Central effects of somatostatin and atrial natriuretic peptide on tracheal tone

The effects of somatostatin and atrial natriuretic peptide applied topically to the ventral surface of the medulla (VMS) on tracheal tone and phrenic nerve activity (Phr) were studied in chloralose-anesthetized and paralyzed cats artificially ventilated with 7% CO2 in O2. Surface application of drugs to the chemosensitive areas of the VMS significantly decreased tracheal tension measured by changes in pressure in a balloon placed in a bypassed segment of the trachea (Ptseg). Application of somatostatin (9 cats) caused a mean decrease in Ptseg from 17.3 +/- 1.8 (SE) to 4.3 +/- 1.4 cmH2O (P < 0.01) and a reduction in Phr from 24.9 +/- 3.4 to 10.3 +/- 3.4 units (P < 0.05). Like somatostatin, application of atrial natriuretic peptide to the VMS (5 cats) produced tracheal relaxation (Ptseg decreased from 19.3 +/- 2.6 to 9.9 +/- 1.3 cmH2O, P < 0.01), but in contrast there was an insignificant reduction in Phr (from 18.5 +/- 3.6 to 16.1 +/- 3.8 units, P > 0.05). When parasympathetic activity was abolished by atropine methylnitrate and tracheal tone was restored with 5-hydroxytryptamine, somatostatin and atrial natriuretic peptide applied on the VMS had no effect on tracheal pressure, suggesting that observed changes were not caused by direct action of peptides on tracheal smooth muscle via the bloodstream or by facilitation of inhibitory pathways. Both somatostatin and atrial natriuretic peptide applications were associated with a slight but significant decrease in arterial blood pressure. These data suggest that somatostatin and atrial natriuretic peptide acting on the chemosensitive structure of the VMS may play significant roles in modulating para-sympathetic outflow to airway smooth muscle.