A vagally mediated response to metabolic acidosis in anesthetized rabbits.

Pentobarbital sodium-anesthetized rabbits received 10-min infusions of acetic, lactic, or propionic acid delivered via a catheter to the right atrium at a rate of 1 mmol/min (n = 14). Arterial [H+] increased by 35.8 +/- 7.

Chemoreflexes in rabbits.

Criteria defining chemoreflexes (called responses) in rabbits have been established in relation to right atrial injection of 16 chemicals, and compared with previously-defined chemoreflexes of cats. A vagally mediated 'pulmonary' response elicited at latencies less than 1.6 sec consists only of an increased frequency of breathing due primarily to decrease of expiratory duration.

CO2/H+ receptors in the lungs of anaesthetized rabbits.

The CO2/H+ sensitivity of 'pulmonary' non-myelinated vagal afferent endings was investigated in anaesthetized rabbits using 'natural' stimuli of lactic (LA) and acetic (AA) acids, for comparison with previous results using sodium dithionite (NaD) and phenyl biguanide (PDG). Right atrial injections of these four chemicals demonstrated a respiratory reflex from 'pulmonary' endings, consisting primarily of a decrease in expiratory duration and consequent increase in respiratory frequency coincident with transient increase in PETCO2. Three of the chemicals (AA, LA and NaD) apparently activated the endings by increased [CO2] and/or [H+], since equimolar doses of sodium lactate and acetate were without effect.

Role of vagal C-fiber afferents in respiratory response to hypercapnia.

The respiratory response to hypercapnia has been investigated in 10 anesthetized rabbits by use of a rebreathing technique. The responses were obtained in three situations: with one intact vagus nerve (control), during differential block of conduction, and after vagotomy. Differential block was achieved using anodal hyperpolarization by application of a direct current to the cervical vagus nerve.

Non-myelinated vagal lung receptors and their reflex effects on respiration in rabbits.

The response characteristics of non-myelinated vagal lung receptors have been studied in the anaesthetized rabbit. The results indicate that the behaviour of these endings strongly resembles those found in cats and dogs and that they can be classified into 'pulmonary' 'bronchial' and 'pulmonary-bronchial' groups depending on their accessibility from either circulation. Experiments involving pericardial block with local anaesthetic to exclude responses from cardiac receptors and the use of sodium dithionite as a novel stimulus to 'pulmonary' endings alone, have shown that the predominant effect of these endings in the anaesthetized rabbit is to increase respiratory frequency.