A method for the study of mechanisms of drug disposition in smooth muscle

1969

British J Pharmacology

Self Cite

129

Hydrocortisone potentiates responses to adrenaline and noradrenaline in aortic strips by inhibiting their inactivation by catechol-O-methyl transferase (Kalsner, 1969). It was of interest to determine whether other steroid hormones also enhance responses to catecholamines and decrease their rate of inactivation by 0-methylation. In the present study the effects of 17f-oestradiol, progesterone and desoxycorticosterone on responses to a variety of sympathomimetic amines were investigated. MethodsRabbit aortic strips, prepared according to Furchgott (1960), were suspended under 2 g tension in 15 ml. chamibers containing Krebs-Henseleit (Krebs) solution

Section: Methodsmentioning

confidence: 99%

Steroid potentiation of responses to sympathomimetic amines in aortic strips

1969

British J Pharmacology

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129

“…This trapped a fixed quantity of drug in the tissue. The rate of relaxation of aortic strips in oil can then be equated with intrinsic inactivation of drug involved in the response (11). The possibility must be considered that compounds with high lipid solubility could escape from the tissue aqueous phase during oil immersion.…”

Section: Methodsmentioning

confidence: 99%

Mechanism of Hydrocortisone Potentiation of Responses to Epinephrine and Norepinephrine in Rabbit Aorta

1969

Circulation Research

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199

Hydrocortisone potentiated responses of rabbit aortic strips to catecholamines (epinephrine, norepinephrine, nordefrin, isoproterenol) but not to amines lacking the catechol nucleus (phenylephrine, synephrine, methoxamine). Contractions in response to epinephrine were increased much more than those to norepinephrine. Neither the presence of cocaine nor pretreatment of the rabbits with reserpine impaired the potentiating action of hydrocortisone. Experiments with the oil immersion technique (to prevent loss of amine by diffusion from the tissue) demonstrated that hydrocortisone reduced the rate at which aortic strips inactivated epinephrine, apparently by inhibiting catechol-O-methyl transferase (COMT). Known inhibitors of COMT (U-0521, tropolone, pyrogallol) potentiated responses of aortic strips to epinephrine much more than to norepinephrine and also enhanced responses to isoproterenol and nordefrin to the same extent as did hydrocortisone. Known inhibitors of COMT consistently abolished the enhancing effects of hydrocortisone without materially interfering with potentiation produced by cocaine which is mediated through an independent mechanism unrelated to amine inactivation. Hydrocortisone also abolished the enhancing effects of known COMT inhibitors. It is concluded that hydrocortisone enhances the responses of vascular smooth muscle to epinephrine and norepinephrine by inhibiting a major enzymatic pathway for the inactivation of these amines. Others have observed that responses of the conjunctival vascular bed of rabbits and man to norepinephrine were potentiated 15 minutes after local application of hydrocortisone or cortisone (3,4).Several reports indicate that hydrocortisone potentiates the pressor effects of epinephrine but not that of norepinephrine in the cat, rabbit, and dog (5, 6). In agreement with these findings, Kadowitz and Yard (7) observed that the blood vessels of the denervated and pump-perfused hindquarters of cats show an increased constriction in response to epinephrine but not to norepinephrine after hydrocortisone. However, in-vitro preparations of arterial smooth muscle show increased responsiveness to both epinephrine and norepinephrine within several minutes after exposure to hydrocortisone (6,8,9).

“…This process of relaxation towards the pre-contraction baseline rpflects the rapidly declining concentration of agonist in the vicinity of receptors due to efficient intrinsic processes of inactivation and also removal by diffusion into the surrounding bathing medium (Kalsner & Nickerson, 1968a, b) (Figure la, Table 1). As shown in Table 1, inhibition of neuronal uptake alone, with cocaine, only had a slight effect on the relaxation rate of strips contracted by adrenaline whereas inhibition of extraneuronal uptake with GD-131 produced a material slowing of relaxation, reflecting the importance of this latter process in termination of action, even in the presence of a competing gradient of diffusion of the agonist into the external bathing medium (Table 1, Figure 1).…”

Section: Relaxation Of Adrenaline-and Noradrenalinecontracted Strips mentioning

confidence: 99%

Role of Extraneuronal Mechanisms in the Termination of Contractile Responses to Amines in Vascular Tissue

1975

British J Pharmacology

1The role of the uptake and release of agonist from extraneuronal sites in the termination of responses of rabbit aortic strips to amines was studied. 2 Strips were contracted with adrenaline or noradrenaline and after a response plateau was reached, the muscle chambers were washed free of agonist and the relaxation in Krebs solution recorded. After inhibition of catechol-O-methyl-transferase, monoamine oxidase and neuronal uptake the relaxation rate was greatly prolonged. Evidence is provided that this very slow relaxation resulted from the accumulation of intact amine at extraneuronal sites during exposure to the agonist and its subsequent release past receptors due to a reversal of the concentration gradient after washout.3 Pretreatment with the haloalkylamine, GD-131 (N-cyclohexylmethyl-N-ethyl-,B-chloroethylamine), an inhibitor of extraneuronal uptake, returned the slow relaxation rate after enzyme inhibition towards that of control strips. By blocking the extraneuronal transport of amines their accumulation at intracellular loci after enzyme inhibition was prevented. 4 The effects of GD-131 and 1 7,B-oestradiol on the relaxation rate of untreated strips contracted by adrenaline and noradrenaline confirmed that extraneuronal uptake to sites of enzymatic activity is the major mechanism terminating their action. 5 Inactivation of extraneuronal transport sites by GD-1 31 was prevented by protecting them with 17,B-oestradiol or normetanephrine during exposure to the haloalkylamine, pointing to a common site of action of these agents on a specific carrier system for amines. 6 Evidence is presented that the relaxation from contractions induced by histamine and 5-hydroxytryptamine also involves extraneuronal accumulation and release, probably by an uptake process which is identical to the one for catecholamines.