Reversal of respiratory responses to dopamine after dopamine antagonists

239

Respiration Physiology (1982) 47, 239-255 Elsevier Biomedical Press

REVERSAL OF RESPIRATORY RESPONSES TO D O P A M I N E AFTER D O P A M I N E ANTAGONISTS

P. ZAPATA* and A. ZUAZO Laboratory of Neurobiology, Catholic University of Chile, P.O. Box l14-D, Santiago 1, Chile

Abstract. The effects of dopamine (DA) antagonists upon resting ventilation and ventilatory reactions

to DA, apomorphine, hyperoxia and hypoxia were studied in pentobarbitone-anesthetized cats. Intravenous administration of spiroperidol, haloperidol, perphenazine and chlorpromazine increased resting ventilation, the intensity and duration of the effect being dependent on the dose of the blocker. The enhanced ventilation was associated to increased frequency of chemosensory discharges recorded from one carotid nerve, and it was absent after section of the four buffer nerves. The drugs also provoked a dose-dependent block of the transient chemosensory inhibitions and ventilatory depressions induced by DA or apomorphine. In addition, spiroperidol and perphenazine reversed the inhibitory reactions to DA into excitatory ones, the ventilatory responses being abolished by section of carotid and aortic nerves. The ventilatory depressions caused by a few breaths of I00~ 02 and the ventilatory excitations onset by a few breaths of 100% N 2 persisted after applying DA blockers. Results indicate that DA antagonists enhance ventilation by increasing peripheral chemosensory drive and may invert DA-induced reflex withdrawal into transient ventilatory excitation, without reversing the reflex ventilatory depression provoked by hyperoxia. Apomorphine Arterial chemoreceptors Carotid body Chemosensory drive Chlorpromazine

Control of breathing Dopamine Haloperidol Perphenazine Spiroperidol

It has been recently shown that dopamine (DA) evokes ventilatory depression when injected to humans (Welsh et al., 1978), cats (Zapata and Zuazo, 1980b) and rats (Cardenas and Zapata, 1981). This effect is due to reflex withdrawal, produced by DA-induced inhibition of chemosensory drive (Zapata and Zuazo, 1980b). Since DA appears to be the predominant catecholamine in the carotid bodies of humans (Steele and Hinterberger, 1972), cats (Chiocchio et al., 1971 ; Zapata et al., 1969) and rats (Hanbauer and Hellstr6m, 1978), it is tempting to assume that endogenous Accepted for publication 4 November 1981 0034-5687/82/0000-0000/$02.75 © Elsevier Biomedical Press

240

P. ZAPATA AND A. ZUAZO

DA may inhibit transiently or tonically carotid chemosensory discharges under physiological conditions. In fact, it has been postulated that carotid body chemoreception is tonically inhibited by a resting release of DA under normoxia and eucapnia, and that hypoxic stimulation is produced by cessation of DA release (Osborne and Butler, 1975). However, more recent experiments have shown in rats that hypoxia elicits selective depletion of carotid body DA stores (Hanbauer and Hellstr6m, 1978). Inhibition of carotid body chemosensory discharges by DA can be blocked by butyrophenones and phenothiazines, and two of these agents - spiroperidol and perphenazine - reverse the DA inhibitory effects into excitatory ones (Llados and Zapata, 1978). Therefore, searching for possible changes in ventilatory effects produced by DA after administration of these blocking agents was attractive. Furthermore, these experiments could disclose changes in resting ventilation and tonic chemosensory discharges, possibly reflecting an interference with the actions of DA endogenously released. These are the purposes of the present work.

Methods

Experiments were performed on 37 adult cats of either sex, weighing 2.69 + 0.63 (mean_+ SD) kg, anesthetized with sodium pentobarbitone (Nembutal, Abbott) 40 mg. kg =1 i.p. and maintained with supplementary i.v. doses as needed. Body temperature was monitored through a rectal thermo-probe connected to a telethermometer and was maintained at about 38 °C through a heating pad. Cannulae in the saphenous vein and femoral artery allowed the administration of drugs and continuous monitoring of pulsatile and mean arterial pressures (Pa). In most cats, after tracheal intubation per os, ventilation was assessed through paired pneumographs fastened around the middle thorax and upper abdomen, both being connected to the same chamber of a volumetric transducer (see Zapata and Zuazo, 1980a). In some cats, a tracheal cannula was inserted low in the neck and connected to a heated Fleisch pneumotachograph head, air flow being measured by a differential low pressure transducer, and tidal volume (VT) by electronic integration of the flow signal. Instantaneous respiratory frequency (fR) was obtained through a tachograph triggered by the ventilatory signals. Breath-by-breath minute volume (V) was calculated by multiplying each VT by the reciprocal of the corresponding cycle duration (1 •TR-l). All recordings were made on a polygraph. The carotid (sinus) nerves were sectioned at their junction with the glossopharyngeal nerves; the aortic (depressor) nerves were cut at their junction with the superior laryngeal nerves, near the nodose ganglia. Chemosensory activity was recorded from the peripheral end of one carotid nerve, after crushing the arterial wall between the carotid body and sinus and cutting the ganglio-glomerular nerves, to suppress barosensory and sympathetic discharges. Electrical. nerve recordings were obtained by a pair of Pt electrodes, connected to an oscilloscope through an

RESPIRATORY EFFECTSOF DOPAMINEANTAGONISTS

241

AC preamplifier (frequency response, 30 to 3000 Hz). Chemosensory frequency (fx) was measured by means of an electronic counter, which was connected to one channel of the polygraph through a digital-analog converter. The electrophysiological signals were also registered on a multi-channel FM tape recorder (frequency response, DC to 1250 Hz) for later analysis. Changes in ventilatory and chemosensory activities are expressed as percentages of their respective mean control values. They are considered as such only when exceeding the amplitude of spontaneous fluctuations. Furthermore, new procedures (drugs injections or gas tests) were initiated only after ventilatory and chemosensory activities were stabilized and within 99% confidence limits of the initial mean basal values. Drugs used were: apomorphine hydrochloride hydrate (Lilly), chlorpromazine hydrochloride (Smith Kline and French), dibenamine hydrochloride (Smith Kline and French), dopamine hydrochloride (ICN), haloperidol (Janssen), perphenazine (Schering), spiroperidol (Janssen) and d-tubocurarine chloride (Mann Research). They were freshly prepared in Locke's solution and kept in stoppered amber flasks. Dopamine and apomorphine required the addition of ascorbic acid 500/~g-ml -~ as preservative; spiroperidol required a few drops of glacial acetic acid to be dissolved. Drugs were injected i.v. in boluses of 200 /~1, immediately followed by 200 pl Locke's solution. They were given at times when no spontaneous gasps were expected. Doses refer to the forms described above. Experiments were conducted at the prevailing atmospheric pressure of 742-745 Torr and at ambient temperature of 22-26°C. At least five experiments were performed with each blocker.

Results

EFFECTS OF SPIROPERIDOLON RESTING VENTILATION Spiroperidol was injected i.v. in doses of 0.5-10.0 #g. kg -t to 8 cats with their buffer nerves intact. In all of them, moderate to pronounced increases of VT (122 to 170%) were observed; they were accompanied by increased fR (106 to 137%) in 4 cats, and by decreased fR (86%) in one animal in which VT increased to 170~. In all cases, V increased significantly during the 1st min following administration of spiroperidol. Doses of spiroperidol 0.5-2.5 /ag • kg -~ did not change Pa; however, larger doses (10 p g - k g -~) provoked a fall in Pa of between 0 and 45 Torr. Figure 1A illustrates the ventilatory effects of spiroperidol 1/~g • kg-~ in one animal. Ventilatory changes appeared within 10 to 20 s after the injections; they subsided within 1 to 20 rain. Hypotension, when present, developed and recovered later. When spiroperidol injections were repeated after 30 to 90 min, ventilation was increased only transiently (for less than 1 rain) or was unchanged (in most cases). Spiroperidol was also injected to 4 cats, previously submitted to bilateral sectioning

242

P. Z A P A T A A N D A. Z U A Z O

o

SPIROPERIDOL IJJg*kg -l l.v.

min

Fig. 1. Effects of i.v. injections of spiroperidol l /~g • kg I on ventilation in a cat with intact buffer nerves (A) a n d in a different cat after bilateral section of the carotid and aortic nerves (B). Recordings obtained through paired p n e u m o g r a p h s (inspiration upwards). Time calibration, 1 min.

of their carotid and aortic nerves. Figure 1B illustrates that no changes in ventilation occurred in response to spiroperidol 1 ~g • kg -~ in one of these animals; ventilation was also unchanged in another cat receiving 10/~g. kg -~. The two other animals, which were injected with spiroperidol 10/~g • kg-~, presented only minimal increases in VT (114 and 115~o), beginning nearly 30 s after the injection (coincidentally with a transient fall in Pa from 177 to 107 Torr and from 170 to 125 Torr, respectively), and lasting 90 and 120 s respectively, fR and V were unchanged by spiroperidol in all 4 cats with transected buffer nerves. Above results indicate that spiroperidol-induced hyperventilation, occurring independently of changes in Pa, requires integrity of the buffer nerves. Therefore, we studied the simultaneous changes in chemosensory activity recorded from one carotid nerve and in ventilation evoked by spiroperidol in 9 cats with the contralateral carotid nerve and both aortic nerves intact. In one cat receiving 0.5 ~g • kgo f the drug, a mild and slow increase in fx was observed, without significant changes in ventilation, but an additional dose of 9.5/~g • kg -] provoked a more pronounced increase in fx, this time associated with a transient increase in VT and a decrease of Pa. In another cat receiving 0.5/~g • kg -~ of spiroperidol, increases in fx and VT lasting several minutes were observed. In the other cats, to which initial doses of 4 to 10 /~g-kg -~ were administered, transient increases in both fx and VT were observed; fR was also augmented in one of them. Figure 2 illustrates the concomitant increases in ventilation and chemosensory discharges induced by spiroperidol 10 /~g. kg-l: the initial bursts of chemosensory impulses apparently resulted in a pronounced increase in VT, which in turn provoked a dampening of fx. This temporal correlation between ventilatory and chemosensory changes induced by spiroperidol was observed in all cases. Furthermore, the increase in VT was more pronounced when the increase in fx was more abrupt. In all cases, the enhancement

RESPIRATORY EFFECTS OF D O P A M I N E ANTAGONISTS

7

fx 0

243

J"

6PIROPERIDOL I0 l J g . k g - ' i.v

rain

Fig. 2. Effects of spiroperidol 10 #g • kg -1 i.v. on ventilation (upper trace) and chemosensory frequency (lower trace) in cat after unilateral carotid neurotomy. Time calibration, 1 min.

of "V declined to control values within 3 min. Otherwise, although Paco: was not monitored, recordings of chemosensory discharges provided a global assessment of the chemical drive, reducing the possibility that responses to subsequent procedures occur against an altered background. No significant changes were observed in the mean interval between spontaneous gasp complexes after spiroperidol, but their pattern was modified. Figure 3A illustrates the appearance of a spontaneous gasp: the augmented inspiration (lst phase) is followed by a prolonged expiration (2nd phase) and then by a few respiratory cycles of decreased amplitude (3rd phase). Figure 3B, obtained from the same animal 12 rain after administration of spiroperidol 10 Fg "kg -~, shows the attenuation of the 3rd phase and the appearance of a series of respiratory cycles of increased amplitude (4th phase). This 4th phase, absent or minimal in untreated cats (Zuazo and Zapata, 1980), was prominent in all cats receiving spiroperidol, and was suppressed after sectioning both carotid nerves. In cats

F®

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Fig. 3. Spontaneous gasp complexes in cat with unilateral carotid neurotomy, before (A) and 12 rain after i.v. administration of spiroperidol 10 /~g.kg -I (B). Upper traces, instantaneous frequency of chemosensory impulses recorded from peripheral end of cut carotid nerve (saturation occurred at upper limit). Lower traces, ventilation recorded through paired pneumographs (inspiration upwards).

244

P. ZAPATA AND A. ZUAZO

subjected to prior section of one carotid nerve, recording from this transected nerve showed that the transient silencing of chemosensory discharges occurring immediately after the augmented breath was shortened in duration after spiroperidol and followed by a rebound in fx preceding the appearance of the 4th phase (fig. 3). Gasp complexes, although very infrequent in cats subjected to section of all the buffer nerves (see also Zuazo and Zapata, 1980), were not modified by spiroperidol administration.

EFFECTS OF SPIROPERIDOLON VENTILATORYRESPONSESTO DA AND APOMORPHINE In confirmation of a previous report (Zapata and Zuazo, 1980b), DA injections in doses of from 10 -8 to 10 -4 g .kg -1 i.v. provoked immediate, transient and dose-dependent decreases in V. The responses to the lower doses consisted of a decrease in only VT; those to larger doses were contributed by decreases in both VT and fR. The medium doses also provoked transient and minimal hypotension, while the largest ones produced transient hypertension; these vascular reactions had longer delays and durations than the ventilatory reactions. Spiroperidol 0.5 to 2.0 /~g.kg -~ i.v. resulted in abolition of the ventilatory responses to the lower doses of DA and biphasic reactions to the higher doses, consisting of very transient and mild ~? decreases followed by increases in X?. Spiroperidol 5 to 20 pg • kg -1 provoked complete disappearance of the inhibitory ventilatory responses to DA and the appearance of dose-dependent increases in X?, consisting exclusively of increases in VT. The spiroperidol effects on the DA actions were fully developed within 1 min of its administration and persisted unchanged for many hours; successive doses had additive effects. The dose-response curves of fig. 4 show that spiroperidol 0.5 #g • kg -~ induces a displacement to the right and attenuation of the inhibitory ventilatory reactions to DA, which are followed by ventilatory increases. Addition of spiroperidol to attain 10.0/~g • kg -~ results in the reversal of the inhibitory responses to DA into excitatory ones. Subsequent bilateral sectioning of carotid and aortic nerves provoked the disappearance of the excitatory ventilatory reactions to DA, an indication of their reflex origin from carotid and aortic receptors. Since it has been reported that DA-induced carotid chemosensory excitation in dogs is blocked by d-tubocurarine 50/~g. kg -~ i.v. (Bisgard et al., 1979), we tried the effect of the same dose of this drug (which proved to be without effect on ~' and Pa) when DA ventilatory responses in cats had been made excitatory after spiroperidol treatment. However, these excitatory responses to DA persisted after d-tubocurarine administration. Since the DA-induced ventilatory excitations observed after spiroperidol treatment were partly coincident in time-course with hypertensive reactions, we blocked the vascular reactions to DA with dibenamine 10 mg. kg -t i.v. (delivered slowly in a solution containing dextrane to prevent hypotension). However, ventilatory excita-

RESPIRATORY EFFECTS OF DOPAMINE ANTAGONISTS • •

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Fig. 4. Dose-response curves for ventilatory changes induced by DA in cat with intact buffer nerves (solid squares), after receiving spiroperidol 0.5 #g. kg-a i.v. (solid circles), following a cumulative dose of spiroperidol 10.0 #g. kg -j (open circles) and finally after bilateral sections of the carotid and aortic nerves (BCAN, triangles). Abscissa, doses of DA. Ordinate, minimal and/or maximal values of VT (in percentages of resting VT) attained after each DA injection. After the initial dose of spiroperidol, DA-induced biphasic reactions, inhibitions preceding excitations. tion provoked by D A injections was not only preserved after a-adrenergic blockade, but ventilatory responses to the largest doses of D A were clearly enhanced and prolonged. Spiroperidol treatment in cats previously submitted to unilateral carotid neurotomy, also resulted in blockade of DA-induced ventilatory depression and its reversal into ventilatory stimulation, providing the opportunity of studying the simultaneous changes in chemosensory activity recorded from the peripheral end of the cut carotid nerve. In control conditions, all D A injections evoking ventilatory depression produced marked chemosensory inhibition or silencing of chemosensory discharges for periods of 1 to 15 s. After applying low doses of spiroperidol, D A injections induced biphasic chemosensory reactions - inhibition followed by excitation. When they attain a certain magnitude, nerve reactions were associated with biphasic ventilatory responses following the same sequence and close temporal correlation. Large doses o f spiroperidol fully blocked the DA-induced chemosensory inhibition and ventilatory depression, allowing the chemosensory excitation and ventilatory stimulation in response to the larger doses of D A (see fig. 5). Figure 6 illustrates the correlation between changes in fx and VT induced by DA-injections before and after spiroperidol treatment. In control conditions, mild reductions in fx were without consequences on VT but when the decrease in fx became more pronounced and prolonged, it was correlated with decreases in VT to nearly one half o f its resting amplitude (see also Zapata and Zuazo, 1980b). After spiroperidol, mild to moderate increases in fx caused by D A injections were also without effect on VT, but when the increase in fx became more pronounced, it was correlated with increases in VT. Since D A doses evoking these correlative excitatory changes were hypertensive, the vascular reactions were blocked by dibenamine,

246

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Fig. 5. Dose-response curves for chemosensory (squares) and ventilatory (circles) changes induced by DA in cat after unilateral carotid ncurotom 5. under control conditions (solid signs) and after receiving spiroperidol 10/~g • kg-J (open signs). Abscissa, doses of DA. Ordinates, maximal or minimal values of fx (left) and VT (right) obtained after each DA injection and expressed in percentages of their resting levels.

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Fig. 6. Correlation between changes in chemosensory frequency (abscissa) and tidal volume (ordinate) induced by i.v. injections of DA in one cat after unilateral carotid neurotomy. Solid circles, decreases evoked in control conditions and increases after receiving spiroperidol 10/Jg.kg-] i.v. Open circles, increases obtained after additional administration of dibenamine HC1 10 rag. kg -] i.v., which suppressed hypertensive effects of larger doses of DA. Values are expressed as percentages of their respective basal values. Straight lines were fitted from least-squares linear regression of series of 5 correlative points each one, obtained before and after dibenamine treatment (r = 0.95 and 0.96, P< 0.02 and 0.01, respectively)• after w h i c h the c o r r e l a t i v e curve o f VT

vs.

fx u s u a l l y b e c a m e

more abrupt and

d i s p l a c e d to the left. T h e effects o f s p i r o p e r i d o l w e r e also tested o n the v e n t i l a t o r y r e a c t i o n s e v o k e d b y a p o m o r p h i n e ( 1 0 - 7 - 1 0 -4 g • kg -] i.v.), a D A a n a l o g u e . A d i s p l a c e m e n t to the right a n d a t t e n u a t i o n

o f the a p o m o r p h i n e - i n d u c e d

ventilatory

depression

was

o b s e r v e d after s p i r o p e r i d o l , w i t h o u t reverting into v e n t i l a t o r y s t i m u l a t i o n , e v e n in e x p e r i m e n t s in w h i c h the v e n t i l a t o r y r e a c t i o n s to D A h a d b e e n reversed into

RESPIRATORY

EFFECTS OF DOPAMINE

ANTAGONISTS

247

excitation. In two cats previously subjected to unilateral carotid neurotomy, dosecorrelation between chemosensory inhibition and ventilatory depression caused by apomorphine was observed, both responses being partially blocked after spiroperidol (4 and 10 #g • kg -~) administration.

SPIROPERIDOL

EFFECTS ON VENTILATORY

REACTIONS TO 0 2 AND N 2 TESTS

We also studied the spiroperidol effects on the ventilatory reactions to transient hyperoxia and hypoxia. For this purpose, the inhaled gas mixtures were switched from room air to 100K 02 or 100~ N2 for periods of 5, l0 and 15 s. Sudden exposure to inhalation of pure 02 resulted in rapid reduction of VT and a slight decrease of fR; maximal ~" depression at the end of the 02 test usually resulted in 50 to 60~ reduction of resting values. No significant differences in the intensity or duration of these ventilatory depressions were observed after administration of spiroperidol 0.5 to 20.0/~g • kg -1, even when ventilatory responses to DA had been converted into pronounced excitation. Recording of chemosensory activity in cats subjected to unilateral carotid neurotomy also showed that the transient depression or silencing of chemosensory discharges observed during O2 tests persisted without significant changes after spiroperidol treatment. Ventilatory responses to 02 tests were abolished after bilateral sectioning of the carotid nerves. Inhalation of pure N2 for 5-s periods provoked variable increases in VT occasionally followed by slight fR increases; larger exposures produced one or a few gasps. When recorded, carotid chemosensory discharges also increased in frequency during these tests. These ventilatory and chemosensory reactions were not modified to a significant extent by spiroperidol 0.5 to 20.0/~g • kg-~, given alone or in combination with dibenamine. However, the ventilatory reactions were considerably reduced by bilateral carotid neurotomy and abolished by additional bilateral aortic neurotomy.

EFFECTS OF HALOPERIDOL

ON VENTILATION

In two cats with intact buffer nerves, haloperido130 #g • kg -1 i.v. produced immediate but transient increases in VT, resulting in increased V during the 1st rain following the injections. Repetition of the same doses after 30 rain produced new transient increases in VT and "~', but these effects did not occur later in response to third injections of the same or larger doses. The 4th phase in gasp complexes, although moderate, was constantly present after haloperidol treatment, disappearing after sectioning of the buffer nerves. In three other cats in which one carotid nerve had been previously sectioned for nerve recording, haloperidol 30 to 60 #g • kg -z also produced increases in VT (up to 157~ of control values), associated with increases in fx, both attaining their maxima between 10 and 20 s after the injections and subsiding within 0.5 to 5 min.

248

P. ZAPATA AND A. ZUAZO

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Fig. 7. Dose-response curves for ventilatory changes induced by DA in a cat with intact buffer nerves (solid circles), after receiving haloperidol in cumulative doses of 30 (open circles), 60 (open triangles) and 120 (open squares)/~g.kg -~ i.v. and after bilateral carotid and aortic neurotomies (solid squares) and dibenamine HC1 10 rag. kg -1 i.v. (solid triangles). Abscissa, doses of DA. Ordinate, minimal values of VT (in percentages of resting Vx) obtained after each DA injection.

Figure 7 illustrates that the dose-response curves for ventilatory inhibition evoked by DA were displaced to the right by cumulative doses of haloperidol. The inhibitory ventilatory responses to very large doses of DA given after haloperidol 120 #g • kg-~, concomitant with hypertensive responses, were not abolished by bilateral carotid and aortic neurotomies. But, both vascular and ventilatory responses disappeared after ~-adrenergic blockade with dibenamine. In cats subjected to previous transection of one carotid nerve, haloperidol produced simultaneous attenuations and displacements to the right of the dose-response curves for the inhibition of chemosensory and ventilatory activities evoked by DA and apomorphine. Although both types of inhibitions were surmountably blocked by haloperidol, they were not reverted into excitation. In one experiment in which ventilatory and chemosensory responses to DA had been made excitatory by treatment with spiroperidol (see above), additional administration of haloperidol did not cause further changes in these responses. EFFECTS OF PERPHENAZINE ON VENTILATION

In 6 cats, perphenazine, administered in initial doses of 0.1 to 1.0 mg .kg -j i.v., produced ventilatory stimulation. VT increased within a few seconds; in some cases, gasp responses were observed; "v"returned to control values usually within 10 rain. Moderate hypotension was observed in some experiments. When recordings of carotid chemosensory impulses were available, sharp increases in fx were observed, followed by mild but prolonged fx increases. Spontaneous gasps recorded after perphenazine showed a reduction of the 3rd phase and appearance of 4th phase in some cases; the electrical silence of carotid chemosensory discharges was now followed by a rebound in fx.

249

RESPIRATORY EFFECTS OF DOPAMINE ANTAGONISTS

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Fig. 8. Dose-response curves for ventilatory changes induced by DA in cat with intact buffer nerves, under control conditions (solid squares), after receiving perphenazine 0.5 mg. kg-1 i.v. (open squares) and after additional administration of dibenamine HCI 10 mg. kg -l i.v. (triangles). Abscissa, doses of DA. Ordinate, minimal or maximal values of breath-by-breath V (in percentages of resting ~') obtained after each DA injection.

Figure 8 shows that in a cat with intact buffer nerves, perphenazine 0.5 mg • kg -~ blocks ventilatory inhibition in response to low and medium doses of DA, while inhibition induced by large doses of D A was reversed into excitation. Since these doses of D A evoked clear hypertensive responses, vascular reactions were blocked by subsequent administration of dibenamine. However, the hyperventilatory responses to D A were enhanced after ~-adrenoceptor blockade. In cats subjected to previous section of one carotid nerve and recording from ~% 200

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Fig. 9. Dose-response curves for chemosensory (squares) and ventilatory (circles) changes induced by DA (A) and apomorphine (B) in cat with unilateral carotid neurotomy, under control conditions (solid signs) and after receiving perphenazine 450 ,ug. kg-1 i.v. (open signs). Abscissae, doses in logarithmic scales. Ordinates, minimal or maximal values of fx (left sided scales) and VT (right sided scales) obtained after each injection and expressed as percentages of their resting levels.

250

P. ZAPATA A N D A. ZUAZO

its peripheral end, correlations between changes in chemosensory and ventilatory responses were studied. Figure 9 shows that perphenazine 450 /~g.kg -~ reversed both responses to DA. However, inhibition of both chemosensory discharges and ventilation caused by apomorphine showed only a displacement to the right, without reversal into excitation. It must be noted that blockade or reversal of DA-evoked inhibitory responses after perphenazine occurred in association with persistence of ventilatory depressant responses induced by 02 tests. Furthermore, after perphenazine treatment, no significant changes occurred in the magnitude of hyperventilatory responses to N2 tests of 5-s duration.

EFFECTS OF C H L O R P R O M A Z I N E ON VENTILATION

In 5 cats, chlorpromazine, 50/~g • kg -1 to 5 mg • kg -L i.v., provoked a rapid increase in VT, sometimes accompanied by increased fR, and usually lasting for about 1 min. Occasionally, the hyperpnea was preceded by a very brief (around 5 s) period of apnea. Similar phenomena occurred when repeating the injections after ventilation had returned to control values. Most injections also provoked a moderate decrease in Pa, prolonged for 2 to 20 min. Spontaneous gasps became less frequent after chlorpromazine, but their 4th phase became prominent. When recording chemosensory activity from one previously cut carotid nerve, abrupt and pronounced increases in fx were observed in response to chlorpromazine injections, fx returned to control values more slowly than ventilatory parameters. Figure 10 illustrates that transient inhibition of ventilation induced by low doses of DA was blocked after chlorpromazine 0.5 mg • kg -~, but biphasic ventilatory responses (increased VT followed by decreased VT) were provoked by medium to large doses of DA. After an additional injection of chlorpromazine to attain a cumulative dose of 2.5 mg • kg -~, only the larger doses of DA were able to evoke these biphasic ventilatory responses. Under chlorpromazine, no significant changes were observed in ventilatory responses to O2 and N 2 tests. However, bilateral sectioning of carotid and aortic nerves abolished the ventilatory responses to DA, as those to 02 and N: tests. In other experiments, chlorpromazine only provoked a displacement to the right of dose-response curves for the inhibition of ventilation evoked by DA injections, without appearance of biphasic or excitatory reactions. When recording carotid chemosensory activity, the decrease in fx observed in response to DA injections was changed into a biphasic response (decreased fx followed by increase) to medium and large doses of DA. When these biphasic responses were minimal, no changes in ventilation occurred, but when more pronounced they were associated with the biphasic ventilatory responses described above. It must be noted that the hypertensive effects evoked by large doses of DA gained in amplitude and duration after chlorpromazine. That this drug had not attained

RESPIRATORY EFFECTS OF DOPAMINE ANTAGONISTS

251

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Fig. 10. Dose-responsecurves for ventilatory changes induced by DA in cat with intact buffer nerves. under control conditions (solid squares), after chlorpromazine HCI in cumulative doses of 0.5 (open squares) and 2.5 (circles) rag. kg-1 i.v. and bilateral sections of carotid and aortic nerves (BCAN, triangles). Abscissa, doses of DA. Ordinate, minimal and maximal values of VT (in percentages of resting VT) obtained after each DA injection. Biphasic reactions consisted of decreases followed by increases in VT.

the dosage adequate for blockade of vascular ~-adrenoceptors has also been previously reported, on the basis of unchanged hypertensive responses to noradrenaline injections (Llados and Zapata, 1978).

Discussion Results show that i.v. administration of four different DA antagonists provoke an immediate but transient increase in ventilation in pentobarbitone-anesthetized cats. Dopaminoceptors possibly involved in this effect occur at least at two sites: in peripheral arterial chemoreceptors (Dinger et al., 1981; Llados and Zapata, 1978; Monti-Bloch and Eyzaguirre, 1980; Sampson and Vidruk, 1977) and in bulbar respiratory neurons (Bolme et al., 1977). To explain their neuroleptic activity, all the DA blockers employed in these experiments must cross the blood-brain barrier. However, the delay of ventilatory effects reported here and the absence of such effects when spiroperidol was administered to cats after section of the buffer nerves, are indicative that they originated from stimulation of peripheral arterial chemoreceptors. An increased VT, starting within 10 s and lasting several rain, has been reported to occur in pentobarbitone-anesthetized rabbits in response to intracarotid injections of haloperidol (Matsumoto et al., 1980). Although this blocker has also been administered i.v. to dogs (Bisgard et al., 1979), this report does not mention the immediate effects following its injection. However, V, Paco2 and Pao, were unchanged in humans 10 min after administering haloperidol 2.5 mg intramuscularly (Bainbridge

252

P. ZAPATA AND A. ZUAZO

and Heistad, 1980); similarly, arterial Po.~was unchanged in patients with left heart failure after 10 and 30 min of receiving haloperidol 5 mg i.v. (Huckauf et al., 1976). Furthermore, ~' and alveolar ventilation were normal under normoxia in healthy humans receiving chlorpromazine for a week; but they increased more than in control conditions when these subjects were exposed to hypoxia (Boll et al., 1976). This finding led to the hypothesis of an increased chemosensory drive during chlorpromazine treatment. Decline of the initial V enhancement within minutes of administration of butyrophenones and phenothiazines here reported is in line with the reports mentioned above, suggesting the attainment of a steady-state of resting ventilation within normal limits, by the concurrence of reflex ventilatory adjustments (e.g., to decreased Paco2 as consequence of hyperventilation) and/or opposite effects of these DA antagonists on arterial chemoreceptors and ventilatory centers. Our results confirm those of a previous report (Llados and Zapata, 1978), in which an increase in the basal frequency of carotid chemosensory discharges was observed in cats in response to i.v. injections of butyrophenones and phenothiazines. An haloperidol-induced increase in fx has also been reported in cats (Lahiri et al., 1980) and dogs (Bisgard et al., 1979). The parallel increases in fx and VT after DA antagonists observed in cats subjected to unilateral carotid neurotomy strongly suggests that the transiently increased ventilation caused by these agents is reflexly evoked from an augmented peripheral chemosensory drive. The increase in chemosensory discharge caused by DA antagonists may be explained by disinhibition at the level of arterial chemoreceptors, i.e., blockade of inhibitory dopaminoceptors (DA i) tonically activated by continuous release of endogenous DA. Such disinhibition may be reinforced by the unmasking of excitatory dopaminoceptors (DA~) present in glomus tissues, whose activation by endogenous DA would be now unopposed. These two types of dopaminoceptors (DAi and DA~) have been postulated in several brain areas (Cools and van Rossum, 1980) and their coexistence in glomus tissue has been postulated for the carotid bodies of cats (Llados and Zapata, 1978), dogs (Bisgard et al., 1979) and rabbits (Monti-Bloch and Eyzaguirre, 1980). Since the access of DA to the brain parenchyma is prevented by structural, uptaking and enzymatic barriers at the blood-brain (Oldendorf, 1971) and blood-c.s.f, interphases (Lindvall et al., 1980), the ventilatory responses to DA are only derived from peripheral action, while those to apomorphine and to DA antagonists can be produced by effects on peripheral and central dopaminoceptor sites (Bolme et al., 1977; Farber and Maltby, 1980; Lundberg et al., 1979). Since a reduced chemosensory input, produced by section of the carotid and aortic nerves markedly decreases the frequency of spontaneous gasp complexes (Zuazo and Zapata, 1980), one should expect an increased frequency of gasps after augmenting the chemosensory drive by DA blockade. However, our results did not reveal such maintained increase, although in several experiments the transient increase in VT caused by DA antagonists attained the threshold of the augmented inspiratory reflex, thus provoking gasps. Maintenance of the 3rd phase

R E S P I R A T O R Y EFFECTS OF D O P A M I N E A N T A G O N I S T S

253

in spontaneous gasp complexes and the concomitant chemosensory silence following dopaminergic blockade indicates that they did not depend on increased DA release evoked by the augmented breaths. The appearance of the 4th phase concomitantly with chemosensory rebound following this treatment suggests that release of endogenous DA occurred during gasps, normally attenuating a rebound in chemosensory and ventilatory activities. Although the transient increases in chemosensory and ventilatory activities following DA blockers are favourable to the model of Osborne and Butler (1975), the above changes in spontaneous gasp complexes and the preservation of responses to O2 and N2 tests argue against the possibility that hyperoxic and hypoxic effects on chemoreceptors should be mediated by changes in DA release from glomus cells. Otherwise, these results can be explained within the framework of a modulatory role of DA in chemoreception (Lahiri et al., 1980; Llados and Zapata, 1978). All DA blockers employed in these experiments, when given in low doses, displaced to the right the dose-response curves for ventilatory depression evoked by DA and apomorphine. Increasing the doses of spiroperidol and phenothiazines gave place to biphasic ventilatory reactions to DA injections, consisting of short inhibition followed by excitation. Finally, larger doses of spiroperidol and perphenazine resulted in abolition of the DA-induced ventilatory inhibition, and pronounced but transient ventilatory excitation in response to the larger doses of DA. These purely inhibitory, biphasic or purely excitatory ventilatory reactions were prevented by section of the buffer nerves. The chemo-reflex nature of the ventilatory effects induced by DA and apomorphine is supported by the concomitant changes in chemosensory discharges frequency, which confirm a previous report (Llados and Zapata, 1978). Figure 6 illustrates that when fx is transiently reduced below a certain value by DA injections, the withdrawal of this chemosensory drive produces a transient decrease in VT; when fx increases above certain levels in response to DA injections after spiroperidol, this transiently enhanced chemosensory drive produces an increase in VT, although the relative threshold (i.e., level of increased fx at which VT starts augmenting) is variable from one animal to another (compare figs. 5 and 6). Thus, ventilatory responses here described are mostly of reflex origin and onset by transient changes in peripheral chemosensory activity. The possibility that the excitatory effects elicited by DA after DA blockade should originate from glomeral vasoconstriction requires consideration. They occurred concomitantly with hypertensive doses of this agent, while apomorphine (a DA analog without hypertensive actions) provokes chemosensory and ventilatory effects which are not reverted into excitatory ones. However, blocking the vascular effects produced by large doses of DA through dibenamine administration did not suppress and even enhanced the excitatory chemosensory and ventilatory reactions. These responses may result from the full expression of DAe activation, when unopposed by reflex depression of ventilation produced by bar0receptor stimulation (Grunstein et al., 1975), since ventilatory depression in response to large (hypertensive) doses

254

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of DA in untreated animals may be partly contributed by this inhibitory reflex initiated from baroreceptor stimulation.

Acknowledgements

This work was supported by grants 88-78 and 83-81 from the Catholic University Research Division, and by the Gildemeister Foundation. Spiroperidol was kindly provided by Dr. T. Goossens, from Janssen Pharmaceutica. Thanks are expressed to Professor C. Eyzaguirre, Department of Physiology, University of Utah, for critical reading of this manuscript, and to Mrs. Carolina Zapata for her expert technical assistance.

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