Pulmonary peptides, norepinephrine and endocrine cells in monocrotaline pulmonary hypertension

The concentrations of norepinephrine and of the peptides bombesin, calcitonin gene-related peptide and neurotensin were measured in rats with monocrotaline pulmonary hypertension. The numbers of pulmonary endocrine cells showing positive immunoreactivity for calcitonin, calcitonin gene-related peptide, protein gene product 9.5 and bombesin were counted in a second group of rats with monocrotaline pulmonary hypertension. The concentration of norepinephrine in the lungs decreased significantly in the test rats but this could be attributed to dilution by an increased mass of tissue. The pulmonary concentration of all three peptides showed a decrease in the rats treated with monocrotaline but this was highly significant only in the case of bombesin. The pulmonary content of bombesin showed a substantial and significant decrease in the test rats. No neuroendocrine cells immunopositive for bombesin were identified in any of the control or test rats. There was no difference between the control and test rats with respect to the form or distribution of the cells immunoreactive for the other three The lack of pulmonary endocrine cells showing immunoreactivity for bombesin may be related to the absence of intimal proliferation in the pulmonary arteries in this species. This is in striking contrast to what occurs in plexogenic pulmonary arteriopathy in man and suggests that monocrotaline-induced pulmonary hypertension in rats is not a good animal model for this disease.