An intact median preoptic nucleus is necessary for chronic angiotensin II-induced hypertension

Abstract

The median preoptic nucleus (MnPO) receives afferent input from the subfornical organ, a circumventricular organ that has been shown to be necessary in mediating the full chronic hypertensive response to angiotensin II (ANG II) administration. In addition, intravenous ANG II infusion has been shown to cause activation of a number of neurons in both the dorsal and ventral part of MnPO. Taken together, we hypothesized that the MnPO is necessary for the full hypertensive response observed during chronic ANG II-induced hypertension. To test this hypothesis, male Sprague-Dawley rats were subjected to either sham (SHAM) or electrolytic lesion of both the dorsal and ventral part of the MnPO (MnPOx). During the same surgery, rats were instrumented with venous catheters, and radiotelemetric transducers for the intravenous administration of ANG II and the measurement of blood pressure and heart rate, respectively. Rats were then given a week recovery period. After 3 days of saline control infusion, ANG II was intravenously infused (10 ngxkg(-1).min(-1)) in both sham and MnPOx animals for 10 consecutive days, and followed by 3 recovery days. By day 7 of ANG II infusion, MAP had increased 38+/-3 mm Hg in sham lesion rats (n=6), but MAP of MnPOx rats (>90% MnPO ablated; n=5) had only increased 18+/-2 mm Hg. This trend continued through day 10 of ANG II treatment. These results support the hypothesis that the MnPO is necessary for the chronic hypertensive response to ANG II administration.

Figure 1

Photomicrographs of 40 μm mid-sagittal sections of the Median preoptic nucleus (MnPO). A. Section from a sham lesion rat demonstrating dorsal and ventral MnPO (* and #, respectively). B. Section from a MnPOx rat demonstrating ablated dorsal and ventral MnPO. 3V = Third ventricle.

Figure 2

Average 24 h mean arterial pressure (MAP) and heart rate (HR) recorded during control period (3 days of saline), treatment (10 days of ANGII), and recovery (3 days of saline) in MnPOx and sham lesion rats. *P < 0.05 between groups.

Figure 3

Water intake, urine output, and water balance during control, treatment, and recovery periods in MnPOx and sham lesion rats.

Figure 4

Sodium intake, sodium excretion, and sodium balance during control, treatment, and recovery periods in MnPOx and sham lesion rats.