Effects of vasodilation on plasma distribution in SHR cremaster muscle microvessels.

Alterations in the structure, number, reactivity, contractility and sensitivity of resistance vessels of hypertensive animals have been reported. If the etiology of hypertension is due to one or a combination of these factors, it could logically be expected that the distribution of blood flow from the arterial to venous circulation through parallel microcirculatory circuits could be affected. The right cremaster muscles of pentabarbital anesthetized Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) (6-8 weeks old) were exposed and prepared for fluorescent videomicroscopy. The right iliac artery was cannulated with PE-10 tubing, the tip of which was placed at the aortic bifurcation for bolus injections of FITC-dextran (70,000 molecular weight) and arterial pressure measurement. Passage of the indicator through the microcirculation was recorded on videotape during control and during vasodilation by topical application of adenosine (0.2 M). Time-concentration curves were recorded by means of dual window videodensitometry upon replay of the tape. Arterial pressure averaged 85 +/ 3 mm Hg in WKY rats and 110 +/- 5 mm Hg in SHR. Arteriolar flow velocity varied directly with small arteriolar diameter. Dilation significantly reduced the venular appearance (ta), mean transit time (t), and curve width time (tE) in WKY and SHR. The ta was significantly more reduced in SHR than WKY. This would suggest that, in WKY, dilation may have opened some new parallel circuits but principally increased flow velocity through existing circuits. In SHR, new shorter and/or higher velocity circuits were opened as evidenced by the reduced ta with the longer and/or lower velocity circuits largely unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential serotonin responses in the skeletal muscle microcirculation.

Closed circuit television microscopy was used to quantitate in vivo responses of small vessels in the rat cremaster muscle to topically applied serotonin. Sprague-Dawley rats were anesthetized with a combination of urethane (800 mg/kg) and alpha-chloralose (60 mg/kg). The cremaster muscle with intact circulation and innervation was suspended in a bath which had controlled pH, pCO2, and pO2. Microvascular diameters of first order arterioles and venules and fourth-order arterioles were measured from the television monitor while serotonin (10(-9)M-10(-4)M) was added to the bath. Fourth-order arterioles (3-11 micron diameter) dilated to a maximum of 267% of their control value with a serotonin concentration of 10(-6)M. Serotonin (10(-4)M) constricted first-order arterioles (78-121 micron) to 61% of their control value. The threshold concentration (10(-8)M) for a serotonin-induced dilation of fourth-order arterioles was 1000 fold less than the threshold concentration (10(-5)M) for serotonin-induced constriction of first-order arterioles. Serotonin (10(-8)M - 10(-4)M) did not alter the diameter of first-order venules (115-195 micron) from the control value. The dose-dependent constriction of first-order arterioles and dose-dependent dilation of fourth-order arterioles by serotonin appear to be independent of each other. In addition, the lack of constriction of first-order venules suggests a heterogenous distribution of serotonin receptors and that the predominate control mechanisms are different at different levels of the arteriolar and venous microcirculation of rat skeletal muscle.

Elevated body temperature and increased blood vessel sensitivity in spontaneously hypertensive rats.

Body temperature (BT) was significantly greater in spontaneously hypertensive rats (SHR) than in Wistar-Kyoto (WKY) rats regardless of the time of day, length of rectal probe, sex, age, or commercial vendor. Bath temperature (theta) for excised aortic rings was controlled by a thermoelectric Peltier module with an accuracy of 0.1 degree C. At peak force in individual contractions of norepinephrine (NE) dose-response experiments, theta was changed from 37 to 39 degrees C. Active and resting wall tension (Tw) were increased, and the mean effective dose (ED50) was decreased in the SHR aorta with and without endothelium. For the WKY aorta, active and resting Tw were increased, but ED50 was the same with and without endothelium. These results were supported by experiments where theta was decreased from 39 to 37 degrees C and by experiments on Sprague-Dawley rats. Potassium dose-response experiments with aorta from SHR and WKY rats show an increase in sensitivity at 39 degrees C, but active Tw is the same at 39 and 37 degrees C. When compared at the BT of each rat, the NE ED50 was lower and resting Tw was higher in the SHR aorta than in the WKY aorta, but active Tw was the same.(ABSTRACT TRUNCATED AT 250 WORDS)

Microvascular responses to E. coli endotoxin with altered adrenergic activity.

The cremaster muscle microcirculation of pentobarbital-anesthetized Wistar rats was studied using videomicroscopy. The left cremaster muscle was spread over an optical port in a bath filled with modified Krebs solution (pH 7.4, 34 degrees C). The right femoral artery was cannulated for determination of mean arterial pressure (Pm). Following control measurements of Pm and arteriolar and venular dimensions, dose-response curves of arteriolar and venular dimensions to topical norepinephrine (10(-10) M to 10(-3) M) was obtained. The rats were then administered E. coli endotoxin (6 mg/kg, iv, LD100) over a 1-hr period. The dose response curves were than repeated at intervals of 30 min. Before endotoxin the threshold dose for norepinephrine was consistently 10(-9) M or 0(-8) M. Pm decreased progressively with time postendotoxin. After endotoxin infusion, there was a gradual and progressive constriction of both arterioles and venules. The threshold dosage for norepinephrine to produce constriction of both arterioles and venules increased progressively with time. At 3 hr postendotoxin the threshold dose had increased to 10(-6) M to 10(-4) M. This is the dose that produces maximum constriction of arterioles in the preendotoxin control period. The study was terminated when the animal died or the field was obscured by petechiae. The microvessel sensitivity to norepinephrine is markedly reduced during endotoxin shock possibly due to increase in the active state of the vascular smooth muscle or to change in length of the muscle fibers or to changes in sympathetic alpha-adrenergic activity. The response was not prevented by H1 and H2 receptor blockade, but was prevented by alpha-adrenergic blockade with phentolamine.

Norepinephrine effects on SHR muscle vessel diameters, RBC and plasma flow.

The distribution of blood flow through the cremaster microcirculation of pentobarbital anesthetized WKY and SHR rats was studied using fluorescence videomicroscopy and videodensitometry. The left cremaster muscle was spread over an optical port in a bath filled with modified krebs solution (pH = 7.4, 34 degrees C). The right femoral artery was cannulated with PE-10 tubing for the measurement of mean arterial blood pressure and bolus injections of indicators (DTAF-RBC's and FITC-dextran) into the aorta. The passage of indicators through the microvessels and vessel diameters were recorded on video tape during the topical application of norepinephrine (10(-10) M to 10(-6) M). Mean arterial blood pressure was 95 +/- 4 mmHg for WKY rats and 146 +/- 6 for SHR. Venular diameters were greater in WKY than in SHR. Norepinephrine decreased vessel diameters and blood flow velocity in a dose dependent manner. Mean transit time (t) for DTAF-RBC's was less than for FITC-dextran in first order arterioles for both normotensive and hypertensive animals. At high concentrations of norepinephrine differences in t for the two indicators disappeared. The t of both indicators were not different between normotensive and hypertensive animals in arterioles. However, t for both indicators were significantly increased in venules at all concentrations of norepinephrine in SHR but significantly less than in WKY. t for both indicators were increased in a dose dependent manner in both arterioles and venules. Arterioles of SHR appear to be constricted reducing the number of parallel circuits available for flow which allows passage of both RBC and plasma more directly and rapidly through shorter routes than in WKY, but restricts flow of RBC through the terminal arterioles.

Dependence of media cross-sectional area on circumference of aortic rings from normal and hypertensive rats.

The purpose of this study is to determine if cross-sectional area and media thickness depend on circumference in excised vessels. Measurements were obtained from rat aortic rings chemically fixed after excision. Rings were fixed without distention or after mounting on circular rods of different diameters. Media cross-sectional area increased with circumference but thickness decreased. Thickness and area were significantly greater in the SHR than the WKY rat at all circumferences. Results of a theoretical analysis predict that cross-sectional area and thickness will depend on circumference in excised rings. Best-fit curves of the experimental data to the theoretical relationships show that neither thickness nor cross-sectional area of the aorta is consistently better correlated with circumference in SHRs and WKY rats. The following conclusions are made: (i) Media cross-sectional area and thickness depend on circumference in excised-aortic rings, and (ii) for a specific method of preparation, thickness and cross-sectional area are equally accurate when comparing aortic rings from normal and hypertensive rats. If an experimental determination of the relationship between circumference and cross-sectional area (or thickness) cannot be done, we suggest that a reasonable alternative is to compare these measurements at the same circumference.

RBC and plasma distribution changes in cat mesenteric microvessels after hemorrhage and reinfusion.

The mesenteries of ten cats (0.6 kg) anesthetized with Dial-urethane were exposed and studied using fluorescence television microscopy. Femoral artery pressure was determined. FITC-dextran, the plasma label, or DTAF-labeled red cells (DTAF-RBCs) were injected as a bolus (0.005 ml in 0.5 sec) into a small branch of the mesenteric artery. Animals were hemorrhaged from the left femoral artery into a reservoir. Control mean arterial pressure averaged 100 +/- 2 mmHg and decreased to 84 +/- 1 mmHg subsequent to an average bled volume of 13 ml/kg. Time-concentration curves were recorded from videotape recordings of the passage of indicator by videodensitometry. Following hemorrhage, arteriolar (N = 134) FITC-dextran mean transit time (t) was increased significantly to 194 +/- 10% of control, while t for DTAF-RBCs increased significantly to 211 +/- 10% of the control value. In the venules (N = 180) hemorrhage significantly increased FITC-dextran t to 197 +/- 9% of control while venular DTAF-RBC t was significantly increased to 182 +/- 5% of control. Arteriolar t was significantly lower for DTAF-RBC than for FITC-dextran during the control period and following reinfusion. Following hemorrhage, arteriolar t for DTAF-RBCs was not different from that for FITC-dextran. Venular values were significantly lower for DTAF-RBCs than FITC-dextran during all three periods. Dispersion was increased (reduced ta/t) by hemorrhage in arterioles and venules. The elevated t after hemorrhage would appear to be the result of increased peripheral resistance and resulting reduced flow velocity through the circuits. The absence of a difference in arteriolar t between the two indicators post-hemorrhage would indicate reduced Fahraeus effects owing to reduced blood flow velocity and perfusion pressure.

Reduced RBC versus plasma microvascular flow due to endotoxin.

The microvascular circuits traversed by red blood cells (RBCs) and plasma from first-order arterioles to first-order venules are complicated by variations in hemodynamic, rheologic, and dimensional parameters. Escherichia coli endotoxin causes microcirculatory derangements expected to alter RBC and plasma transport through these circuits. Wistar male rats were anesthetized with pentobarbital; the left cremaster muscle was spread over an optical port in a Krebs solution bath and administered endotoxin (6 mg/kg) iv over a 1-h period. The right femoral artery was cannulated for measurement of aortic pressure (Pm) and ia bolus injections of fluorescent DTAF-RBC and FITC-dextran. Fluorescence epi-illumination videomicroscopy and densitometry were used to obtained time-concentration curves (TCCs) in arterioles and venules. Control Pm averaged 106 +/- 8 mm Hg and progressively decreased during the 150-min observation period following endotoxin infusion. Arteriolar and venular diameters decreased approximately 50% during the 150-min observation period. At control DTAF-RBC flow velocity exceeded FITC-dextran velocities but by 90 min postendotoxin, even though both velocities were greatly reduced, plasma velocity, significantly exceeded red cell velocity. The control mean transit times for FITC-dextran exceeded the DTAF-RBC times in all vessels; 90 min postendotoxin the DTAF-RBC mean transit times significantly exceeded the FITC times and cell aggregates were in venous blood. The data suggest that cell aggregation, vasoconstriction and use of longer alternate parallel vascular circuits occur in endotoxin shock, restricting red cell flow. Plasma bypasses RBCs, flowing more rapidly than red cells in terminal shock.

Microvascular responses of intact and adrenal medullectomized rats to hemorrhagic shock.

Evidence indicates that during the later stages of hemorrhagic shock there appears to be a loss of response to the control systems that would normally maintain an adequate peripheral resistance. Therefore, the reactivity of the cremaster muscle microcirculation of pentobarbital-anesthetized Wistar rats, intact and adrenal medullectomized, was studied using videomicroscopy. The left cremaster muscle was spread over an optical port in a bath filled with modified Krebs solution (pH 7.4, 34 degrees C). The right femoral artery was cannulated for determination of mean arterial pressure (Pm) and for hemorrhage of the rat. Following control measurements of Pm and microvessel diameters, cumulative dose-response curves of arteriolar and venular diameters to topical norepinephrine (NE) (10(-9) - 10(-4) M) were obtained. The protocols for intact and medullectomized groups were: 1) hypovolemic shock (shed blood not reinfused)--hemorrhage of 3.2 ml/100 g, compensation allowed, and NE dose-response curves repeated and obtained again during late shock as determined by Pm declining below 60 mmHg; and 2) normovolemic shock (condition after reinfusion of shed blood)--hemorrhage into a reservoir to Pm of 40 mmHg, maintenance at this level until 25% of the bled volume had been taken back (irreversible shock), and then reinfusion of the remainder of the blood. After blood reinfusion, the NE dose-response curves were repeated and obtained again during late shock, as determined by Pm below 60 mmHg. In all of the bled animals, the A1 arterioles were constricted posthemorrhage. The A2 arterioles were constricted only in the hypovolemic intact group. The A3 arterioles of all groups were not significantly changed from control. The constricted arterioles remained so. However, the other arterioles in all groups were unchanged during the several hours until death. The threshold concentration of NE for constriction of arterioles (10% or greater) was significantly increased (decreased sensitivity) during shock in all four groups. The response of the medullectomized rats to normovolemic shock was similar to that of the intact group, indicating that the circulating catecholamines were not essential. The response of medullectomized rats to hypovolemic shock was more severe and indicated the need for circulating catecholamines to compensate for the blood volume loss.

Red blood cell and plasma distribution in SHR cremaster muscle microvessels.

Distribution of blood in the cremaster muscle microvasculature of spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats was determined by fluorescence videomicroscopy and densitometry. Bolus intra-arterial injections of fluorescein isothiocyanate (FITC)-dextran or dichlorotriazenylaminofluorescein-treated red blood cells (DTAF-RBC) produced time-concentration curves in the series-coupled segments. WKY and SHR mean arterial pressure averaged 89 +/- 6 and 125 +/- 5 mmHg, respectively. Arteriolar diameters were not different between the two groups. The smallest SHR venules (V4) and larger diameters than those of WKY (P less than 0.05), whereas V3 and V2 were not different. WKY diameters for V1 were significantly greater than those of SHR. The mean transit (t) and appearance times (ta) of both indicators were equal at the largest arteriole (A1) in both groups. In A2, A3, and A4 the t for both indicators were generally lower in SHR than in WKY rats but not significantly. The venular t were significantly greater in SHR than in WKY rats with DTAF-RBC consistently less than FITC-dextran values. The greater cross-sectional area of V4 in SHR than WKY rats would reduce flow velocity and elevate t. Dispersion (ta/t = 1.0 indicates no dispersion) of both indicators was less in WKY than in SHR. The ratios for both groups increased at V4 because ta increased more than t. Shorter circuits for red blood cells than for plasma and less plasma skimming exists in WKY than in SHR.

Survival and microvascular responses to hemorrhage with three anesthetic combinations.

The effects of different anesthetic combinations on the responses to hemorrhage were investigated while using a single fixed protocol. Small artery (x +/- SE = 112 +/- 3 micron)) and vein (172 +/- 5 micron) responses to hemorrhage were quantitated in the cremaster muscle of 38 Sprague-Dawley rats via closed-circuit television microscopy. Rats were anesthetized intraperitoneally with pentobarbital (50 mg/kg), urethan (800 mg/kg), and alpha-chloralose (60 mg/kg), or urethan (600 mg/kg) and alpha-chloralose (120 mg/kg). After a 15-min control period, arterial blood pressure was lowered to 30 mmHg and maintained at that level for 60 min via hemorrhage from the femoral artery. The hemorrhaged blood was then reinfused, and recovery was monitored for 30 min. Survival was monitored for 7 days. Rats with heavier body weights (greater than or equal to 160 g) had a significantly greater survival rate, 81%, than did the lighter weight rats (less than 160 g), with a 32% survival rate. There were, however, no statistical differences in survival or microvascular responses among rats anesthetized with the three combinations of anesthetics. The combined data for all rats were: survival, 53%; small artery constriction, 45 +/- 2%; and small vein constriction, 21 +/- 3%.