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Local venomotor response to intravenous infusion of substance P and glyceryl trinitrate in systemic sclerosis.

Endothelial injury has been shown in ultrastructural studies in systemic sclerosis (SSc). In the present study, we tested the functional response of the endothelium in the early phase of the disease and at a more advanced stage. Substance P (SP) (25 and 50 ng) and glyceryl trinitrate (GT) (100 and 200 ng) were infused intravenously in 6 control subjects and in 6 female patients affected with early systemic sclerosis (SSc) to verify whether or not a lack of endothelial function could be detected. Venous compliance was assessed with a linear variable differential technique. Endothelial injury was evaluated by the von Willebrand Factor Antigen (vWF:Ag) plasma level and platelet aggregation by the platelet aggregate ratio (PAR). Endothelial-mediated response to SP was deficient in SSc patients in comparison with controls, whereas endothelium independent vasodilation was detected after the infusion of GT both in patients and controls. All vWF:Ag levels were in the normal range while in vivo platelet aggregation was increased as demonstrated by the PAR levels in the SSc subjects. The experiment was repeated in the same patients when the clinical status worsened and the levels of vWF:Ag were noted to rise: the endothelium dependent vasodilatory response to SP was still deficient as before and a decrease in vasodilatory response to GT was noted. vWF:Ag levels were significantly increased and the PAR still demonstrated an increased platelet aggregation. These data clearly indicate that an early functional deficit of the endothelial function is present before the onset of extensive visceral and skin involvement. The mechanism that provokes the impairment of the endothelial function need further investigation.

Female↗
PubMed1977

Inhibition of canine adrenergic transmission by an analog of dopamine: GJH-166.

Experiments were conducted to investigate the effect of GJH-166 [Trans-4-methyl-7,8-dihydroxy-1,2,3,4,4a,5,6,10b-octahydrobenzo (f) quinoline HBr], a potential dopamine agonist, on responses to adrenergic vasoconstrictor stimuli in dogs. The hindlimb, gracilis muscle and spleen were isolated and perfused with arterial blood at constant flows. Responses of the nictitating membrane to adrenergic stimuli were aso studied. Intravenous injections of GJH-166 in doses of 0.25 to 4.00 micron/kg impaired responses to sympathetic nerve stimulation of the perfused hindlimb, gacilis muscle and spleen, and also inhibited responses of the nictitating membrane. GJH-166 had a preferential inhibitory effect on responses induced by low frequency stimulation of nerves. Haloperidol antagonized the inhibitory effect of GJH-166 on sympathetic transmission. The changes induced by norepinephrine at the perfused sites were not affected by the compound. Pressor responses to norepinephrine and tyramine were not inhibited by GJH-166. As a result of this study, the suggestion has been made that GJH-166 impairs sympathetic transmission by acting on certain inhibitory dopaminergic receptors located on the adrenergic nerve terminals.

Animals↗
PubMed1977

Peripheral vascular actions of alpha-methyldopa in the dog.

The aim of these study was to investigate peripheral vascular actions of alpha-methyldopa. The following experimental procedures were used: hind-limb of the dog perfused with the animals own blood or with Krebs solution; nictitating membrane of the dog; isolated and perfused segments of the saphenous vein of the dog; superfused strips of the saphenous vein of the dog. In these preparations, effects of alpha-methyldopa on responses elicited by electrical stimulation and on release of 3H-noradrenaline were studied. In dogs pretreated with alpha-methyldopa (200 mg/kg, i.v., 36, 24 and 4 hr before the experiment) contractions of the nictitating membrane caused by cervical sympathetic electrical stimulation were markedly reduced: however, the frequency--response curve to stimulation in the hind-limb and responsiveness to noradrenaline were not significantly different of controls. Perfusion of the hind-limb with Krebs containing alpha-methyldopa (2.2 mM) resulted in a significant reduction of perfusion pressure responses to lumbar sympathetic electrical stimulation with augmented responsiveness to exogenous noradrenaline. Similar results were obtained in in vitro experiments. Effects of alpha-methyldopa were not prevented by cocaine nor by inhibition of decarboxylase by Ro 4-4602 (D,L-serine,2-(2,3,4-,trihydroxybenzyl) hydrazine hydrochloride). Alpha-methyldopa depresses the release of tritiated compounds evoked by electrical stimulation, in saphenous vein strips. This suggests that inhibition of transmitter release could be an important factor to understand peripheral actions of alpha-methyldopa.

Animals↗
PubMed1987

Denervation augments alpha-2 but not alpha-1 adrenergic responses in canine saphenous veins.

Experiments were performed in order to determine the influence of sympathetic denervation on alpha-1 and alpha-2 adrenergic responses in canine saphenous veins. In female dogs anesthetized with sodium pentobarbital, the left lumbar sympathetic chain was excised from L1 to L7. After a 3- to 5-week period, the left (denervated) and right (innervated) saphenous veins were removed, cut into rings and suspended for isometric tension recording in organ chambers filled with modified Krebs-Ringer bicarbonate solution. Denervation reduced significantly the norepinephrine content of the venous rings and the contractile responses evoked by the indirect sympathomimetic amine, tyramine. The contractile responses evoked by exogenous norepinephrine were augmented by denervation under control conditions (16.7-fold shift in concentration-effect curve) and also after inhibition of neuronal and extraneuronal uptake and beta adrenoceptors (3.8-fold shift in curve). Denervation increased the contractile responses evoked by the alpha-2 adrenergic agonist, UK 14,304 (5-fold shift in concentration-effect curve), but not those produced by the alpha-1 adrenergic agonist, phenylephrine. The selective augmentation of alpha-2 adrenergic responses by denervation may reflect the preferential innervation of alpha-2 adrenoceptors in the canine saphenous vein.

Animals↗