Cardiovascular effects of microinjection of atrial natriuretic factor (ANF) in the nucleus tractus solitarii of spontaneously hypertensive rats.

The effects on mean arterial pressure (MAP) and heart rate (HR) of unilateral microinjections of atrial natriuretic factor (ANF) into discrete sites of the nucleus tractus solitarii (NTS) of spontaneously hypertensive rats (SHR) were compared with those observed in normotensive Wistar-Kyoto rats (WKY). NTS sites were identified to be involved in cardiovascular control on the basis of the bradycardia and hypotension elicited by microinjections of 20 nl of 0.1 M L-glutamate. Microinjection of 20 nl of 10(-7) M ANF into 38 NTS 'cardiovascular sites' in rats of the SHR strain decreased MAP (-8.7 +/- 1.8 mmHg) and HR (-7.8 +/- 1.9 bpm) in 9 sites (24%), but caused no changes in the remaining 29 sites (76%). In WKY rats 35 cardiovascular sites within the NTS were studied. In 18 sites (51%) ANF microinjections induced a decrease in MAP (-15.1 +/- 1.9 mmHg) and in HR (-18.1 +/- 3.9 bpm), whereas the remaining 17 sites (49%) were unaffected. The decreased responsiveness of the NTS to ANF in the SHR animals could play a role in the development and/or maintenance of the elevated arterial blood pressure in genetically hypertensive rats.