Structural differences in the mesentery microcirculation between normotensive and spontaneously hypertensive rats

Abstract

The mesentery preparation of normotensive rats (NR) (Pcarotis97 +/- 4 mm Hg) and of spontaneously hypertensive rats (SHR) (161 +/- 2 mm Hg) of comparable age (20 +/- 3 weeks) was used to study morphological changes of the microvasculature in established hypertension. The arterioles, classified according to their branching order, had an increased inner diameter in SHR (by 20%). The smooth muscle hypertrophy decreased with smaller vessel size. Pre- and postcapillary vessels were shorter in SHR than in NR by 17 to 35%. The number of these vessels related to the number of the feeding terminal arterioles was found to be reduced by nearly 50% in SHR. The data suggest a lowered arteriolar flow resistance in individual vessels of the hypertensive group concomitant with a gradually disappearing smooth muscle hypertrophy towards the capillary bed. The elevation of the resistance to blood flow in the hypertensive rats is obviously caused by a reduced number of resistance vessels, as seen in the mesentery vascular bed. Similar results were obtained in the true capillaries, which showed greater inner diameters (SHR vs NR:7.2 micron vs 6.4 micron), shortened lengths (141 vs 170 micron) and a reduced number (50 vs 70). Red cell velocity in true capillaries did not differ (0.51 mm/s vs 0.49 mm/s). Arterio-venous shunt vessels were described with an average inner diameter of 11 micron. In SHR these vessels were shorter (424 vs 654 micron) and increased in number. The 'hydraulic hindrance' of AV-shunt vessels and true capillaries together was decreased in SHR; the surface area did not differ between SHR (55.7 . 10(3) micron2) and NR (50.1 . 10(3) micron2) suggesting no major variation in the exchange functions.

Arterial Morphometry in Neonatal and Infant Spontaneously Hypertensive Rats

“…Thus the high salt diet exaggerated a pattern al ready present in standard salt SHR. Our re sults showing not significantly different me dia/lumen area ratios between SHR and WKY in the smallest arteriolar category are consistent with those of Henrich et al [1978] on the mature in vivo mesenteric vascular bed. These investigators showed a gradually disappearing difference in relative wall thick ness between SHR and WKY with decreasing size arterioles.…”

Do Resistance Vessel Abnormalities Contribute to the Elevated Blood Pressure of Spontaneously-Hypertensive Rats?

“…measured directly by microscopy, it appears that the lumen diameter and media thickness of resistance vessels with lumen diameters of less than 100 pm are essentially the same as for those in WKYs, but that the number of resistance vessels is reduced [Henrich et al, 1978]. In more extensive studies on the vascular bed of the cremaster muscle a similar rarefication [Hutchins and Darnell.…”

Hypertension

“…Studies have reported microvascular structural rarefaction in many experimental hypertensive models and tissues, including skeletal muscle, 18,30 -33 intestine, 34 and skin, 35 although not the brain. 36 Interestingly, structural rarefaction can be detected at a very young age (4 weeks) in spontaneously hypertensive rats.…”