Positive inotropic effects of hydralazine in human subjects: comparison with prazosin in the setting of congestive heart failure

Hydralazine possesses positive inotropic properties in animal model preparations. To determine whether this vasodilator elicits a positive inotropic response in the failing human ventricle, hydralazine, 75 or 100 mg, was administered orally to 14 patients with left ventricular dysfunction and congestive heart failure; the results were compared with those of first-dose prazosin at 5 and 10 mg. The duration of the preejection period and the isovolumic developed pressure/duration of isovolumic contraction (delta P/delta t) were used as indexes of inotropy. Prazosin did not effect a significant response in the duration of the preejection period or in the delta P/delta t. Hydralazine significantly shortened the preejection period and increased the delta P/delta t over 8 hours after administration; these data suggest that hydralazine elicits a positive inotropic response in the failing human ventricle.

Development of pharmacodynamic tolerance to prozosin in congestive heart failure

In order to determine and compare the pharmacodynamic responses to single and multiple dose prazosin therapy in cardiac failure, 14 patients with severe low-output heart failure underwent central and regional hemodynamic measurements after random placement in one of two prazosin dosing schedules. A single 5 mg oral dose of prazosin (Group A, no. = 7) significantly increased the cardiac index and stroke volume index while significantly decreasing systemic, pulmonary and pulmonary capillary wedge pressures and vascular resistances. Hepatic plasma flow and limb blood flow increased after the single dose. Striking attenuation of these hemodynamic effects occurred when the same dose was administered after 24 hours of pretreatment with oral prazosin, 2 mg every 8 hours (Group B, no. = 7). The plasma prazosin levels of the two groups, drawn 2 hours after administration, were 24.5 and 30.5 ng/ml, respectively. Repeated administration of prazosin in patients with congestive heart failure results in rapid attenuation of its beneficial central and regional hemodynamic effects. The usefulness of this vasodilator as a preload- and afterload-reducing agent in the clinical setting of chronic congestive heart failure may be limited by the development of pharmacodynamic tolerance.

Demodex canis: redescription and reevaluation

A brief review of the taxonomy of Demodex canis is followed by a complete redescription. Demodex canis is diagnosed with D. odocoilei of the white-tailed deer. In view of the continued speculation that dogs and man share the same demodicid, simple morphological characters are noted which distinguish D. canis from D. folliculorum and D. brevis in all stages of their life cycles.

Demodex adocoilei sp. nov. from the white-tailed deer, Odocoileus virginianus

A new species of Demodex which is parasitic in the pilosebaceous complex of the white-tailed deer is figured and described in detail. The life cycle, habitat, and several pathogenic manifestations, including invasion of the blood system, are described.