Oestradiol-induced hypotension in spontaneously hypertensive rats: putative role for intracellular cations, sodium-potassium flux and prostanoids

1. The effect of oestradiol alone and in combination with indomethacin on blood pressure, erythrocyte cation concentration and Na(+)-K+ flux has been studied in adult female normotensive and spontaneously hypertensive rats. 2. Oestradiol alone resulted in a significant decrease in blood pressure in spontaneously hypertensive rats (from 165.3 +/- 3.9 to 146.4 +/- 2.7 mmHg, P less than 0.001), whereas it induced a significant increase in normotensive rats (from 111.8 +/- 1.8 to 124.1 +/- 3.6 mmHg, P less than 0.001). When indomethacin and oestradiol were administered simultaneously or when indomethacin was given alone, no change in blood pressure occurred in spontaneously hypertensive rats (158.6 +/- 6.9 and 159.8 +/- 6.2 mmHg, respectively). 3. The fall in blood pressure induced by oestradiol in spontaneously hypertensive rats was associated with significant reductions in erythrocyte K+ concentration (from 127.4 +/- 1.2 to 116.9 +/- 1.7 mmol/l of cells, P less than 0.001), in erythrocyte Na+ concentration (from 14.3 +/- 0.8 to 13.0 +/- 0.6 mmol/l of cells, P less than 0.02), in ouabain-sensitive erythrocyte Na+ flux (from 17.8 +/- 0.3 to 16.0 +/- 0.4 mmol h-1 (l of cells)-1, P less than 0.01) and in ouabain-sensitive erythrocyte K+ flux (from 11.4 +/- 0.2 to 10.4 +/- 0.2 mmol h-1 (l of cells)-1, P less than 0.01). No change in blood pressure, erythrocyte cation concentration or Na(+)-K+ flux occurred when oestradiol and indomethacin were given together or when indomethacin was administered alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of age on glomerular binding of angiotensin II in normotensive and spontaneously hypertensive rats

1. Glomerular angiotensin II (ANG II) binding has been studied in normotensive (NTR) and spontaneously hypertensive (SHR) rats at 5, 10, 15 and 20 weeks of age. 2. Binding of 125I-labelled ANG II by glomeruli from NTR and SHR was similar at 5 and 10 weeks of age, with 5 week values of 426.4 (range 384-469) and 400.2 +/- 245 fmol/mg of protein; however, at 15 and 20 weeks ANG II binding by SHR glomeruli was significantly greater than by NTR, with 20 week values of 614.7 +/- 245 and 308.3 +/- 31.8 fmol/mg of protein, respectively (P less than 0.01). 3. The ANG II binding affinity constant (Ka) of glomeruli from NTR and SHR was comparable at 5, 10 and 15 weeks of age, with values of 1.5 (range 1.1-1.9) and 1.08 +/- 0.35 nmol/l, respectively, at 5 weeks; whereas at 20 weeks the Ka for SHR glomeruli was significantly greater than for NTR, with values of 1.85 +/- 0.45 and 0.66 +/- 0.22 nmol/l, respectively (P less than 0.001). 4. Age-related changes in glomerular binding of ANG II in SHR were not found to be related to changes in either plasma renin activity or systolic blood pressure.

Differences in glomerular binding and response to angiotensin II between normotensive and spontaneously hypertensive rats

1. Angiotensin II (ANG II) binding and the physiological response to exogenous ANG II have been studied in isolated glomerular preparations from normotensive (NTR) and spontaneously hypertensive (SHR) rats. 2. The binding of 125I-labelled ANG II by glomeruli from SHR was significantly greater than that by glomeruli from NTR, whereas the binding affinity constant (Ka) showed that the SHR ANG II glomerular receptor had a lower affinity for the hormone than the NTR glomerular receptor. 3. Glomeruli from SHR were significantly less responsive to exogenous ANG II than those from NTR. 4. Sodium loading resulted in a significant increase in ANG II binding by glomeruli from NTR, whereas a decrease in binding occurred in glomeruli from SHR. 5. Although a high sodium intake caused a reduction in the response of glomeruli from both NTR and SHR to exogenous ANG II, these changes were not statistically significant. In NTR this was associated with a decrease in the concentration of agonist required to cause half-maximal response (EC50), whereas an increase in EC50 was shown by glomeruli from SHR.

Tetanus toxin: a marker of amphibian neuronal differentiation in vitro

Tetanus toxin may be used to specifically mark neurones in cultures of mammalian and chick nervous tissue. We have prepared cultures of neural ectoderm and underlying mesoderm from late neurula Xenopus laevis embryos, and shown that in this Amphibian species, neurones are labelled by tetanus toxin. Aggregate cultures of ectoderm and mesoderm from late blastula embryos were than examined to determine whether tetanus toxin might be used to mark neuronal precursor cells. Our observations suggest that this is not possible; neurones are seen to have acquired tetanus toxin receptors only after they have become morphologically differentiated.

The function of the sodium pump during differentiation of amphibian embryonic neurones

1. A method has been developed for studying the differentiation in tissue culture of ectoderm and mesoderm derivatives, dissected from amphibian embryos which have just completed neurulation. 2. Neurones, striated muscle cells and pigment cells, together with other unidentifiable cell types, differentiated as a monolayer with approximately the same time course as in the whole embryo. The proportion of different cell types in the cultures was measured quantitatively by cell counting. 3. Treatment of embryos during neurulation with the cardiac glycoside strophanthidin reduced the number of neurones which subsequently differentiated in culture. Other cell types were not affected. 4. The relationship between inhibition of neural differentiation and strophanthidin concentration was sigmoid, with maximum inhibition at 10(-5) M-strophanthidin and the mid-point at 5 X 10(-7) M-strophanthidin. 35% of neurones differentiating in culture were not affected by glycoside treatment. 5. The glycoside hexahydroscillaren A had no effect on neural differentiation. 6. Increasing extracellular potassium to 100 nM during strophanthidin treatment completely protected differentiating neurones from the inhibitory effect of strophanthidin. 7. Treatment of embryos with 100 mM-KCl during neurulation had no effect on the subsequent differentiation of neurones. 8. Treatment of cultures with an antibody to mouse salivary gland Nerve Growth Factor reduced the number of neurones by 30%. 9. Exposure to strophanthidin while the embryo moved from the early neural fold stage to the late neural fold stage was as effective in reducing subsequent neural differentiation as treatment throughout neurulation. 10. The proportion of nerve cells in the cultures was not affected if strophanthidin treatment ended before the early neural fold stage or did not begin until the late neural fold stage. 11. Embryos treated with strophanthidin during neurulation and then allowed to grow into tadpoles developed abnormal nervous systems. 10(-6) M-strophanthidin had little effect on the volume of grey matter, but reduced the white matter by 50%. 12. The results are consistent with the view that strophanthidin achieves its effect on neural differentiation by inhibiting the sodium pump. They are discussed in the light of the suggestion that activation of the sodium pump is an essential part of nerual differentiation.

The action of melatonin on single amphibian pigment cells in tissue culture

1. Neural crest material from neurula stage Xenopus embryos was tissue cultured as small aggregates of cells or a single cell suspension. Isolated pigment cells differentiated after 2 days in culture. 2. Melatonin (10(-15) to 10(-13) M) induced pigment granule condensation; it was 10,000 times more effective than any other compound tested. 3. Tests with appropriate agents showed the pigment cells to have beta-adrenoceptors and 5-hydroxytryptamine receptors; these sites could be blocked without affecting the response to melatonin. Phentolamine blocked the effect of melatonin. 4. Removal of Na+ or Ca2+ from the bathing medium inhibited melatonin-induced pigment granule condensation; 10 mM K+ induced pigment granule condensation. D600, Mn2+ and La3+, which inhibit Ca2+ entry, blocked the effect of melatonin. 5. Cyclic GMP induced pigment condensation and cyclic AMP pigment dispersion (10(-2) to 10(-4) M). 6. It is suggested that the action of melatonin is accompanied by depolarization and the entry of calcium ions. 7. Pigment cells in tissue culture could provide a useful bioassay method for melatonin.