The influence of isotonic saline administration on the urinary excretion of kallikrein in rats

Acute saline loading is known to increase kallikrein excretion. To clarify whether this is a specific stimulatory effect or rather a non-specific wash-out, pentobarbital anesthetized rats were loaded thrice (5 min infusions) at 40 min intervals with a volume of 150 mM NaCl equal to 5% of their body wt. The effect of such a load on the central venous pressure was studied in a separate group of rats. Control animals did not receive the infusions. Kallikrein excretion (amidolytic assay) increased with the first, but decreased with the subsequent saline administrations. The rise observed after the first load lost significance when kallikrein excretion was related to that of creatinine. The reduction observed after the second and third infusions remained significant even when expressed per mg of creatinine. Thus, saline load induced kallikrein "stimulation" is due to a non-specific wash-out. Similar transient enhancements of central venous pressure were observed after each of the three loads. This, together with the unchanged creatinine excretion (except for the rise seen after the first load) indicate that the lack of kallikrein stimulation after the second and third loads was not due to the appearance of heart failure. Saline loaded rats had a renal kallikrein activity at the end of the experiment which did not differ from that of controls. Plasma aldosterone concentration was reduced in saline infused rats, and it correlated with the kallikrein excretion when both, NaCl loaded and control rats, were taken into account.