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

Accumulation of norepinephrine by tissue slices from spontaneously hypertensive rats

Accumulation of 3H-1-norepinephrine (3H-1-NE) by heart and spleen slices from different aged spontaneously hypertensive rats (SHR) was compared with accumulation by slices from comparably aged normotensive rats (Wistar-Kyoto, WKY). Between weeks 4 and 9 there was a significant increase in accumulation by heart slices of the WKY; there was no further increase at weeks 13 and 16. The developmental pattern in slices of WKY spleen was different. Accumulation was the same at weeks 4 and 9; subsequently, there were significant increases at weeks 13 and 16. Slices of heart from SHR showed the same pattern of development as those from WKY. However, accumulation by slices of SHR spleen was significantly different from that by slices of WKY spleen. At all ages studied, SHR slices accumulated less 3H-1-NE. Furthermore, there was no significant increase in accumulation with age. The data show: 1. the course of development of the adrenergic neuron transport system is different in heart and spleen, and 2. accumulation of 3H-1-NE by SHR spleen, but not heart slices, is different from accumulation by the respective control tissues.

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.

Uptake and release of catecholamines in sympathetic nerve fibres in the spleen of the cod, Gadus morhua

The effects of drugs known from mammalian experiments to interfere with uptake and release of adrenergic transmitters in the sympathetic nerve terminals have been investigated on perfused spleen and isolated spleen strips from the cod. Cocaine and desipramine inhibit the accumulation of 3H-noradrenaline in the perfused spleen, probably by interfering with uptake mechanisms. Both drugs also shift to the left the dose-response curves for noradrenaline and adrenaline on isolated strips, cocaine being most potent. The maximal contraction force of isolated strips also increases after cocaine when noradrenaline is the agonist, but not when methacholine is used or on chronically denervated strips. This effect of cocaine is therefore not due to a general postsynaptic effect. Tyramine and amphetamine both release stored 3H-noradrenaline from the perfused spleen, and tyramine also contracted the spleen strips. In contrast to the situation in mammals, the dose-response curve for tyramine is not affected by cocaine, and tyramine (up to 10(-3) M) present in the bath does not potentiate the dose-response curve for noradrenaline on isolated strips. Different uptake mechanisms for tyramine and noradrenaline into the nerve terminal are therefore suggested for the cod sympathetic fibres. The alpha-adrenoceptor blocking agent phentolamine produces an increase in overflow of label during nerve stimulation at 5Hz in the perfused spleen preloaded with 3H-noradrenaline. An alpha-adrenoceptor-mediated control of the release of catecholamines, similar to that in mammals, appears to be present in the cod.