The influence of H1- and H2-receptor blockade on responses of resistance and capacitance vessels to noradrenaline in working skeletal muscles in cats.

The effects of an H1- and H2-histamine receptor blockade upon the responses to noradrenaline (NA) of pre- and post-capillary segments of the microcirculation of the hind leg of cats were investigated. The responses to the resistance and capacitance vessels to noradrenaline injected in the coll. of femoral artery were reflected as changes in peripheral vascular resistance and in tissue volume respectively and determined during the following exercise before and after the H1 and H2-histamine receptor blockade. Muscular exercise was induced by sciatic nerve stimulation. The results show that H1- and H2-histamine receptor blockade applied together unmasked the vasodilator effects in both NA and that muscle exercise potentiated these effects in both pre- and post-capillary sections. This suggests that histamine may inhibit the response of the resistance and capacitance vessels in the working skeletal muscles to noradrenaline.

Influence of alpha and beta adrenergic receptors blockade on the adrenolytic effect of muscular work.

The changes in the response of adrenergic receptors alpha and beta in the blood vessels in the working muscles in a hindlimb in cats were studied after intra-arterial administration of noradrenaline, isoprenaline and during electric stimulation of the sympathetic trunk. The experiments were carried out during alpha-adrenergic receptors blockade with dihydroergotamine (0.3 mg/kg) beta-adrenergic receptors blockade with propranolol (1 mg/kg) and blockade of acetylcholine M receptors with atropine (0.5 mg/kg). The investigations were performed at rest, during exercise (electric stimulation of the sciatic nerve) and after the exercise. The following results deserve attention: 1) beta-adrenergic receptors blockade reduced significantly the alpha-adrenolytic effect of exercise restoring the ability of blood vessel to constriction in response to noradrenaline; 2) the vasodilator effect of isoprenaline evident in resting state and maintained to some extent during exercise was abolished completely by preceding alpha-adrenergic blockade. The changes in the reactivity of resistance vessels in working skeletal muscles to noradrenaline, with abolition of its vasoconstrictor effect, have been shown by Rein [7] and others authors [2, 5]. Similarly, it is well known that the resistance vessels contain two types of adrenergic receptors alpha and beta, and that the response of the vessels to stimulation of these receptors are different [1]. In view of the recently published observations of Jarhult and Lundvall suggesting that the beta-adrenergic receptors play an important physiological role [6] in the arterial part of the microcirculation [6] and in view of the hypothesis put forward by Kunos and Szentivanyj that alpha and beta receptors can be transformed depending on the intensity of tissue metabolism [8] it seemed worth while to study more systematically the changes of the reactivity of alpha and beta adrenergic receptors in the vascular bed of the skeletal muscles during and after muscle exercise.

Comparative investigations of aspirin and indomethacin effects on blood flow in the vascular bed of skeletal muscles at rest and during muscle contractions in dogs and cats.

The effecs of two different inhibitors of prostaglandin synthesis--aspirin and indomethacin--on the blood flow in the vascular bed of the hindleg of vagotomized animals were studied before, during and after muscular activity of this limb. The responses of resistance and capacitance vessels were recorded simultaneously. Muscular contractions were evoked stimulating electrically (4 impulses/second) the peripheral part of the sciatic nerve. It was found that both inhibitors reduced exercise hyperaemia and postexercise hyperaemia. The response of the capacitance vessels was also reduced during muscular contractions. The obtained results confirmed that endogenous prostaglandins participate in the vascular response during exercise in the precapillary and postcapillary sections of microcirculation in the muscles. The particularly important effect of aspirin on postexercise hyperaemia in dogs in relation to cats is stressed.

Muscular work and the release of prostaglandin-like substances.

Experimental evidence for the release of prostaglandin-like substances, mainly of the E type, into the venous outflow from working skeletal muscles in the dog is described. Muscular exercise of the hind-leg produced by sciatic nerve stimulation evoked the release of prostaglandin-like substances detected in femoral venous blood by the bioassay method. This release occurred during and after muscular work, was abolished by indomethacin, and was not present in gallamine-treated dogs. The results suggest that endogenous vasodilator prostaglandins released during and after muscular work may contribute to local hyperaemic response during and, mainly, after muscular activity.

Effects of acetylcholine and other vasodilatory substances in the vascular bed of skeletal muscles during and after muscular contractions.

In dogs and cats perfusion pressure or femoral venous outflow and changes in the volume of the hind limb were measured. The influence of muscular contractions on the effects of acetylcholine, histamine, isoprenaline and papaverine in the vascular bed of the limb was investigated. It was found that after muscular excerise the effects of i. a. injection of acetylcholine into the isolated limb were markedly potentiated, whereas the effects of histamine and isoprenaline were diminished.

The influence of muscular contractions on acetylcholine effects on nutritive blood flow in the hindpaw of dog.

In the earlier investigations it was shown that muscular exercise augmented the dilator effects of ACh in the vascular bed of the hind leg of dog. To get a closer insight into this phenonenon the effects of acetylcholine on the nutritive blood flow in contracting skeletal muscle in the dog were studied. It was found that i.a. acetylcholine administration raises the nutritive blood flow in the investigated vascular bed within about 30--36 minutes after muscular contractions. The nutritive blood flow during and following muscular contractions induced by stimuli of varying frequency was also investigated.