Laura V. Brown

Longitudinal analysis of arterial blood pressure and heart rate response to acute behavioral stress in rats with type 1 diabetes mellitus and in age-matched controls

We recorded via telemetry the arterial blood pressure (BP) and heart rate (HR) response to classical conditioning following the spontaneous onset of autoimmune diabetes in BBDP/Wor rats vs. age-matched, diabetes-resistant control (BBDR/Wor) rats. Our purpose was to evaluate the autonomic regulatory responses to an acute stress in a diabetic state of up to 12 months duration. The stress was a 15-s pulsed tone (CS+) followed by a 0.5-s tail shock. The initial, transient increase in BP (i.e., the “first component,” or C1), known to be derived from an orienting response and produced by a sympathetic increase in peripheral resistance, was similar in diabetic and control rats through ∼9 months of diabetes; it was smaller in diabetic rats 10 months after diabetes onset. Weakening of the C1 BP increase in rats that were diabetic for >10 months is consistent with the effects of sympathetic neuropathy. A longer-latency, smaller, but sustained “second component” (C2) conditional increase in BP, that is acquired as a rat learns the association between CS+ and the shock, and which results from an increase in cardiac output, was smaller in the diabetic vs. control rats starting from the first month of diabetes. A concomitant HR slowing was also smaller in diabetic rats. The difference in the C2 BP increase, as observed already during the first month of diabetes, is probably secondary to the effects of hyperglycemia upon myocardial metabolism and contractile function, but it may also result from effects on cognition. The small HR slowing concomitant with the C2 pressor event is probably secondary to differences in baroreflex activation or function, though parasympathetic dysfunction may contribute later in the duration of diabetes. The nearly immediate deficit after disease onset in the C2 response indicates that diabetes alters BP and HR responses to external challenges prior to the development of structural changes in the vasculature or autonomic nerves.

Effect of Concentration and Hyaluronidase on Albumin Diffusion Across Rabbit Mesentery

OBJECTIVE To measure the diffusion coefficient of albumin through rabbit mesentery using the steady-state flux of radioactive tracer 125I-albumin. The effect of albumin concentration and testicular hyaluronidase were also studied. METHODS Mesenteric tissue was bonded between two plates, exposing a 7 mm diameter surface, with two chambers on either side. One chamber was filled with a test solution of albumin containing the radioactive tracer and the other with lactated Ringer solution. The solutions in both chambers were stirred with small magnetic cylinders. The chamber filled with lactated Ringer solution was placed in a well-type NaI(Tl) detector, and the radiation emitted from the tracer that diffused across the mesentery was monitored continuously for 9 hours. The diffusion coefficient (D) was calculated using Ficks law of diffusion. The diffusion coefficient was measured at albumin concentration differences (delta C) between approximately 0 and 10 g/dL. The diffusion coefficient was also measured with testicular hyaluronidase at three different albumin-concentration differences. RESULTS The diffusion coefficient increased significantly (P < 0.0001) approximately three-fold from a mean value of 2.2 x 10(-8) +/- 1.2 x 10(-8) (SD) cm2/s at 0-0.5 g/dL delta C to 5.9 x 10(-8) +/- 1.1 x 10(-8) (SD) cm2/s at 10 g/dL delta C. The values are much less than the free diffusion coefficient of albumin (6 x 10(-7) cm2/s). Testicular hyaluronidase added to the albumin solution decreased D by approximately 60%, but did not eliminate the increase in D with delta C. CONCLUSIONS The increase in D with delta C and the reduced D with hyaluronidase were attributed to a reduced albumin-excluded volume caused by an interaction between albumin and hyaluronan. Further studies are required to define this interaction.

Effect of blood flow on capillary transit time and oxygenation in excised rabbit lung

We used an isolated perfused lung preparation of the rabbit to study the effect of increasing blood flow on pulmonary capillary transit time by two methods. In one method, capillary transit time was measured from fluorescent dye dilution curves from arterioles and venules of the subpleural microcirculation. Values of transit time were similar to those for the whole lung determined by dividing capillary blood volume by blood flow. Capillary transit times averaged 0.50-0.62 sec at a control blood flow of 80 ml min-1 kg-1 and decreased to 0.14-0.18 sec as blood flow increased to 6 times control. To determine whether the reduced transit time would limit O2 transport, we studied the effect of blood flow on oxygenation. Two isolated rabbit lungs were perfused in series. Blood from one lung deoxygenated by ventilation with a N2-CO2 mixture was oxygenated by the test lung ventilated with air. Ventilation was matched to blood flow. PO2 and PCO2 were measured in blood flowing into and out of the test lung. At all flows, no significant alveolar gas-to-end-capillary blood PO2 gradient (A-aDO2) was measured. The isolated perfused rabbit lung showed no transit time limitation to oxygenation for blood flows that are consistent with heavy exercise in vivo.

Effect of Flow on Hydraulic Conductivity and Reflection Coefficient of Rabbit Mesentery

Objective: To measure the hydraulic conductivity and reflection coefficient for albumin, as defined by the Starling equation, in rabbit mesentery.

Two-component arterial blood pressure conditional response in rat

The objective of these experiments was to quantify the pattern of change in arterial blood pressure (BP) during a discriminative aversive classical conditioning paradigm in rat using a new “high resolution” computer analysis. Sprague-Dawley rats (n=5) were restrained in a soft, conical cloth pouch and conditioned using a 6 sec. pulsed tone (CS+) followed by a 0.5 sec. tail shock; a steady tone, never followed by shock, served as a CS-. BP peaked at 16.4±6.5 mm Hg (mean±SD) above control at 1.5±0.1 sec. after onset of CS+. This “first component” (“C1”) also occurred during CS- (12.1±3.8 mm Hg), although the magnitudes of the two were significantly (p<0.05) different. Another group of rats (n=8) was treated identically except the tones were 15 seconds long. The conditional BP response consisted of two components. C1 was reminiscent of that seen using the short tone: for CS+ a peak of 13.6±5.6 mm Hg at 1.5 sec. or, for CS-, of 10.0±4.3 at 1.3 sec. (p<0.05). In CS+ trials BP peaked again (“C2,” 7.4±2.5 mm Hg) at 8.3±1.2 sec. There was no statistically significant C2 for CS- trials, clearly demonstrating discrimination between tones. The unconditional BP response in both groups consisted of two large, closely spaced peaks in BP. Respiration was recorded in 3 additional rats. After shock delivery these subjects often showed a sudden shift between (1) a regular respiratory pattern with moderate chest excursion and (2) apneic episodes interspersed with single, deep breaths. This latter pattern was associated with large, low frequency fluctuations in BP. Continued development of the rat conditioning paradigm is especially warranted because of the ability to record sympathetic nerve activity in intact, awake subjects and the large number of readily available genetic strains, which model human pathological states.

Effect of hyaluronidase on albumin diffusion in lung interstitium.

Abstract. Albumin diffusion measured in an isolated segment of rabbit lung interstitium with a radioactive tracer (125I-albumin) technique was independent of albumin concentration and similar to the free diffusion of albumin in water (Qiu et al, 1998. J Appl Physiol 85: 575–583). We studied the effect of hyaluronidase on the diffusion of albumin. Isolated rabbit lungs were inflated with silicon rubber by way of airways and blood vessels, and two chambers were bonded to the sides of a ∼0.5-cm thick slab enclosing a vessel with an interstitial cuff. One chamber was filled with 2 g/dl albumin solution containing 125I-albumin and 0.02 g/dl hyaluronidase. Unbound 125I was removed from the tracer by dialysis before use. The other chamber filled with Ringers solution was placed within a NaI(Tl) scintillation detector. Diffusion of tracer was measured continuously for 120 h. Albumin diffusion coefficient (D) and interstitial area (A) were obtained by fitting the tracer-time curve with the theoretical solution of the equation describing one-dimension diffusion of a solute across a membrane. D averaged 5.2 × 10−7 cm2/s for albumin diffusion with hyaluronidase, 20% less than that measured previously without hyaluronidase. Hyaluronidase had no effect on A. Results indicated an interaction between albumin and interstitial hyaluronan that was the opposite of the steric effect on albumin excluded volume measured in solution.

Nicotinic Regulation of Sympathoadrenal Catecholamine Secretion: Cross-Tolerance to Stress

The effects of nicotine on the regulation of sympathoadrenal secretion have long been recognized (1,2). Recent demonstration of endogenous opioid peptides colocalized with catecholamines in the adrenal medulla and in sympathetic nerve terminals has provided new impetus for the further study of both the physiologic regulation of sympathoadrenal secretion by nicotinic cholinergic receptors and the pharmacologic effects of this alkaloid (3,4). In addition to actions on adrenal chromaffin cells and sympathetic ganglia (5), it is thought that nicotine may stimulate sympathoadrenal secretion of catecholamines and opioid peptides by acting in brain to increase central sympathetic outflow. However, the latter issue has not been established, and we have initiated a series of studies comparing plasma catecholamine and cardiovascular responses to peripheral (intraarterial; ia) versus central (intraventricular; ivt) administration of nicotine.

Plasma Met-enkephalin and Cardiovascular Responses to Stress

Met-enkephalin (ME) and a number of other proenkephalin A-derived peptides are localized in chromaffin cells of the adrenal medulla, in sympathetic ganglia, and in sympathetic nerve terminals distributed widely in the periphery (Schultzberg et al. 1978). Cosecretion of enkephalin-related peptides and catecholamines has been demonstrated from chromaffin cells in culture, from isolated perfused adrenal glands, and from dog adrenals in vivo (Livett et al. 1981; Wilson et al. 1982; Hanbauer et al. 1982; Asada et al. 1983; Chaminade et al. 1983). Although circulating ME has been quantitated by a number of laboratories (see Van Loon et al. 1987 for review), considerable variability ( 200 pg/ml) in basal plasma concentration has been described and responses to stimuli have been documented in very few studies. Furthermore, the function of circulating enkephalins remains poorly understood.

Chapter 21 Differential brain and peripheral nicotinic regulation of sympathoadrenal secretion

Publisher Summary This chapter describes some of studies comparing the initial responses of plasma epinephrine and norepinephrine and the development of tolerance to intracerebroventricular (ICV) versus intra-arterial administration of nicotine in conscious rats. To determine whether alterations in sympathoadrenal sensitivity to nicotine might affect sympathoadrenal responses to other stimuli, the plasma catecholamine responses to a physiologic stress in two models is compared in which the animals were tolerant to nicotine. The responses to restraint in conscious rats tolerant to either systemic or ICV nicotine and to hypoglycemia in nicotine-tolerant, pentobarbital-anesthetized dogs is discussed. Finally, recent demonstration of endogenous opioid peptides colocalized with catecholamines in the adrenal medulla and in sympathetic nerve terminals has provided new impetus to study further the physiologic and pharmacologic regulation of sympathoadrenal secretion by nicotinic receptors. Thus, the chapter describes the differences between in vivo adrenal secretory responses of not only catecholamines but also Met-enkephalin to initial and subsequent systemic administration of nicotine.

Effect of hydration on lung interstitial conductivity response to electrically charged solutions

In interstitial segments of rabbit lung, we compared the flow of a solution containing cationic protamine sulfate (0.08 mg/ml) or cationic dextran (0.1%) to that of Ringer or neutral dextran solution. Also compared, were the flow of solutions containing anionic dextran (0.1 or 1.5%) to those containing neutral dextran and the flow of hyaluronidase solution (0.02%) to that of Ringer solution, at mean interstitial pressures (Pm) between -5 and 15 cmH2O. Driving pressure was set at 5 cmH2O. Cationic protamine or cationic dextran-to-Ringer flow ratio increased with Pm (presumably as hydration increased) but in nonedematous interstitium (-5 cmH2O Pm), flow ratio was 1, indicating a viscosity-dependent flow. In contrast, the flow of anionic dextran solution decreased relative to that of neutral dextran; this decrease was constant with hydration, but was greater at the higher concentration of dextran. Interstitial conductivity to the flow of hyaluronidase increased with hydration. However, this behavior was absent after the flow of 1.5% anionic dextran, indicating an inhibitory effect of the higher concentration of anionic dextran on the hyaluronidase response. A negative charge in microvascular filtrate may control fluid clearance in normal interstitium, while a positive charge would enhance clearance only in edema formation.