acase@tulane.edu

An in vivo mechanical analysis and a detailed quantitative morphological study of the arteries in the carotid baroreceptor region from normotensive (NTR) and spontaneously hypertensive (SHR) adult (9-10 month old) male rats were completed The morphological studies incorporated a newly developed vascular perfusion technique (Engle and Kirby, 1986) that allowed for the preservation of vascular dimensions at distending pressures equivalent to the physiological mean arterial pressures (PMAP) obtained under normal resting conditions for each individual animal. The following changes in the carotid arteries were documented and quantified. (1) There is a generalized thickening of the tunica intima which is primarily associated with an expansion of the subendothelial space and which resembles the early atherosclerotic lesions developed in man. (2) The internal elastic lamina contains a greater number of fenestration profiles. (3) The volume of the tunica media is increased due to a proportional increase in the absolute amounts of collagen, elastin, and smooth muscle A new index of vessel wall distensibility, defined as the incremental mechanical sensitivity $({\rm S\sb{m}})$, has been developed. Using this parameter, it was demonstrated that the distensibility functions of the carotid arterial walls from both NTRs and SHRs exhibit a distinct peak value $({\rm S\sb{m}MAX})$ which occurs consistently at or near PMAP. The vessel walls are stiffer at pressures both above and below PMAP. The pressure at which ${\rm S\sb{m}MAX}$ occurs (PMAX) is strongly correlated with PMAP, being nearly equal with it. The magnitude of the peak value of ${\rm S\sb{m}}$ decreases as a function of increasing PMAP. These functional relationships are so strong that they indicate physiological significance. The fact that the carotid arterial wall is maximally distensible at PMAP demonstrates the existence of a physiological mechanism for optimizing baroreflex efficiency about the defined set-point pressure. The strong functional relationship between PMAX and PMAP indicates a mechanical mechanism for the long-term resetting of the carotid sinus baroreceptors. Finally, the observed mechanical resetting and decreased sensitivity of the carotid sinus baroreceptors in adult SHRs appear to be the result of a stress induced growth adaptation phenomenon associated with the hypertensive disease state.(Abstract shortened with permission of author.) / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu