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PubMed2003

Antibody responses elicited against the Treponema pallidum repeat proteins differ during infection with different isolates of Treponema pallidum subsp. pallidum.

Variation in the expression of the different Tpr proteins in the syphilis spirochete, Treponema pallidum subsp. pallidum, may have important implications in its ability to evade host immune detection and cause persistent infection. In the present study we examined the pattern of antibody responsiveness to different Tpr members during infection with three isolates of T. pallidum. There was variability in the specificities and temporal patterns of reactivity of the antibodies elicited against the individual Tpr proteins, suggesting that isolates may express different repertoires of Tpr proteins during infection.

Amino Acid Sequence↗

PubMed2004

Human U4/U6 snRNP recycling factor p110: mutational analysis reveals the function of the tetratricopeptide repeat domain in recycling.

After each spliceosome cycle, the U4 and U6 snRNAs are released separately and are recycled to the functional U4/U6 snRNP, requiring in the mammalian system the U6-specific RNA binding protein p110 (SART3). Its domain structure is made up of an extensive N-terminal domain with at least seven tetratricopeptide repeat (TPR) motifs, followed by two RNA recognition motifs (RRMs) and a highly conserved C-terminal sequence of 10 amino acids. Here we demonstrate under in vitro recycling conditions that U6-p110 is an essential splicing factor. Recycling activity requires both the RRMs and the TPR domain but not the highly conserved C-terminal sequence. For U6-specific RNA binding, the two RRMs with some flanking regions are sufficient. Yeast two-hybrid assays reveal that p110 interacts through its TPR domain with the U4/U6-specific 90K protein, indicating a specific role of the TPR domain in spliceosome recycling. On the 90K protein, a short internal region (amino acids 416 to 550) suffices for the interaction with p110. Together, these data suggest a model whereby p110 brings together U4 and U6 snRNAs through both RNA-protein and protein-protein interactions.

Animals↗

PubMed2005

Metabolite ligands of estrogen receptor-beta reduce primate coronary hyperreactivity.

Previous reports showed that 17beta-estradiol implants attenuate in vivo coronary hyperreactivity (CH), characterized by long-duration vasoconstrictions (in coronary angiographic experiments), in menopausal rhesus monkeys. Prolonged Ca2+ contraction signals that correspond with CH in coronary vascular muscle cells (VMC) to the same dual-constrictor stimulus, serotonin + the thromboxane analog U-46619, in estrogen-deprived VMC were suppressed by >72 h in 17beta-estradiol. The purpose of this study was to test whether an endogenous estrogen metabolite with estrogen receptor-beta (ER-beta) binding activity, estriol (E3), suppresses in vivo and in vitro CH. E3 treatment in vivo for 4 wk significantly attenuated the angiographically evaluated vasoconstrictor response to intracoronary serotonin + U-46619 challenge. In vitro treatment of rhesus coronary VMC for >72 h with nanomolar E3 attenuated late Ca2+ signals. This reduction of late Ca2+ signals also appeared after >72 h of treatment with subnanomolar 5alpha-androstane-3beta,17beta-diol (3beta-Adiol), an endogenous dihydrotestosterone metabolite with ER-beta binding activity. R,R-tetrahydrochrysene, a selective ER-beta antagonist, significantly blocked the E3- and 3beta-Adiol-mediated attenuation of late Ca2+ signal increases. ER-beta and thromboxane-prostanoid receptor (TPR) were coexpressed in coronary arteries and aorta. In vivo E3 treatment attenuated aortic TPR expression. Furthermore, in vitro treatment with E3 or 3beta-Adiol downregulated TPR expression in VMC, which was blocked for both agonists by pretreatment with R,R-tetrahydrochrysene. E3- and 3beta-Adiol-mediated reduction in persistent Ca2+ signals is associated with ER-beta-mediated attenuation of TPR expression and may partly explain estrogen benefits in coronary vascular muscle.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed2004

Test of dynamic closed-loop baroreflex and autoregulatory control of total peripheral resistance in intact and conscious sheep.

This is the first study able to examine and delineate the actual actions of the physiological mechanisms responsible for the dynamic couplings between cardiac output (CO), arterial pressure (Pa), right atrial pressure (PRA), and total peripheral resistance (TPR) in an individual subject without altering the underlying regulatory mechanisms. Eight conscious male sheep were used, where both types of baroreceptors were independently exposed to simultaneous beat-to-beat pressure perturbations under intact closed-loop conditions while CO, Pa, PRA, and TPR were measured. We applied the cardiovascular system identification method proposed in a companion paper (4) to quantitatively characterize the dynamic closed-loop transfer relations CO-->Pa, PRA-->Pa, Pa-->TPR, and PRA-->TPR from the measured signals. To validate the dynamic properties of the estimated transfer relations, the essential parts of the linear dynamics of the model were independently and comprehensively evaluated via error model cross-validation, and the overall model's steady-state behavior was compared with a separate random effects regression approach. In addition to numerous physiological findings, we found that the cardiovascular system identification results were exceptionally consistent with the analytically derived solutions previously discussed in Ref. 4. In conclusion, this study presents the first time validation of a cardiovascular system identification method by means of experimentally acquired animal data in the intact and conscious animal and offers a set of powerful quantitative tools essential to advancing our knowledge of cardiovascular regulatory physiology.

Animals↗

PubMed2003

Gender differences on the effects of aging on cardiac and peripheral adrenergic stimulation in old conscious monkeys.

We examined the effects of gender and aging on cardiac and peripheral hemodynamic responses to beta-adrenergic receptor (beta-AR) stimulation in young (male = 5.9 +/- 0.4 yr old and female = 6.5 +/- 0.7 yr old) and old (male = 19.8 +/- 0.7 yr old and female = 21.2 +/- 0.2 yr old) conscious monkeys (Macaca fascicularis), chronically instrumented for measurements of left ventricular (LV) and arterial pressures as well as cardiac output. Baseline LV pressure, the first derivative of LV pressure (LV dP/dt), cardiac index, mean arterial pressure, total peripheral resistance (TPR), and heart rate in conscious monkeys were not different among the four groups. Increases in LV dP/dt in response to 0.1 microg/kg isoproterenol (Iso) were diminished (P < 0.05) in old males (+99 +/- 11%) compared with young males (+194 +/- 18%). In addition, the inotropic responses to norepinephrine (NE) and forskolin (FSK) were significantly depressed (P < 0.05) in old males. Iso-induced reductions of TPR were less (P < 0.05) in old males (-28 +/- 2%) than in young males (-49 +/- 2%). The changes of TPR in response to NE and FSK were also significantly attenuated (P < 0.05) in old males. However, the LV dP/dt responses to BAY y 5959 (15 microg. kg-1. min-1), a Ca2+ channel promotor independent of beta-AR signaling, were not significantly different between old and young males. In contrast to results in male monkeys, LV dP/dt and TPR responses to Iso, NE, and FSK in old females were similar to those observed in young females. Thus both cardiac contractile and peripheral vascular dynamic responses to beta-AR stimulation are preserved in old female but not old male monkeys. This may explain, in part, the reduced cardiovascular risk in the older female population.

Aging↗

PubMed1979

Depressed responsiveness of the carotid sinus reflex in conscious newborn animals.

The responsiveness of the carotid sinus reflex was evaluated by comparing the effects of bilateral carotid occlusion (BCO) in conscious adult dogs and puppies on measurements of arterial pressure, cardiac output, heart rate, and calculations of total peripheral resistance (TPR). In eight adult dogs, BCO increased mean arterial pressure by 57 +/- 6%, TPR by 48 +/- 5%, and heart rate by 45 +/- 15%. In puppies, BCO induced smaller increases (P less than 0.05) in mean arterial pressure (30 +/- 5%) and TPR (29 +/- 4%), while heart rate did not change. After elimination of opposing vagal and aortic baroreceptor reflexes, the differences in responses to BCO of mean arterial pressure and TPR between adults and newborns were even greater. Thus, the carotid baroreceptor reflex appears to be depressed in the newborn when compared with the fully developed reflex in the normal, conscious adult.

Animals↗

PubMed1981

Properties of intestinal and cutaneous arteries and veins in two-kidney one-clip Goldblatt hypertension.

This study evaluates whether changes in arterial and venous smooth muscle contractility and extensibility precede or result from the elevated arterial pressure (MAP) and total peripheral resistance (TPR) of two-kidney one-clip Goldblatt hypertension (2-KGH). The experiments measure the contractile and extensibility properties of rings of canine mesenteric, cutaneous, gracilis, and pulmonary arteries and veins (0.4-1.0 mm OD) prior to and days 1 and 32 after the initiation of two-kidney one-clip Goldblatt hypertension (2-KGH), produced by unilateral constriction of the renal artery (URAC). The reactivity (ED50) and tension development to norepinephrine (NE), angiotensin II (ANG II), potassium chloride (KCl), serotonin (5-HT), 9 alpha, 11 alpha-epoxymethano prostaglandin H2 (EMP), prostaglandin B2 (PGB2), and CaCl2 were determined. Mean arterial pressure (MAP) and TPR were unchanged from pre-URAC values 24 h post-URAC but were significantly elevated 32 days post-URAC. The ED50's for 5-HT, ANG II, EMP, and PGB2 were decreased in each of the arteries and veins obtained from dogs with 2-KGH, within 24 h post-URAC, and either became more pronounced (PGB2, EMP, and 5-HT) or returned to pre-URAC values by day 32 post-URAC. The ED50's for NE, KCl, and CaCl2 were unchanged from pre-URAC values. Maximal tension development of the arteries and veins to each of the agonists increased within 24 h post-URAC, prior to an increase in MAP or TRP. Within 32 days post-URAC, maximal tension development of the veins obtained from 2-KGH was increased from pre-URAC values, whereas tension development by the arteries was decreased. Extensibility decreased in each of the arteries and veins obtained from dogs with 2-KGH 24 h post-URAC. The extensibility decreased further by day 32 post-URAC as the level of MAP and TPR increased. These data support the postulate that altered venous and arterial smooth muscle contractility and extensibility precede the elevated MAP and TPR of 2-KGH in dogs. Moreover, since these changes occur in both artery and vein, they must reflect the action of circulating humoral or intrinsic vascular or neural substances. Finally, the decrease in arterial contractility suggests that the enhanced vascular responses in vivo and in situ may reflect the greater mechanical advantage of the hypertrophied blood vessel and not an arterial vasculature with enhanced contractility.

Angiotensin II↗

PubMed1985

Norepinephrine-induced beta 1-adrenergic peripheral vasodilation in conscious dogs.

Norepinephrine (NE) elicits alpha-adrenergic vasoconstriction and beta 1-adrenergic increases in heart rate and myocardial contractility. To determine whether NE can also elicit peripheral beta 1-adrenergic vasodilation, conscious dogs were studied after recovery from instrumentation for the measurement of cardiac output, arterial pressure, and left ventricular (LV) pressure and calculations of LV dP/dt and total peripheral resistance (TPR). NE, after pretreatment with hexamethonium and phentolamine, reduced mean arterial pressure 40 +/- 5% from 117 +/- 9 mmHg and TPR 60 +/- 5% from 0.058 +/- 0.007 mmHg X ml-1 X min and increased cardiac output 55 +/- 11% from 2,159 +/- 188 ml/min. beta 1-Adrenergic blockade with atenolol reversed the vasodilation induced by NE completely, while at this time isoproterenol was still able to reduce peripheral resistance further, by 67 +/- 7%, indicating that beta 2-adrenergic receptors were not blocked. Administration of phentolamine to intact dogs caused a fall in mean arterial pressure (23 +/- 5%) and TPR (34 +/- 5.4%) and an endogenous increase in plasma NE (2,987 +/- 905 pg/ml) and epinephrine (584 +/- 92 pg/ml). These increases in cardiac output and decreases in TPR were also reversed by atenolol (0.5 mg/kg). Moreover, this dose of atenolol blocked the increases in iliac blood flow induced by local injection of NE in the limb. Thus, in the presence of alpha-adrenergic receptor blockade, either administration of NE or release of endogenous NE elicits potent peripheral vasodilation, which appears to involve a beta 1-adrenergic receptor mechanism.

Adrenergic beta-Agonists↗

PubMed1989

Hemodynamics and blood volume in angiotensin II salt-dependent hypertension in dogs.

The sequential effects of an increased daily NaCl intake on hemodynamics, fluid electrolyte balances, and hormonal responses were evaluated in dogs (n = 7) with fixed circulating levels of angiotensin II (ANG II). During the control period, ANG II was infused at 3 ng.kg-1.min-1 while dogs were maintained on an 8 meq NaCl/day diet. Water intake was fixed at 700 ml/day. Continuously recorded (24 h/day) changes of total body weight (TBW) were used as an index of total body water. Cardiac stroke volume and arterial pressure were recorded, and each beat was digitized to provide hourly and 24-h average cardiac output (CO), mean arterial pressure (MAP), and total peripheral resistance (TPR). After three stable control days, daily salt intake was increased to 120 meq for 7 days. TBW increased gradually to 448 +/- 111 g (2.9%, P less than 0.05) above control by day 3. An 11% expansion of blood volume (P less than 0.05) was found (51CR-labeled red blood cells) on day 2 of high NaCl. CO rose 12% and MAP 20% (P less than 0.05) in parallel with TBW by day 4. By day 7, CO remained only 5% elevated, whereas MAP had stabilized at 20% above control levels. TPR remained significantly elevated from days 3 through 7. A positive Na balance averaging 91 +/- 8 meq (P less than 0.05) occurred on day 1. Plasma Na concentration was increased 2-3 meq/l above control throughout the period of high-salt intake. Plasma renin activity and aldosterone levels decreased to nearly undetectable levels, vasopressin rose slightly, and atrial natriuretic peptide levels increased significantly. Dogs maintained at 8 meq/day NaCl during the same infusion of ANG II showed no changes in MAP, CO, TPR, or TBW. In summary, the salt-induced hypertension was consistently related to small but significant fluid retention, blood volume expansion, elevations of cardiac output, and a gradual increase in TPR.

Angiotensin II↗

PubMed1990

Effects of hypercapnia and hypoxia on the cardiovascular system: vascular capacitance and aortic chemoreceptors.

Aortic chemoreceptor influences on vascular capacitance after changes in blood carbon dioxide and oxygen were studied in mongrel dogs anesthetized with methoxyflurane and nitrous oxide. The mean circulatory filling pressure (Pmcf), measured during transient cardiac fibrillation, provided a measure of capacitance vessel tone. Hypercapnia, hypoxia, and hypoxic hypercapnia significantly increased most variables, except that hypercapnia caused the total peripheral resistance (TPR) to decrease. Hypocapnia caused a significant decrease in mean systemic (Psa) and pulmonary (Ppa) arterial blood pressures, cardiac output (CO), and central blood volume and an increase in TPR and heart rate. The changes in Pmcf on changing blood gas tensions could be described by the equation delta Pmcf = -1.60 + 0.036 (arterial PCO2) + 50.8/arterial PO2. Thus a 10 mmHg increase in arterial PCO2 caused a 0.36 mmHg increase in Pmcf with receptors intact. Cold block (2 degrees C) of the cervical vagosympathetic trunks did not significantly influence the measured variables at control. During severe hypercapnia, vagal cooling caused a small but significant decrease in Pmcf, Psa, Ppa, and CO but not TPR. During hypoxia, vagal cooling caused the Pmcf, Psa, and TPR to decrease. We conclude that although hypercapnia or hypoxia acts reflexly to increase the capacitance vessel tone (an increase in Pmcf), the aortic and cardiopulmonary chemoreceptors with afferents in the vagi have only a small influence on the capacitance system, accounting for only approximately 25% of the total body response.

Animals↗

PubMed1992

Effects of birth-related stimuli on L-arginine-dependent pulmonary vasodilation in ovine fetus.

To determine the effects of birth-related stimuli on L-arginine-dependent vasodilation or nitric oxide (NO) activity in the perinatal lung, we studied the fetal pulmonary vascular effects of nitro-L-arginine (L-NA), a specific inhibitor of NO formation, during 1) mechanical ventilation without altering fetal blood gas tensions; 2) administration of high oxygen concentrations; and 3) increased flow or shear stress. In the first protocol, 13 late-gestation fetal lambs were ventilated with low fraction of inspired oxygen concentration (FIO2 less than or equal to 0.10) for 60 min after infusion of L-NA or saline into the left pulmonary artery (LPA). In control animals, LPA flow steadily increased during 60 min of ventilation. With L-NA treatment, the rise in flow and decrease in total pulmonary resistance (TPR) were reduced 67% (P less than 0.001 vs. control) and 28% (P less than 0.01 vs. control), respectively. Subsequent ventilation with high FIO2 (1.00) decreased mean pulmonary arterial pressure (PAP) in control but not in L-NA-treated animals. TPR remained fourfold greater in L-NA-treated animals than in control animals (P less than 0.001). In the second protocol, with partial compression of the ductus arteriosus, LPA flow increased 300% and TPR decreased 61% over 30 min. After L-NA treatment the rise in blood flow and decrease in TPR was markedly attenuated (P less than 0.001). We conclude that the perinatal pulmonary vasodilator response to ventilation without changing arterial oxygen tension and ventilation with increased oxygen tension are modulated by NO.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Progressive loss of vasodilator responsive component of pulmonary hypertension in neonatal calves exposed to 4,570 m.

Severe neonatal pulmonary hypertension (PH) may have both reversible (vasoconstrictive) and "fixed" (vasodilator unresponsive) components. To assess when and to what degree vasodilator unresponsive PH developed in the neonate, pulmonary arterial pressures (PAP) and cardiac outputs (CO) were measured, and total pulmonary resistances (TPR) were calculated in neonatal calves exposed to chronic hypoxia (CH) (barometric pressure of 430 mmHg = 4,570 m) for 1, 3, 7, and 14 days under both normoxic (barometric pressure of 640 mmHg = 1,500 m) and hypoxic conditions with and without an infusion of the vasodilator acetylcholine (ACh). Studies were done at 4 h and at 2, 4, 8, and 15 days of life in both control and CH animals. The fixed component of PH was defined as that PAP or TPR above the control baseline value which remained in CH animals after an infusion ACh at 1,500 m. Small pulmonary arteries were also examined histologically in an attempt to correlate relative changes in the reversible and fixed elements of PH with alterations in vessel structure. Chronic exposure to 4,570 m altitude prevented the normal postnatal fall in PAP and TPR observed in control animals. Instead, PAP, TPR, and the structure of small pulmonary arteries initially remained similar to those of the 4-h-old newborn. By 7 days exposure to 4,570 m, a significant element of fixed PH developed, which increased dramatically between the 7- and 14-day exposure periods and appeared to correlate with a narrowed pulmonary artery lumen and increased medial and adventitial thickness.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1994

Factors involved in delaying the rise in peripheral resistance in developing heart failure.

The development of heart failure (HF) on peripheral vascular control was studied in 10 conscious dogs with measurements of cardiac output (CO) and left ventricular (LV), arterial, and right atrial pressures. At 3 wk after pacing-induced HF, CO was not decreased from 2.5 +/- 0.2 l/min, whereas LV dP/dt fell (from 2,858 +/- 71 to 1,409 +/- 69 mmHg/s) and LV end-diastolic pressure increased (from 4.8 +/- 0.4 to 27.3 +/- 1.1 mmHg) (P < 0.05). At 4-7 wk after pacing, CO was significantly decreased (to 1.6 +/- 0.1 l/min; P < 0.05), but total peripheral resistance (TPR) did not rise, despite increases in plasma norepinephrine and renin activity (P < 0.05). In the presence of ganglionic blockade, TPR was still not increased in HF. In vitro studies in isolated femoral artery segments demonstrated reduced intrinsic tone (0.028 +/- 0.007 g/mg; P < 0.05) as compared with vessels from sham-operated controls (0.124 +/- 0.023 g/mg), whereas the intracellular calcium level was not altered in HF. Thus, during the development of HF, severe contractile dysfunction precedes the fall in CO, which, in turn, precedes the rise in TPR. The delayed rise in TPR appears to involve a reduction in intrinsic peripheral vascular tone, despite neurohumoral activation.

Animals↗

PubMed1994

Cardiovascular regulation in humans in response to oscillatory lower body negative pressure.

The frequency response characteristics of human cardiovascular regulation during hypotensive stress have not been determined. We therefore exposed 10 male volunteers to seven frequencies (0.004-0.1 Hz) of oscillatory lower body negative pressure (OLBNP; 0-50 mmHg). Fourier spectra of arterial pressure (AP), central venous pressure (CVP), stroke volume (SV), cardiac output (CO), heart rate (HR), and total peripheral resistance (TPR) were determined and first harmonic mean, amplitude, and phase angles with respect to OLBNP are presented. AP was relatively well regulated as demonstrated by small oscillations in half amplitude (3.5 mmHg) that were independent of OLBNP frequency and similar to unstressed control spectra. Due to the biomechanics of the system, the magnitudes of oscillations in calf circumference (CC) and CVP decreased with increasing frequency; therefore, we normalized responses by these indexes of the fluid volume shifted. The ratios of oscillations in AP to oscillations in CC increased by an order of magnitude, whereas oscillations in CVP to oscillations in CC and oscillations in AP to oscillations in CVP both tripled between 0.004 and 0.1 Hz. Therefore, even though the amount of fluid shifted by OLBNP decreased with increasing frequency, the magnitude of both CVP and AP oscillations per volume of fluid shifted increased (peaking at 0.08 Hz). The phase relationships between variables, particularly the increasing lags in SV and TPR, but not CVP, indicated that efferent responses with lags of 5-6 s could account for the observed responses. We conclude that, at frequencies below 0.02 Hz, the neural system of humans functioned optimally in regulating AP; OLBNP-induced decreases in SV (by as much as 50%) were counteracted by appropriate oscillations in HR and TPR responses. As OLBNP frequency increased, SV, TPR, and HR oscillations increasingly lagged the input and became less optimally timed for AP regulation.

Adult↗

PubMed1995

Alterations in systemic arterial mechanical properties during septic shock: role of fluid resuscitation.

The effects of septic shock (endotoxin; EDTX) on arterial mechanical properties were studied in anesthetized rabbits, both in the absence (EDTX alone) and presence (EDTX + fluids) of fluid resuscitation. Aortic pressure-flow (n = 20) and pressure-diameter (n = 10) measurements were used to calculate systemic arterial and regional aortic mechanical properties. At 3 h of EDTX shock, EDTX-alone rabbits had elevated total peripheral resistance (TPR, + 30%, P < 0.05), reduced cardiac output (CO, -40%, P < 0.05), and increased aortic characteristic impedance (Zc, +78%, P < 0.05). In contrast, the EDTX + fluids group responded with decreased TPR (-30%, P < 0.05), a tendency to increase CO (+23%), and elevated Zc (+46%, P < 0.05). A reduction in aortic diameter (-20%, P < 0.05) and an increase in elastic modulus (+50%, P < 0.05) and water content (+23%, P < 0.02) of the aortic wall were observed following endotoxemia. Thus following EDTX 1) "hyperdynamic" septic shock profile (i.e., low TPR, high CO) was observed only when concomitant fluid replacement was provided, 2) aortic wall stiffening was present due to both increased smooth muscle tone and vessel wall edema, and 3) fluid resuscitation resulted in discordant changes in TPR and Zc, suggesting differential flow-induced vasodilation between arteriolar and aortic smooth muscle.

Animals↗

PubMed2002

Role of hypoxemia for the cardiovascular responses to apnea during exercise.

We sought to define the role of hypoxemia in eliciting the cardiovascular responses to apnea during exercise. Eleven men performed repeated apneas during 100-W steady-state exercise, either with normoxic gas (air) or 95% oxygen (oxygen). Beat-by-beat arterial blood pressure, arterial oxygen saturation, and heart rate (HR) were determined, and stroke volume (SV) was estimated from impedance cardiography calibrated with soluble gas rebreathing. There were large interindividual variabilities of HR, mean arterial pressure (MAP), and total peripheral resistance (TPR) at end-apnea (ea). However, for each individual, HR(ea), MAP(ea), and TPR(ea) were highly correlated between air and oxygen (R = 0.94, 0.78, and 0.93). HR decreased and MAP increased faster during apnea with air than with oxygen (ANOVA, P < 0.05), but MAP(ea) was not different between conditions. Cardiac output was reduced by 33% with air and by 11% with oxygen (P < 0.001 for air vs. oxygen). We conclude that the hypoxemia component cannot account for the wide interindividual differences of HR and TPR responses to apnea. However, hypoxemia augments the HR and TPR responses and may limit the MAP response to apnea by preventing a bradycardia-associated increase of SV.

Adolescent↗

PubMed1983

Factors that alter the plasma renin activity of the marmot.

The effects of low doses of norepinephrine (NE) and furosemide and a volume load (nonhibernators only) on plasma renin activity (PRA), mean arterial pressure (MAP), heart rate (HR), left renal (RBF) and right iliac (IBF) blood flow, cardiac index (CI), and total peripheral resistance (TPR) were determined in euthermic and hibernating marmots. In nonhibernating marmots NE produced an increase in CI and TPR and a decrease in RBF. In hibernators this dose of NE caused an increase in MAP, HR, and renal resistance, whereas it decreased PRA and did not alter iliac resistance. Furosemide infusions led to an increase in PRA in both groups and an increase in TPR in nonhibernators. The volume load in nonhibernators produced only a decrease in PRA. A comparison of control data from the two groups indicated that the renal and iliac beds contribute only a small portion to the increase in TPR that occurs during hibernation.

Animals↗

PubMed1989

Systemic vascular autoregulation amplifies pressor responses to vasoconstrictor agents.

Experiments were performed in seven conscious dogs to evaluate the contribution of total systemic autoregulation to the increase in mean arterial pressure (MAP) produced by the intravenous administration of pressor agents. Each dog was instrumented for the measurement of aortic pressure, central venous pressure, and cardiac output, and all dogs received hexamethonium to block autonomic ganglionic transmission. Angiotensin II (ANG II), arginine vasopressin (AVP), or norepinephrine (NE) were titrated over a 15- to 20-min period until MAP was increased to a new steady-state value approximately 50-55% above the normotensive control. Then while a constant infusion of the pressor agents was maintained, MAP was controlled via a gravity reservoir for 15-min periods at either the hypertensive value or at the animal's normotensive value. With all three pressor agents, total peripheral resistance (TPR) was greater when MAP was controlled at the hypertensive value than when the vasculature was protected from the elevated pressure by controlling MAP at the normotensive value. Thus a portion of the increase in TPR during the infusion of ANG II, AVP, or NE was due to autoregulatory-mediated vasoconstriction elicited by the increase in MAP. The fractions of the increases in TPR and MAP contributed by primary vasoconstriction vs. autoregulation were determined from the pressure-flow relationships. The pressure-induced increases in TPR accounted for 74% of the total increase in MAP produced by AVP, 62% of the pressor response to NE, and 34% of the response to ANG II. These results demonstrate that the direct vasoconstrictor effects of pressor agents can be significantly amplified by secondary autoregulatory responses.

Algorithms↗