Selective blockade of oxytocin and vasopressin V(1a) receptors in anaesthetised rats: evidence that activation of oxytocin receptors rather than V(1a) receptors increases sodium excretion.

BACKGROUND: Although it is known that moderate-to-high doses of the neurohypophysial hormones oxytocin and vasopressin are natriuretic, doubts remain over the identity of the receptors responsible. To address this issue, we have used highly selective antagonists of oxytocin and vasopressin receptors in animals with elevated endogenous circulating levels of the 2 hormones. METHODS: Rats were anaesthetised and prepared surgically for clearance studies, thereby raising plasma oxytocin and vasopressin concentrations. Sodium excretion, glomerular filtration rate and lithium clearance (an index of end-proximal fluid delivery) were measured: first during a control period, then after administration of the selective oxytocin receptor antagonist desGly-NH(2),d(CH(2))(5)[D-Trp(2),Thr(4),Dap(5)]OVT, the selective vasopressin V(1a) receptor antagonist d(CH(2))(5)[Tyr(Me)(2),Dab(5)]AVP, or vehicle alone. RESULTS: Absolute and fractional sodium excretion fell in rats given the oxytocin antagonist (by 32 and 27%, respectively, compared with corresponding values in vehicle-infused rats), but not in those given the V(1a) antagonist or vehicle. Antinatriuresis was associated with a small reduction in the ratio of sodium clearance to lithium clearance (an index of the fraction of distally delivered sodium that escapes reabsorption in the distal nephron). CONCLUSIONS: These results corroborate previous studies showing that activation of oxytocin receptors increases sodium excretion and imply that the natriuretic effect of elevated plasma vasopressin concentrations results from stimulation of oxytocin receptors.

NMR and pattern recognition studies on the time-related metabolic effects of alpha-naphthylisothiocyanate on liver, urine, and plasma in the rat: an integrative metabonomic approach.

We present here a novel integrative metabonomic approach to probe toxic effects of drugs in experimental animals using alpha-naphthylisothiocyanate (ANIT) as a model hepatotoxicant. Male Han-Wistar rats were dosed with ANIT (150 mg/kg, n = 25), and plasma and liver samples were collected for NMR and magic-angle spinning (MAS) NMR spectroscopy at 3, 7, 24, 31, and 168 h postdosing. Urine was collected continuously for 3 days prior to dosing and up to 168 h postdose. Histopathology and plasma clinical chemistry was also performed at all time points. Liver samples were analyzed either intact by 600 MHz 1H MAS NMR techniques or using high resolution (liquid state) 1H NMR of water-acetonitrile extracts. These data were related to sequential 1H NMR measurements in urine and plasma using pattern recognition methods. 1D 1H NMR spectra were data-reduced and analyzed using principal components analysis (PCA) to show the time-dependent biochemical variations induced by ANIT toxicity. From the eigenvector loadings of the PCA, those regions of the 1H NMR spectra and hence the combinations of endogenous metabolites marking the main phase of the toxic episode were identified. The ANIT-induced biochemical manifestations included a hepatic lipidosis associated with hyperlipidaemia; hyperglycaemia and glycosuria; increased urinary excretion of taurine and creatine; a shift in energy metabolism characterized by increased plasma ketone bodies with reduced urinary excretion of tricarboxylic acid cycle intermediates and raised hepatic bile acids leading to bile aciduria. The integration of metabolic data derived from several sources gives a holistic approach to the study of time-related toxic effects in the intact system and enables the characterization of key metabolic effects during the development and recovery from a toxic lesion.

High-resolution magic angle spinning (1)H NMR spectroscopy of intact liver and kidney: optimization of sample preparation procedures and biochemical stability of tissue during spectral acquisition.

High-resolution magic angle spinning (MAS) (1)H NMR spectroscopy has been used to investigate the biochemical composition of whole rat renal cortex and liver tissue samples. The effects of a number of sample preparation procedures and experimental variables have been investigated systematically in order to optimize spectral quality and maximize information recovery. These variables include the effects of changing the sample volume in the MAS rotor, snap-freezing the samples, and the effect of organ perfusion with deuterated saline solution prior to MAS NMR analysis. Also, the overall biochemical stability of liver and kidney tissue MAS NMR spectra was investigated under different temperature conditions. We demonstrate improved resolution and line shape of MAS NMR spectra obtained from small spherical tissue volume (12 microl) rotor inserts compared to 65 microl cylindrical samples directly inserted into the MAS rotors. D(2)O saline perfusion of the in situ afferent vascular tree of the tissue immediately postmortem also improves line shape in MAS NMR spectra. Snap-freezing resulted in increased signal intensities from alpha-amino acids (e.g., valine) in tissue together with decreases in renal osmolytes, such as myo-inositol. A decrease in triglyceride levels was observed in renal cortex following stasis on ice and in the MAS rotor (303 K for 4 h). This work indicates that different tissues have differential metabolic stabilities in (1)H MAS NMR experiments and that careful attention to sample preparation is required to minimize artifacts and maintain spectral quality.