Short and long term analysis of heart rate variations in spontaneously hypertensive rats: effects of DSP-4 administration

The purpose of this study was to investigate whether or not central noradrenergic neurons were involved in the time structure of circadian variation of heart rate (HR) in hypertension. We used spontaneously hypertensive rats (SHRIzm) and normotensive controls (Wistar Kyoto rats, WKYIzm). We selectively destroyed the noradrenergic neurons in the central nervous system (CNS) by administering noradrenergic neurotoxin, N-(2-chloroethy)-N-ethyl-2-bromobenzylamine (DSP4). Frequency domain measures of variation of HR (VHR) were obtained using the maximum entropy method. The 24-h time frame in VHR is usually dominant in both SHRIzm and WKYIzm. Fourteen days after the administering of DSP4, the mean 24-h systolic arterial pressure (SAP) remained higher in SHRIzm than in WKYIzm. After chemical lesion, ultradian rhythms (12-, 8-, 6-, and 4-h periods) in VHR became more remarkable in both SHRIzm and WKYIzm than before chemical lesion. Before chemical lesion, an inverse relationship existed between frequency and power spectral density in VHR, demonstrating 1/fβ characteristics. The slope of 1/fβ in VHR did not differ between SHRIzm and WKYIzm. After the chemical lesion it did not also differ from that of each strain in control period (before lesion). Therefore, the noradrenergic neurons may not affect the time structure of HR in SHRIzm and WKYIzm for short-term time analysis. However, the intact noradrenergic neurons in CNS may be important to keep normal cardiac autonomic function in SHRIzm for long-term analysis