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The effects of exogenous histamine on nasal mucosal blood flow and the systemic activity of intranasally administered desmopressin, a vasopressin analogue, were studied in normal volunteers. Ten subjects received either saline or histamine (1, 20, 100, and 500 pg) by intranasal spray. Maximal nasal mucosal blood flow response, determined by laser doppler velocimetry, demonstrated a signifcant (P < 0.05) linear relationship to histamine dose. Eight additional subjects received each of the following intranasal treatments: 20 jug histamine followed by 10 gtg desmopressin; normal saline followed by 10 ,g desmopressin; 20 Mg histamine followed by vehicle; or normal saline and vehicle. Nasal blood flow was determined before and after each treatment. Desmopressin activity was assessed by measuring urine osmolality, flow rate, electrolyte, and creatinine concentration for 24 h after each treatment. The effect of histamine and desmopressin was greater than desmopressin alone, with respect to nasal blood flow response (103±24 vs. 4±17%, mean±SEM, P < 0.02), initial urine osmolality (520±123 vs. 333±75 mosM, P < 0.03), urine electrolyte (potassium, 45±11 vs. 28±7 meq/liter, sodium, 68±21 vs. 36±8 meq/liter, P < 0.03) and creatinine concentrations (95±23 vs. 60±13 mg/dl, P < 0.03), and the duration of decrease in urine flow rate compared with saline and vehicle. These results suggest that the systemic activity of intranasal desmopressin is enhanced by increasing local nasal blood flow and are consistent with increased transnasal absorption of the peptide.

Encainide and flecainide have a low efficacy rate and a high incidence of worsening of arrhythmia in patients with sustained ventricular arrhythmias, particularly when this condition is associated with poor left ventricular function.

Oral flecainide therapy was effective in 33 of 63 patients who had tachycardia and an extranodal accessory connection. Hospital monitoring during initial therapy is recommended, and flecainide should be used with caution, if at all, in patients with structural heart disease. An isoproterenol challenge appears to be helpful in predicting late recurrence of tachycardia.

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