Site of autoregulatory reactions in the vascular bed of cat skeletal muscle as determined with a new technique for segmental vascular resistance recordings

Abstract

An arterial and venous microcannulation technique was developed for circulatory studies in the cat gastrocnemius muscle which, based on detailed morphological and functional observations of the microvascular arrangement, seems to permit continuous recordings of pressure in arterioles (diameter approximately 25 microns) and capillary pressure. These variables in combination with measurements of arterial and venous pressure and blood flow provided a means of continuous simultaneous recordings of total as well as segmental resistances in defined sections of the vascular bed, viz. in large arterial vessels (diameter greater than 25 microns), arterioles (less than 25 microns), and on the venous side. This new technique was applied to a study of the site(s) of autoregulatory reactions along the vascular bed evoked by changes of arterial pressure over the range 50-150 mmHg. The results indicated that active autoregulation mainly occurred within arterioles smaller than about 25 microns. In larger arterial vessels concomitant moderate active smooth muscle adjustments barely balanced out the pressure-induced passive calibre changes, and the venous vessels did not seem to contribute actively to autoregulation, but exhibited a passive change in postcapillary resistance (Rven). The described pattern of response results in quite effective autoregulation of blood flow and capillary pressure (PC). The observed passive Rven change, via its effect on the pre- to postcapillary resistance ratio, seems to explain the fact that autoregulation of PC can be more efficient than flow autoregulation. The study also provided quantitative data for the level of active intrinsic vascular tone in defined consecutive sections of the muscle vascular bed at normal arterial pressure and for segmental redistributions of tone evoked by pressure alterations.

Location of Resistance Arteries

“…Selective dilation of the smallest arteries has likewise been observed – e.g. in the cat gastrocnemius muscle during manipulation of feeding pressure [46], in the cat brain during bicuculline-induced seizures [43]and during postocclusive hyperemia in the rat cremaster muscle [47]. …”

Role of Endothelium Sensitivity to Shear Stress in Noradrenaline-Induced Constriction of Feline Femoral Arterial Bed under Constant Flow and Constant Pressure Perfusions

“…With this aim, a thin catheter was inserted in the distal direction into the sural artery and connected to an electromanometer. The value measured in this way represents the pressure within small intra-organ arteries or arterioles (distal pressure, P dist ) [10, 11]. In our experiments, the resting P dist was averagely 45% of P perf (table 1), that corresponds to the boundary between small and medium-sized arterioles [11].…”

Effects of selective ETB‐receptor stimulation on arterial, venous and capillary functions in cat skeletal muscle

“…In brief, the muscle region was auto-perfused in situ via an arterial shunt placed between the femoral and popliteal artery. The muscle preparation, with intact arterial and venous supply, was enclosed in a Ringer fluid-filled plethysmograph, using special cannulation and instrumentation techniques described in detail elsewhere (Mellander et al, 1987;Bjornberg et al, 1988). With this method, it is possible to obtain reliable continuous recordings of the following circulatory variables: arterial, arteriolar, capillary and venous pressures, regional blood flow, net transcapillary fluid flux, and resistances in the whole muscle vascular bed (RT) and in the following consecutive vascular sections: large-bore arterial resistance vessels (>25 ,sm; Raprox), small arterioles (<25 gsm; a and the veins (Rv).…”

“…Implicit in this methodological approach is that the sum of the three segmental resistances always equals the simultaneously recorded RT value. These vascular resistances were continuously recorded with the aid of electronic divider circuits (for technical details see Bjornberg et al, 1988). All resistances are expressed as PRU values (peripheral resistance units; mmHg ml-' min 100 g tissue).…”