AJP - Heart and Circulatory Physiology, Vol 258, Issue 5 1395-H1401, Copyright © 1990 by American Physiological Society
Long-term effects of nimodipine on pial microvasculature and systemic circulation in conscious rats
X. Q. Yuan, T. L. Smith, D. S. Prough, D. S. De Witt, J. W. Dusseau, C. D. Lynch, J. M. Fulton and P. M. Hutchins
Department of Physiology, Wake Forest University Medical Center, Winston-Salem, North Carolina 27103.
The chronic cranial window preparation allows repeated measurements of the
same pial vessels in unanesthetized rats for several weeks and correlation
with 24-h monitoring of hemodynamic variables. Nimodipine (20 mg) or
placebo was given via two subcutaneous pellets. Large arterioles dilated 26
and 16%, at hour 1 and days 6-13, respectively (P less than 0.02). There
was an increase in number of small arterioles throughout the whole
observation period with the maximal increment of 47% (P less than 0.05) at
days 6-13. Maximal vasodilation with 10% CO2 indicated that the increase in
number of small arterioles after administering nimodipine was not caused by
the opening of previously closed vessels. The total length of small
arterioles and venules increased 47 and 23% at days 6-13, respectively (P
less than 0.001). These increases seem to be caused by the increases in the
numbers of vessels, because the average length of the small vessels did not
appear to change. This suggests that nimodipine reduces cerebral vascular
resistance by causing cerebral microvessel neovascularization. Our data
demonstrate that the administration of nimodipine (20 mg) is potent in
dilating pial arterioles in the short-term without affecting systemic
arterial pressure, and that its long-term effect results in new vessel
growth.
