Catherine Gatto

Metabolic response of preterm infants to variable degrees of respiratory illness

In older children and adults, physiologic instability associated with severe illness causes increased cellular oxygen consumption (VO2), increased serum lactate and cortisol levels, and more negative nitrogen balance. To determine the metabolic response of preterm infants to severity of respiratory illness, we analyzed VO2, nitrogen balance, urinary 3-methyl-histidine and norepinephrine concentrations, and serum levels of lactate and cortisol as a function of ventilatory index (VI). Twelve 2-day-old premature infants who were appropriate in size for gestational age (mean +/- SEM birth weight: 1460 +/- 251 gm) and who required mechanical ventilation for respiratory distress syndrome had VO2 and carbon dioxide production measured by indirect calorimetry and blood and urine samples obtained concurrently. All infants received amino acids, 1.0 gm/kg per day, and a mean energy intake of 27 +/- 3 kcal/kg per day, provided as a parenteral dextrose solution. The resting energy expenditure exceeded energy intake in all infants. The VO2 value ranged from 5.5 to 9.2 ml/kg per minute and was directly correlated with VI (r = 0.79; p = 0.002). Nitrogen balance ranged from -160 to 53 mg/kg per day (mean: -33 +/- 21 mg/kg per day) but was not dependent on VI (r = 0.04) or VO2 (r = 0.01). The serum lactate level correlated directly with VI (r = 0.82; p = 0.002) and VO2 (r = 0.60; p = 0.05), but cortisol and urinary norepinephrine levels did not. We conclude that preterm infants with respiratory distress syndrome have increased VO2 rates and serum lactate concentrations directly related to the degree of respiratory illness. They are generally in a state of mildly negative nitrogen balance, the degree of which is not related to severity of illness. Although these infants may require increased energy delivery during illness, they do not appear to require excessive amounts of amino acids.

PARATHYROID HORMONE-RELATED PEPTIDE (PTHrP) AND CALCITONIN GENE-RELATED PEPTIDE (CGRP) DO NOT INHIBIT UTERINE CONTRACTION THROUGH ATP-SENSITIVE K+ CHANNELS IN THE RAT UTERUS. † 423

PTHrP has been localized in the uterine endometrium and myometrium while CGRP has been localized in nerves in the uterus. We have previously reported that both peptides relax uterine contraction in a dose-related manner using tissue from nonpregnant and pregnant rats. We have been interested in the signal transduction of these peptides in the uterus. ATP-sensitive K+ channels are present in various tissues including smooth muscle and have been suggested to play a role in the vasodilatory effect of CGRP in uterine arteries. Thus, we investigated the role of ATP-sensitive K+ channels and PTHrP, CGRP and ritodrine, a β-agonist, on the relaxation of rat uterine tissue. We used an in vitro uterine assay utilizing 3-10 tissue strips for each dose from 38 nonpregnant rats. PTHrP(5×10-7-10-9 M), CGRP (10-6-10-9 M), ritodrine (10-6-10-9 M) and cromakalim (10-4-10-7 M), an ATP-sensitive K+ channel activator, inhibited acetylcholine(Ach)-stimulated (10-6 M) uterine contraction in a dose-related manner. Glyburide (10-4-10-5 M), an ATP-sensitive K+ channel blocker significantly blocked the ability of cromakalim at all doses to inhibit Ach-stimulated uterine contraction. However, using the same paradigm, glyburide at effective doses failed to block PTHrP, CGRP and ritodrine inhibition of Ach-stimulated uterine contraction. These data suggest, that in our assay, cromakalim reactive ATP-sensitive K+ channels do not play a role in PTHrP, CGRP and ritodrine relaxation of Ach-stimulated uterine contraction.

Calcitonin and Calcitonin Gene‐Related Peptide Block Bombesin‐ and Substance P‐ Induced Increases in Airway Resistance

Incomplete understanding of the multiple overlapping mechanisms controlling bronchomotor tone continues to be a major factor limiting therapeutic modification of elevated airway resistance in human lung disease. This task is further complicated by the existence of putative control systems containing multiple bioactive peptides, such as the pulmonary peptidergic innervation and the pulmonary neuroendocrine cells, whose identification is currently ongoing. Substance P (SP), localized within afferent fibers innervating airway smooth muscle, and bombesin (B), identified in neuroendocrine epithelial cells proximate to airway smooth muscle, are both potent bronchoconstrictors. However, the interactions of these agents with other, associated peptides have not been investigated. The present study was undertaken to investigate the interactions of these agents with two peptide products of the calcitonin gene, calcitonin (C) and calcitonin gene-related peptide (CGRP), peptides which are likely co-contained and co-released with B and SP within the lung. Male Duncan-Hartley guinea pigs (435-670 g) were anesthetized (Chloropent) and had carotid and internal jugular catheters and a tracheostomy tube placed through an anterior cervical incision and an intrapleural catheter placed percutaneously through a posterior lateral intercostal space. Changes in lung mechanics were measured in spontaneously breathing anesthetized animals in the prone position using a PeDS computerized pulmonary function system (Medical Associated Services, Hatfield, PA). Agents, diluted in 1.0-1.5 cc of 0.01 M acetic acid (HAc) in 0.9% NaCI, were infused through the jugular catheter over a 10-min time period, using a continuous infusion pump. Data from each experimental group as a whole (baseline values through 30-min postinfusion) were subjected to one-way analysis of variance. If significant changes were noted from baseline, further comparisons were performed using the Bonferroni method for analyzing multiple t-tests. Infusion of the 0.01 M HAc alone (controls, n = 10) caused little change in pulmonary mechanics, arterial blood gases, or systolic (SBP) or diastolic (DBP) blood pressure. Infusion of 0.3 nmol/kg/min of CGRP (n = 12) or 2 nmol/kg/min of C (n = 6) caused little change in most parameters. While C did not affect blood pressure, CGRP caused a marked decrease in SBP (50 5% of baseline) and DBP (46 * 5% of baseline) ( p < 0.001) during the infusion. Infusion of 0.07 nmol/kg/min of B (n = 8)

1770 PULMONARY ENDOTHELIAL PERMEABILITY IN ASTHMA

The hypothesis that pulmonary endothelial permeability (PEP) is increased in asthma was tested in a guinea pig model. Animals were sensitized to ovalbumin by subcutaneous injection two weeks prior to testing (asthmatic group). Normal animals did not receive the sensitizing ovalbumin. A third group of animals was desensitized by repeated exposure to nebulized ovalbumin, with epinephrine rescue, over a 4-6 week period (desensitized group). Pulmonary function was assessed by plethysmography in each group during a control period and after challenge with nebulized ovalbumin. PEP was assessed by the rate of appearance of the albumin tag, Evans blue, in the lung, and systemic endothelial permeability (SEP) by the rate of decline of serum concentrations of Evans blue. All groups had comparable pulmonary function during the control period. Ovalbumin inhalation produced a decrease in dynamic lung compliance and an increase in airway resistance only in the asthmatic group. PEP was increased in the asthmatic animals, while SEP was comparable in all groups. Pulmonary edema occurred in both the asthmatic and desensitized groups.Pulmonary dysfunction in asthma is accompanied by increased PEP. Pulmonary edema, alone, does not explain these changes.

1761 ANATOMIC DISTRIBUTION AND QUANTITATIVE CHANGES IN GUINEA PIG PULMONARY β-RECEPTORS IN EXPERIMENTAL ASTHMA

Quantitation using tissue homogenates has demonstrated a decrease in pulmonary β-receptors in experimental asthma. However, techniques using disrupted tissue have not permitted precise identification of the pulmonary structures where such decreases occur. Experimental asthma (A) was produced in guinea pigs by the sc injection of ovalbumin then daily exposure to ovalbumin aerosol for 4–5 weeks. Animals initially developed dyspnea during the aerosol exposures, but showed a tolerence to increasing ovalbumin concentrations over time. Using 3H-dihydroalprenolol, β-receptors were radioautographically localized and quantitated in lung sections of saline control (C) (n=6) and (A) (n=9) guinea pigs. Scatchard analysis showed a single class of binding sites with a Bmax of 368±32(C) and 258±15(A) fmole/mg protein (p<.005). Binding was of high affinity Kd=0.89±.09(C), 0.77±0.07(A) nM (N.S.). A 25–30% decrease in β-receptor number in alveolar, bronchiolar and bronchial epithelium (E) and bronchiolar smooth muscle (SM) (p<.001) appeared to be responsible for the 30% decrease in total (A) lung β-receptors. No decreases were noted in bronchial, arterial or venous SM. Despite the decrease in β-receptors no significant differences were noted in tidal volume, dynamic compliance and airway resistance between (C) and (A) animals in response to antigen challange as determined by body plethysmography immediately prior to sacrifice. These data suggest that decreases in β-receptor number can occur without changes in pulmonary function and decreases in E rather than SM β-receptors account for the majority of the observed change.

ANATOMIC DISTRIBUTION AND QUANTITATIVE DEVELOPMENTAL CHANGES IN GUINEA PIG PULMONARY BETA RECEPTORS

Quantitation using tissue homogenates has demonstrated an increase in pulmonary β-receptors during development. However, techniques using disrupted tissue have not permitted the precise anatomic localization of pulmonary β-receptors or identification of the structures where increases occur. Using 3H-dihydroalprenolol, β-receptors were radioautographically localized and quantitated in sections of newborn (NB) and adult (A) guinea pig lung. Specific binding on lung sections, defined as that prevented by 2μ M propranolol (80-90% of total counts), was rapid and saturable. Scatchard analysis showed a single class of binding sites with a maximum binding capacity of 189±3 (NB) and 305±37 (A) fmole/mg protein (p<.003). Binding was of high affinity Kd = 1.46±.2 (NB) 1.26±.3 (A) nM (N.S.). The majority of β-receptors were localized in the alveolar wall and airway epithelium (alveolar >> bronchiolar > bronchial) (p<.0001) and averaged 2.8 (A) and 1.3 (NB)-fold greater in number than β-receptors in corresponding airway smooth muscle (p<.005). Arterial and venous smooth muscle had few demonstrable β-receptors. The increased number of β-receptors in the adult appeared to be due primarily to a 2.0±.2 fold increase in alveolar wall and airway epithelium as opposed to only a 1.3±.4 fold increase in the already low number in airway and vascular smooth muscle (p<.003). While receptor density may not necessarily correlate with response or physiologic importance, the role of β-receptors in airway and alveolar epithelium/endothelium function deserves further investigation.