[Effect of monoiodoacetate and ouabain on cholinergic vasodilation in cat skeletal muscles]. / Vliianie monoiodatsetata i uabaina na kholinérgicheskii rasshiritel'nyi éffekt v sosudakh skeletnykh myshts koshki.

The effects of a glycolysis blocking agent monoiodoacetate and of the sodium pump blocker ouabain, on cholinergic vasodilatation in skeletal muscle were studied. In acute experiments on cats, i. v. administration of monoionoacetate eliminated both the cholinergic vasodilation and the increase in the osmotic pressure of the venous blood. I. v. injections of ouabain also abolished the vasodilatative effect of the sympathetic chain stimulation and of intraarterial injection of acetylcholine. Ouabain had no effect on the development of a sympathetic vasoconstrictive response and the vasodilative effect caused by intraarterial injection of papaverine. The data obtained indicate that cholinergic vasodilative response is due to activation of anaerobic metabolism in skeletal muscle and that hyperosmolarity resulting from the enhanced Na+ transport is a key link between tissue metabolism and vascular tone.

Increase in osmolality of venous blood from skeletal muscle during cholinergic vasodilatation.

The arterio-venous difference in the osmolality of blood plasma of cat m. triceps surae was studied during sympathetic cholinergic nerve excitation. The vasodilatation was induced by stimulation of hypothalamus or the sympathetic chain, the latter after alpha-adrenoceptor blockade. The vasodilator effect induced by intraarterial injection of acetylcholine was also tested. In all cases studied the vasodilatation was associated with an increase in osmolality (on the average by 10 mOsm/kg H2O with a maximum at the 30-40th s after the beginning of stimulation). Atropine (0.1 mg/kg) considerably decreased the vasodilator effect elicited by hypothalamic stimulation. The increase in osmolality was much smaller after atropine, a small peak remaining at the 50-60th s after the beginning of stimulation. The latter effect was blocked by propranolol (0.5 mg/kg). Atropine similarly almost completely abolished the vasodilator effect and the increase in osmolality produced by lumbar sympathetic stimulation and acetylcholine. The increase in osmolality was caused by a rise in the contents of Na+ (7.4%), lactate (8.2%) and K+ (13.2%); Ca2+, inorganic phosphate and total protein concentrations remained unchanged. Our data indicate that acetylcholine released by sympathetic endings activates muscle fibre metabolism via the muscarin-receptors. The increase in tissue osmolality resulting from activation of metabolism causes, at least partly, the vasodilator effect.

[Changes in plasma composition resulting in an increase in the osmotic pressure of venous blood during the cholinergic dilatation effect]. / Izmeneniia sostava plazma, privodiashchie k uvelicheniiu osmoticheskogo davleniia venoznoi krovi pri kholinergicheskom rasshiritel'nom éffekte.

Stimulation of the sympathetic chain in the presence of alpha-receptor blocking agents caused cholinergic vasodilatation of the cat hind-limb vessels. The arterial-venous difference with respect to osmotic pressure (Posm), as well as to the content of K+, Na+, Ca2+, lactate, total protein, and inorganic phosphate was determined in blood samples collected during vasodilatation. Sympathetic stimulation in the presence of alpha-receptor-blocking agents agents increased the conductance of the hind-limb vessels and Posm of the venous blood (7.6 +/- 0.8 mOsm/l); both effects were abolished by atropine. During vasodilatation the content of K+, Na+ and lactate in venous blood plasma was increased, while that of total protein, inorganic phosphate and Ca2+ remained unchanged. The increase in Posm (73.7%) was found to be due to the rise in Na+. The data obtained suggest an increased intensity of metabolism in skeletal muscle during cholinergic vasodilatation.

[Cholinergic sympathetic influences on blood flow and cyclic nucleotide concentration in skeletal muscles]. / Kholinergicheskie simpaticheskie vliianiia na krovotok i soderzhanie tsiklicheskikh nukletotidov v skeletnykh myshtsakh.

The content of 3.5 cGMP increased twofold and the content of 3.5 cAMP remained unchanged in the cat skeletal muscle during vasodilatation evoked by hypothlalamic stimulation. Cholinergic vasodilatation increased also phosphorylase activity by 90%. These effects were blocked by atropine. Possible existence of an interrelationship among the vasodilator effect, phosphorylase activity and increase in cGMP, is discussed.

The content of cyclic nucleotides (3',5'-cGMP and 3',5'-cAMP) in cat skeletal muscle during sympathetic cholinergic vasodilatation.

Phosphorylase activity and content of cyclic GMP and AMP were investigated in the gastrocnemius muscle of the cat during the development of cholinergic vasodilatation evoked by stimulation of the hypothalamus. Samples of muscle tissue were taken during an early stage of the vascular effect. One of the hindlimbs was denervated and served as control. With the development of the dilator response the conductance in the bed of the femoral artery increased by 143 +/- 12%, phosphorylase "a" activity reached 76.1 +/- 2.1% of the total phosphorylase activity as compared with 49.2 +/- 1.9% in the control, the content of cGMP increased approximately 2-fold. The content of cAMP remained unchanged. All these effects - the increase in blood flow, phosphorylase activation and the increase in cGMP content - were abolished by atropine. It is suggested that acetylcholine, released by sympathetic endings during hypothalamic stimulation, has the effect of increasing the level of intracellular cGMP and that the vasodilatation is secondary to the metabolic changes.

Cholinergic and adrenergic influences upon cat skeletal muscle performance induced by stimulation of the anterior hypothalamus.

The influence exerted by stimulation of the anterior hypothalamus (zone of cholinergic vasodilatation) on the performance of triceps surae during tetanic contraction has been investigated. Hypothalamic stimulation, if combined with indirect muscle stimulation, improves muscle performance, i.e. slows down the rate of decrease of contraction. The effect is abolished by atropine (0.5 mg/kg) and insensitive to propanolol (0.1 mg/kg). The cholinergic influence is only effective if hypothalamic stimulation coincides with the beginning of motor nerve stimulation. In some of our experiments stimulation of the same central structures elicited another influence on muscle performance, associated with the release of adrenaline into the blood. In this case, contrary to the cholinergic influence, the force of contraction increases only when hypothalamic stimulation does not start earlier than 100 s after the initiation of contraction (phase of slow decline of tension). The effect is insensitive to atropine (0.1 mg/kg) and abolished by propanolol (0.1 mg/kg).

Activation of anaerobic metabolism in cat skeletal muscle during cholinergic sympathetic vasodilatation.

Phosphorylase activity was found to increase 2-fold as compared with the control value (79% and 39% respectively) within the first 2-3 s of the vasomotor effect elicited in the skeletal muscle by sympathetic stimulation. Phosphorylase activity was still high during the period of maximum blood flow, although to a lesser extent (54% and 45%). During the phase of restoration of the initial rate of blood flow the values of phosphorylase activity were the same in the experimental and the control sample. The AMP content did not increase with the initiation of the vasomotor effect, and this fact suggests that the increase in phosphorylase activity is due to an increase in phosphorylase "a" rather than to the activation of phosphorylase "b" by AMP. Atropine blocks both the dilator effect and phosphorylase activation elicited by sympathetic stimulation. Acetylcholine, injected intraarterially or added to a muscle homogenate, increases phosphorylase activity. It is concluded that acetylcholine, released by sympathetic nerve endings, performs a second mediator function, that of activating anaerobic metabolism in the skeletal muscle. The two mediator functions of acetylcholine seem to be spatially delimited.

[Effect of acetylcholine on phosphorylase from skeletal muscle]. / Deistzie Atsetilkholina Na Fosforilazi Skeletnoi Myschtsy

Acetylcholine (1-10(-5) g/ml) was shown to increase the content of active form of phosphorylase A in homogenate of cat skeletal muscle. Atropine (1-10(-5) g/ml) diminished acetylcholine-induced increase in the phosphorylase activity from 22% to 5.28%. Activating effect of acetylcholine was observed also in superatant (105000 g), although it was 2-fold decreased. No acetylcholine-induced phosphorylase activation was observed in the presence of Mg2+. Addition of Ca2+ (2.2-10(-14) M) did not affect considerably the activation process. It is concluded that the mechanism of acetylcholine-induced phosphorylase activation is different from the effect of adrenaline on phosphorylase.