Relation between peripheral chemoreceptors stimulation and pulmonary arterial blood pressure in rats

As interactions between peripheral chemoreceptors stimulation (PCS) and pulmonary vasomotor tone remain controversial, experiments were made in rats in order to clear up the effects of PCS on pulmonary arterial pressure (PAP). Different stimulations varying in intensities were used, in rats nervously intact (IR-rats), after vagotomy (XT-rats), after chemodenervation obtained without vagotomy (CDN not XT-rats) or with XT (CDN + XT) and finally after alpha 1-receptors blockade (P-rats = pretreated rats). The observed variations were analysed in view of disentangling reflex part of PCS from a direct activity on the pulmonary vascular bed. Ventilation, PAP and systemic blood pressure (BP) were studied in anaesthetized rats. N2 test, NaCN test, 20 s of 5% O2 inhalation and almitrine bismesylate (ALM) were used as PCS, ranged in the order of their relative intensities, from the ventilatory responses observed in IR-rats. In IR-rats, N2-and CN test produced a similar transient increase of PAP, slightly more extended than the hyperventilation. After XT, the responses were prolonged, but amplified only in CN test. Ventilatory responses disappear after CDN, but as far as pulmonary hypertension is concerned, CDN + XT is more potent than CDN without XT to reduce or even suppress them. This fact is particularly evident with ALM who is the strongest PCS used. Similar reduction of PAP rise was also produced in P-rats in which ventilatory responses remain unchanged. Prolonged hypoxic inhalation induced a progressive fall of systolic BP and of PAP. The return to normal air breathing is followed by BP restoration and a long-lasting PAP increase.(ABSTRACT TRUNCATED AT 250 WORDS)