Heat flows in rock cracks naturally optimize salt compositions for ribozymes.

Catalytic nucleic acids, such as ribozymes, are central to a variety of origin-of-life scenarios. Typically, they require elevated magnesium concentrations for folding and activity, but their function can be inhibited by high concentrations of monovalent salts. Here we show that geologically plausible high-sodium, low-magnesium solutions derived from leaching basalt (rock and remelted glass) inhibit ribozyme catalysis, but that this activity can be rescued by selective magnesium up-concentration by heat flow across rock fissures. In contrast to up-concentration by dehydration or freezing, this system is so far from equilibrium that it can actively alter the Mg:Na salt ratio to an extent that enables key ribozyme activities, such as self-replication and RNA extension, in otherwise challenging solution conditions. The principle demonstrated here is applicable to a broad range of salt concentrations and compositions, and, as such, highly relevant to various origin-of-life scenarios.

Reduced periinfarction mortality as a result of long-term therapy with captopril but not hydralazine or propranolol in spontaneously hypertensive rats.

Hypertension and left ventricular hypertrophy (LVH) are known to increase susceptibility to ventricular arrhythmias during and before myocardial ischemia and to increase the risk of periinfarction mortality. Although regression of LVH has been advocated as a therapeutic goal, little evidence exists to suggest that it can reduce periinfarction mortality, and if it does, by which mechanisms it may do this. In this study, we evaluated the effects of control of systemic arterial blood pressure, of regression of myocardial hypertrophy, and of cardiac fibrosis on the susceptibility to ventricular arrhythmias and periinfarction mortality in the spontaneously hypertensive rat (SHR) model of hypertension and LVH. After 12 weeks of treatment, captopril and hydralazine reduced systolic blood pressure to 93 +/- 14 and 126 +/- 13 mm Hg, respectively, as compared with 193 +/- 12 mm Hg, p < 0.05, in the untreated control SHR group. The decrease with propranolol (to 185 +/- 12 mm Hg) was of borderline significance. There was a significant decrease in inducibility of ventricular arrhythmias by programmed electrical stimulation with captopril (5%; p < 0.05). One hour after infarction, there was a trend toward reduced mortality in the rats treated with hydralazine, 9.5% (p = 0.20 vs. control; p = 0.10 vs. propranolol), and captopril, 5% (p = 0.08 vs. control; p = 0.010 vs. propranolol). However, only captopril reduced 3-h postinfarction mortality (40%; p = 0.022) compared with 72% in the control group. The results showed a significant decrease of the left ventricular weight/body weight ratio in the rats treated with hydralazine (2.6 +/- 0.2 mg/g; p < 0.05) and captopril (2.2 +/- 0.2 mg/g; p < 0.05) compared with the control group (2.8 +/- 0.2 mg/g). An assessment of cardiac fibrosis indicated that captopril decreased the volume percentage of collagen the most (2.01 +/- 0.53; p < 0.05), followed by propranolol (2.29 +/- 0.64; p < 0.05) and hydralazine (2.92 +/- 0.58; p < 0.05) versus controls (3.23 +/- 0.61). This study suggests that regression of myocardial hypertrophy or long-term normalization of arterial systolic blood pressure or both are the major determinants of very early mortality (within 1 h after infarction) and that later mortality (3 h after infarction) may be the result of a more complex interplay of regression of myocardial hypertrophy and fibrosis and of control of blood pressure.

Postinfarction survival and inducibility of ventricular arrhythmias in the spontaneously hypertensive rat : effects of ramipril and hydralazine.

BACKGROUND: Hypertensive patients with left ventricular hypertrophy (LVH) have been found to have greater peri-infarction and postinfarction mortality. In this study, we evaluated the postinfarction survival, susceptibility to ventricular arrhythmias, and degree of LVH and cardiac fibrosis in the spontaneously hypertensive rat (SHR) and the effects of the ACE inhibitor ramipril and the direct vasodilator hydralazine on these characteristics. METHODS AND RESULTS: An acute myocardial infarction (MI) was produced by ligation of the left anterior descending coronary artery. Rats were randomized to either control (n=50), hydralazine (n=41), or ramipril (n=45). Treatments were started 4 hours after infarction and continued for 8 weeks. Ramipril and hydralazine reduced arterial pressure similarly. Medications were stopped 72 hours before euthanasia, at which time hemodynamic, programmed electrophysiological stimulation (PES), and morphological studies were performed. Mortality was decreased in ramipril (56%) compared with hydralazine (78%) and control (82%) SHRs (P=0.008). This was accompanied by a decrease in myocardial hypertrophy and fibrosis and a decrease in inducibility of ventricular arrhythmias by PES in the ramipril group regardless of MI size. Treatment with hydralazine had little or no effect on LVH and cardiac fibrosis and did not modify inducibility of ventricular arrhythmias by PES. Ramipril but not hydralazine prevented the increase in LV end-diastolic pressure in rats with large MIs. CONCLUSIONS: In the SHR, the ACE inhibitor ramipril reduces LVH, cardiac fibrosis, and susceptibility to ventricular arrhythmias by PES and improves survival and LV function. Despite a similar decrease in arterial pressure, hydralazine does not have these beneficial effects.