Effect of age on isoproterenol-induced maximal heart rate in horses.

This research investigates how a certain drug (Isoproterenol) induces a maximum heart rate in horses and how this effect changes as the horses age. The findings suggest that with increasing age, the horses’ maximum heart rate in response to the drug decreases.

Study Design and Procedure

• The researchers conducted the study on 19 healthy horses with ages ranging from a quarter of a year to almost ten years. The horses lived a sedentary lifestyle and had normal body temperature.
• A drug named Isoproterenol was administered intravenously (directly into the bloodstream), at a rate of 1.0 microgram per kilogram of a horse’s body weight every minute, for a duration of three minutes.
• The researchers measured the horse’s heart rate during the last 30 seconds of the Isoproterenol infusion. This heart rate is referred to as the ‘maximal heart rate’.

Findings and Interpretation

• The study found that there was a decrease in the maximal heart rate of horses with an increase in age. This trend was observed and described in a mathematical relation: maximal heart rate (beats/min) = 209.63 – 3.28 x age (years).
• It implies that for every year of age, the maximal heart rate decreases by approximately 3.28 beats per minute when under the effect of Isoproterenol.
• The correlation between the age of the horses and the maximal heart rate was strong (as indicated by the regression coefficient ‘r’ of 0.769) and statistically significant (P value less than 0.001).
• This study concludes that the maximal heart rate response to Isoproterenol, which is mediated through beta-adrenoceptors (a type of protein that interacts with adrenaline), diminishes in horses as they age.