Vagal control of pulmonary peripheral circulation in the rattlesnake modulates relevant hemodynamic adjustments to temperature change

The vagal influence over large pulmonary arteries has been clearly demonstrated in Squamates. Additionally, diverse in situ experiments suggest that pulmonary circulation was either not responsive or much less responsive than the systemic circuit to known local, humoral, and nervous modulators. We suggest that the systemic alterations should be counterbalanced by pulmonary circuit modulation in awaken animals with a cardiac shunt, and the lack of pulmonary circuit responses is a collateral effect of the anesthesia used in in situ experiments. The use of a decerebrate experimental model allowed for diverse concomitant cardiovascular and respiratory measurements in two rattlesnake groups: left-vagotomized - LV (i.e. without vagal innervation of pulmonary arteries) and non-vagotomized (NV) at a range of body temperatures (T_b - 10, 20, and 30 °C). Aerobic metabolism increased proportionally to T_b. Unexpectedly, systemic conductance remained stable while the right-to-left shunt reduced. Therefore, inactive rattlesnakes change blood oxygenation rather than tissue perfusion to support alterations in aerobic demands. Peripheral pulmonary circulation was the main target of vascular modulatory adjustments following T_b change. Although LV snakes were unable to modulate pulmonary compliance, cardiac shunt was compensated as they reached the same O₂ uptake, which was attained by the modulation of the pulmonary conductance. This was the first time such modulation was recorded. Our findings also suggest the presence of bilateral vagal innervation of the unique rattlesnake lung, in which the left vagus innervates the proximal arteries, while the right vagus modulates functioning of the distal vasculature.