Vasoconstrictor response to prostacyclin in rabbit pulmonary circulation

We have determined the effect of prostacyclin (PGI2) on segmental vascular resistance in rabbit lungs. Lungs of 26 rabbits were isolated and perfused with blood; 16 adult, greater than 6 months old, five juvenile, 6-8 week old and five neonatal, 2-3-week old. Six of the adult lungs were pretreated with indomethacin to block cyclooxygenase, prior to infusion of PGI2. In all lungs, flow was adjusted initially to keep pulmonary artery pressure approximately 20 cmH2O, left atrial and airway pressures being 8 and 6 cmH2O, respectively (zone 3), and then kept constant. We measured pulmonary artery pressure continuously and in the 10 untreated adult lungs, in which a vasoconstrictor response to PGI2 was obtained, we also measured pressures in 20-50 microns diameter subpleural arterioles and venules by the micropipette-servonulling method. We found that in juvenile and neonatal rabbit lungs, PGI2 did not change total vascular resistance significantly but in untreated adult lungs, it caused a significant increase in total vascular resistance only after a dose of 10 micrograms/kg. This age-related difference in vasoconstrictor response to PGI2 was not related to baseline total vascular resistance in the three groups of lungs. In adult lungs, vasoconstriction occurred mainly in arteries with a small effect in veins. Circulating levels of thromboxane B2, leukotriene C4, and 6-keto-PGF1 alpha increased following PGI2 infusion in adult lungs, whereas in neonatal lungs, only 6-keto-PGF1 alpha increased significantly. Indomethacin pretreatment completely abolished the vasoconstrictor response to PGI2. We conclude that PGI2-induced vasoconstriction is age and dose dependent in isolated rabbit lungs and that a cyclooxygenase product, such as thromboxane A2, may play a role in mediating the vasoconstriction.     

Hypothalamic D2 receptors mediate the preferential release of somatostatin-28 in response to dopaminergic stimulation

We have studied the effect of dopamine (DA) together with agonist and antagonist drugs of varying specificity on the release of immunoreactive forms of somatostatin (SS) from the perfused, adult rat hypothalamus in vitro. Levels of SS increased from 14.7 +/- 3.7 pg (mean +/- SE) under basal conditions to 137 +/- 23.0 pg after exposure to 10(-6) M DA. This dopaminergic effect was mimicked by the specific D2 agonists bromocriptine (10(-7) M) and LY 171555 (10(-6) M) but not by the D1 agonist SKF 38393A (10(-6) M). The stimulatory action of DA (10(-6) M) was blocked by the active (d) but not the inactive (l) isomer of butaclamol (10(-7) M). Similar blockade was achieved with the specific D2 antagonists metoclopramide (10(-8) M) and domperidone (10(-8) M), whereas the D1 antagonist SCH 23390 partially blocked the stimulation of DA but only when used at X100 greater concentration (10(-6) M). SCH 23390 (10(-8) M) did not affect the dopaminergic stimulation of SS release. HPLC characterization of the immunoreactive forms of SS yielded two peaks which corresponded to SS-28 and SS-14. The ratio of these forms varied significantly under different conditions. In the basal state the ratio of SS-28 to SS-14 was 1:4.4; in response to stimulation with DA, the ratio was 1:1.7 and in response to depolarization with 60 mM K+ the ratio was 1:3.1. In conclusion, the stimulatory action of DA on SS release is mediated via hypothalamic D2 receptors. Furthermore dopaminergic stimulation increases the molar ratio of SS-28 to SS-14 in the total immunoreactive SS which is released.     

Glucocorticoids increase pulmonary beta-adrenergic receptors in fetal rabbit

beta-Adrenergic agonists stimulate surfactant release and decrease fluid in lung alveoli of fetuses. Both effects are most evident toward the end of gestation. We used [3H] dihydroalprenolol (DHA) to investigate the development of pulmonary beta-adrenergic receptors in rabbit fetuses and to study the effect of glucocorticoid treatment on the beta-receptor number. In the lung particulate preparation, DHA binding was rapid, reversible, stereoselective, and of high affinity. The order of potency for adrenergic agonists in competing for DHA binding was isoproterenol > epinephrine = norepinephrine, which is typical of interactions at a beta 1-adrenergic receptor. Using DHA, we demonstrated that the concentration of pulmonary beta-receptors increased significantly between 28 and 31 days of gestation; however, there was no change in the dissociation constant during gestation. After injecting betamethasone (0.17 mg/kg, 24 hours) into rabbits at 25 days of pregnancy, we found that the concentration of pulmonary beta-receptors increased from 44.2 +/- 6.6 fmol/mg protein in untreated fetuses to 77.9 +/- 5.6 fmol/mg protein in treated fetuses. However, this treatment did not affect the DHA binding sites in the fetal rabbit heart. Maternal treatment with the T3 analogue 3,5-dimethyl-3'-isopropyl-L-thyronine (0.5-1 mg/kg) at a dosage which increased both surfactant synthesis and release did not alter pulmonary receptor concentration. Our results indicate that the concentration of pulmonary beta-adrenergic receptors increases in the fetus at term and suggest that this increase is stimulated by endogenous glucocorticoid in fetal circulation.     

Phenoxybenzamine selectively and irreversibly inactivates dopaminergic D2 receptors on primary cultured rat lactotrophs.

Lactotrophs have several different kinds of receptors, such as dopaminergic D2, somatostatin, angiotensin II and thyrotropin-releasing hormone receptors, which stimulate or inhibit prolactin release. We have studied the specificity of phenoxybenzamine on receptors in lactotrophs. Phenoxybenzamine is a beta-haloalkylamine which alkylates chemically active radicals such as hydroxy, sulfhydryl, and amino groups. This alkylation is an irreversible chemical reaction in contrast to the receptor-secretagogue complex which is present in a state of dynamic equilibrium. Primary cultured rat adenohypophyseal cells were used in this study. A dose-response relationship was examined between concentrations of phenoxybenzamine pretreatment and prolactin release using a monolayer cell culture system. The inhibitory action of dopamine (10 mumol/l) on the control group (13.0 +/- 0.1 ng/ml or 86% inhibition relative to the control) was significantly higher than on the 0.1-mumol/l phenoxybenzamine-pretreated group (39.0 +/- 0.2 ng/ml or 58% inhibition relative to the control), but the stimulatory effect of thyrotropin-releasing hormone on prolactin release was not significantly affected up to a 10-mumol/l phenoxybenzamine pretreatment as compared with the control group. We thus selected a phenoxybenzamine concentration of 0.1 mumol/l for the next series of perifusion experiments in order to examine dynamic changes in prolactin release. The basal prolactin release was decreased to almost half by phenoxybenzamine pretreatment. The inhibitory action of dopamine (0.1 mumol/l containing 0.1 mmol/l ascorbic acid) was significantly less in the phenoxybenzamine-pretreated group (68% of the basal prolactin concentration) than in the control group (31% of the basal concentration).(ABSTRACT TRUNCATED AT 250 WORDS)     

Multiple pulmonary neurofibromas with hypoxemia. Occurrence due to pulmonary arteriovenous shunts within the tumors

A 62-year-old woman with multiple neurofibromas of the lung was found to have severe hypoxemia due to right-to-left shunting within the tumors. Pulmonary angiograms demonstrated that the major area of shunting was in a large tumor mass in the right lower lobe. Pathologically the neurofibromas were vascular with hyperplastic small arteries and arterioles and large dilated veins. Multiple pulmonary neurofibromas are rare; and, to our knowledge, never previously reported in association with pulmonary arteriovenous shunting.     

Activation of dopamine D2-like receptors attenuates pulmonary C-fiber hypersensitivity in rats

This study was performed to determine whether activation of dopamine D2-like receptors inhibits the hyperresponsiveness of pulmonary C fibers induced by inflammatory mediators such as prostaglandin E2 (PGE2). In anesthetized, open-chest rats, constant infusion of PGE2 (1.5-4.5 microg/kg per minute, 2 minutes) significantly enhanced the C-fiber response to capsaicin injection. At 20 minutes after pretreatment with quinpirole (3 mg/kg, intravenous), a D2-like receptor agonist, the hyperresponsiveness to capsaicin of the same C fibers induced by PGE2 infusion was markedly attenuated, and this inhibitory effect lasted for more than 90 minutes. The effect of quinpirole was dose dependent and was antagonized by pretreatment with domperidone (5 mg/kg, intravenous), a D2-like receptor antagonist, administrated 10 minutes before the quinpirole injection. In a separate series of experiments, C-fiber responses to injections of phenyl biguanide and lactic acid and to constant-pressure lung inflation were augmented by PGE2; these potentiating responses were also significantly reduced by quinpirole. Furthermore, the effect of quinpirole was equally effective in inhibiting the increase in excitability of pulmonary C fibers induced by alveolar hypercapnia or constant infusion of adenosine. In conclusion, these results clearly show that activation of the dopamine D2-like receptors attenuates the hyperresponsiveness of pulmonary C fibers to both chemical stimuli and lung inflation.     

Aspirin-Intolerant Asthma (AIA) Assessment Using the Urinary Biomarkers, Leukotriene E(4) (LTE(4)) and Prostaglandin D(2) (PGD(2)) Metabolites

The clinical syndrome of aspirin-intolerant asthma (AIA) is characterized by aspirin/nonsteroidal anti-inflammatory drug intolerance, bronchial asthma, and chronic rhinosinusitis with nasal polyposis. AIA reactions are evidently triggered by pharmacological effect of cyclooxygenase-1 inhibitors. Urine sampling is a non-invasive research tool for time-course measurements in clinical investigations. The urinary stable metabolite concentration of arachidonic acid products provides a time-integrated estimate of the production of the parent compounds in vivo. AIA patients exhibits significantly higher urinary concentrations of leukotriene E(4) (LTE(4)) and 1,15-dioxo-9α-hydroxy-2,3,4,5-tetranorprostan-1,20-dioic acid (tetranor-PGDM), a newly identified metabolite of PGD(2), at baseline. This finding suggests the possibility that increased mast cell activation is involved in the pathophysiology of AIA even in a clinically stable condition. In addition, lower urinary concentrations of primary prostaglandin E(2) and 15-epimer of lipoxin A(4) at baseline in the AIA patients suggest that the impaired anti-inflammatory elements may also contribute to the severe clinical outcome of AIA. During the AIA reaction, the urinary concentrations of LTE(4) and PGD(2) metabolites, including tetranor-PGDM significantly and correlatively increase. It is considered that mast cell activation probably is a pathophysiologic hallmark of AIA. However, despite the fact that cyclooxygenease-1 is the dominant in vivo PGD(2) biosynthetic pathway, the precise mechanism underlying the PGD(2) overproduction resulting from the pharmacological effect of cyclooxygenease-1 inhibitors in AIA remains unknown. A comprehensive analysis of the urinary concentration of inflammatory mediators may afford a new research target in elucidating the pathophysiology of AIA.     

Prominence of the dopamine D2 short isoform in dopaminergic pathways

As a result of alternative splicing, the D2 gene of the dopamine receptor family exists in two isoforms. The D2 long is characterized by the insertion of 29 amino acids in the third cytoplasmic loop, which is absent in the short isoform. We have produced subtype-specific antibodies against both the D2 short and D2 long isoforms and found a unique compartmentalization between these two isoforms in the primate brain. The D2 short predominates in the cell bodies and projection axons of the dopaminergic cell groups of the mesencephalon and hypothalamus, whereas the D2 long is more strongly expressed by neurons in the striatum and nucleus accumbens, structures targeted by dopaminergic fibers. These results show that the splice variants of the dopamine D2 receptor are differentially distributed and possess distinct functions. The strategic localization of the D2 short isoform in dopaminergic cell bodies and axons strongly suggests that this isoform is the likely dopamine autoreceptor, whereas the D2 long isoform is primarily a postsynaptic receptor.     

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

In ewes, photoperiod modulates LH release and dopaminergic terminals in the median eminence (ME) have a critical role in the establishment of long-day inhibition of LH secretion. This study was undertaken to determine the type of dopaminergic receptors, D1-like or D2-like, that mediate the action of dopamine on LH secretion at the ME level in this situation. This was assessed, in ovariectomized and estradiol-treated ewes, with the use of reverse microdialysis in the ME in three experiments: first, when LH secretion was stimulated by short days, by determining the response to three doses (0.01, 0.1 or 1 mg/ml) of a D1-like (SKF38393) and a D2-like (quinpirole) agonist; secondly, during early long-day inhibition of LH secretion, by determining the ability of SKF38393 and quinpirole (1 mg/ml) to mimic the inhibitory effects of dopamine, after a blockade of its synthesis with alpha-methyl-para-tyrosine (alphaMPT; 2 mg/ml); and thirdly, during early long-day inhibition of LH secretion, by determining the response to three doses (0.009, 0.09 or 0.9 mg/ml) of a D1-like (SCH23390) and a D2-like (sulpiride) antagonist. In none of the conditions was effect of the D1-like analogs on LH secretion found, compared with the control treatments. In contrast, the D2-like analogs caused changes in LH secretion. First, with short days, quinpirole in the highest dose significantly reduced mean LH concentration (P<0.05) and LH pulse frequency (P<0.01). Secondly, with long days, addition of quinpirole to alphaMPT caused a significant decrease in LH secretion relative to alphaMPT alone (P<0.05). Thirdly, with long days, sulpiride at the highest dose significantly increased mean LH concentration (during the first 3 h of treatment, P<0.05) and LH pulse frequency (P<0.05). Prolactin secretion was also determined in these experiments, and D2-like agonist and antagonist caused an inhibition and a stimulation of prolactin secretion, respectively. These results demonstrate that, in the ME, inhibitory action of dopamine on LH secretion, critical for the initiation of long-day-induced inhibition, is mediated by D2-like, not D1-like, dopaminergic receptors.     

Expression of 1,25(OH)2D3 receptors on alveolar lymphocytes from patients with pulmonary granulomatous diseases.

1,25(OH)2D3 is known to be produced at sites of granulomatous reactions. In order to characterize the cell types that are targets for this immunoregulatory hormone, we have evaluated the expression of 1,25(OH)2D3 receptors on peripheral blood T-lymphocytes and those recovered from the lung by bronchoalveolar lavage from patients with pulmonary granulomatous diseases (tuberculosis and sarcoidosis) and from normal control subjects using combined autoradiographic and immunohistochemical techniques. Lavage T-lymphocytes from patients with tuberculosis or with sarcoidosis, but not those from normal control subjects, expressed 1,25(OH)2D3 receptors as demonstrated by binding of [3H]1,25(OH)2D3, which was inhibited by the presence of excess unlabeled 1,25(OH)2D3, but not by the presence of unlabeled 25(OH)D3 (receptor-positive lymphocytes: sarcoidosis, 20 +/- 12%; tuberculosis, 31 +/- 17%). In contrast, blood lymphocytes from patients with granulomatous diseases did not express detectable 1,25(OH)2D3 receptors. The percentage of lavage T-lymphocytes expressing 1,25(OH)2D3 receptors was significantly greater for patients with tuberculosis presenting with isolated hilar adenopathy than for patients with pulmonary infiltrates and/or cavities. 1,25(OH)2D3 receptors were expressed to a greater extent on CD8+ T-lymphocytes than on CD4+ T-lymphocytes in sarcoidosis, whereas a greater proportion of CD4+ than of CD8+ T-lymphocytes from patients with tuberculosis were receptor-positive. These findings support the conclusion that the interaction of 1,25(OH)2D3 with its receptor on T-lymphocytes may play an important role in the regulation of granulomatous reactions, but because these receptors are expressed on different lymphocyte populations, the net effect of this potent immunoregulatory molecule is likely different in sarcoidosis and tuberculosis.     

Function of pulmonary neuronal M(2) muscarinic receptors in stable chronic obstructive pulmonary disease

Anticholinergic drugs often cause a considerable degree of bronchodilation in patients with chronic obstructive pulmonary disease (COPD). Pulmonary neuronal M(2) muscarinic receptors function to limit the magnitude of vagally induced bronchoconstriction. We hypothesized that the effectiveness of anticholinergic agents in patients with COPD may reflect increased vagal reactivity due to dysfunction of M(2) muscarinic receptors. The function of M(2) receptors and the magnitude of vagally induced bronchoconstriction were assessed in subjects with normal lung function and in subjects with COPD. A nasal cold dry air challenge was used to induce a bronchoconstriction, measured as a change in airway resistance (Raw) at 5 Hz (R5) using impulse oscillometry. In subjects with COPD R5 rose from 0.68 +/- 0.06 to 0.74 +/- 0.07 kPa/L/s after the cold dry air challenge (p < 0.01) and in the control subjects R5 rose from 0.34 +/- 0.03 to 0.39 +/- 0.03 kPa/L/s (p < 0.01). The bronchoconstriction was inhibited by pretreatment with ipratropium bromide, indicating that it was vagally mediated. In both groups of subjects pretreatment with the selective M(2) muscarinic receptor agonist pilocarpine (5 mg/ml) prevented the cold air-induced bronchoconstriction, indicating normal function of M(2) receptors. These studies indicate that M(2) muscarinic receptors are functional in subjects with stable COPD.     

Digitalis and the pulmonary circulation

In anesthetized dogs, the intravenous injection of acetyl strophanthidin caused a slight decrease in pulmonary arterial pressure which could not be explained by the effect on left atrial pressure. There was a marked decrease in the pulmonary venous flow, which was often accompanied by cardiac slowing and an increase in the calculated pulmonary vascular resistance. The cause of the increased pulmonary resistance is a combination of (a) the passive sive nature due to the decreased blood flow, and (b) local vasoconstriction of the perfused lung. The performance of vagotomy and thoracic sympathectomy, and the intravenous injection of bretylium excluded nervous factors as a cause of the vasoconstriction.