Arteriolar reactivity to pressure stimuli in hamsters with renal hypertension.

Abstract

SUMMARY The responses to alterations in extravascular pressure were studied in five orders of arterioles in the cheek pouch of normotensive and renal hypertensive hamsters. Renal hypertension was induced by bilateral compression of both kidneys using figure-of-eight ligatures. Ten to 16 days later, hamsters were anesthetized with pentobarbital (6.0 mg/100 g body weight) and a Plexiglas chamber was positioned in the cheek pouch. Chamber pressure, or extravascular pressure, was increased and decreased by ± 10, 20, and 40 mm Hg, and arteriolar diameters were monitored continuously. The responses at -20 mm Hg and the slope of the linear portion of the chamber pressure-diameter curve (arteriolar gains) were compared between groups for each branching order of arteriole. Arteriolar responses at one chamber pressure and the arteriolar gains were enhanced in third and fourth order arterioles of the renal hypertensive group compared with the normotensive group, and the responses of these small arterioles were greater than those of larger arterioles in both groups. Control diameters of second and third order arterioles were significantly smaller in the renal hypertensive group, while the diameters after adenosine were not different. These results suggest that the enhanced responses of small arterioles in the renal hypertensive group were hot related to structural alterations but may be related to an increased reactivity of smooth muscles in these small arterioles to volume expansion, thus a pressure stimulus. (Hypertension 10: 82-92, 1987) KEY WORDS • renal hypertension • microcirculation • arteriolar diameter autoregulation • arteriolar tone • medial area • transmural pressure S TRUCTURAL and functional alterations of blood vessels are associated with human essential,' renal, 2 and genetic 3 hypertension. The relative contribution of arteriolar vasoconstriction, medial hypertrophy, and rarefaction to altered peripheral resistance associated with microvessels in spontaneous and renal hypertension varies according to the vascular bed studied and the progression of the hypertension. Small arterioles contribute markedly to the local control of blood flow/resistance in individual tissues because of their intrinsic tone, enhanced reactivity to vasoactive agents, and reactivity to nerve stimulation.4 " 8 The relative contribution of small arterioles to peripheral resistance in vascular beds has been demon-

Angiotensin reactivity in the cheek pouch of the renovascular hypertensive hamster.

“…In the two-kidney, two figure-8 and one-kidney, one figure-8 hypertensive hamsters, plasma volume is elevated 10 to 16 days after induction of hypertension. 20 Alternative mechanisms for maintenance of elevated blood pressure in our model are functional or anatomical rarefaction, 21 -24 increased peripheral resistance proximal to the cheek pouch, 25 dynamic alterations in vasomotor activity, and, possibly, increased sympathetic tone, which supports the increase in blood pressure but does not reduce the diameter of the cheek pouch arterioles because they are not innervated.…”

Heterogeneity of Endothelial Cell Function for Angiotensin Conversion in Serial-Arranged Arterioles

“…Arterioles selected A2 (30-50 pm) and A4 (10-20 pm) branch orders which were 2nd and 4th generations from the largest arteriole entering the cheek pouch [13], Agents to be tested were applied topi cally to these arterioles via a micropipette positioned beside these vessels. A microliter pump was connected to the pipette and the ago nist was microapplied at a rate of 10 pl/min for 1 min.…”

Resistance Artery Tone Is Influenced Independently by Pressure and by Flow

“…The effective stimulus for the myogenic response is stretch and that for flow is pre sumably shear stress. The mechano-transducers for these effects are different and are located either in the vascular smooth muscle cells or their surrounding extracellular matrix.Resistance arteries in vivo possess a con siderable level of intrinsic muscle tone [1][2][3]. Changes in this tone in small arteries and veins are to a great extent responsible for homeostatic circulatory adaptations [4].…”