Cycloheximide-induced amnesia for taste aversion memory in rats

Male hooded rats were conditioned in one trial to avoid saccharin by pairing saccharin drinking with an intragastric injection of LiC1. A 24 hr water-saccharin preference test showed that conditioned rats exhibited a very low preference for saccharin whereas rats injected intraventricularly with cycloheximide (CXM, 400 mug) 5, 7, or 9 hr before training exhibited a greatly increased saccharin preference which differed significantly from NaC1 injected controls. This 24 hr amnesia was found to be dependent upon the time of administration of CXM, since injection at 1, 3 or 17 hr before training did not confer amnesia. The nature of the task, a control measure and a control experiment indicate that the CXM-induced change in saccharin preference at 24 hr is not due to a CXM-induced aversion, nor a loss in drinking ability nor an inability to retrieve information whilst under the influence of CXM.

Pulmonary microembolism: attenuated pulmonary vasoconstriction with prostaglandin inhibitors and antihistamines

The mechanism(s) involved in the pulmonary vascular and airway responses to pulmonary microembolism have not been clearly defined. Therefore, we determined the effects of specific prostaglandin and histamine blockade on the hemodynamic and arterial blood gas tension responses to particulate microembolism (200 mu glass beads) in intact anesthetized dogs. The marked increases in pulmonary arterial pressure and pulmonary vascular resistance observed in the untreated dogs were attenuated, but not abolished, following both prostaglandin blockade (with either meclofenamate or polyphloretin phosphate) and histamine blockade (with chlorpheniramine and metiamide) at 5 minutes, and were still attenuated 30 minutes post embolization. Combined prostaglandin and histamine blockade further attenuated, but again did not abolish, the pulmonary vascular responses. Cardiac outputs and systemic arterial pressures were unchanged from control by embolism. The alveolar hypoventilation (decreased arterial oxygen tension and increased carbon dioxide tension) observed in the untreated embolized dogs was prevented only with the prostaglandin inhibitors. Pulmonary microembolism in intact dogs, therefore, appears to induce vasoconstriction mediated partially by prostaglandin and histamine action, and alveolar hypoventilation mediated by prostaglandin, but not histamine, action.

Histamine H1- and H2-receptors in pulmonary and systemic vasculature of the dog

This study was conducted to identify and clarify the actions of pulmonary and systemic H1- and H2-receptors by utilizing specific histamine receptor antagonists. Histamine was infused in anesthetized dogs during control conditions, after H2-receptor blockade with metiamide, after H1-receptor blockade with chlorpheniramine, and after combined H1- and H2-receptor blockade. Histamine infusion, alone, induced marked systemic vasodilatation, pulmonary vasoconstriction, and transient increases in cardiac output and heart rate. H2-receptor blockade prevented the systemic vasocilatation and potentiated the pulmonary vasoconstriction induced by histamine. H1-receptor blockade augmented the systemic vasodilatation, prevented the pulmonary vasoconstriction, and increased the cardiac output and heart rate responses induced by histamine. Thus, H2-receptors appear to mediate the vasocilatation, tachycardia, and increased cardiac output induced by histamine, whereas H1-receptors appear to mediate the vasoconstrictor and the minimal cardiac depressent actions of histamine. Histamine stimulates only H1- and H2-receptors, since combined H1- and H2-receptor antagonism prevented almost all of the cardiovascular actions of histamine.

Nonsustained pulmonary vasoconstriction during acute hypoxia in anesthetized dogs

The objectives of this study were to describe in greater detail the initial rise and spontaneous decline in acute hypoxic pulmonary vasoconstriction and to investigate a number of mechanisms that could have caused this secondary vasodilation. With the onset of isocapnic hypoxia (Pao2 of 28, 44, or 56 mmHg), pulmonary vascular resistances increased to maximum values at 3 min and then spontaneously declined toward control values. Pulmonary perfusion pressures rose to maxima at approximately 4 min and then also declined. During severe hypoxic exposures (Pao2 of 30-37 mmHg) this secondary vasodilation was found not to be due to beta-adrenergic-induced vasodilation, withdrawal of alpha-adrenergic-induced vasoconstriction, vasodilation caused by a sustained increase in pulmonary blood flow, fatigue of the vascular smooth muscle contractile mechanism, or release of vasodilatory prostaglandins. It is suggested that the decline in hypoxic pulmonary vasoconstriction may be due to an exhaustion of a chemical mediator, release of a pulmonary vasodilator agent, or myogenic stress relaxation.

Lung vascular smooth muscle as a determinant of pulmonary hypertension at high altitude

The pulmonary hypertensive response to chronic hypoxia varies markedly among mammalian species. An explanation for this variability was sought by exposing seven species to hypobaric hypoxia (PB equal to 435 mmHg) for 19-48 days. Control animals were studied at 1,600 m (PB equal to 630 mmHg). The pulmonary hypertension that developed varied in the following order of decreasing severity: calf and pig (severe); rat and rabbit (moderate); sheep, guinea pig, and dog (mild). Right ventricular hypertrophy developed in proportion to the elevation in right ventricular systolic pressure. These interspecies variations in response were not correlated with the degree of arterial hypoxemia, degree of polycythemia, elevation in heart rate, or postnatal age. However, the medial thickness of the small pulmonary arteries in control animals was highly correlated with the development of pulmonary hypertension and right ventricular hypertrophy in hypoxic animals. Thus, the amount of lung vascular smooth muscle inherent within each species is a major determinant of the pulmonary hypertensive response to high altitude and contributes to the interspecies variability in this response.

Isolation of pulmonary pressor substances from bovine amniotic fluid

The pulmonary pressor activity of bovine amniotic fluid resides in substances that appear to be non-polar lipids as suggested by the various chemical and chromatographic procedures. In preliminary experiments, it was found that the pressor activities of the hexane extracts were blocked by prior administration of aspirin to the calf (1 mg/kg), suggesting that pressor effect was mediated via the prostaglandin system. The amniotic fluid lipids, however, differed from the known prostaglandins in being less polar as indicated by thin layer chromatography and in possessing greater pressor activity. It is possible, of course, that the lipids with pulmonary pressor activity participate in the metabolism of the prostaglandins.