Sergio De Moraes

Noradrenaline supersensitivity of the mouse vas deferens after long‐term treatment with morphine

It has been reported recently that withdrawal from morphine increases the maximum response of the isolated vas deferens, colon and anococcygeus muscle of the rat without a leftward displacement of dosereponse curves (Muir & Pollock, 1972; Pollock, Muir & others, 1972; Gardiner, Gibson & Pollock, 1974). Gibson & Pollock (1975) found that morphine withdrawal increased the pD, value for acetylcholine on the rat isolated anococcygeus muscle. Collier (1 966) proposed a theoretical model to explain dependence on and withdrawal reactions from drugs, based on the development of a specific supersensitivity to an appropriate neurotransmitter. The same author raised the question of whether drug dependence could be induced by an increase in the number of receptors (Collier, 1968). Morphine is known to inhibit noradrenaline release in the transmurally stimulated mouse vas deferens (Hughes, Kosterlitz & Leslie, 1975; Henderson & Hughes, 1976) and prolonged interruption of the contact between a neurotransmitter and its target cells causes supersensitivity (Fleming, McPhillips & Westfall, 1973). In the work presented here we have examined the influence of pretreatment with morphine on the responsiveness of the mouse isolated vas deferens to noradrenaline and potassium. The results clearly indicate that dependence on morphine induces a supersensitivity to noradrenaline probably caused by an alteration in affinity for the adrenoceptors. Swiss albino mice, 20 to 25 g, at the start of the experiments, were housed in groups of five under a 12 h day-night cycle in an air-conditioned room. The animals were chronically treated with morphine hydrochloride (two daily subcutaneous injections at 8.00 a.m. and 6.00 pm.) in increasing doses during 10 days according to a previously reported schedule (Kaneto, Koida & others, 1973). Between 1 and 2 h after the last morphine injection, one saline-treated and one morphinized animal were killed by stunning and bleeding and their vasa deferentia set up for organ bath studies. Vasa deferentia were also excised from acutely morphine treated (100 mg kg-’, subcutaneously 1-2 h before killing) and morphine withdrawn mice. The peak intensity of the morphine withdrawal reaction was detected using a behavioral scoring test (Kaneto & others, 1973). The isolated vasa deferentia were set up as previously described by Hughes & Leak (1973). Briefly, the tissues were bathed in McEwen solution (McEwen, 1956) at 36.5”, gassed with 5 % carbon dioxide in oxygen and equilibrated under 0.25 g

Forced swim stress: supersensitivity of the isolated rat pacemaker to the chronotropic effect of isoprenaline and the role of corticosterone.

1. Forced swim (three daily sessions) resulted in an increased plasma corticosterone level and supersensitivity of the isolated rat pacemaker to the chronotropic effect of isoprenaline. 2. Bilateral adrenalectomy, performed 2 days before forced swim, abolished the development of pacemaker supersensitivity to isoprenaline. 3. Administration to rats of the antiglucorticoid compound RU-38486 prevented the development of pacemaker supersensitivity to isoprenaline. Pretreatment of rats not submitted to forced swim with the synthetic glucocorticoid RU-28362 causes pacemaker supersensitivity to isoprenaline. 4. Pretreatment of rats with diazepam or imipramine which block the forced swim-induced increase in the plasma level of corticosterone prevented the development of pacemaker supersensitivity to isoprenaline. 5. It is concluded that corticosterone plays a critical role in the modulation of the sensitivity to catecholamines of the pacemaker beta-adrenoceptors during adaptation to repeated stress.

Hypoxia and response of human umbilical artery strips to 5-hydroxytryptamine: Role of prostaglandin F2α

1. This article examines the effects of hypoxia on the contractile response of isolated human umbilical artery strips to 5-hydroxytryptamine (5-HT). 2. Hypoxic conditions produce a large increase in the contractile response to 5-HT without a significant alteration of the sensitivity evaluated at the level of the pD2 value. Indomethacin (10 microM) reduced hypoxia-induced potentiation of the response to 5-HT and decreased the response to the monoamine under oxygenated conditions. 1-NAME (100 microM) did not further increase the effect of hypoxia on the vessel response to 5-HT and increased the response to 5-HT under oxygenated conditions. 3. Taken together, these results suggest that, at least partially, the response of human umbilical artery strips to 5-HT depends on 5-HT release of a contracting prostanoid which is a product of the cyclooxygenase pathway. Furthermore, during hypoxia in human umbilical artery strips, there appears to be impairment of the basal production and/or release of EDRF/NO. 4. A subthreshold concentration of prostaglandin F2 alpha (1 nM) potentiates the response to 5-HT in indomethacin-pretreated umbilical artery strips. The data raise the possibility that prostaglandin F2 alpha might be the prostanoid released during hypoxia, which in turn potentiates the response of the human umbilical artery to 5-HT.

Effects of estrogen pretreatment of the spare α1-adrenoceptors and the slow and fast components of the contractile response of the isolated female rat aorta

1. Estrogen pretreatment increases the responsiveness to noradrenaline and to clonidine in isolated rat female aortae. 2. Determinations of the pKA and pA2 of noradrenaline and prazosin, respectively suggest that the isolated female aorta possess a homogeneous alpha 1-adrenoceptor population. 3. The fast and slow components of clonidine-induced aorta contraction were determined using nifedipine. 4. Considering that after estrogen pretreatment, an increase in spare alpha 1-adrenoceptors probably occur and only the fast component of clonidine-induced contraction was enhanced we concluded that estrogen pretreatment increases the number of alpha 1-adrenoceptors and the amount of intracellular calcium available for contraction.

Denervation supersensitivity to noradrenaline in the guinea-pig vas deferens in vivo: Absence of the postjunctional component

The effects of denervation and cocaine on the responsiveness of the guinea-pig vas deferens to noradrenaline (NA) were studied. The magnitude of the denervation supersensitivity differed in vivo and in vitro. Cocaine-induced supersensitivity to NA was similar in vivo and in vitro. Only denervation increased the maximum response in experiments in vitro. It is suggested that in the guinea-pig vas deferens the postjunctional component of denervation supersensitivity to NA could result from the experimental conditions involving the isolation procedure.

Responsiveness of the guinea-pig vas deferens to phenylephrine and norepinephrine in vivo

A method is described for the study of guinea-pig vas deferens in vivo response to phenylephrine and norepinephrine. Tissue sensitivity to both agonists did not differ in vivo but the maximum response to phenylephrine was smaller. Responsiveness to norepinephrine was depressed in vitro after in vivo experiments. No such effect was observed for phenylephrine. This method allowed the comparison of the responsiveness of the guinea-pig vas deferens to adrenoceptor agonists in vivo and in vitro.

Effects of simulated myocardial ischemic conditions on the responses of isolated human umbilical artery strips to 5-hydroxytryptamine and prostaglandin F2α

1. The effects of simulated myocardial ischemic conditions on the contractile response of isolated human umbilical artery (HUA) strips to 5-hydroxytryptamine (5-HT) and prostaglandin F2 alpha (PGF2 alpha) were studied. 2. During simulated myocardial ischemic conditions the contractile response of HUA strips to 5-HT was lower than the response to the monoamine under oxygenated conditions. Under simulated ischemic conditions the response to 5-HT was further depressed by the cyclooxygenase inhibitor indomethacin (10 microM) and increased by the NO synthase inhibitor L-NAME (100 microM). 3. During simulated ischemic conditions the response of the HUA to a submaximal concentration of PGF2 alpha (3 microM) was reduced. Indomethacin (10 microM) further reduced the response to the prostanoid whereas L-NAME (100 microM) enhanced the response to PGF2 alpha. 4. It is concluded that during simulated myocardial ischemic conditions lactate negatively modulates the contractile response of HUA strips to 5-HT. Apparently, during simulated myocardial ischemic conditions in the HUA the production and/or release of EDRF/NO was not affected.

The effects of ethanol dependence on drug responsiveness of mouse isolated vas deferens

The effects of ethanol dependence on the responsiveness of the mouse vas deferens to noradrenaline (NA), carbachol, barium and calcium were studied. Ethanol dependence increases the maximum responses to NA and carbachol whereas responsiveness to barium remains unaltered. The concentration‐effect curve to calcium was shifted to the left (3·0‐fold at the EC50 level). It is concluded that in vas deferens isolated from ethanol‐dependent mice the increased responsiveness to NA, carbachol and calcium is a consequence of an enhanced calcium entry through voltage‐independent calcium channels, as it has been reported for brain tissue.

Supersensitivity to isoprenaline in right atria isolated from cold-exposed rats.

It is generally accepted that cold exposure increases the cardiovascular effects of catecholamines (Estler & Ammon 1969; Himms-Hagen 1975). However, there are few reports on drug responsiveness of organs and tissues isolated from cold-exposed and/or coldacclimated animals. Recently, it has been reported that hearts isolated from cold-acclimated rats were not supersensitive to the chronotropic effect of noradrenaline (Ostman-Smith 1979). The aim of the present investigation was to examine the responsiveness of right atria, isolated from cold-exposed rats, to the chronotropic effect of isoprenaline. Furthermore, the apparent dissociation constant (KB) for the competitive antagonist propranolol was determined in an effort to shed light on the role of p-cardiac adrenoceptors in coldinduced increased responsiveness to catecholamines.

The effects of chronic reserpine treatment on the contractile activity of the isolated vas deferens of the guinea pig

Chronic reserpine treatment of guinea pigs during 5 days (1 mg/kg/day) induces postjunctional supersensitivity in the isolated vas deferens. It has been previously proposed that postjunctional supersensitivity occurs as a result of an ionic and/or membrane mechanism. Contrasting with previous observations in vascular smooth muscle the present results demonstrate that chronic reserpine treatment did not increase the sensitivity of the depolarized vas deferens to calcium. Experiments on drug responsiveness show that the supersensitive depolarized tissues have a greater and slower rate of loss of responsiveness than do control vasa deferentia. However, in a Ca2+-free Krebs solution responsiveness of supersensitive vasa deferentia did not differ from that of control tissues. These findings suggest that, in the guinea-pig vas deferens, reserpine-induced supersensitivity could be at least partially dependent on the increased availability of a calcium store(s) probably located at the cell membrane and/or cytoplasmic compartments.