Manabu Takita

Subtype selectivity of a new α1-adrenoceptor antagonist, JTH-601: comparison with prazosin

Abstract The existence of α1-adrenoceptors with low affinity for prazosin (α1L group: α1L and α1N subtypes) has been proposed in addition to α1-adrenoceptor subtypes with high affinity for prazosin (α1H group: α1A, α1B and α1D subtypes). A newly synthesized α1-adrenoceptor antagonist, JTH-601 (N-(3-hydroxy-6-methoxy-2,4,5-trimethylbenzyl)-N-methyl-2-(4-hydroxy-2-isopropyl-5-methyl-phenoxy) ethylamine hemifumarate) showed approximately a 10 times higher affinity for the α1L group, a similar affinity for the α1A subtype, but a more than 10 times lower affinity for the α1B and α1D subtypes when compared with prazosin. These results provide a further pharmacological evidence that α1-adrenoceptors with low affinity for prazosin exist in addition to those with high affinity for prazosin, suggesting that JTH-601 may be useful for characterising the α1-adrenoceptor subtypes.

Chronic nicotine treatment delays the developmental increase in brain muscarinic receptors in rat neonate.

Developmental increase in the muscarinic receptors ([3H]quinuclidinyl benzylate binding sites) of rat neonate brain (cerebral cortex and cerebellum) was significantly inhibited by chronic nicotine treatment of the dams during pregnancy and lactation. However, development of the nicotinic receptors ([3H]cytisine binding sites) was not inhibited and rather was up-regulated in the cerebral cortex and brainstem by the nicotine treatment. Such inhibition and up-regulation were not seen in nicotine-withdrawn rats after birth. These results suggest that nicotine treatment during lactation may cause a remarkable delay in development of muscarinic neurotransmission in rat neonates.

Heterogeneity of α1-adrenoceptor subtypes involved in adrenergic contractions of dog blood vessels

1 We determined the α1‐adrenoceptor subtypes involved in adrenergic contractions of eight different blood vessels isolated from the dog. 2 Noradrenaline produced concentration‐dependent contractions in all the blood vessels tested, which were competitively inhibited by prazosin, WB4101, HV723 and 5‐methylurapidil. However, there was considerable difference between the vessels with regard to the pKB values for all the antagonists. The α1‐adrenoceptors of dog vertebral and carotid arteries had high affinity for prazosin (pKB > 9.0) but low affinity for WB4101 (< 8.5), 5‐methylurapidil (< 7.5) and HV723 (≤ 8.5). By contrast, HV723 had higher affinity (> 9.0) than prazosin (< 8.3), WB4101 (< 8.7) and 5‐methylurapidil (< 8.2) in the portal vein, mesenteric artery and vein, and renal artery. In the femoral artery and vein, however, the four antagonists showed pKB values in the range 8.0–8.7. 3 Chloroethylclonidine (10 μm) produced a remarkable reduction of the contractile responses to noradrenaline in the vertebral and carotid arteries as compared with those in the other vessels. Nifedipine inhibited the responses to noradrenaline in all the tissues tested, and had marked effects in the portal vein. 4 Sympathetic adrenergic contractions induced by transmural electrical stimulation were also inhibited by prazosin and HV723 at different potencies among tissues. The relative potencies of both the antagonists paralleled the relationship in inhibiting the responses to exogenous noradrenaline in each vessel. 5 According to recent α1‐adrenoceptor subclassification, the present results suggest that the contractions of blood vessels induced by endogenous and exogenous noradrenaline are mediated through different α1‐adrenoceptor subtypes heterogeneously distributed in each vessel; presumably, the α1B subtype in the carotid and vertebral arteries, the α1N subtype in the visceral region and the α1L subtype in the femoral region. Regionally different expression of α1‐adrenoceptor subtypes may be in part associated with the regional heterogeneity of sympathetic responses in the blood vessels.

Cloning, functional expression and tissue distribution of rabbit alpha 1d-adrenoceptor.

We have cloned a cDNA encoding rabbit alpha 1d-adrenoceptor from the rabbit liver cDNA library. The deduced amino-acid sequence of this clone encodes a protein of 576 amino acids that shows strong sequence homology to previously cloned human, rat and mouse alpha 1d-adrenoceptors. The pharmacological radioligand binding properties of this clone expressed in COS-7 cells were similar to those of rat alpha 1d-adrenoceptors. Competitive RT/PCR assays revealed wide tissue distribution of the alpha 1d-adrenoceptor mRNA in rabbit, especially abundant in vas deferens, aorta, prostate and cerebral cortex.

Alteration of brain nicotinic receptors induced by immobilization stress and nicotine in rats

Immobilization stress (2 h.day-1, for 2 weeks) caused downregulation of the nicotinic receptors ([3H]cytisine binding sites) in the rat brain (cerebral cortex and midbrain). However, chronic nicotine treatment abrogated stress induced downregulation of the [3H]cytisine binding sites, suggesting that chronic nicotine treatment may block stress activated nicotinic receptor-mediated neurotransmission.

Effects of propranolol and atenolol on immobilization stress-induced hypertension and down-regulation of central β-adrenoceptors in rats

Effects of chronic treatment with propranolol or atenolol on stress-induced changes in blood pressure, body weight, and cerebral beta-adrenoceptors in rats were examined and compared with the effects of chronic treatment with prazosin. Immobilization stress (2 h daily for 2 weeks) induced a moderate elevation of blood pressure, loss of body weight gain, and downregulation of cerebral beta-adrenoceptors, but produced no changes in the cerebral alpha 1-adrenoceptors. Chronic administration of propranolol (5 or 50 mg.kg-1), atenolol (5 or 50 mg.kg-1) or prazosin (2 or 20 mg.kg-1) inhibited stress-induced hypertension but did not affect loss of body weight gain. Propranolol increased the density of cerebral beta-adrenoceptors by 77% and reduced the downregulation induced by stress. Atenolol also increased the density of cerebral beta-adrenoceptors by 34% and abolished the stress-induced downregulation in cerebral beta-adrenoceptor density. In contrast, prazosin had no effect on the cerebral beta-adrenoceptors in nonstressed or stressed rats. These results suggest that the antihypertensive action of propranolol and atenolol may be partly associated with the inhibition of stress-activated central beta-adrenoceptor transmission.

Effects of chronic treatment with (+)-nicotine on the stress-induced hypertension and downregulation of central nicotinic receptors in rats: comparative study with (-)-nicotine.

The effects of chronic treatment with (+)-nicotine on the immobilization stress-induced changes in blood pressure, body weight, and [3H]cytisine binding to brain nicotinic receptors were examined in rats and were compared with those of (-)-nicotine. Immobilization stress (2 hr/day(-1), for 2 weeks) induced a moderate elevation of blood pressure, loss of body weight gain, and downregulation of [3H]cytisine binding sites in cerebral cortex and midbrain. Chronic treatment with (+)- or (-)-nicotine inhibited the stress-induced hypertension but did not suppress the inhibition of body weight gain by stress. Body weight before stress load was also reduced by (-)-nicotine but not (+)-nicotine treatment. Treatment with each isomer increased the maximum number of [3H]cytisine binding sites (Bmax) of brain stem, cerebral cortex, and hippocampus. The Bmax in midbrain was also increased by (+)-nicotine but not by (-)-nicotine. Stress-induced downregulation in cerebral cortex was inhibited by both isomers. These results suggest that (+)- and (-)-nicotine cause various effects, including anti-stress effect, on the central nervous system in rats, which are slightly different between the isomers.

Cloning, functional expression and tissue distribution of rabbit αla-adrenoceptor

A cDNA clone, which has an open reading frame of 1398 nucleotides encoding a 466-amino-acid peptide, has been isolated from rabbit liver cDNA library. Compared with the peptide sequence, it shows high homology to alpha1a adrenoceptors of human, bovine and rat. We expressed this clone in COS-7 and investigated the pharmacological properties, revealing similarity to those of human alpha1a adrenoceptors. Competitive RT/PCR has detected the mRNA in variety of rabbit tissues, especially abundantly in liver, vas deferens, brain, and aorta, but not in heart.

Effects of bevantolol HCl on immobilization stress-induced hypertension and central β-adrenoceptors in rats

Effects of chronic treatment with bevantolol, a beta-adrenoceptor blocker, and of repeated immobilization stress on blood pressure, body weight, and [3H]dihydroalprenolol ([3H]DHA) binding to the cerebral cortex were examined in rats. Systolic blood pressure increased to approximately 150 mmHg when stress was applied for 14 days (2 h day-1). This increase was inhibited by chronic treatment with bevantolol (250 mg kg-1 daily). However, bevantolol did not suppress the inhibition of body weight gain by stress. The maximum number of [3H]DHA binding sites (Bmax) in the cerebral cortex was decreased by stress without changing the affinity, and the decrease in Bmax mainly reflected the reduction of beta 1-adrenoceptors. Bevantolol treatment (250 mg kg-1) increased the Bmax to 137% and completely inhibited the downregulation of beta-adrenoceptors by stress. These results show that bevantolol can inhibit both the hypertension and downregulation of the central beta 1-adrenoceptors induced by stress.

Chronic Treatment with Prazosin Causes a Subtype‐specific Increase in the α1‐Adrenoceptor Density of the Stressed Rat Cerebral Cortex

The effects of chronic treatment with prazosin and of immobilization stress on the α1‐adrenoceptor subtypes in rat cerebral cortex have been examined.