Active and inactive renin in the rabbit

Grace, Sheila Ann (1977) Active and inactive renin in the rabbit. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Resin and angiotensin are hormones involved in the homeostasis of extracellular fluid volume, total body sodium and blood pressure. The renin-angiotensin system may be regulated at many levels. One aspect which has excited much recent interest is the demonstration of an inactive, but activatable form of resin, perhaps a precursor form, or renin bound to a protein inhibitor. The role of such compounds, and how plasma levels respond to changed physiological situations was not known. An assay system for active and inactive renin was developed, and used to study the relative amounts of active and inactive renin in rabbit kidney extracts and plasma. The inactive component comprised 40% of total renal renin and 15% of plasma renin. Plasm levels of inactive renin were investigated in acute haemorrhage and dietary sodium depletion and repletion. Haemorrhage increased total plasma renin activity but the proportion of inactive renin remained constant. When bilaterally nephrectomised rabbits were haemorrhaged, there was no increase in either form of renin, showing that both are of renal origin.Sodium depletion caused a 97% rise in plasma renin activity, but in contrast to the response to haemorrhage, the proportion of inactive renin initially fell to zero. During sodium repletion, it rose above control levels to constitute 20% of total plasma renin. These results can be interpreted as changes in the relative rates of synthesis of active and inactive renin, or in the degree of suppression by the binding protein. The long term dietary experiment also showed that variation in sodium intake altered potassium and water homeostasis. Sodium depletion resulted in redistribution of potassium excretion from the urine to the faeces, so that the faecal component of potassium excretion rose from 17% to 25%. These changes may be important in the control of plasma levels of active and. inactive renin.

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