Organ-specific disposition of group B streptococci in piglets: evidence for a direct interaction with target cells in the pulmonary circulation.

Despite the serious pulmonary manifestations of early onset group B streptococcal (GBS) sepsis, it is not known whether the organism distributes into lung tissue and whether adverse pulmonary hemodynamic abnormalities relate to an interaction between the organism and target cells in the pulmonary vascular bed. Accordingly, this study evaluated the distribution and fate of GBS in the lung, liver, and spleen of anesthetized infant piglets and in isolated, salt solution-perfused piglet lung preparations. GBS were radiolabeled with 111Indium-oxine and infused at a dose of 10(8) organisms/kg/min for 15 min into anesthetized piglets ranging in age from 5-10 d. Forty-five min after termination of the infusion, animals were killed and specimens of lung, liver, spleen, and blood were excised and the relative deposition and viability of GBS were determined. Most of the recovered bacteria were detected in the lung (53.2 +/- 3.9%) followed by the liver (41.4 +/- 2.0%) and spleen (2.2 +/- 0.38%). GBS detected in the blood was estimated to be only 3.2 +/- 1.0% of the infused dose. Viability of GBS was least in the lung (21.4 +/- 2.6%) relative to the liver (45.7 +/- 11.2%) and spleen (83.4 +/- 19.5%). After a 60-min GBS infusion, transmission electron microscopy localized the organism within pulmonary intravascular macrophages in the lung; there was no evidence for bacterial interaction with either neutrophils or endothelial cells. In the liver, GBS was found exclusively in Kupffer cells. In isolated piglet lungs perfused at a constant flow rate with blood-free physiologic salt solution, GBS (10(6) to 10(8) organisms/mL) provoked concentration-dependent increases in pulmonary vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Group B streptococcus promotes oxygen radical-dependent thromboxane accumulation in young piglets.

Both thromboxane A2 and oxygen-derived free radicals appear to play central roles in group B streptococcus (GBS)-induced pulmonary hypertension in piglets. This study tested the hypothesis that GBS promotes oxygen radical-dependent thromboxane accumulation and pulmonary hypertension in infant piglets. Piglets 4-12 d old were anesthetized and prepared for assessment of pulmonary arterial pressure and arterial blood gases. In control animals, GBS (10(8) organisms/kg/min for 15 min) increased mean pulmonary artery pressure by 30 +/- 1.5 torr and reduced arterial PO2 by 100 +/- 20 torr. Thromboxane A2, radioimmunoassayed in venous blood as thromboxane B2, increased by 2452 +/- 800 pg/mL. A second group of piglets was treated with dimethylthiourea (DMTU: 750 mg/kg), a putative oxygen radical scavenger. In these animals, GBS increased pulmonary arterial pressure by only 7 +/- 1 torr and reduced arterial PO2 by a modest 10 +/- 8 torr. Importantly, thromboxane B2 content in venous blood failed to increase above control levels in DMTU-treated animals. The protective effects of DMTU in GBS-treated piglets could not be ascribed to inhibition of cyclooxygenase or thromboxane synthase because the oxygen radical scavenger failed to attenuate increases in pulmonary arterial pressure and venous thromboxane B2 content or reductions in arterial PO2 caused by i.v. infusions of arachidonic acid. DMTU also did not ameliorate pulmonary hypertension evoked by the thromboxane mimetic U44069, thereby suggesting that the scavenger did not act as an end-organ antagonist of thromboxane receptors. These observations suggest that GBS promotes accumulation of thromboxane A2 and attendant pulmonary hypertension through an oxygen radical-dependent mechanism.

Oxygen radical-dependent bacterial killing and pulmonary hypertension in piglets infected with group B streptococci.

The mechanism by which bacteria are cleared by the pulmonary circulation and the relation of this process to development of hemodynamic abnormalities are not understood. This study tested the hypotheses that clearance of Group B Streptococcus (GBS) during transit through the pulmonary circulation of infant piglets is related to oxygen radical-dependent bacterial killing and that killing of the organism is linked to development of pulmonary hypertension. GBS were radiolabeled with 111In and infused intravenously for 15 min (10(8) organisms/kg/min) into infant piglets ranging in age from 5 to 14 days. Lung specimens were excised at termination of the GBS infusion or 45 min thereafter, and both the relative deposition and viability of the bacteria were determined. The percentage of infused GBS recovered in lung tissue did not differ between the two time points (26 +/- 7% versus 29 +/- 8%), but the relative viability at termination of the infusion, 50 +/- 11%, was reduced to 19 +/- 4% within 45 min. Treatment with an oxygen radical scavenger, dimethylthiourea (DMTU), failed to influence the pulmonary deposition of GBS but significantly increased viability of the organism from 21.4 +/- 2.6 to 33.3 +/- 5.3%. As expected, GBS infusion was accompanied by pulmonary hypertension and arterial hypoxemia; DMTU attenuated these responses by 52 and 78%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for hydroxyl radical involvement in group B streptococcus-induced pulmonary hypertension and arterial hypoxemia in young piglets.

Early onset neonatal GBS infection is associated with pulmonary hypertension, pulmonary edema, and arterial hypoxemia. Although the mechanisms underlying these cardiopulmonary disturbances are not completely understood, multiple lines of evidence suggest that inflammatory mediators may be involved. This study examined the actions of dimethylthiourea (DMTU), a relatively selective scavenger of hydroxyl radical, on GBS-induced pulmonary hypertension, arterial hypoxemia, and pulmonary edema formation in young piglets. Relative to control animals, intravenous infusion of GBS (10(8) organisms/kg/min for 60 min) provoked sustained increases in pulmonary arterial pressure (Ppa: +88%) and total pulmonary resistance (TPR: 128%). GBS infusion also was associated with profound decreases in arterial PO2 (-58%). Pulmonary edema was present in GBS-treated animals as evidenced by an 8.4% increase in the lung wet-to-dry weight ratio. After pretreatment with DMTU (0.75 g/kg administered intravenously over 30 min), GBS increased Ppa by 33% and TPR by only 16%. Similarly, after DMTU pretreatment GBS decreased arterial oxygen tension by only 12%. DMTU also limited the GBS-induced increase in lung wet-to-dry weight ratio to 2.6%. These findings demonstrate that DMTU attenuates GBS-induced pulmonary hypertension, pulmonary edema, and arterial hypoxemia and suggest that hydroxyl radicals play an important role in these cardiopulmonary disturbances.

Impact of platelet activating factor on vascular responsiveness in isolated rat lungs.

Platelet activating factor (PAF), a suspected mediator of acute lung injury, has been shown to potentiate contraction in isolated porcine carotid arteries. Such an action of PAF, if it occurred in the pulmonary circulation, could be of significance to the evolution of pulmonary hypertension in acute lung injury. Accordingly, we used isolated rat lungs perfused at a constant flow rate with physiologic salt solution to test the hypothesis that PAF-induced lung injury is associated with pulmonary vascular hyperresponsiveness to constrictor stimuli. PAF in concentrations of 0.1 to 10 ng/ml failed to influence pressor responses evoked by i.a. bolus injections of angiotensin II (Ang II) whereas 1 micrograms/ml of PAF significantly blunted Ang II-induced vasoconstriction. Similarly, 1 micrograms/ml, but not 0.1 ng/ml, of PAF attenuated constriction induced by ventilation with 3% O2. PAF at all concentrations tested failed to influence pressor responses evoked by i.a. bolus injections of KCI. Concentrations of PAF which blunted Ang II and hypoxic responses were associated with increased lung wet-to-dry weight ratios indicative of pulmonary edema. Another agent that provokes edema, cytochalasin B, also increased lung wet-to-dry weight ratios and blunted Ang II-, hypoxia-, and KCI-induced pressor responses. PAF delivered as i.a. bolus injections caused acute vasodilation in preparations preconstricted with Ang II but not in those preconstricted with KCI. Collectively, these observations demonstrate that PAF fails to augment and instead blunts pulmonary vascular responsiveness to pressor stimuli, possibly by mechanisms that relate to PAF-induced edema formation and/or vasodilation.

Leu-enkephalin provokes naloxone-insensitive pulmonary vasoconstriction.

Leu-enkephalin evoked dose-dependent pulmonary vasoconstriction in isolated perfused rat lungs. The pressor responses were not attenuated by either naloxone or naltrexone nor were they mimicked by morphine. Blockade of histamine receptors with pyrilamine or blockade of serotonin receptors with methysergide also failed to antagonize leu-enkephalin-induced pulmonary vasoconstrictor responses. These results suggest that neither opiate, histamine, nor serotonin receptors are involved with the pressor effects of leu-enkephalin on the pulmonary circulation. We propose that leu-enkephalin may have direct vasoconstrictor effects on the pulmonary circulation of isolated perfused rat lungs that may not be mediated by conventional opiate receptors.

Pulmonary vasoactivity of lung endocrine cell-related peptides.

Lung endocrine-like cells are believed to contain three immunohistochemically distinct peptides: bombesin, calcitonin, and Leu-enkephalin. Because these peptides exhibit smooth muscle stimulatory or inhibitory activity in some tissues, it has been suggested that their release from endocrine-like cells may influence airway or pulmonary vascular smooth muscle tone. To determine whether lung endocrine cell-related peptides could exert a regulatory influence in the pulmonary circulation, we evaluated their ability to constrict or dilate the vasculature of isolated perfused rat lungs. Neither bombesin nor calcitonin exhibited any pulmonary vascular effects. However, Leu-enkephalin provoked dose-dependent pulmonary vasoconstriction. These results suggest that Leu-enkephalin released from lung endocrine-like cells could be involved with regulation of pulmonary vascular tone.