Perfusion of the spleen with blood containing prostaglandin E1: transmitter liberation and uptake

Neuropeptide Y-, substance P- and VIP-immunoreactive nerves in cat spleen in relation to autonomic vascular and volume control

Neuropeptide Y (NPY)-immunoreactive (IR) nerve fibres were found around both arteries and veins and in smooth muscle trabeculae of the cat spleen with the highest density on the arterial side. Considerably more tyrosine hydroxylase (TH)- and dopamine-beta-hydroxylase (DBH)-positive than NPY-IR nerves were seen in the trabeculae and splenic capsule. The NPY-IR nerves in the spleen most likely originated in the coeliac ganglion, since (1) splanchnic nerve sectioning did not change the splenic NPY-IR nerves, (2) most neurones in the coeliac ganglion were NPY-IR, as well as DBH- and TH-positive, and (3) NPY-IR was transported axonally from the coeliac ganglion towards the spleen via the splenic nerve. Local NPY infusion in the isolated, blood-perfused cat spleen caused a marked increase in splenic vascular resistance and a small volume reduction. NA caused a comparatively larger reduction in splenic volume than NPY in addition to vasoconstriction. VIP-IR cell bodies in the coeliac ganglion were NPY- and TH-negative. VIP-IR nerves were seen both around the splenic artery and vein as well as around arterioles and within venous trabeculae of the spleen. VIP infusion caused reduction of splenic perfusion pressure (i.e. vasodilation) as well as an increase in splenic volume. Substance P-IR nerves, most likely of splanchnic afferent origin, were present in the coeliac ganglion around the splenic artery and arterioles of the spleen. Infusion of substance P induced marked reduction in perfusion pressure and a reduction in splenic volume. Enkephalin-immunoreactive nerves of splanchnic origin surrounded some TH- and NPY-positive, coeliac ganglion cells. It is concluded that several vasoactive peptides are located in splenic nerves. NPY is present in noradrenergic neurones and causes mainly increased vascular resistance. VIP occurs in non-adrenergic neurones of sympathetic origin and induces vasodilation and relaxation of the capsule. Finally, substance P is present in peripheral branches of spinal afferent nerves and causes vasodilation and capsule contraction. Stimulation of the splenic nerves may thus release several vasoactive substances in addition to noradrenaline, exerting a variety of actions.

The effects of piperoxan on uptake of noradrenaline and overflow of transmitter in the isolated blood perfused spleen of the cat

1 The competitive alpha-adrenoceptor blocking agent, piperoxan, in concentrations up to 2 x 10(-4) M, produced large dose-dependent increases in transmitter overflow from the isolated blood perfused spleen of the cat following nerve stimulation at 10 hertz. 2 At concentrations greater than 2 x 10(-4) M, piperoxan produced a rise in perfusion pressure, a contraction of the splenic capsule, and a marked dose-dependent decrease in transmitter overflow. 3 Phenoxybenzamine (10(-4) M) and desmethylimipramine (3 x 10(-5) M) produced further increases in transmitter overflow when added after piperoxan. 4 Piperoxan (5.8 to 6.6 x 10(-6) M) had no effect on the recovery of 3H in the venous blood following the close arterial infusion or injection of (3H)-(--)-noradrenaline, indicating that the drug does not inhibit uptake of the amine. 5 Piperoxan produced dose-dependent inhibition of responses of the splenic vasculature to close arterial injection of 1 microgram of (--)-noradrenaline but was much less effective at inhibiting responses to nerve stimulation. At 2 x 10(-6) M piperoxan produced a considerable reduction of the response to injected noradrenaline but potentiated the response to nerve stimulation. 6 In isolated strips of cat splenic capsule, piperoxan produced a shift to the right of the dose-response curve to noradrenaline with no change of the maximum response. There was no evidence of a postsynaptic sensitizing effect of the type observed in the rat vas deferens.

The effects of labetalol (AH 5158) on adrenergic transmission in the cat spleen

1. The competitive alpha- and beta-adrenoceptor blocking agent labetalol, in concentrations up to 10(-4) M, produced dose-dependent increases in transmitter overflow from the isolated blood perfused spleen of the cat following nerve stimulation at 10 and 30 Hz. 2. At concentrations above 10(-4) M labetol produced a pronounced decrease in transmitter overflow. 3. Labetalol (1.5 X 10(-4) M) increased the recovery of 3H label in the venous blood following the close-arterial infusion of [3H]-(-)-noradrenaline indicating that the drug inhibits uptake of the amine. 4. Both labetalol (3.8 X 10(-5) M) and piperoxan (7.4 X 10(-6) M) produced parallel shifts to the right of the dose-response curves to noradrenaline and oxymetazoline in isolated strips of cat splenic capsule. In this preparation both drugs acted as competitive postsynaptic alpha-adrenoceptor blocking agents. 5. Labetalol (3.3 X 10(-5) M) increased the transmitter overflow following stimulation of the splenic nerves with 200 impulses at 10 Hz. The overflow could be further increased by subsequent addition of piperoxan (7.2 X 10(-6 M). Piperoxan (5.7 X 10(-6) M) alone produced a marked increase in transmitter overflow which could be further increased by subsequent addition of desmethylimipramine (DMI; 3.2 X 10(-5) M). Cocaine (1.5 X 10(-5) M) or DMI (5.4 X 10(-5 M) produced a small increase in transmitter overflow which was not further increased by addition of labetalol (2.8 X 10(-5) M). 6. Labetalol produced a biphasic effect on the responses of the isolated blood perfused spleen of the cat to nerve stimulation. With low doses (up to 10(-4) M) vascular responses were potentiated and with high doses (greater than 10(-4) M) inhibited. The potentiation was related to uptake blockade and the inhibition to decreased transmitter overflow and postsynaptic alpha-adrenoceptor blockade. 7. Labetalol appears to act as a postsynaptic alpha-adrenoceptor antagonist in the isolated blood perfused spleen of the cat with little effect on presynaptic alpha-adrenoceptors. The moderate elevation of transmitter overflow by the drug is related to the inhibitory effect of the drug on neuronal uptake rather than on presynaptic alpha-adrenoceptors.

An uptake mechanism for L-noradrenaline in the cat spleen, associated with the nerves but distinct from uptake

1. The characteristics of the uptake of [(3)H]L-noradrenaline from 1 mug pulses injected close arterially to the isolated blood perfused cat spleen are described.2. The spleen took up 355.0+/-16.0 ng from a first pulse and 321.1+/-43.6 ng from a second.3. Uptake from a second pulse was 254.0+/-30.3 ng in the presence of the Uptake(1) inhibitor desmethylimipramine (DMI) (3.3 x 10(-5)M) and the Uptake(2) inhibitor 17-beta-oestradiol (17beta0) (1.8 x 10(-4)M).4. Uptake from small 10 ng pulses was also insensitive to DMI and 17beta0.5. Uptake from pulses was abolished by surgical denervation of the spleen, or pre-treatment with phenoxybenzamine (PBA) (8.8 x 10(-5)M).6. The pulse uptake process was impaired by omission of red cells from the perfusate.7. Stimulation of the splenic nerves at 3Hz halved the pulse uptake.8. Uptake from infusion in the presence of DMI and 17beta0 occurred only during the first few minutes of the infusion.9. It is concluded that an uptake process for L-noradrenaline distinct from Uptakes(1) and (2) is present in the spleen and this might be important physiologically.

The response of the cat anococcygeus muscle to nerve or drug stimulation and a comparison with the rat anococcygeus

1 The cat anococcygeus muscle is shown to possess a dual innervation similar to the rat anococcygeus, with a motor adrenergic innervation and an inhibitory innervation whose transmitter is unknown. The pharmacological properties of the cat muscle were investigated and compared with those of the rat muscle.2 The cat muscle contracts to noradrenaline, 5-hydroxytryptamine, tyramine, amphetamine, guanethidine, cocaine and lysergic acid diethylamide (LSD). The effects of noradrenaline and 5-hydroxytryptamine are blocked by phentolamine and methysergide respectively.3 The cat anococcygeus is relaxed by acetylcholine, carbachol, isoprenaline, ATP, prostaglandins E(1), E(2) and F(2alpha) and vasopressin, all of which contract the rat muscle. The effects of acetylcholine and carbachol are blocked by atropine and those of isoprenaline by propranolol.4 Field stimulation produces contraction of the cat anococcygeus, which is blocked by phentolamine and guanethidine but unaffected by hexamethonium, atropine or neostigmine.5 In the presence of guanethidine (10(-5)M), the tone of the muscle is raised and field stimulation produces relaxation of the muscle. These inhibitory responses are unaffected by phentolamine, hexamethonium, atropine or neostigmine.6 Neostigmine potentiates the effects of acetylcholine, but not of carbachol in relaxing the cat anococcygeus and in contracting the rat anococcygeus, but has no effect on either motor or inhibitory responses to field stimulation.7 Cold storage for up to eight days had little effect on either the motor response to noradrenaline or the motor or inhibitory response to field stimulation of the cat anococcygeus. Beyond eight days, the response to field stimulation diminishes more rapidly than the response to noradrenaline.

The effects of pargyline on overflow of transmitter and uptake of noradrenaline in the cat spleen

1. Twenty minutes after the addition of pargyline (5 x 10(-4)M) to blood perfusing the isolated spleen of the cat, the overflow of transmitter resulting from stimulation of the sympathetic nerves increased 2.3-3-fold. Lower doses of pargyline did not significantly affect overflow.2. Monoamine oxidase activity, measured with either radioactively labelled tyramine or noradrenaline as substrate, was almost completely inhibited by doses of pargyline in the range of 10(-4)M to 5 x 10(-4)M. Inhibition of enzyme activity was not correlated with the effect on overflow. Pargyline had only a slight inhibitory effect on catechol-O-methyl transferase.3. Uptake of a 1 mug injection (pulse) of labelled noradrenaline, following pargyline (5 x 10(-4)M), was increased to 199.1% of that found in control experiments.4. Pargyline significantly reduced the vascular responses to nerve stimulation but had no significant effect on capsular responses.5. The inhibitor had no effect on resting overflow of labelled noradrenaline from the spleen but doubled the overflow of labelled noradrenaline following nerve stimulation.6. It is suggested that the effect of pargyline on overflow is due to increased release of transmitter during nerve stimulation.7. The possible clinical significance of these findings is discussed.

Vascular responses and noradrenaline overflows in the isolated blood-perfused cat spleen: some effects of cocaine, normetanephrine and -blocking agents

1. Vascular responses and noradrenaline overflows have been studied in the isolated blood-perfused cat spleen in response to electrical stimulation of the splenic nerve with trains of 200 supramaximal pulses at a frequency of 10 Hz given at 10 min intervals.2. In the absence of blocking agents the spleen gave well-defined responses and a mean maximum overflow of 436 +/- 96 pg noradrenaline per stimulus (n = 4) at the third train of stimuli.3. Cocaine (2 x 10(-5)M) increased the response nearly threefold and raised the overflow to 840 +/- 131 pg/stim (n = 4). At later stimulations the responses remained stable, but the overflows rose progressively to 1076 +/- 51 pg/stim after five trains of stimuli.4. Normetanephrine (10(-4)M) had no significant effect on response, but elevated the overflow to a mean maximum of 868 +/- 169 pg/stim (n = 4).5. Cocaine (2 x 10(-5)M) and normetanephrine (10(-4)M) given together increased the response by a factor of 6.5 and raised the overflow to 1258 +/- 247 pg/stim (n = 4).6. Hydergine (approx. 10(-5)M) almost completely abolished the response and raised the overflow to 859 +/- 173 pg/stim (n = 4).7. Cocaine (2 x 10(-5)M), normetanephrine (10(-4)M) and hydergine (approx. 10(-5)M) given in combination abolished the response and raised the overflow to 4089 +/- 1148 pg/stim (n = 4).8. Phenoxybenzamine (10(-4)M) abolished the response and elevated the overflow to 4215 +/- 738 pg/stim (n = 4).9. These results are interpreted in terms of selective and combined block of ;uptake I', ;uptake II' and alpha-adrenergic receptors. Facilitation of transmitter release by alpha-blocking drugs, and the possible existence of an uptake process associated with the alpha-receptors are discussed.