Effects of specific alpha-adrenoceptive agents on extraneuronal uptake (uptake2) of isoproterenol in perfused rat heart

Visualizing the Brain's Astrocytes with Diverse Chemical Scaffolds

Astrocytes are the most abundant cells in the brain. They support neurons, adjust synaptic strength, and modulate neuronal signaling, yet the full extent of their functions is obscured by the dearth of methods for their visualization and analysis. Here, we report a chemical reporter that targets small molecules specifically to astrocytes both in vitro and in vivo. Fluorescent versions of this tag are imported through an organic cation transporter to label glia across species. The structural modularity of this approach will enable wide-ranging applications for understanding astrocyte biology.

Expression and pharmacological profile of the human organic cation transporters hOCT1, hOCT2 and hOCT3

1. Organic cation transporters (OCTs) are involved in the elimination of monoamines and cationic xenobiotics. To examine whether some cell lines express several different OCTs, we investigated seven human cell lines for the mRNA expression pattern of the human (h) transporters hOCT1, hOCT2 and hOCT3. hOCT1 mRNA was found in all cell lines, six additionally expressed hOCT3 and only two cell lines contained all three hOCTs. 2. Among the three OCTs only for the OCT3 (also designated as 'uptake(2)' or 'extraneuronal monoamine transporter') 'selective' inhibitors are described in the literature. The affinities of the OCT3 inhibitors for the other two OCTs are largely unknown. Therefore, we compared the potencies of eight compounds as inhibitors of hOCT-mediated uptake of the organic cation [(3)H]-1-methyl-4-phenylpyridinium ([(3)H]-MPP(+)) in human embryonic kidney 293 (HEK293) cells stably expressing hOCT1, hOCT2 or hOCT3. Decynium-22 inhibited hOCT3 with 10 fold higher potency than hOCT1 and hOCT2. Corticosterone was about 100 fold more potent as inhibitor of hOCT3 than of hOCT1 or hOCT2, and O-methylisoprenaline (OMI) inhibited almost exclusively hOCT3. Progesterone and beta-Oestradiol preferentially inhibited hOCT3 and hOCT1, whereas prazosin was a potent inhibitor of hOCT1 and hOCT3. Phenoxybenzamine (PbA) inhibited with about equal apparent potency all three hOCTs, whereas the PbA derivative SKF550 ((9-fluorenyl)-N-methyl-beta-chloroethylamine) preferentially inhibited hOCT3 and hOCT2. 3. PbA reversibly inhibited hOCT1 and irreversibly hOCT2 and hOCT3; SKF550 also irreversibly inhibited hOCT3 but hOCT2 in a reversible manner. 4. These compounds enable a functional discrimination of the three hOCTs: hOCT1 is selectively inhibited by prazosin, reversibly inhibited by PbA and it is not sensitive to inhibition by SKF550 and OMI; hOCT2 is reversibly inhibited by SKF550, irreversibly by PbA and not by prazosin, beta-oestradiol and OMI, whereas hOCT3 is selectively inhibited by corticosterone, OMI and decynium22.

Alpha-adrenergic blocking drugs in the management of benign prostatic hyperplasia: interactions with antihypertensive therapy

Management of benign prostatic hyperplasia (BPH) is often complicated by concomitant hypertension, a life-threatening condition that must be managed optimally. Many of the alpha blockers used to treat BPH also decrease blood pressure, and terazosin and doxazosin have been shown to have significant cardiovascular side effects, such as asthenia/fatigue, postural hypotension, and dizziness when used to treat BPH patients. Furthermore, these drugs are not first-line therapies for hypertension, and the majority of hypertensive BPH patients will be receiving other antihypertensive agents. Therefore, it is possible that the introduction of these drugs will affect blood pressure control, at least temporarily, with possible adverse effects. In contrast, the selective alpha1A blocker tamsulosin does not appear to have significant cardiovascular side effects and produces minimal blood pressure reductions. Therefore, urologists can choose either to use alpha blockers to treat both hypertension and BPH or to treat BPH using alpha blockers that do not interact with antihypertensive therapy. This review focuses on the alpha blockers currently being used to treat BPH, their effects on the cardiovascular system, and their interaction with antihypertensive drugs.

Prazosin-induced blockade of extraneuronal uptake facilitates dopaminergic modulation of muscle twitches in rat vas deferens

Preliminary findings in our laboratory have shown that prazosin augmented the inhibitory effects of dopamine on the electrically-evoked muscle twitches in rat vas deferens. In this study, we opted to investigate the underlying mechanism and whether a prazosin-induced blockade of extraneuronal uptake process may be involved. Cumulative additions of dopamine (1.8 x 10(-7)-4.4 x 10(-5) M) elicited slight (< 30%) but dose-related inhibition of electrically-evoked (0.05 Hz, 1 ms duration and supramaximal voltage) muscle twitches of the vas deferens. Pretreatment with cocaine (10 microM), prazosin (50 nM) or oestradiol (10 microM) produced comparable potentiation of the inhibitory responses of dopamine; the pD2 values to dopamine amounted to 4.47 +/- 0.20, 4.72 +/- 0.21 and 4.56 +/- 0.19, respectively. A lower concentration of prazosin (5 nM) failed to alter dopaminergic responses. Further potentiation of dopamine responses was demonstrated in tissues preincubated with a combination of cocaine plus prazosin (50 nM), or cocaine plus oestradiol (pD2, 5.40 +/- 0.11 and 5.42 +/- 0.05, respectively). However, a mixture of all three drugs failed to elicit any further increase in dopamine responses, a finding that may suggest an extraneuronal uptake blocking activity for prazosin. Inhibition of muscle twitches evoked by bromocriptine, a dopaminoceptor agonist which is not a substrate for extraneuronal uptake, was not affected by prazosin (50 nM) pretreatment. The findings presented in this study emphasize the role of dopamine in modulating noradrenergic neurotransmission in rat vas deferens. More importantly, the results suggest that prazosin may act to block the extraneuronal uptake at noradrenergic sites, an effect that may account for its capability to facilitate dopaminergic modulation of noradrenergic neurotransmission.

Intracellular accumulation of isoproterenol enhances the lactate production in the perfused rat heart

Effects of intracellular accumulation of isoproterenol (ISO) on lactate production were examined in perfused rat heart. The lactate production during ISO perfusion in rat heart was increased and subsequent addition of an inhibitor of catechol-O-methyl transferase (COMT) further enhanced the production, and the enhanced production was significantly reduced by uptake2 inhibitor. The perfusion with ISO free-medium in the heart with high intracellular accumulation of ISO produced lactate more than that in the low intracellular accumulation. The present experiments demonstrated that the enhanced lactate production is accompanied by intracellular accumulation of ISO in the perfused rat heart, and suggested that the accumulated ISO may activate intracellular beta-adrenoceptors in the rat heart.