Sex Differences in Kidney Function and Metabolism Assessed Using Hyperpolarized [1-13C]Pyruvate Interleaved Spectroscopy and Nonspecific Imaging.

Metabolic sex differences have recently been shown to be particularly important in tailoring treatment strategies. Sex has a major effect on fat turnover rates and plasma lipid delivery in the body. Differences in kidney structure and transporters between male and female animals have been found. Here we investigated sex-specific renal pyruvate metabolic flux and whole-kidney functional status in age-matched healthy Wistar rats. Blood oxygenation level-dependent and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) were used to assess functional status. Hyperpolarized [1-13C]pyruvate was used to assess the metabolic differences between male and female rats. Female rats had a 41% ± 3% and 41% ± 5% lower absolute body and kidney weight, respectively, than age-matched male rats. No difference was seen between age-matched male and female rats in the kidney-to-body weight ratio. A 56% ± 11% lower lactate production per mL/100 mL/min was found in female rats than in age-matched male rats measured by hyperpolarized magnetic resonance and DCE MRI. Female rats had a 33% ± 11% higher glomerular filtration rate than age-matched male rats measured by DCE MRI. A similar renal oxygen tension (T2*) was found between age-matched male and female rats as shown by blood oxygenation level-dependent MRI. The results were largely independent of the pyruvate volume and the difference in body weight. This study shows an existing metabolic difference between kidneys in age-matched male and female rats, which indicates that sex differences need to be considered when performing animal experiments.

Can Hyperpolarized 13C-Urea be Used to Assess Glomerular Filtration Rate? A Retrospective Study.

This study investigated a simple method for calculating the single-kidney glomerular filtration rate (GFR) using dynamic hyperpolarized 13C-urea magnetic resonance (MR) renography. A retrospective data analysis was applied to renal hyperpolarized 13C-urea MR data acquired from control rats, prediabetic nephropathy rats, and rats in which 1 kidney was subjected to ischemia-reperfusion. Renal blood flow was determined by the model-free bolus differentiation method, GFR was determined using the Baumann-Rudin model method. Reference single-kidney and total GFRs were measured by plasma creatinine content and compared to 1H dynamic contrast-enhanced estimated GFR and fluorescein isothiocyanate-inulin clearance GFR estimation. In healthy and prediabetic nephropathy rats, single-kidney hyperpolarized 13C-urea GFR was estimated to be 2.5 ± 0.7 mL/min in good agreement with both gold-standard inulin clearance GFR (2.7 ± 1.2 ml/min) and 1H dynamic contrast-enhanced estimated GFR (1.8 ± 0.8 mL/min), as well as plasma creatinine measurements and literature findings. Following ischemia-reperfusion, hyperpolarized 13C-urea revealed a significant reduction in single-kidney GFR of 57% compared with the contralateral kidney. Hyperpolarized 13C MR could be a promising tool for accurate determination of GFR. The model-free renal blood flow and arterial input function-insensitive GFR estimations are simple to implement and warrant further translational adaptation.