# Negative Alterations in the Respiratory Activity of Isolated Crude Heart Mitochondria Following In Vivo Isoproterenol Injection in Rats Are Not Observed in Heart Homogenate Suggesting That the Isolation Procedure Generates Experimental Artefacts

## TL;DR

This study shows that negative effects of isoproterenol on heart mitochondria may be due to the isolation process, not the drug itself.

## Contribution

The study identifies that mitochondrial isolation procedures may generate experimental artefacts in isoproterenol studies.

## Key findings

- Heart homogenates showed improved mitochondrial function after isoproterenol.
- Isolated mitochondria showed negative effects at 48 hours, suggesting artefacts from isolation.
- Mitochondrial isolation procedure may distort results in isoproterenol studies.

## Abstract

Mitochondrial respiratory parameters (state 2 mitochondrial respiratory activity (state 2), state 3 mitochondrial respiratory activity (state 3), respiratory control (RC), mitochondrial ATP synthetic activity (MASA), and oxidative phosphorylation efficiency (ADP:O)) were assayed in heart homogenates (HHs) and in unwashed isolated mitochondria (isolated crude heart mitochondria (CHMs)), using rats sacrificed 3, 6, 24, and 48 h after receiving a subcutaneous injection of (−)-isoproterenol (67 mg/kg body weight). With HHs, the following was observed: (a) a statistically significant activation of RC and MASA at 3 h and 6 h after drug infusion; at those times, state 2, state 3, and ADP:O were not different. (b) No studied (−)-isoproterenol mitochondrial parameters were statistically different at 24 h and 48 h after drug administration. So extrapolating, (−)-isoproterenol treatment does not negatively impact mitochondrial respiratory function in vivo; on the contrary, a better 3 h and 6 h (−)-isoproterenol mitochondrial energetic functional state was observed. With CHMs, the following was observed: (a) a statistically significant activation of RC and MASA at 3 h, but no longer at 6 h after drug infusion. (b) No studied mitochondrial parameters were statistically different at 24 h after (−)-isoproterenol treatment, but at 48 h, a statistical decrease took place in (−)-isoproterenol RC, so the mitochondrial isolation procedure (MIP) causes additional negative alterations to the mitochondrial samples; therefore, isoproterenol-induced negative alterations of mitochondrial respiratory parameters reported in the literature using isolated heart mitochondria (IHMs) are possibly an experimental artefact.