Atrial natriuretic factor in cats subjected to acute myocardial ischaemia

Abstract

Eighteen anaesthetized open chest cats were subjected to 10, 30, or 50 min occlusion of the left anterior descending coronary artery (LAD). Heart rate, left ventricular end-diastolic (LVEDP) and systolic pressure (LVSP), and dp/dt were continuously recorded during the experiments. Prior to LAD-occlusion, and just before termination of the experiments, blood samples were collected from the left femoral artery for measurements of atrial natriuretic factor (ANF), catecholamines, electrolytes, urea, and creatinine. Simultaneously, biopsies were collected from the right auricular wall. The tissue was embedded in Lowicryl K4M, and ultrathin sections were incubated with anti-ANF antibodies and secondary antibodies conjugated to gold particles. The density of ANF-containing atrial-specific granules labelled with gold particles was morphometrically calculated. LVEDP increased significantly in all three time groups, and when pooling the pre- and postocclusion values, there was an increase from 5.1±0.4 to 10.3+1.2 mmHg (p<0.05). The noradrenaline level increased from 0.93±0.18 to 2.34±0.75 nmol l⁻¹ (p<0.05) after LAD-occlusion. Similarly, the mean plasma level of ANF in the 18 cats increased from 57.6±11.9 to 98.9±22.6 pmol l⁻¹ (p<0.05). Atrial granular density appeared to decline after 10 min of occlusion (from 0.141 ±0.017 to 0.127±0.022 granules⁻¹ p.m² sarcoplasm), and after 30 min there was a significant decrease (0.080±0.012 granules/μm², p<0.05). However, after 50 min occlusion the granular density was almost restored (0.133±0.017 granules/μm²). Plasma ANF showed a positive linear correlation to LVEDP and to the noradrenaline level. The present study demonstrates that the plasma ANF level is increased in cats subjected to acute LAD-occlusion, and it is suggested that elevated LVEDP and plasma noradrenaline contribute to the ANF secretion from the heart.

Key Words:

• Atrial natriuretic factor
• atrial specific granules
• acute myocardial ischaemia
• immunocytochemistry
• morphometry