner at proper concentrations, specifically 50pM putrescine increased GH secretion, DFMO or MGBG, which is polyamine biosynthetic inhibitor, inhibited GH secretion in a dose-dependent fashion, In the cells treated with 20mM or 0.01mM MGBG, total protein synthesis were decreased only to 90 or 76% of the control levels and cell proliferation was also slightly inhibited. However the secretion of GH was severely blocked to 37% or 35% of the control. Hydrocortisone at 5 pM stimulated the secretion of GH to 153% of basal secretion, also doubled intracellular putrescine content. CONCLUSION: The present data show that externally added polyamines induced cell proliferation and GH secretion. Also, extemally added putrescine stimulated GH secretion significantly. GH secretion was inhibited by polyamine metabolic inhibitor in a dose-dependent manner and polyamine metabolic inhibitors, at proper concentrations, specifically blocked GH secretion without any significant influence on the total protein synthesis. The above results imply the involvement of polyamine in GH secretion.