The influence of chronic administration of desmethylimipramine (DMI) on the actions of thyroxine (T4) on rat heart was studied. Administration od DMI (10 mg/kg, i.p., twice daily) for 7 days did not alter the cardiac beta-adrenergic receptor density or the affinity for (-)[3H]dihydroalprenolol (3H-DHA) but diminished the activation of myocardial phosphorylase produced by isoproterenol. Chronic injections of T4 (500 microgram/rat) for 5 days caused an increase in the number of beta-adrenergic receptors in the heart and potentiated the stimulatory effect of isoproterenol on cardiac phosphorylase alpha activity. When DMI was administered concomitantly with T4, there was no increase in the density of myocardial beta-adrenergic receptors and the T4-induced potentiation of the activation of heart phosphorylase by isoproterenol was abolished. However, simultaneous treatment of the rats with DMI and TR4 did not diminish the positive chronotropic effect of T4. It was concluded that DMI, while not affecting the population of cardiac beta-adrenergic receptors by itself, prevents the increase in these receptors produced by T4 and obviates the T4-induced potentiation of phosphorylase activation by isoproterenol. That the tachycardia caused by T4 persists in hearts in which DMI has impeded the increase in myocardial beta-receptors suggests that the increase in heart rate is not dependent on cardiac beta-adrenergic receptor density.

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PubMedDate not supplied

Interaction between thyroxine and tricyclic antidepressant drugs on cardiac neurotransmitter receptors.

The effect of chronic administration of desmethylimipramine (DMI) and iprindole on cardiac neurotransmitter receptors was studied. In addition, the influence of these drugs on the action of thyroxine (T4) on myocardial receptors was investigated. Administration of iprindole (10 mg/kg i.p., twice daily for 11 days) markedly increased the number of beta- adrenergic receptors in the heart and significantly reduced the affinity of these receptors for (-)[3H]dihydroalprenolol ([3H]DHA). Injection of T4 (500 mg/rat i.m., for 5 days) concomitantly with iprindole resulted in a lower beta-adrenergic receptor density that with iprindole treatment alone, but significantly higher than that measured in control rats. Affinity of the receptors for (-)[3H]quinuclidinyl benzilate ([3H]QNB) in heart membrane preparations of animals pretreated with T4 alone or with T4 plus iprindole was not different from control. Neither pretreatment with DMI nor with iprindole affected the density of cholinergic muscarinic receptors in the heart or their affinity for [3H]QNB. The decrease in cardiac cholinergic receptors induced by administration of T4 was not prevented by simultaneous injections of DMI. Combined administration of iprindole and T4 caused a reduction in the affinity of myocardial cholinergic muscarinic receptors, but restored the number of these receptors to normal. The results demonstrate distinct differences between DMI and iprindole in their effects on cardiac neurotransmitter receptors and in the influence of these drugs on the actions of T4 on receptors in the heart.

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PubMedDate not supplied

A review of portal screen-film technology and five radiologists' evaluations of some existing products.

Portal radiographs, radiographs made to document the accuracy of radiotherapy treatment fields, are typically of poor image contrast. Recently, a new portal film and screened-cassette system was marketed, the Kodak EC-L system, with the claim of greatly improved image contrast. This new EC-L system was tested on a canine cadaver exposed to Cobalt-60 teletherapy gamma radiation, and image quality was compared to earlier marketed Kodak portal film products. The EC-L system was found to provide portal images of improved contrast/quality.

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PubMedDate not supplied

Neural and local control of arterioles in SHR.

This study sought to determine if neural influences and/or alterations in arteriolar responses to oxygen could contribute to an elevated microvascular resistance in spontaneously hypertensive rats (SHR). Diameters of third-order arterioles (3A) and fourth-order arterioles (4A) were measured in the cremaster muscle of 12- to 15-week-old SHR and normotensive Wistar-Kyoto (WKY) controls anesthetized with pentobarbital. The preparation was suffused with physiological salt solution (PSS) equilibrated with various concentrations of oxygen (0% O2, 5% O2, or 10% O2) with and without local neural blockade with 10(-7) g/ml tetrodotoxin (TTX). Total active tone was assessed with 10(-4) M adenosine. SHR 3A (but not 4A) exhibited a smaller resting diameter than WKY, and larger dilations in response to TTX and adenosine. When suffusion solution PO2 was elevated in the presence or absence of TTX, SHR arterioles constricted more than did those of WKY, and SHR 4A exhibited a higher incidence of complete closure. Therefore, both neural influences and local vascular control mechanisms may contribute to an elevated microvascular resistance in SHR.

Adenosine↗

PubMedDate not supplied

Cardiac phosphorylase in different species and after reserpine administration.

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