Fukio Konno

Comparison of the muscarinic cholinoceptors in the rabbit ciliary body and the guinea-pig ileum

Interactions of several muscarinic drugs with their receptors were studied in the ciliary body smooth muscle of rabbits and the ileal longitudinal muscle of guinea-pigs, using pharmacological and biochemical procedures. The dissociation constants of carbachol, pilocarpine, atropine and pirenzepine estimated by these procedures indicate no heterogeneity of muscarinic receptors in either tissue; thus both are probably of the M2 type. However, the density of the receptors in the ciliary body is lower than in the ileum. Pilocarpine, with lower intrinsic efficacy, demonstrated a pronounced organ selectivity when compared to carbachol as it was a potent full agonist in the ileum and a competitive antagonist in the ciliary body. These results suggest the importance of both receptor density and threshold as determinants of agonist potency.

Actions of tizanidine on α1- and α2-adrenoceptors in the peripheral tissues

Abstract 1. 1. Tizanidine behaved as the partial agonist on the α1-adrenoceptor in high doses (10−6−10−4 M) and as the α2-adrenoceptor agonist in low doses (3 × 10−9−10−6 M). 2. 2. Tizanidine is about one-third as potent as clonidine in α2-agonistic effects.

Newly synthesized α1-adrenoceptor blockers (SM911 and SM2470) and characterization of α-adrenoceptors in rat aortic strips, rat vas deferens preparations and rabbit aortic strips

Abstract 1. 1. α 1 -adrenergic potencies of SM911 and SM2470, whose chemical structures are similar to that of prazosin, a selective α 1 -adrenoceptor blocker, were tested in rabbit aortic strips, rat aortic strips and rat vas deferens preparations. 2. 2. SM2470 was as potent as prazosin in α 1 -adrenoceptor blocking effects, though SM911 was 0.5-0.1 as potent as prazosin. 3. 3. The p A 2 -values for prazosin, SM911 and SM2470 were approximately one order of magnitude lower in rabbit aortic strips and rat vas deferens preparations than in rat aortic strips, suggesting that α 1 -adrenoceptors in these tissues may not be identical. 4. 4. SM911 and SM2470 as well as prazosin did not interact with α 2 - and β-adrenoceptors, muscarinic and nicotinic cholinoceptors, and histamine and serotonin receptors in doses up to 10 −5 M.

Some pharmacological effects of tizanidine on smooth muscle organs and α2-adrenoceptor

1. 1.|Microsomal and crude synaptosomal fractions were prepared from the longitudinal muscle of guinea-pig ileum. 2. 2.|A specific binding of [3H]yohimbine (10 nM) to α2-adrenoceptor in the crude synaptosomal fraction was inhibited by tizanidine and clonidine. Tizanidine is about one-third as potent as clonidine. 3. 3.|A specific binding of [3H]QNB (0.3 nM) to muscarine receptor in the microsomal fraction was inhibited by atropine (10−8−10−7M) but not by tizanidine (up to 10−4M). 4. 4.|Tizanidine inhibited spontaneous movements of guinea pig ileum and rat stomach (in situ) and intestinal transit in mice, and induced mydriasis in mice. 5. 5.|These effects induced by tizanidine might be due to activation of α2-adrenoceptor but not to atropine like action.

PROTECTIVE EFFECTS OF ME3221 ON HYPERTENSIVE COMPLICATIONS AND LIFESPAN IN SALT-LOADED STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

1. A comparison was made on the protective effects of the following: ME3221, a competitive angiotensin AT1 receptor antagonist; losartan, in which a major active metabolite is a non‐competitive angiotensin AT1 receptor antagonist; and enalapril, an angiotensin‐converting enzyme inhibitor, using the salt‐loaded stroke‐prone spontaneously hypertensive rats (SHRSP).

EFFECT OF CHRONIC TREATMENT WITH ME3221 ON BLOOD PRESSURE AND MORTALITY IN AGED STROKE‐PRONE SPONTANEOUSLY HYPERTENSIVE RATS

1. The protective effect of ME3221, a surmountable AT1 antagonist, on the hypertension and its concomitant complications in aged (32 week old) stroke‐prone spontaneously hypertensive rats (SHRSP) was studied following long‐term (32 weeks) oral administration, and compared with those of losartan (metabolite EXP3174 is an insurmountable AT1 antagonist) and enalapril.

Interaction of newly synthesized N-cyclopropylmethyl derivatives of (−)-6β-acetylthionormorphine with opioid receptors

1. Analgesic activities of N-cyclopropylmethyl derivatives of (-)-6 beta-acetylthionormorphine, KT-89 and KT-90 and their interactions with opioid receptors were studied. 2. KT-89 and KT-90, as well as morphine inhibited the twitch response of the guinea-pig ileal preparation to electrical stimulation. Their pD2 values indicated that KT-89 and KT-90 are about 6.5 and 10 times as potent as morphine, respectively. In guinea-pig ileal preparation KT-89 and KT-90 also behaved as a mu-antagonist. 3. In rabbit vas deferens which contains kappa-receptors, these substances inhibited the twitch response to electrical stimulation and were about 6 times as potent as dynorphin. 4. Their effects on specific binding of [3H]naloxone (mu-selective ligand), [3H]ethylketocyclazocine (kappa-selective ligand) and [3H]D-Ala2-D-Leu5-enkephalin (delta-selective ligand) to the synaptosomal fractions from rat brain were tested. Though both drugs had a nonselectively high affinity to mu-, kappa- and delta-receptors, affinities of KT-89 and KT-90 to kappa-receptors were about 6 and 13 times higher than that of morphine, respectively. 5. Analgesic activities of KT-89 and KT-90 were 6 and 10 times as potent as morphine in an acetic acid-induced writhing test, and 4 and 5 times as potent in a pressure test. 6. The present results suggest that KT-89 and KT-90 induced analgesic actions are mediated through an activation of kappa-receptors. Both the drugs acted as delta-receptor antagonists. Further experiments are needed to study effects of their property as a delta-antagonist on analgesic action.

Involvement of threshold level in the contractile responses for some α1-adrenoceptor agonists in the rabbit iris dilators

1. The relationship between receptor occupancies and contractile responses for some alpha 1-adrenoceptor agonists were investigated in rabbit iris dilator smooth muscles. 2. Noradrenaline acted as a full agonists, while oxymetazoline and xylometazoline behaved as partial agonists with moderately higher intrinsic activity, and tizanidine and clonidine were partial agonists with lower intrinsic activity. 3. The pD2-values of oxymetazoline and xylometazoline were practically equal to the corresponding pKB-values, the negative log of dissociation constant, estimated by the partial irreversible blockade of alpha 1-adrenoceptors with phenoxybenzamine. However, the pD2-values of tizanidine and clonidine were significantly lower than the corresponding pKB-values. 4. The threshold phenomena lay between the receptor occupations and tissue responses, therefore, the pKB-values of partial agonists with lower intrinsic activity were different from their pD2-values. 5. These results suggest that the threshold phenomena in the tissue used may be an important factor in determining the agonist sensitivity.

Kappa-receptor mechanisms in synaptosomal Ca uptake.

1. Inhibition of Ca uptake by certain opioids was tested in synaptosomes of rat brain. The potency order was dynorphin A 1-13, a kappa-selective agonist greater than nalorphine greater than nalorphine epoxide greater than morphine. 2. The pA2 values (negative logarithms of dissociation constant) of naloxone against four opioids were not significantly different from each other, suggesting that the site of action of the four opioids is identical. 3. Morphiceptin, a mu-selective agonist and DADLE, a delta-selective agonist had no effect on Ca uptake. 4. These results suggest that the site of action of the four opioids is kappa-receptors. 5. Potency order estimated from competition inhibition curves of specific binding of [3H]ethylketo-cyclazocine (kappa-selective ligand) by the test opioids was nalorphine greater than nalorphine epoxide greater than dynorphin A 1-13 greater than morphine. 6. The difference between the two potency orders suggests that affinities and intrinsic activities of the drugs are important factors in determining their agonistic activity in kappa-receptor mechanisms.

Intrinsic activity and effects of guanyl-5′-yl imidodiphosphate, Gpp(NH)p and sodium ion on the affinity of dynorphin 1–13, nalorphine and nalorphine-7,8-oxide to kappa-opioid receptor

Nalorphine and nalorphine-7,8-oxide (nalorphine epoxide) behaved as partial agonists on the kappa-receptor in the electrically stimulated mouse vas deferens. The effects of a GTP-analogue, GppNHp and Na+ on the inhibition of [3H]ethylketocyclazocine binding by dynorphin 1-13, nalorphine, its epoxide and naloxone (antagonist) were studied with a synaptosomal fraction of guinea pig brain (except a cerebellum) and compared with the intrinsic activity of the test drugs, which was estimated in the electrically stimulated mouse vas deferens. The effects of GppNHp and Na+ on the affinity of the drugs to the kappa-receptor correlated with their intrinsic activities.