Selectivity of oxymetazoline for urethral pressure vs blood pressure in the anaesthetized female rabbit.

OBJECTIVE: The aim of this study was to test alpha-adrenergic reference agonists for tissue selectivity in the urethra and to pharmacologically characterize the functional alpha-adrenoceptor type of the female rabbit urethra in vivo. MATERIAL AND METHODS: The effect of alpha-adrenergic agonists and antagonists on the urethral pressure was compared with that on blood pressure and heart rate measured simultaneously in the anaesthetized female rabbit. RESULTS: Oxymetazoline, NS-49, phenylephrine and phenylpropanolamine enhanced the urethral pressure in a dose-dependent manner. Phenylephrine and phenylpropanolamine also enhanced the blood pressure with significantly lower ED50 (dose that gives half of the maximal enhancing effect) values than for the urethral pressure. This was in contrast to oxymetazoline and NS-49. The ED50 values for oxymetazoline on urethral pressure, and systolic and diastolic blood pressure were 0.00067, 0.0030 and 0.0020 mg/kg, respectively. The ED50 values for NS-49 on urethral pressure, and systolic and diastolic blood pressure were 0.019, 0.21 and 0.18 mg/kg, respectively. Clonidine and UK 14,304 had no effect on urethral or blood pressure. The oxymetazoline-evoked increase in urethral pressure was inhibited by WB-4101 with an ID50 (dose that gives half of the inhibitory effect) significantly lower than that for rauwolscine. CONCLUSIONS: The results suggest that in the female rabbit in vivo activation of alpha1-adrenoceptors increased the urethral pressure. Phenylephrine and phenylpropanolamine, in contrast to oxymetazoline and NS-49, selectively enhanced blood pressure as compared with urethral pressure. Provided that the present results also have validity in humans, it would seem possible to develop urethra-selective drugs for treatment of stress incontinence with few or no cardiovascular side-effects.

Lesioning of locus coeruleus projections by DSP-4 neurotoxin treatment: effect on amphetamine-induced hyperlocomotion and dopamine D2 receptor binding in rats.

DSP-4 is a neurotoxin highly selective for the noradrenergic nerve terminals of the locus coeruleus projections. Data on the effect of DSP-4 treatment on amphetamine-induced hyperlocomotion are contradictory. In this study, DSP-4 (50 mg/kg) caused reduction of noradrenaline levels by 70% in the cerebral cortex and by 79% in the cerebellum. This treatment resulted in upregulation of dopamine D2 receptors in the striatum as evidenced by [3H]-raclopride binding. In an open field test, DSP-4 reduced locomotor activity. D-Amphetamine (1.5 mg/kg) caused a similar increase in locomotor activity in control and DSP-4-pretreated animals not familiar to the apparatus. However, when the rats were habituated to the test apparatus, the effect of amphetamine on horizontal activity was significantly larger in the DSP-4-pretreated animals. These data suggest that supersensitivity of D2 receptors develops after locus coeruleus denervation, but that the enhanced efficacy of amphetamine in DSP-4-treated rats is masked by neophobia.

Pharmacological characterisation of the enantiomers of BM-5, a muscarinic partial agonist with opposed enantioselectivity between affinity and efficacy.

The interaction of (R) and (S) enantiomers of the chiral oxotremorine analogue BM-5 with muscarinic acetylcholine receptors was studied in vitro using radioligand binding and isolated tissue preparations. The in vivo effects of (R)-BM-5 were also studied in anaesthetised cat. No receptor or tissue selectivity was found for either enantiomer in radioligand binding studies in cells expressing human muscarinic receptors (M1-M5) or in guinea pig tissues. The affinity of (R)-BM-5 was about 40 times, or 15-60 times higher than that of (S)-BM-5 in recombinant cells or in guinea pig tissues, respectively. Both enantiomers induced contraction of the guinea pig isolated urinary bladder and ileum. (R)-BM-5 was more potent than (S)-BM-5 in bladder (EC50 590 and 3500 nM, respectively) and in ileum (EC50 39 and 2600 nM, respectively). The maximal agonist effect was lower for (R)-BM-5 than for (S)-BM-5 in bladder (2.7% and 6.6%, respectively) and in ileum (32% and 48%, respectively). Contractions were completely inhibited by atropine (1 microM). In vivo, (R)-BM-5 induced bladder contraction and salivation after intravenous administration in the anaesthetised cat (ED50 4.1 and 6.2 microg kg(-1), respectively). In conclusion, (R)- and (S)-BM-5 act as partial muscarinic agonists in the isolated bladder and ileum. (R)-BM-5 was the more potent enantiomer but had a lower maximal agonist effect giving an opposed enantioselectivity for affinity and efficacy. (R)-BM-5 showed agonist activity in vivo, confirming in vitro findings. From affinity and efficacy data it can be concluded that the effects of racemic BM-5 are mediated by the (R)-enantiomer.

Chronic mild unpredictable stress after noradrenergic denervation: attenuation of behavioural and biochemical effects of DSP-4 treatment.

Chronic mild unpredictable stress, which reduces rewarded behaviour in rats, is becoming increasingly popular as an animal model of depression. The effect of chronic mild stress (applied to animals housed five per cage for 15 days) on forced swimming and open field behaviour, and on beta-adrenoceptor binding was studied in naive rats and after the denervation of the locus coeruleus projections by DSP-4 (50 mg kg(-1)) treatment. In the forced swimming test, chronic mild stress reduced the immobility time on the second day of testing in both vehicle- and DSP-4-treated rats, indicating rather an antidepressant-like effect. This antidepressant-like effect of chronic mild stress in the forced swimming test was not present in individually housed rats which suggests that this paradigm is sensitive to housing conditions. Stress had no clear effect on the open field locomotion in naive animals (but caused a reduction in defecations), but completely blocked the DSP-4-induced decrease in the exploratory activity. As measured by 3H-dihydroalprenolol binding, DSP-4 treatment increased the beta-adrenoceptor affinity in the frontal cortex and the number of binding sites in the hippocampus and in the cerebral cortex (total-frontal cortex). Stress had no effect on the beta-adrenoceptor binding in the frontal cortex and cerebral cortex, but prevented the increase in affinity caused by DSP-4 treatment in the frontal cortex. In the hippocampus, chronic mild stress and DSP-4 treatment increased the number of beta-adrenoceptor binding sites. Neither chronic mild stress nor DSP-4 treatment had any effect on CCK(B) receptor binding in the cerebral cortex and striatum. These results show that chronic mild stress applied to group-housed rats can prevent the development of certain behavioural and biochemical changes caused by the denervation of the locus coeruleus projection areas.

Ethylmorphine O-deethylation cosegregates with the debrisoquin genetic metabolic polymorphism.

The single oral dose kinetics of ethylmorphine and its fractional metabolic clearance by O-dealkylation and N-dealkylation was investigated in five extensive and four poor metabolizers of dextromethorphan. In addition, the urinary metabolic ratios for these pathways (MRO and MRN, respectively) were investigated in a larger group of 27 extensive metabolizers and six poor metabolizers. The mean values for the fractional metabolic clearance by O-dealkylation and the MRO differed significantly between the poor metabolizers and extensive metabolizers without overlap between the values of either of these parameters in the two groups of subjects. In contrast, the corresponding parameters for the N-demethylation did not differ between poor metabolizers and extensive metabolizers. The area under the plasma concentration versus time curve was significantly higher (about three times higher) in the poor metabolizers compared with the extensive metabolizers (p = 0.004). Our data suggest that ethylmorphine is O-deethylated by the cytochrome P4502D6 isozyme inasmuch as both the fractional metabolic clearance by O-dealkylation and the MRO were found to cosegregate with the phenotype for the O-demethylation of dextromethorphan in our group of subjects.