Thyroidectomized rats were used to study the effects of a single injection of T3 on pituitary mRNA synthesis and hormone secretion. T3 was injected ip at doses of 0, 0.2, 1, or 5 micrograms/100 g body weight, and and animals were killed 24 h later. T3 caused a significant decrease in serum TSH, but caused no significant change in either serum GH or PRL. Pituitary mRNA was quantified by slot blot hybridization with cDNA probes specific for alpha-TSH, beta-TSH, PRL, and GH. We found that both the alpha and beta mRNA subunits decreased, that PRL mRNA remained relatively unchanged, and that GH mRNA increased with increasing T3 dose. The data show that a single dose of T3 can profoundly influence mRNA levels in the anterior pituitary; the lowest dose of T3 caused maximum inhibition of alpha-TSH mRNA while beta-TSH mRNA declined further in a dose-dependent manner.
Mass spectrometry imaging (MSI) has emerged as a powerful technique enabling spatially defined imaging of metabolites within microbial biofilms. Here, we extend this approach to enable differentiation of newly synthesized versus pre-existing metabolites across a co-culture. This is accomplished by MS imaging two soil microbes, Shewanella oneidensis MR1 and Pseudomonas stutzeri RCH2, that were administered heavy water (D 2 O) during growth on agar plates. For two species-specific diglyceride (DG) lipids, isotopic analysis was performed on each spectra collected across the co-culture to determine the relative amount of newly synthesized versus pre-existing lipid. Here, highest levels of new synthesis of RCH2 lipid was localized to border regions adjacent to S. oneidensis MR1, while the MR1 lipid showed highest levels in regions further from RCH2. Interestingly, regions of high lipid abundance did not correspond to the regions with highest new lipid biosynthesis. Given the simplicity and generality of using D 2 O as a stable isotopic probe combined with the accessibility of kMSI to a range of MSI instrumentation, this approach has broad application for improving our understanding of how microbial interactions influence metabolite biosynthesis.
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