Effects of vinblastine on catecholamine-biosynthetic enzymes in heart, sympathetic ganglion and adrenal glands of rats

Detection of neuropeptide Y-like immunoreactivity and messenger RNA in rat platelets: the effects of vinblastine, reserpine, and dexamethasone on NPY expression in blood cells

Rat plasma contains high basal levels (220 pmol/liter) of neuropeptide Y (NPY)-like immunoreactivity (LI) compared to pig (30 pmol/liter) and man (25 pmol/liter). The platelet-enriched fraction (PEF), obtained from rat blood contained 10,061 pmol/g NPY-LI. However, in human and pig blood, the PEF contained very low levels of NPY-LI. Gradient centrifugation of rat blood showed the highest concentration of NPY-LI (10.8 +/- 0.4 pmol/g) in the platelet fraction. The mononuclear cell fraction contained 1.64 +/- 0.16 pmol/g, whereas only 0.56 +/- 0.06 pmol/g of NPY-LI was found in the red blood cell/polymorphonuclear cell fraction. Characterization of NPY-LI in rat plasma and platelets by high-pressure liquid chromatography showed one predominating peak which coeluted with synthetic NPY (1-36) as well as three minor peaks, one of which coeluted with oxidized NPY. Analysis of NPY messenger RNA (mRNA) in bone marrow of the rat revealed a 0.79-kb-long NPY mRNA. This size is intermediate to the 0.82-kb NPY mRNA in brain and the 0.76-kb NPY mRNA in spleen. The highest level of NPY mRNA in rat blood was found in the mononuclear cell fraction but NPY mRNA was also detected in the platelet fraction. No NPY mRNA was detected in bone marrow or blood from pig and rabbit or from human blood or bone marrow. Forty-eight hours after treatment of rats with vinblastine the content of NPY mRNA and NPY-LI in rat blood was decreased, while the level of NPY-LI in bone marrow was markedly enhanced. Reserpine treatment caused an increase in NPY mRNA content in bone marrow and spleen. After administration of dexamethasone the level of NPY mRNA increased in both spleen and peripheral blood cells with increased NPY-LI content in the spleen. It is concluded that in addition to megakaryocytes in spleen and bone marrow, platelets and possibly also lymphocytes/monocytes in peripheral blood of the rat contain NPY mRNA and peptide. The expression of NPY mRNA in bone marrow, spleen, and blood is influenced by vinblastine, reserpine, and dexamethasone.

Differential effects of transection of the spinal cord and splanchnic nerve on adrenal tyrosine hydroxylase and catecholamines

The role of spinal pathways in the regulation of adrenal medullary tyrosine hydroxylase and catecholamines was studied in adult rats subjected to spinal cord transection at the third thoracic level. In these animals the sympathoadrenal preganglionic neurons were isolated from their supraspinal afferents. This treatment led after three days to a progressive reduction of tyrosine hydroxylase activity and dopamine content (as compared to unoperated controls) until at least the 10th day. The results of the administration of dexamethasone or adrenocorticotropic hormone to spinalized rats suggest that in these animals glucocorticoid hypersecretion is not involved in the decline of adrenal tyrosine hydroxylase and that in fact adrenocorticotropic hormone supplementation can prevent it. A neurogenic origin for the depression of adrenomedullary function is favoured because unilateral splanchnicotomy (which by itself does not affect adrenal tyrosine hydroxylase), prior to cord section, prevented the diminution of tyrosine hydroxylase activity in the denervated gland. The decline of adrenal tyrosine hydroxylase and dopamine after spinal section may result from a decrease of modulatory impulses to the adrenal from decentralized sympathoadrenal preganglionic neurons in the isolated cord, following the loss of a descending facilitation of these neurons and/or the release of a segmental interneuronal inhibition of these neurons from a descending inhibitory influence. Such descending pathways may decussate partially below the low cervical level because rats with hemisection of the cord at C6-C7 exhibited no decline of adrenal tyrosine hydroxylase or of dopamine measured on either side seven days postoperatively.

Characterization of vinblastine-induced supersensitivity in the rat

A single dose of vinblastine (3 mg/kg, i.v.) in the rat produced a long lasting depletion of endogenous (-)noradrenaline (NA) in atria as well as in vasa deferentia, the depletion being greater in atria than in vasa deferentia. The maximum depletion of NA in atria occurred between 60 and 90 h after vinblastine, while in vasa deferentia the maximum depletion was 35%, 120 h after vinblastine. The 30 min in vitro uptake of (-)-(3H) NA in atria was inhibited between 78 and 83% at 30, 60 and 120 h after vinblastine. In vasa deferentia the maximum inhibition of 25% was seen 15 h after vinblastine, however the NA uptake had returned to control level between 60 and 120 h after vinblastine. The effect of vinblastine pretreatment on the sensitivity of atria to NA and (-)isoprenaline(ISOP), and of vasa deferentia to NA, (-)phenylephrine (PHE), and methoxamine (ME) was evaluated. It was found that atria became highly sensitive to the (+) chronotropic effect of NA without significant change in sensitivity to ISOP. The sensitivity of vas deferens to NA and PHE was moderately increased without significantly affecting the sensitivity to ME. The magnitude of the supersensitivity was expressed in terms of the ratio of the geometric mean ED50 of an agonist in control tissue to that obtained in the same tissue from treated animals. The sensitivity of atria to NA increased 1.5, 3.9, 7.8, and 6.7 fold, 15, 30, 60 and 120 h after vinblastine, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective noradrenergic denervation of the heart following intravenous injections of vinblastine or vincristine

1. The progressive effects of a single injection (3mg/kg i.v.) of either vinblastine or vincristine on the innervation of the rat atria have been examined. 2. Functional studies were performed by stimulating electrically the noradrenergic or cholinergic nerve fibres within isolated left atria from treated and control rats. In addition, the effects of the drugs on the ultrastructure of both types of nerve fibre were examined. The noradrenergic innervation was further examined by fluorescence histochemistry and measurement of the noradrenaline content of the atria. 3. On the basis of these studies it appeared that both drugs caused degeneration of noradrenergic nerves; cholinergic nerves seemed to be unaffected. Marked effects were seen 48 h after vinblastine treatment or 30 h after vincristine treatment. 4. Evidence is presented and discussed as to whether or not this action of the vinca alkaloids can be ascribed to their well-established effects on microtubules and intra-axonal transport processes.

Effects of vinblastine on noradrenergic axons

1 The effects of vinblastine and 6-hydroxydopamine (6-OHDA) on various parameters of adrenergic neurone functions in the rat were examined and compared.2 During the first 12 h after injection of vinblastine, although the concentration of cardiac noradrenaline was unaltered, the turnover rate of the catecholamine in the heart was reduced to 40 ng g(-1) h(-1) compared to a rate of 66 ng g(-1) h(-1) in the hearts of animals treated with 0.9% w/v NaCl solution.3 The uptake of noradrenaline by rat atria in vitro was inhibited by vinblastine (2.5 x 10(-4) M) or 6-OHDA (5 x 10(-5) M), but only the inhibitory effect of vinblastine was readily reversible. The in vitro uptake of noradrenaline by atria of vinblastine- or 6-OHDA-treated rats was found to be impaired two days after injection of the drugs. After 14 days, however, the noradrenaline uptake was 71% of control values after vinblastine and 91% after 6-OHDA.4 In addition to intensely fluorescent nerve trunks in epicardial connective tissue septa, a decrease in the number of fluorescent adrenergic terminals in the atria and ventricles could be observed two days after vinblastine injection. It is suggested that intravenous vinblastine treatment, like 6-OHDA, results in the destruction of adrenergic nerve terminals.