Recordings of multiunit sympathetic activity were made in muscle branches of the peroneal nerve in 22 healthy subjects at rest in recumbent position. Nerve activity was quantitated in terms of burst incidence (number of pulse synchronous sympathetic bursts per 100 heart beats or per min). In a separate session, 4-45 months later, blood was drawn from an antecubital vein for noradrenaline analysis. Both sympathetic activity and plasma concentrations of noradrenaline varied widely between subjects and both parameters increased with age. There was a significant positive correlation between a subject's level of sympathetic activity and his plasma concentration of noradrenaline. It is suggested that overflow of transmitter from sympathetic terminals in muscles contributes significantly to plasma levels of noradrenaline at rest.
Left coronary artery ligation was performed in pentobarbitone anaesthetised rats. Following 1/2 and 2 1/2 h of coronary artery occlusion or sham-operation the right and left ventricular myocardium and the interventricular septum were analysed for tissue content of catecholamines. In control rats and in rats with coronary artery ligation for various time periods (1/2, 2 1/2 and 5 h), the Hillarp-Falck fluorescence histochemical technique was used to visualise the catecholamines of the ventricular myocardium. The tissue noradrenaline content of the left ventricle was markedly reduced after 2 1/2 h of ischaemia while noradrenaline levels in the other parts of the ventricles were unaffected. The adrenergic innervation of the normal rat ventricles is described for the purpose of comparing the normal innervation picture with the appearance after ischaemia. A reduced catecholamine fluorescence was found mainly in the centre of the left ventricular free wall 30 min after coronary artery occlusion. After 2 1/2 and 5 h large areas of the ischaemic myocardium were found to be completely devoid of fluorescent terminals. The border zone between the areas of fluorescence disappearance and normally innervated myocardial tissue was generally quite sharp and occasionally terminals with a diffuse appearance were found in this zone. It is concluded that coronary artery ligation caused a time-dependent loss of noradrenaline from the adrenergic nerve terminals in the ischaemic myocardium. Catecholamine thus released may activate myocardial adrenoceptors and hence be related to increased ischaemic damage and ventricular arrhythmias.
1. Plasma noradrenaline and adrenaline were measured radioenzymatically in twelve hypertensive and four normotensive subjects before and during handgrip. In the resting arm (n=11), plasma noradrenaline increased by 17% (P<0.01) and plasma adrenaline by 27% (P<0.001). In the exercising arm, plasma adrenaline increased by 97% (P<0.005) but the mean increase of noradrenaline of 10% was not significant (P>0.1). 2. The noradrenaline response suggests a small and variable sympathetic adrenergic response; the significant difference (P<0.05) in adrenaline responses between resting and exercising arms may reflect local variation in tissue clearance.
The antihypertensive e f f e c t o f padrenoceptor antagonists manifests i t s e l f i n t h e course o f prolonged treatment as a gradual decrease i n peripheral resistance. I n manr cardiac output i s s i m i l a r l y reduced by acute and prolonged administration, whereas mean a r t e r i a l pressure (BPI i s lowered o n l y by long-term treatment as the r e f l e x l y increased peripheral resistance i s gradually reduced (Tarazi and Dustan, 1972). The mechanism underlying the apparent v a s o d i l a t a t i o n remains t o be c l a r i f i e d .Among the various mechanisms suggested, we have studied t h e possible interference w i t h the adrenergic vasomotor c o n t r o l i n experimental animals. I n the spontaneously hypertensive r a t (SHR), a s i n g l e i.v. dose o f metoprolol reduced heart r a t e without a f f e c t i n g BP whereas repeated a d m i n i s t r a t i o n by t h e i.v. o r o r a l route resulted i n BP reduction w i t h i n the f i r s t week o f a d m i n i s t r a t i o n (Ljung e t at. 1976). Furthermore, long-term a d m i n i s t r a t i o n o f propranolol o r metoprolol t o growing SHR has been shown t o prevent the development o f hypertension (Weiss e t e l . 1974). Long-term antihypertensive treatment was found t o be associated w i t h impaired vasoconstrictor responses t o sympathetic nerve s t i m u l a t i o n i n the i s o l a t e d p o r t a l v e i n (Ljung e t at. 1975) and w i t h reduced r a t e o f adrenal catecholamine synthesis (Zlblad e t a1.1977). -The present experiments were designed t o elucidate uhether any changes i n the adrenergic system found a f t e r long-term preventive treatment w i t h the B1-selective antagonist metoprolot could also be observed a f t e r short term c u r a t i v e antihypertensive treatment o f a d u l t SHR, and thus make i t possible t o d i s t i n g u i s h between secondary changes and primary e f f e c t s . MATERIAL AND METHODSFemale SHR o f t h e Okamoto s t r a i n (Hdllegaards avlsleb. A/S) were used. A long-term treated group was fed p e l l e t e d food containing 3 mg/g from the age o f 6 weeks f o r 6.5 months. The short-term treated group received c o n t r o l food during t h e i n i t a l 6 months o f the study and then the same d i e t w i t h metoprolol added f o r two weeks, whereas a c o n t r o l group received the standard d i e t throughout. I n the course o f the study long-term treated and c o n t r o l r a t s were housed i n metabolic cages f o r two weeks and u r i n e was c o l l e c t e d i n a c i d over 24 h periods during the 2nd week for determinrtion o f catecholamines by a radioenzymatic method.Towards t h g end o f the study chronic catheters were implanted i n t o t h e a o r t a v i a the l e f t femoral a r t e r y and e x t e r i o r i z e d i n t h e neck i n every second r a t o f each group. 4t t h i s time metoprolol a d m i n i s t r a t i o n was discontinued. Mean a r t e r i a l blood pressure and heart r a t e (HU) were continously monitored i n a computer based system during ...
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