Previous work from this laboratory has demonstrated that the chemical activation of cell bodies in the caudal ventrolateral medulla of chloralose-anesthetized dogs decreased bronchomotor tone by withdrawing cholinergic input to airway smooth muscle. In the present study we determined the bronchomotor responses to microinjection of DL-homocysteic acid (100 mM; 25-50 nl) into the rostral ventrolateral (RVL) medulla of chloralose-anesthetized dogs. Total lung resistance was used as a functional index of bronchomotor tone. Microinjection of DL-homocysteic acid into the 20 sites located in the lateral aspect of the RVL medulla increased both total lung resistance [from 6.5 ± 0.4 to 9.1 ± 0.8 (SE) cmH2O · 1-1 · s; P < 0.05] and mean arterial pressure (from 125 ± 5 to 148 ± 8 mmHg; P < 0.05). Microinjection of this amino acid into nine sites located in the medial aspect of the RVL medulla increased mean arterial pressure (from 130 ± 6 to 153 ± 6 mmHg; P < 0.05) but had no effect on total lung resistance. We confirmed in three sites that the increase in total lung resistance evoked by microinjection of DL-homocysteic acid was accompanied by an increase in tracheal smooth muscle tension. The increase in total lung resistance evoked by DL-homocysteic acid was not affected by β-adrenergic blockade but was abolished by muscarinic blockade.
All Science Journal Classification (ASJC) codes
- Physiology (medical)