In this paper we present the flow research of the development of receptor bronchial system in the first month of extra-uterine life up to the sixth month of development, performed by tracking the reactions of isolated tracheal rings in acetylcholine (Ach), propranolol (P), histamine (Hist), and prostaglandin (PGF2-alfa) in concentrations of: 10-4, 10-3, 10-2 and 10-1 mol/dm3; in piglets of ages: 1 month, 2 months, 4 months and 6 months. Results shows that Ach causes reaction of smooth muscles from the first month of extra-uterine life (p < 0.01) and that Propranolol (P) significantly emphasizes the effect of Ach (p > 0.
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