Apatite fission-track analysis of rocks from the Sierra Nevada basement, southern Spain reveals a detailed record of Neogene denudation. This is combined with evidence of the accumulation of clastic sedimentary rocks in the adjacent Granada Basin to provide a comprehensive record of the denudation of the emerging mountain block. Fission-track ages of c . 9–10 and 4 Ma obtained from the basement reveal periods of rapid cooling linked to tectonic denudation of the metamorphic core. The first major pulse of erosion from the Sierra Nevada produced proximal conglomerates in the marine basin and is constrained at c . 7 Ma using Sr-isotope stratigraphy. No major signal of rapid cooling is preserved by the fission-track systems in the basement block associated with this event. Apatite fission-track data from the conglomerates show young ages and short track lengths indicative of reheating. Modelling of the data suggests that heating occurred at around 4 Ma and is linked to movement of hot fluids through the basin. The ability of thermochronometers to record erosional events during the early stages of orogenesis is critically examined and we suggest that in young rising mountain blocks surface processes are incapable of keeping pace with rock uplift, and denudation principally occurs via tectonic processes.

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Hydralazine was dissolved in 0.5% drinking saline (40 mg/1000 ml) labelled with isotope 22Na and given to spontaneously hypertensive rats for four weeks. Another group of rats were given isotope labelled saline only and served as control. Measurements of total exchangeable sodium, blood pressure, pulse rate and weight were performed before and repeatedly during treatment. Before treatment exchangeable sodium, blood pressure, pulse rate, and weight were no different between the groups. The antihypertensive effect of hydralazine was marked and maintained throughout the experiment. No significant changes were found in pulse rate. Both groups gained weight similarly. Exchangeable sodium increased at the same rate in both groups along with the weight increase. Thus, chronic hydralazine treatment effectively reduces blood pressure in spontaneously hypertensive rats without causing measurable sodium or fluid retention.

To study the effects of dietary sodium and plasma aldosterone on pressure-natriuresis (PN) we examined six groups of adult, male Sprague-Dawley rats. Group 1 received normal-sodium diet, group 2 high-sodium diet, and group 3 low-sodium diet for 3 wk; group 4 was given low sodium for 3 wk then high sodium for 3 wk; groups 5 and 6 received high sodium for 3 wk but during the 3rd wk were also given aldosterone by subcutaneous infusion to mimic the plasma aldosterone seen in groups 1 and 3, respectively. After the diets, rats were killed, and urinary sodium excretion, glomerular filtration rate (GFR), and calculated tubular sodium reabsorption (FRNa) were measured during stepwise increases in perfusion pressure in isolated perfused kidneys from each group. No significant differences in blood pressure were seen between any of the groups. The PN curves for groups 2 and 3 were significantly different (P less than 0.001) and shifted to the left and right of group 1, respectively. These shifts appeared to be the result of significant (P less than 0.001) differences in FRNa rather than changes in GFR. PN was not significantly different in groups 4 and 2, indicating that the effects of low-sodium diet were reversible. The infusion of aldosterone in groups 5 and 6 was associated with modest and significant (P less than 0.001) shifts, respectively, of the PN curve to the right of the curve of rats in group 2. In group 6 this shift appeared to be due to significant (P less than 0.001) changes in FRNa, so as to resemble that seen in low-sodium rats of group 3.(ABSTRACT TRUNCATED AT 250 WORDS)