Fig. 1

Continuous infusion of C-type natriuretic peptide (CNP) attenuated bleomycin (BLM)-induced pulmonary fibrosis in mice. BLM (1 mg/kg) was administered intratracheally to C57BL/6 mice on day 0, and the samples were removed on day 14. CNP (2.5 μg/kg/min) or vehicle (5 % w/v glucose solution) was subcutaneously infused throughout the experiment with the use of an osmotic mini-pump. Representative micrographs of lung tissue stained with hematoxylin-eosin (HE; a–c) and with Masson trichrome (MT; d–f)); normal control mice (a, d), BLM-instilled mice treated with vehicle alone (b, e) and BLM-instilled mice treated with CNP (c, f). Scale bar: 500 μm. g Fibrotic area was calculated by using image analyzing software and expressed as a percentage of the whole lung field. Values represent means ± SEM (n = 4 mice per group). *P < 0.05. NA, not assessed because of no fibrotic area in normal lungs. h Total collagen deposition was assessed by analyzing hydroxyproline concentrations in mouse lung tissue. Values represent means ± SEM (n = 6 mice per group). *P < 0.05. i The body weight changes of mice after BLM administration are shown for normal control mice (dotted line), BLM-instilled mice treated with vehicle alone (dashed line), and BLM-instilled mice treated with CNP (solid line). Values represent means ± SEM (n = 6 mice per group). j–l The numbers of total cells (j), macrophages (k), and neutrophils (l) in bronchoalveolar lavage (BAL) fluid on day 14 after BLM administration are shown. Values represent means ± SEM (n = 4 mice per group). *P < 0.05