EFFECTS OF CAFFEINE ON CAROTID-SINUS NERVE CHEMOSENSORY DISCHARGE IN KITTENS AND CATS

Caffeine (C) decreases apneic episodes in premature infants and is tho ught to stimulate breathing mainly by a central mechanism. While the m ethylxanthines theophylline and aminophylline are known to alter the c arotid chemoreceptor activity, there are little data on C. The aim of the study was to examine the effects of C on the carotid sinus nerve d ischarge( CSND) in developing animals. Nine kittens 17-21 days old and six adult cats that were anesthetized and artificially ventilated wer e studied. They received four consecutive doses of C, each of 10 mg/kg , administered at intervals of 20 min either as intravenous bolus inje ction (6 kittens, 3 cats) or continuous infusion (3 kittens, 3 cats). Bolus injections of C invariably induced a prompt but transient increa se in the CSND from 4.1+/-0.6 to 8.1+/-1.0 (SE) impulses/s in kittens (P=0.01) and from 3.9+/-0.1 to 7.9 to 1.0 impulses/s in cats (after th e first injection). This response was associated with a significant de crease in arterial blood pressure. Continuous infusion of C did not in duce any early change in either CSND or blood pressure in kittens or c ats. Fifteen minutes after C injection or infusion was begun, CSND val ues in air, 8% O-2-balance N-2, or 100% O-2 were not significantly dif ferent from control. Haloperidol administered at the end of the experi ment in four cats and four kittens significantly increased CSND and di d not suppress the early response to C injection. Tt is concluded that caffeine administered by bolus in the kitten induces a transient stim ulation of the CSND that is associated with a decrease in the arterial blood pressure and is independent of the dopaminergic mechanisms in t he carotid body. The lack of sustained effect implies the main mechani sm to the ventilatory stimulation by C must be central.