Myocardial <i>meta</i>-[¹²⁵I]iodobenzylguanidine uptake in awake genetically hypertensive rats at different ages: an autoradiographic study

Abstract

The purpose of this work was to evaluate changes in myocardial meta-[125I]iodobenzylguanidine ([125I]MIBG) uptake and distribution with age in awake spontaneously hypertensive rats (SHR) with respect to Wistar-Kyoto (WKY) rats. Rats were randomly divided into two groups, one for measuring myocardial [125I]MIBG uptake and distribution 4 h after its injection and the second for evaluating myocardial catecholamine concentrations. Mean arterial blood pressure, cardiac hypertrophy index (heart/body weight ratio), and heart rate were significantly higher with increasing age in SHR compared with matched WKY rats. Myocardial catecholamine concentrations and turnover did not differ between the two strains and were significantly decreased with increasing age. Myocardial [125I]MIBG uptake determined by gamma counting was similar in WKY rats and SHR and did not vary significantly with age when expressed as uptake density. However, in both strains of rats, [125I]MIBG uptake determined by autoradiography was significantly greater at the base of the heart than at the apex and midventricular levels, and the uptake values of young rats were significantly higher than those of older rats. In 21-week-old WKY rats and SHR, the highest [125I]MIBG uptake values were found in the right ventricle. Thus, quantitative autoradiography allowed detection of significant changes in myocardial [125I]MIBG uptake and showed its heterogeneous distribution in the rat heart.

Sex differences in sympathetic gene expression and cardiac neurochemistry in Wistar Kyoto rats

“…We did not observe significant male-female differences in cardiac NE content (LV Mid-wall, M 5.8±0.7 vs F 6.8±0.4 pmol/mg, p = 0.3; RV, M 8.7±0.9 vs F 11.5±1.9 pmol/mg, p = 0.2)[34], consistent with identical cardiac physiology observed in the male and female rats[34]. We also compared our data to earlier studies that measured cardiac NE content in female Wistar rats [35] and male WKY rats [36]. Female Wistar rats had 6.9±0.8 pmol/mg NE in the RV and 3.3±0.3 pmol/mg in the intraventricular septum, while male WKY rats of a similar age had “myocardial” (presumably left ventricle) NE content of 4.8±0.4 pmol/mg.…”

“…The DHPG:NE ratio can provide information on the efficiency of NE recycling into the pre-synaptic terminal, but we did not detect the NE metabolite DHPG in any of the rat tissue tested. This was surprising, as we and others have previously detected DHPG in mouse and rat heart [2, 35, 36] using the same or similar methods. However, careful analysis of chromatograms from our samples did not reveal a peak eluting at or near 3.2 minutes, when DHPG standards were detected, suggesting that the level of DHPG present after tissue processing was simply too low for detection.…”