Paramedian Reticular Nucleus May be Unrelated to the Development of Hypertension in Spontaneously Hypertensive Rats

The role of paramedian reticular nucleus (PRN), a structure effecting sympathetic inhibition, in the development of hypertension was investigated in young spontaneously hypertensive rats (SHR) and two age-matched normotensive rats, Wistar-Kyoto (WKY) and Sprague-Dawley rats (SD). Three different experimental manipulations, including electrical-lesioning, sham-operated and intact control, were performed in SHR, WKY and SD rats 7 weeks after birth. In the control groups, the systolic arterial blood pressure (SABP) of SHR increased abruptly from 160 mmHg to 230 mmHg from the 6th to 13th week after birth, whereas those of WKY and SD maintained a normal range of SABP. In the lesioned groups, a hypotension and/or bradycardia was evoked by electrical stimulation to verify the location of PRN. Following the verification, a direct current was delivered to lesion the PRN in situ. The effect of PRN lesioning on the subsequent development of hypertension was illustrated by comparing SABP in three experimental groups of age-matched conscious SHR, WKY and SD during 8-13 weeks after birth. We found that the average SABP in the lesioned SHR was consistently elevated and was not significantly different from those of the sham-operated and the control. In contrast, in the normotensive rats, there was no significant increase in SABP within the three experimental groups, i.e., the average SABP of the lesioned, the shamed-operated and the control group maintained a normal range. Our results support the contention that the hypertension of SHR developed within 6-13 weeks after birth. In addition, the sympatho-inhibitory mechanism of PRN was not directly related to the development of hypertension.