The antihypertensive effects of the Jamaican Cho-Cho (Sechium edule)

The experiments reported in this study constitute a preliminary investigation into the possible hypotensive effect of the Jamaican Cho-Cho (Sechium edule). Experiments were conducted in a random and blind fashion on two sub species of Sechium edule. Both the pulp and the peel were examined for hypotensive activity. Water-soluble extracts were prepared from these components of the fruit and injected into anaesthetised rats. Various cardiovascular parameters were measured including heart rate, mean arterial pressure (MAP) and several ECG intervals. We report that all extracts tested produced a fall in blood pressure with little change in ECG intervals. Extract B produced the least change in heart rate with a fall in MAP of approximately 23 mmHg. Changes in heart rate with all extracts appeared to be minimal as an ED25 value could only be determined for extract A, and ED10 values could not be evaluated for extracts C and D. The mechanism(s) by which these extracts produce their hypotensive effects could not be determined in these preliminary experiments. However, it appears not to involve direct effects on cardiac tissue. This conclusion is based on the finding that it took a minimum of 10 to 15 seconds for the hypotensive action to manifest post bolus. Future experiments will be aimed at delineating the mechanism(s) involved in decreasing MAP.(Au)

The effects of potassium channel agonists, cromakalim and adenosine, in diabetic rat hearts

INTRODUCTION: This study was designed to look at ATP sensitive potassium channels (KATP-sc) in diabetic male Sprague-Dawley rat hearts. Diabetes mellitus was induced using streptozocin (ip). KATP-SC can be found in pancreatic B-cells, cardiac muscle, skeletal muscle, neurones, hypothalamus and smooth muscle. Cromakalim and adenosine were used to construct concentration-response curves. These drugs are KATP-SC openers that cause shortening of action potential duration and hyperpolarisation. This is a novel study as there is a sparsity of information on the effect of KATP-SC openers on the hearts of diabetic animals. We therefore hypothesised that cromakalim and adenosine may have both an effect on the electrical activity as well as the contractility in the diabetic myocardium. METHODS: Male Sprague-Dawley rats (150-250 gm) were treated with streptozotocin (STZ) (60 mg/Kg i.p.). All animals were kept under identical living conditions and allowed free access to food and water for 1 week. Animals were then sacrificed after being anaesthetised with 60 mg/Kg pentobarbital containing 1000 Units/ml heparin. Hearts were being rapidly excised, placed in 4 degrees C. Krebs-Henseleit buffer and mounted in a Langendorff system. Concentration-response curves were constructed for cromakalim (0.01nM-0.1uM), and adenosine (0.1uM-100uM). Parameters measured were heart rate (HR), P-R and QRS intervals, systolic pressure (SP), diastolic pressure (DP) and developed pressure (Dev. Pre.). RESULTS: The results found for cromakalim in diabetic rats and adenosine in normal rats mirrored what has been found in previous studies for these drugs in non-diabetic animals, namely, a decrease in HR, an increase in P-R and QRS and a decrease in SP and Dev. Pre. However, adenosine in diabetic rats showed some unexpected results such as a decrease in P-R, and an increase in SP and Dev. Pre. It is possible that the diabetic state interferes significantly with the actions of adenosine but not as significantly with those of cromakalim. Conclusion: The results indicate that adenosine may not be cardioprotective in diabetic animals. This conclusion may be drawn from the fact that P-R interval decreased with increasing concentrations of adenosine. This may lead to the production of arrhythmias such as life threatening ventricular tachycardia or fibrillation (AU)