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

Sympathetic innervation of human and porcine spleens: implications for between species variation in function

BACKGROUND

The vagus nerve affects innate immune responses by activating spleen-projecting sympathetic neurons, which modulate leukocyte function. Recent basic and clinical research investigating vagus nerve stimulation to engage the cholinergic anti-inflammatory pathway (CAP) has shown promising therapeutic results for a variety of inflammatory diseases. Abundant sympathetic innervation occurs in rodent spleens, and use of these species has dominated mechanistic research investigating the CAP. However, previous neuroanatomical studies of human spleen found a more restricted pattern of innervation compared to rodents. Therefore, our primary goal was to establish the full extent of sympathetic innervation of human spleens using donor tissue with the shortest procurement to fixation time. Parallel studies of porcine spleen, a large animal model, were performed as a positive control and for comparison.

METHODS

Human and porcine spleen tissue were fixed immediately after harvest and prepared for immunohistochemistry. Human heart and porcine spleen were stained in conjunction as positive controls. Several immunohistochemical protocols were compared for best results. Tissue was stained for tyrosine hydroxylase (TH), a noradrenergic marker, using VIP purple chromogen. Consecutive tissue slices were stained for neuropeptide Y (NPY), which often co-localizes with TH, or double-labelled for TH and CD3, a T cell marker. High-magnification images and full scans of the tissue were obtained and analyzed for qualitative differences between species.

RESULTS

TH had dominant perivascular localization in human spleen, with negligible innervation of parenchyma, but such nerves were abundant throughout ventricular myocardium. In marked contrast, noradrenergic innervation was abundant in all regions of porcine spleen, with red pulp having more nerves than white pulp. NPY stain results were consistent with this pattern. In human spleen, noradrenergic nerves only ran close to T cells at the boundary of the periarterial lymphatic sheath and arteries. In porcine spleen, noradrenergic nerves were closely associated with T cells in both white and red pulp as well as other leukocytes in red pulp.

CONCLUSION

Sympathetic innervation of the spleen varies between species in both distribution and abundance, with humans and pigs being at opposite extremes. This has important implications for sympathetic regulation of neuroimmune interactions in the spleen of different species and focused targeting of the CAP in humans.

Cocaine administration induces human splenic constriction and altered hematologic parameters

Cocaine is a potent vasoconstrictor that has been shown to alter hemoglobin, hematocrit, and red blood cell counts in both animals and humans. The present study evaluated whether cocaine administration induces splenic constriction in men and whether spleen-volume changes temporally correlate with altered hematologic parameters. Spleen volume was assessed at baseline and after cocaine administration (0.4 mg/kg) by using magnetic resonance imaging. A group of five healthy men, aged 31 +/- 2 (SE) yr and reporting occasional cocaine use (13 +/- 5 lifetime exposures), participated. Cocaine reduced spleen volume by 20 +/- 4% (P < 0.03) 10 min after drug administration. Spleen volume returned to normal (101 +/- 3% baseline) within 35 min after cocaine administration, indicating that the reduction is a transient phenomenon. In subjects administered cocaine from whom blood samples were obtained (n = 3), cocaine increased hemoglobin levels, hematocrit, and red blood cell count to 104.5 +/- 0.9, 105.6 +/- 1.2, and 106.5 +/- 1.0% of baseline levels, respectively (P < 0.03), but it did not alter white blood cell and platelet counts. Placebo administration (n = 5) did not alter hematologic parameters. These results suggest that cocaine induces splenic constriction in humans, and this may contribute to temporally concordant hematologic parameter changes. These events may help to preserve or increase tissue oxygenation in periods of high oxygen demand and/or increased vascular resistance.

Neuropeptide Y and noradrenaline mechanisms in relation to reserpine induced impairment of sympathetic neurotransmission in the cat spleen

The mechanisms underlying the reserpine-induced impairment of the functional responses to sympathetic nerve stimulation and output of noradrenaline (NA) and neuropeptide Y (NPY)-like immunoreactivity (-LI) were studied using the isolated blood-perfused cat spleen. Splenic nerve stimulation (10 Hz for 2 min) during control conditions caused perfusion-pressure increase, volume reduction and an increased output of NA and NPY-LI. After administration of phenoxybenzamine, the nerve stimulation-induced perfusion-pressure increase was almost abolished, the volume reduction inhibited and the output of NPY-LI enhanced. After subsequent addition of propranolol, a clear-cut increase in perfusion pressure upon nerve stimulation reappeared. Local infusion of NPY caused a potent, long-lasting, adrenoceptor-resistant increase in perfusion pressure and a relatively smaller volume reduction of the spleen. Twenty-four hours after reserpine pretreatment (1 mg kg-1 i.v.), which depleted the splenic content of NA greater than 95% and NPY-LI by about 50%, the functional responses upon nerve stimulation were markedly reduced. Preganglionic denervation or pretreatment with the ganglionic-blocking agent chlorisondamine did not influence the NA depletion after reserpine treatment. A considerable, adrenoceptor antagonist-resistant, long-lasting functional response as well as a markedly enhanced output of NPY-LI then occurred upon nerve stimulation. In conclusion, reserpine treatment combined with interruption of preganglionic impulse flow reveals non-adrenergic, nerve stimulation evoked splenic functional responses which could be mediated by release of a cotransmitter peptide like NPY.

Reserpine-induced depletion of neuropeptide Y from cardiovascular nerves and adrenal gland due to enhanced release

The mechanisms underlying reserpine-induced depletion of neuropeptide Y-like immunoreactivity (NPY-LI) in relation to tissue content of noradrenaline (NA) and cardiovascular impairment were studied in guinea-pigs. Reserpine pretreatment (5 mg/kg SC) caused a 5-fold increase in plasma levels of NPY-LI with a maximum after 4 h. This was associated with a progressive fall in systemic arterial blood pressure and heart rate (to about 50% of basal values). The contents of NPY-LI and NA in nerves of the heart and quadriceps muscle were then reduced by about 75% and 85%, respectively. The adrenal content of NPY-LI was reduced by 40% 8 h after reserpine, while the adrenaline content was uninfluenced. Pretreatment with guanethidine depleted NA in the heart but did not influence plasma levels or tissue content of NPY-LI per se. The reserpine-induced increase in plasma NPY-LI and the depletion of NPY-LI in the heart and skeletal muscle was to a large extent prevented by guanethidine. The reserpine-induced bradycardia and hypotension were reduced after guanethidine pretreatment. Chlorisondamine pretreatment depressed heart rate, blood pressure and plasma levels of NPY-LI. Furthermore, chlorisondamine inhibited the reserpine-induced increase in plasma NPY-LI and prevented the reduction in tissue content of NPY-LI in the heart, skeletal muscle and adrenal.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms underlying changes in the contents of neuropeptide Y in cardiovascular nerves and adrenal gland induced by sympatholytic drugs

Neuropeptide Y (NPY) is a recently isolated vasoactive peptide, which is present, together with catecholamines, in sympathetic nerves and in the adrenal medulla. In the present study, we report that pretreatment with sympatholytic agents influences the tissue levels of NPY-like immunoreactivity (NPY-LI) in the guinea-pig. Thus, 24 h after reserpine not only noradrenaline (NA), but also NPY-LI, was depleted in the heart, spleen and the adrenal gland. The levels of NPY-LI in the vas deferens and stellate ganglia, however, were unaffected by reserpine in spite of marked depletions of NA. The reserpine-induced depletion of NPY-LI was probably caused by enhanced nerve-impulse flow and subsequent release from cardiovascular nerves in excess of resupply, since it could be prevented by the ganglionic-blocking agent chlorisondamine. Long-term (6 days) treatment with chlorisondamine reduced the levels of NPY-LI in the stellate ganglion. Short-term treatment (48 h) with guanethidine partially prevented the reserpine-induced depletion of NPY-LI, probably due to inhibition of NPY release. Long-term guanethidine treatment depleted not only NA, but also NPY-LI from the spleen. Pretreatment with the alpha-receptor antagonist phenoxybenzamine did not influence the NA levels but reduced the content of NPY-LI in the spleen via a mechanism that was dependent on intact ganglionic transmission. Since NPY has several cardiovascular actions, changes in NPY mechanisms may contribute to the pharmacological and therapeutical effects of sympatholytic agents.

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.

Guanethidine-sensitive release of neuropeptide Y-like immunoreactivity in the cat spleen by sympathetic nerve stimulation

Splenic nerve stimulation (10 Hz for 2 min) caused a perfusion-pressure increase, a volume reduction and an increase in the output of neuropeptide Y-like immunoreactivity (NPY-LI) from the isolated blood-perfused cat spleen. Gel-filtration HPLC analysis revealed that plasma NPY-LI collected during nerve stimulation was similar to the NPY-LI in the spleen and synthetic porcine NPY. Combined propranolol and phenoxybenzamine pretreatment enhanced NPY output upon nerve stimulation by about 60%. Forty percent of the perfusion-pressure increase and 25% of the volume reduction seen during control stimulations remained after adrenoceptor blockade. Guanethidine abolished the release of NPY-LI, the perfusion-pressure increase and the volume reduction normally seen upon splenic nerve stimulation. Infusion of synthetic porcine NPY caused a long-lasting increase in perfusion pressure and a relatively moderate volume reduction. Noradrenaline (NA) both increased perfusion pressure and induced a marked volume reduction. The NPY effects were resistant to adrenoceptor antagonists in doses which abolished the NA response. In conclusion, the present data show that NPY-LI is released upon sympathetic nerve stimulation by a guanethidine-sensitive mechanism. Furthermore, the sympathetic response is partially resistant to adrenoceptor antagonists and NPY has powerful vasoconstrictor effects. This provides further evidence for a role of NPY in sympathetic vascular control.

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.

Involvement of uptake2 in the termination of activity of neurogenic noradrenaline in the rat isolated atrium

1. An examination has been made of the relative effect of drugs which affect Uptake1 and Uptake2 on the mechanical responses to adrenergic nervous stimulation (0-5-5 Hz for 5 sec) in rat isolated atrium. 2. Inhibition of Uptake1 with desmethylimipramine (2 muM) prolonged by 50-90% the time taken for recovery of normal heart rate after a five sec train of nervous stimulation. Inhibition of Uptake2 with metanephrine (4 muM) prolonged by 20-40% the time taken for recovery of normal heart rate. 3. Neither desmethylimipramine nor metanephrine had any consistent effect on the time course of the inotropic response to stimulation or on the amplitudes of either inotropic or chronotropic responses. 4. After administration of desmethylimipramine, metanephrine had a somewhat greater effect on chronotropic responses than when given alone. After administration of metanephrine, desmethylimipramine still further prolonged chronotropic responses to low frequency stimulation (0-5, 1 Hz) but had no effect at 5 Hz. These results agree with the known affinities of each uptake process for different concentrations of noradrenaline in the rat heart. 5. It is concluded that both Uptake1 and Uptake2 participate in the termination of physiological activity of neurogenic noradrenaline in rat isolated atrium even at low frequencies of nervous activation. 6. No evidence was obtained to indicate that manipulation of circulating oestrogen levels by oöphorectomy and oestrogen-priming of female rats had any effect of the efficiency of the cardiac Uptake2 process.

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.

Binding of catecholamines to connective tissue and the effect upon the responses of blood vessels to noradrenaline and to nerve stimulation

1. Quantitative estimates have been made of the binding of catecholamines to purified collagen and elastin, and the factors influencing this binding have been investigated.2. Collagen shows no specificity towards the binding of either the (-)- or (+)-isomer of adrenaline or noradrenaline, at low concentrations. Elastin binds the (-)-isomer of adrenaline and noradrenaline to twice the extent of the (+)-isomer.3. Tetracyclines inhibit the binding of catecholamines to collagen and elastin. Oxytetracycline 10(-4)M produces a maximum inhibition of the binding of (-)-noradrenaline to collagen of 68.4%.4. The responses of perfused blood vessels to the administration of pulses of catecholamines or to adrenergic nerve stimulation have been measured.5. Oxytetracycline (10(-4)M) potentiates the amplitude of the response of the rabbit ear artery to noradrenaline and to nerve stimulation, ten- and sixfold respectively.6. Those preparations with a high content of collagen and elastic tissue, the rabbit ear artery and the rat tail, are more susceptible to the potentiating effects of oxytetracycline than one with a low content, the rat anococcygeus.7. The results of the study suggest that in tissues with a high content of collagen and elastin, binding to extracellular sites is the major mechanism for terminating the response to noradrenaline or to adrenergic nerve stimulation.