Intact hindquarter vascular responses of young spontaneously hypertensive rats to norepinephrine and tyramine

Intact hindquarter vascular responses to abdominal aortic injections of subpressor doses of norepinephrine (0.01, 0.02, 0.03 μg) or tyramine (5, 10, 15 μg) were examined in young ($\text{2}\text{1}\text{2}\text{–3}\text{months}$) spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) normotensives to ascertain whether altered vascular response to catecholamines in SHR could be detected in the presence of relatively constant systemic arterial perfusion pressure. Increases in vascular resistance (Δ mmHg. min/ml) and total decreases in blood flow volume (Δ ml) were determined by using electromagnetic flowmetry and blood flow integration techniques. Under a resting condition the abdominal aortic flow rate (ml/min) was similar between the SHR (8.7 ± 0.5) and WKY control (9.1 ± 0.5), whereas hindquarter vascular resistance was greater (73.8%) in SHR than in WKY normotensives (P < 0.05). The increase in vascular resistance in response to a low dose of norepinephrine (0.1 μg) was greater (85%) in SHR than in WKY rats (P < 0.05) and at higher doses of norepinephrine (0.02, 0.03 μg) there was a tendency of greater increase in resistance (20–30%) in SHR (0.05 < P < 0.1). Tyramine at all doses tested produced greater increases (50–66%) in resistance in SHR compared to WKY normotensives (P < 0.05). On the other hand, the decreases in the integrated total blood flow volume passing to the hindquarters after norepinephrine or tyramine administration at all doses were less (27–46%) in SHR than in WKY control (P < 0.05). The data demonstrate increased catecholamine vasoconstrictor responses in the intact hindquarters of SHR with attenuated blood flow volume decreases due to the higher resting vascular resistance, supporting the contention that the elevated vascular resistance in SHR may be attributed to vasoconstrictor hyperresponsiveness of catecholamines.     

The effects of race on norepinephrine clearance

Eighteen normotensive and 19 unmedicated hypertensive black and white male subjects were studied twice, during a 10 meq sodium diet for 5 days and a 200 meq sodium diet for 4 days. The subjects received an infusion of 3H-norepinephrine (3H-NE) during both low and high sodium diets to measure NE clearance. Dietary sodium and blood pressure classification had no effect on 3H-NE clearance. Infusion of pressor doses of NE also failed to alter 3H-NE clearance. Both normotensive and hypertensive blacks had increased 3H-NE clearance rates (p less than .001). The increased rate of 3H-NE clearance among blacks was not affected by alterations in dietary sodium or by pressor doses of NE. Increased NE clearance by blacks may help explain observations that white hypertensives in the age range we studied (25-46 years) have elevated plasma NE levels, while blacks have normal NE levels.     

Effects of indomethacin on venoconstrictor responses to bradykinin and norepinephrine

In order to determine whether the venoconstrictor response to BK was dependent on prostaglandin (PG) synthesis, effects of indomethacin (INDO) on responses to bradykinin (BK) and norepinephrine (NE) were studied in canine lateral saphenous vein. Cumulative dose-response curves (10⁻⁹-10⁻⁶M BK or NE) were done in the presence and absence of INDO (10⁻⁶M). In the presence of INDO, responses to BK were markedly enhanced while responses to NE were unchanged. After prolonged periods in the bath, responses to BK were enhanced in control strips while responses of strips which had been treated with INDO were depressed. These results suggest that BK does not normally cause venoconstriction by stimulating synthesis of a venoconstrictor PG and that the increase in response to BK after prolonged periods in the bath may be related to changes in PG synthetase.     

Effects of angiotensin II on pressor responses to norepinephrine in humans

In previous studies in the conscious rabbit and in isolated artery preparations, low doses of angiotensin II synergistically amplified the pressor effects of the sympathetic neurotransmitter, norepinephrine (NE). To determine whether these observations could be replicated in humans, 9 normal adult male volunteers (mean age: 34) each were given 3 i.v. doses of NE (25, 50 and 100 micrograms.kg-1.min-1) during consecutive 10 min infusion periods. On a second study day, the procedure was repeated during infusion of angiotensin II in a subpressor dose (1.25 ng.kg-1.min-1). The angiotensin II didn't alter the BP responses to NE, but it attenuated the heart rate (HR) decreases associated with the NE infusions by 80% (P less than 0.05), 42% (P less than 0.05) and 42% (P less than 0.1). The two study days were then repeated following 2 weeks of oral treatment with the angiotensin converting enzyme inhibitor captopril (which, despite significantly decreasing baseline BP, also tended to decrease HR). In the presence of captopril, the pressor responses to the NE challenges were reduced by 50% (P less than 0.05), 33% (P less than 0.05) and 13% (P less than 0.1) compared with the pre-captopril responses. Thus, angiotensin II in subpressor doses appears to enhance NE pressor effects by attenuating the compensatory HR responses, whereas inhibition of endogenous angiotensin II mechanisms weakens the BP-raising actions of NE. These findings in humans are consistent with earlier observations that the renin-angiotensin system can directly amplify sympathetic pressor effects in two separate ways: by modifying baroreceptor sensitivity and by enhancing the actions of norepinephrine on vascular smooth muscle.     

Effect of age on cutaneous vasoconstrictor responses to norepinephrine in humans

To test the hypothesis that cutaneous vasoconstrictor responsiveness to exogenous norepinephrine is reduced in older compared with young subjects, dose-response relations between norepinephrine and skin blood flow were established. Seven doses of norepinephrine (1.10(-8) to 10(-2) log M) were perfused (2 microl/min) intradermally (4 min/dose) using cutaneous microdialysis (2 probes/subject). To account for possible differences in endogenous norepinephrine between groups, one microdialysis probe was perfused with bretylium tosylate to locally block noradrenergic vesicle release before establishing the norepinephrine dose-response relations. Skin blood flow was indexed via laser-Doppler flowmetry directly over both microdialysis probe sites and is expressed as cutaneous vascular conductance (laser-Doppler flux/mean arterial blood pressure). Local skin temperature was maintained at 34 degrees C at both sites throughout the protocol. Dose-response relation between norepinephrine and cutaneous vascular conductance was similar between control and bretylium-pretreated sites in young subjects (EC50 = -5.18 +/- 0.27 and -5.03 +/- 0.27 log M, respectively). In contrast, the dose-response relation was significantly shifted to the right (i.e., a higher dose of norepinephrine was needed to produce the same vasoconstrictor response) in the bretylium-pretreated site in older subjects (EC50 = -5.46 +/- 0.23 and -4.53 +/- 0.23 log M, respectively). Significant increases in EC50 were observed in older compared with young subjects at the bretylium-pretreated but not the control sites. These data indicate that cutaneous vasoconstrictor responsiveness is decreased in older subjects when endogenous release of norepinephrine is antagonized. Furthermore, these findings suggest that differences in presynaptic norepinephrine release between older and younger subjects are profound enough to affect dose-response relations between norepinephrine and cutaneous vascular conductance.     

Effects of indomethacin on venoconstrictor responses to bradykinin and norepinephrine.

In order to determine whether the venoconstrictor response to BK was dependent on prostaglandin (PG) synthesis, effects of indomethacin (INDO) on responses to bradykinin (BK) and norepinephrine (NE) were studied in canine lateral saphenous vein. Cumlative dose-response curves (10-9-10-6M BK or NE) were done in the presence and absence of INDO (10-6M). In the presence of INDO, responses to BK were markedly enhanced while responses to NE were unchanged. After prolonged periods in the bath, responses to BK were enhanced in control strips while responses of strips which had been treated with INDO were depressed. These results suggest that BK does not normally cause venoconstriction by stimulating synthesis of a venoconstrictor PG and that the increase in response to BK after prolonged periods in the bath may be related to changes in PG synthesis.     

The effects of pregnancy on ethanol clearance

We have studied the effects of pregnancy on ethanol clearance rates and on blood and urine ethanol concentrations (BECs and UECs) in adult Sprague-Dawley rats infused with ethanol intragastrically. Pregnant rats had greater ethanol clearance following an intragastric or intravenous ethanol bolus (3 or 0.75 g/kg, respectively) relative to non-pregnant rats (p<0.05). Pregnant rats infused with ethanol-containing diets for several days had lower (p<0.05) UECs than non-pregnant rats when given the same dose of ethanol. Non-pregnant rats infused ethanol-containing diets at two levels of calories (the higher caloric intake required by pregnant rats [220 kca/kg75/d] or the normal calories required for non-pregnant rats [187 kcal/kg75/d]) had statistically equal UECs, suggesting that increased caloric intake was not responsible for the effect of pregnancy. While the activity of hepatic alcohol dehydrogenase (ADH) did not differ with pregnancy, gastric ADH activity was increased (p<0.001). Furthermore, total hepatic aldehyde dehydrogenase (ALDH) and hepatic mitrochrondrial protein were increased (p<0.05) and hepatic CYP2E1 activity was suppressed (p<0.05). The results suggest that pregnancy increases ethanol elimination in pregnant rats by: 1) induction of gastric ADH; 2) elevated hepatic ALDH activity; and 3) increased mitochondrial respiration. The greater ethanol clearance results in lower tissue ethanol concentrations achieved during pregnancy for a given dose, and this may have clinical significance as a mechanism to protect the growing fetus from ethanol toxicity.     

The effects of ethanol and chlorpromazine on the passive membrane permeability to Na

1.

1. Chlorpromazine and ethanol each reduced the passive influx of Na⁺ into resting sartorius muscle (frog) incubated in a medium containing 1 mM Ca²⁺, ouabain (to preclude active fluxes) and isotonic choline chloride (to preclude membrane depolarization).     

Membrane responses to norepinephrine in cultured brown fat cells

We used the "perforated-patch" technique (Horn, R., and A. Marty, 1988. Journal of General Physiology. 92:145-159) to examine the effects of adrenergic agonists on the membrane potentials and membrane currents in isolated cultured brown fat cells from neonatal rats. In contrast to our previous results using traditional whole-cell patch clamp, 1-23-d cultured brown fat cells clamped with the perforated patch consistently showed vigorous membrane responses to both alpha- and beta-adrenergic agonists, suggesting that cytoplasmic components essential for the thermogenic response are lost in whole-cell experiments. The membrane responses to adrenergic stimulation varied from cell to cell but were consistent for a given cell. Responses to bath-applied norepinephrine in voltage-clamped cells had three possible components: (a) a fast transient inward current, (b) a slower outward current carried by K+ that often oscillated in amplitude, and (c) a sustained inward current largely by Na+. The fast inward and outward currents were activated by alpha-adrenergic agonists while the slow inward current was mediated by beta-adrenergic agonists. Oscillating outward currents were the most frequently seen response to norepinephrine stimulation. Activation of this current, termed IK,NE, was independent of voltage and seemed to be carried by Ca2(+)-activated K channels since the current oscillated in amplitude at constant membrane potential and gradually decreased when the cells were bathed with calcium-free external solution. IK,NE had a novel pharmacology in that it could be blocked by 4-aminopyridine, tetraethylammonium, apamin, and charybdotoxin. Both IK,NE and the voltage-gated K channels also present in brown fat (Lucero, M. T., and P. A. Pappone, 1989a. Journal of General Physiology. 93:451-472) may play a role in maintaining cellular homeostasis in the face of the high metabolic activity involved in thermogenesis.     

The effects of ethanol on the glycosylation of human transferrin

Appearance of a hyposialylated transferrin fraction in the plasma during chronic alcohol exposure is a well-known phenomenon, and it represents the best available marker of chronic alcohol consumption. The mechanisms of its appearance are still not well understood and are extremely complex, involving biosynthesis and catabolism alterations, although the only structural abnormality described corresponds to the loss of an entire glycan chain. We analyzed and compared the oligosaccharides present on the different isoforms of purified transferrin isolated from control and patients with severe alcohol abuse by fluorescent carbohydrate electrophoresis and matrix-assisted laser desorption ionization mass spectrometry. Our data indicate that the major modification observed is the loss of an entire oligosaccharide chain; we also demonstrate that there is a modification of terminal sialylation. Carbohydrate-deficient transferrin (CDT) is the result of multiple alterations of glycosylation. These results give a partial explanation to the poor sensitivity of the measurement of CDT and its controversial use as a marker of chronic alcohol consumption.     

The effects of normobaric hypoxia on the leukocyte responses to resistance exercise

There is growing interest in the use of systemic hypoxia to improve the training adaptations to resistance exercise. Hypoxia is a well-known stimulator of the immune system, yet the leukocyte responses to this training modality remain uncharacterised. The current study characterised the acute leukocyte responses to resistance exercise in normobaric hypoxia. The single-blinded, randomised trial recruited 13 healthy males aged 18–35 years to perform a bout of resistance exercise in normobaric hypoxia (14.4% O₂; n = 7) or normoxia (20.9% O₂; n = 6). Participants completed 4 × 10 repetitions of lower and upper body exercises at 70% 1-repetition maximum. Oxygen saturation, rating of perceived exertion and heart rate were measured during the session. Venous blood was sampled before and up to 24 hours post-exercise to quantify blood lactate, glucose and leukocytes including neutrophils, lymphocytes, monocytes, eosinophils and basophils. Neutrophils were higher at 120 and 180 minutes post-exercise in hypoxia compared to normoxia (p<0.01), however lymphocytes, monocytes, eosinophils and basophils were unaffected by hypoxia. Oxygen saturation was significantly lower during the four exercises in hypoxia compared to normoxia (p < 0.001). However, there were no differences in blood lactate, heart rate, perceived exertion or blood glucose between groups. Hypoxia amplified neutrophils following resistance exercise, though all other leukocyte subsets were unaffected. Therefore, hypoxia does not appear to detrimentally affect the lymphocyte, monocyte, eosinophil or basophil responses to exercise.