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ABSTRACT
31P-Nuclear magnetic resonance (NMR) spectra were obtained in the living rat from 19 implanted prolactin-secreted pituitary tumours. Seven major peaks were found including those arising from the high energy phosphorus metabolites ATP and phosphocreatine. Intracellular pH of the tumours was measured and a relationship with prolactin secretion was observed, the highest plasma prolactin concentrations being associated with an intracellular pH >7·18. Repeated NMR measurements in three tumours over periods of up to 21 days revealed progressive changes with age, shown by an increase in inorganic phosphate, a decrease in high energy phosphorus metabolites and a decrease in prolactin secretion. It is concluded that NMR spectroscopy provides a useful method of studying intracellular events which accompany hormone secretion in vivo.
J. Endocr. (1985) 106, 349–353
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We had previously shown that neonatal leptin treatment programs thyroid function in adulthood. As both thyroid hormones (TH) and leptin increased thermogenesis, it was interesting to evaluate the effect of cold exposure on the thyroid function of neonate rats treated with leptin. Pups were divided into two groups: Lep, injected with leptin (8 μg/100 g/BW, s.c.) for the first 10 days of lactation and control (C), injected with saline. When they were 30 days old, the groups were subdivided into two subgroups: LepC and CC, which were exposed to 8 °C for 12 h and compared with C and Lep groups, maintained at 25 ± 1 °C. Serum leptin, TH, and TSH were measured by RIA. Type I liver deiodinase (D1) and mitochondrial α-glycerol-3-phosphate dehydrogenase (mGPD) activities were assayed by the release of 125I from 125I-reverse and colorimetric method respectively. Leptin receptor (OB-Rb) was evaluated by western blot. Lep group had hyperleptinemia (+22%) and lower free tri-iodothyronine (FT3; −33%). Cold exposure increased TH both in LepC and CC groups compared with respective controls free thyroxine (FT4:+63 and +39%; FT3:+75 and +40%). Liver D1 activity was lower in Lep (−22%) and increased with cold exposure (LepC +51% and CC +22%). The mGPD activity was lower in Lep (−34%) and increased (fourfold) when this group is cold exposed. Hypothalamic and thyroidal OB-Rb receptors were lower in Lep group (−47 and −36% respectively) and they were restored to normal levels after cold exposure. Leptin-programmed rats had higher TH response after cold exposure. OB-Rb had a fast response to cold exposure normalizing the lower levels observed in the leptin-programmed animals and may contribute to the higher TH cold responses.
