Effects of certain vasoactive agents on the long-term pattern of blood pressure, heart rate, and motor activity in cats.

Objective: To determine whether a diurnal pattern exists in cardiovascular variables and motor activity, and whether pharmacologic agents that decrease (angiotensin converting enzyme inhibitor) or increase (N omega-nitro-L-arginine methyl ester [L-NAME]) blood pressure alter the pattern.

Animals: 6 clinically normal cats.

Procedure: Radiotelemetric implants were used to measure systemic arterial pressure, heart rate, and motor activity in conscious cats maintained in cages. Measurements were obtained during absence of treatment (control), treatment with dietary salt restriction plus an inhibitor of angiotensin converting enzyme (2.5 mg of lisinopril, PO, daily) and treatment with an inhibitor of nitric oxide production (0.1% L-NAME in the drinking water).

Results: A diurnal pattern in arterial pressure and motor activity was observed, with highest values obtained during presence of laboratory personnel. Mean values of arterial pressure obtained during light hours varied from those obtained during darkness (P < 0.05), but by < 3 mm of Hg. Dietary sodium restriction did not have an appreciable effect on arterial pressure, but the combined administration of a low sodium diet plus lisinopril decreased (P < 0.05) measured indices of arterial pressure. Administration of L-NAME increased arterial pressure (P < 0.05) and altered its diurnal pattern.

Conclusions: Although a diurnal pattern of arterial pressure was observed, variations were mostly associated with presence of human beings. Administration of L-NAME, but not lisinopril, altered this diurnal pattern.

Clinical Relevance: Factors that modify arterial pressure may alter the diurnal pattern of cardiovascular variables. In measuring arterial pressure in cats, the effects of human contact may artifactually increase such variables.