AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 3 341-R347, Copyright © 1985 by American Physiological Society
Neuropeptide action in nucleus tractus solitarius: angiotensin specificity and hypertensive rats
R. Casto and M. I. Phillips
We have reported that microinjection of angiotensin II (ANG II) into the
nucleus tractus solitarius of urethan-anesthetized normotensive rats
produces an increase in mean arterial pressure (MAP) over the dose range
50-500 pmol. The effect in spontaneously hypertensive rats (SHR) is now
reported. Over the range 100-500 pmol SHR exhibit increases in MAP and
heart rate greater than Wistar-Kyoto or Sprague-Dawley rats. SHR did not
exhibit exaggerated responses to intravenous phenylephrine, suggesting a
central site of increased responsiveness to ANG II. We also found depressor
effects in Sprague-Dawley at lower doses (0.1 and 1 pmol). The decreases in
MAP were extremely variable and not dose related. A selected dose of
additional neuropeptides identified in the NTS was tested. Somatostatin,
bradykinin, and vasoactive intestinal peptide (0.5 nmol) were without
cardiovascular effects. Oxytocin and vasopressin, however, produced
significant increases in MAP. Substance P produced a very small but
significant increase in heart rate and MAP. Interaction between the
vasopressin and ANG II pressor effects was studied, and each proved to be
independent.
