Abstract-Phenylephrine, a selective a-adrenergic stimulant, caused a maximal re laxation of the taenia from guinea pig caecum in the concentration of 10-6 g/ml. Phenylephrine in this concentration did not influence intracellular cyclic AMP and cyclic GMP levels. Although phenylephrine abolished the spontaneous spike discharge, no change was detected in "Ca-uptake and "Ca-efflux on the tissue level after phenyl ephrine. Ca-uptake and Ca-release on the subcellular level were also not influenced by phenylephrine.In Ca free-solution phenylephrine inhibited the response to CaCl2. Phenylephrine increased 42K-efflux in the normally polarized taenia and also in the K-depolarized taenia.Adrenoceptors were classified as a and 3-receptors by Ahlquist (1). As a rule, a receptor is associated with the excitatory functions and 3-receptor with the inhibitory functions. Exceptionally, stimulation of a and (9-receptors in an intestinal smooth muscle causes a relaxation (2). But the inhibitory responses mediated through a and (3-receptors are independent as to mechanical effects and metabolic effects (3).It was reported that stimulation of Q-adrenoceptors elevates the intracellular levels of cyclic AMP and facilitates Ca-accumulation (4). However, little is known of the mechanisms involved in the responses mediated through a-adrenoceptors, except that an a-adrenoceptor stimulant increases K-permeability (5-7). We carried out studies on the effects of an a adrenoceptor stimulant on tissue levels of cyclic nucleotides, Ca-movement and K permeability.
MATERIALS AND METHODS
Phenylephrinewas used as the a-adrenergic stimulant.Male guinea pigs (300-400 g)were sacrificed by a blow on the neck and two pieces of taenia were removed from one caecum and suspended in two 30 ml organ baths filled with physiological solution kept at 32'C and bubbled with air. One was used for measuring the control levels of cyclic nucleotides and the other for estimating the change in levels of cyclic nucleotides after one min treatment with phenylephrine in the presense of propranolol. They were frozen in liquid nitrogen.Cyclic AMP was assayed with the method of Gilman (8)
Dopamine relaxes catch contraction in the anterior byssus retractor muscle of Mytilus edulis and is present in the ganglia of Mytilus (1, 2). However, little is known of dopamine receptors in this muscle. We investigated the effects of dopamine and its derivative on catch contraction of this muscle and compared the findings with the effects of alpha and beta-adrenoceptor stimulants.
MATERIALS AND METHODSSea mussels, Mytilus edulis L., collected from the east side of Tokyo bay were used. Mytilus edulis were stored in aerated artificial sea water (NaCI 456 mM, KCI 11 mM, CaCI22H2O 11 MM, MgC126H2O 48 mM and Tris-HCI 25 mM; pH 7.8-8.0) at a temperature of about 10°C and used within 7 days after collection.Muscle bundles (about 1 mm in diameter) dissected from the anterior byssus retractor muscle under a pair of forceps were suspended in 10 ml organ bath filled with artificial sea water bubbled with air and kept at 23 to 25'C. Responses to drugs were recorded isotonically under a tension of 0.2 g. After a 1 hr immersion, the muscle was exposed to acetylcholine (10-4 M) for 2 min and washed with artificial sea water. We used the muscle in which the relaxation at 5 min after washout of acetylcholine was less than 25% of the maximum relaxation which was obtained by application of serotonin (10-6 M). The test drugs were applied at 5 min after washout of acetyl choline and relaxations following a 10 min exposure to the test drugs were estimated. In order to estimate the maximum relaxation, serotonin (10-6 M) was applied after the
Abstract-Effects of anti-asthmatic drugs on airway resistance and plasma level of cyclic AMP were investigated in guinea pigs sensitized and non sensitized with egg-albumin.
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