Type A natriuretic peptides exhibit different bronchoprotective effects in rats

New developments in lung function measurements in rodents

There are invasive and noninvasive pulmonary function tests available which are sensitive in detecting bronchoconstriction in rodents. Noninvasively measured midexpiratory flow (EF50) has been shown to be an appropriate parameter to monitor bronchoconstriction in a large number of animals, e.g. for screening purposes. Recently, a novel technique for repetitive lung function measurements in orotracheally intubated, spontaneously breathing mice has been established. Bronchoconstriction is assessed by the "gold standard" parameters airway resistance and dynamic compliance in response to aerosolized methacholine or allergens in anesthetized mice. This measurement technique has been combined with an inhalation technique which has been optimized to allow simultaneous lung function measurement in intubated animals and to obtain high aerosol concentrations. A feedback dose control system has been developed to administer a defined and constant aerosol dose to each individual animal. Using this system a prominent early allergic response and late airway hyperresponsiveness could be demonstrated in intubated mice challenged with Aspergillus fumigatus allergen. We conclude: The noninvasive EF50 method seems particularly appropriate for measurements of respiratory function in large numbers of conscious mice in assembly line fashion. The invasive technology--newly established for the mouse--is more sensitive and specific since true airway resistance and dynamic compliance are determined and allows now the adequate detection of an early allergic response in the mouse and also repetitive measurements e.g. to assess the airway hyperresponsiveness in the same animal or for monitoring purposes in chronic models.

Keratinocyte growth factor transiently alters pulmonary function in rats

Keratinocyte growth factor (KGF) is a mitogen for pulmonary epithelial cells. Intratracheal administration of KGF to adult rats results in alveolar epithelial type II and bronchiolar epithelial cell proliferation. While cellular responses to KGF have been intensively studied, functional consequences regarding lung function are unknown. Therefore, in this study, we sought to investigate whether KGF alters pulmonary function variables. Rats received either recombinant human KGF (rHuKGF) (5 mg/kg) or vehicle intratracheally. Before and on days 3 and 7 after treatment, pulmonary function was determined by body plethysmography. Subsequently, lung histological changes were quantified. rHuKGF induced a transient proliferation of alveolar and bronchiolar epithelial cells. The extent of type II cell hyperplasia was significantly correlated with a transient reduction in tidal volume and an increase in breathing frequency. In addition, quasi-static compliance, total lung capacity, and vital capacity were reduced after rHuKGF instillation, suggesting the development of a transitory restrictive lung disorder. Moreover, reduced expiratory flow rates and forced expiratory volumes, as well as increased functional residual capacity after rHuKGF but not vehicle, suggest obstructive lung function changes. In conclusion, the induction of alveolar and bronchiolar epithelial cell proliferation by KGF is paralleled by moderate functional consequences that should be taken into account when the therapeutic potential of KGF is tested.

Hemodynamic effects of continuous urodilatin infusion: a dose-finding study

OBJECTIVE

To evaluate the effects of urodilatin (INN, ularitide) on systemic and renal hemodynamic parameters.

METHODS

Twenty healthy male subjects were included in this double-blind, randomized placebo-controlled trial and assigned to receive either continuous intravenous infusion of different doses of 7.5, 15, or 22.5 ng/kg body weight/min urodilatin or placebo over 300 minutes. Cardiac performance, systolic time intervals, and airway function were measured noninvasively. The effects on renal hemodynamic values were assessed with para-aminohippurate and inulin clearance techniques.

RESULTS

Urodilatin was well tolerated by all subjects at doses of 7.5 and 15 ng/kg/min. Infusion was stopped prematurely for the group that received 22.5 ng/kg/min urodilatin group because of systemic hypotensive responses with nausea and dizziness. Infusion of 15 ng/kg/min urodilatin significantly increased urine flow by a maximum of 165%, filtration fraction by 46%, renal resistance by 49%, and systemic vascular resistance by 45%. It decreased renal plasma flow by a maximum of 31% from baseline value. No change in cardiac inotropic function was detectable, but cardiac output decreased in all dose groups. Effects on glomerular filtration rate, forced expiratory volume, blood pressure, and pulse were not different from those with placebo.

CONCLUSION

Continuous infusion of 7.5 ng/kg/min and 15 ng/kg/min urodilatin exerts a significant increase in systemic and renal vascular resistance. Results of our experiments suggested that the therapeutic window for continuous urodilatin infusion is small and that doses higher than approximately 20 ng/kg/min urodilatin carry high risk for adverse drug reactions.

Bronchodilating effects of natriuretic and vasorelaxant peptides compared to salbutamol in asthmatics

In animal studies, the bronchial effects of urodilatin (URO, CDD/ANP-95-126, INN: ularitide) were superior to those of cardiodilatin/atrial natriuretic peptide (CDD, CDD/ANP-99-126). We compared the bronchodilating properties of intravenous URO and CDD in 36 clinically stable asthmatics showing a beta 2-agonist-induced increase of the FEV1 by > or = 15%. Any aerosol medication was discontinued for at least 8 h prior to the study. After baseline measurements of lung function parameters (FEV1, VC, PEF, MEF75, MEF50, MEF25) an intravenous infusion of 5.7, 11.4 or 17.1 pmol/kg/min URO or CDD was administered for 40 min in the morning. All measurements were repeated every 10 min during the infusion, for 30 min thereafter, and after the inhalation of 1.25 mg salbutamol (SALB). Both peptides had significant effects. While 11.4 pmol/kg/min URO dilated the central airways (FEV1, PEF, MEF75) slightly more potently than the peripheral bronchioles (MEF50, MEF25), 17.1 pmol/kg/min URO was as effective as SALB at all levels of the tracheobronchial tree. CDD reached only 50% of the SALB effect without a predominant localization of its action. The cardiovascular parameters revealed a significantly stronger vasorelaxant activity of CDD. In conclusion, the dose-dependent bronchodilating properties of intravenous URO were significantly superior to those of CDD.

Urodilatin (ularitide, INN): a potent bronchodilator in asthmatic subjects

Atrial natriuretic peptide (CDD/ANP-99-126) has been identified as a bronchodilator in various species including humans. We investigated the effect of urodilatin (CDD/ANP-95-126) in 18 clinically stable asthmatics showing an increase of the FEV1 by > or = 15% after salbutamol inhalation. Prior to the study inhaled beta 2-agonists were withheld for 8 h. After baseline measurements of lung function parameters (FEV1, VC, PEF, MEF75, MEF50, MEF25), blood pressure, and heart rate in intravenous infusion of 20, 40 or 60 ng kg-1 min-1 urodilatin was administered for 40 min in the morning. All measurements were repeated every 10 min during the infusion, for 30 min thereafter, and after the inhalation of 1.25 mg salbutamol. Forty and 60 ng kg-1 min-1 urodilatin showed a significant effect on the central (FEV1, PEF, MEF75) and peripheral airways (MEF50, MEF25) after 10 min infusion (P < 0.05). A bronchodilation not significantly different from 1.25 mg salbutamol was induced by 40 ng kg-1 min-1 in the central airways only, while 60 ng kg-1 min-1 led to a similar effect at all levels of the bronchial tree. Lung function parameters returned to baseline within 30 min after cessation of the urodilatin infusion. Heart rate showed a tendency to increase after 40 min infusion (P < 0.05), but blood pressure did not change significantly. In conclusion, the maximal bronchodilating effect of intravenous urodilatin in clinically stable asthmatics was comparable to 1.25 mg salbutamol.