Changes in Renal Haemodynamics and Electrolyte Excretion During Acute Hyperkalaemia in Conscious Adrenalectomized Sheep

Abstract

The p-aminohippurate (PAH) clearance, inulin clearance and the excretion of electrolytes by 10 adrenalectomized sheep were measured before, during and after the infusion of 0*43 M-KCl at 2 ml./min for 2 hr. The PAH clearance increased as the plasma potassium concentration increased up to approximately 6'0 m-mole/l. Further increases in plasma potassium were associated with a progressive return of the PAH clearance to or below the pre-infusion levels. At its maximum the PAH clearance was 1-228 ±0-032 (S.E. of mean) times the pre-infusion levels. The inulin clearance increased to reach a maximum coincident with or subsequent to the maximum PAH clearance. The maximum level ofinulin clearance during the hyperkalaemia was 1 158 ±0-020 times the pre-infusion clearance. The increments in the clearance of potasium and of bicarbonate rose rapidly to exceed the increment in inulin clearance during the hyperkalaemia in all experiments. The increments in the clearance of sodium and of chloride exceeded the increment in inulin clearance in more than half the experiments. It was concluded that although hyperkalaemia was associated with increased glomerular filtration much of the increased excretion of sodium, chloride and bicarbonate was derived from depressed tubular reabsorption of the ions. When the infusion experiments were repeated on the same animals the sheep demonstrated an improved ability to control the rise in plasma potassium concentration which was similar to potassium adaptation described in other species. There were no apparent differences between sheep maintained on 1*5 mg and 5 mg deoxycorticosterone acetate daily in their adaptation to potassium loading and the effect was tentatively attributed to the level of steroid maintenance being chronically high. The toxicity of hyperkalaemia was not lessened by this adaptation to potassium loading.

Changes in Arterial Blood Pressure, Heart Rate and Haematocrit During Acute Hyperkalaemia in Conscious Sheep

“…In the conscious adrenalectomized sheep changes in renal plasma flow and glomerular filtration rate during hyperosmotic potassium chloride infusion were consistent with the vascular resistance of the kidney being lowered by the acute hyperkalaemia [Beal, Budtz-Olsen, Clark, Cross and French, 1975]. In contrast to animals in the anaesthetized state the conscious animal has full neural control of peripheral resistance and cardiac rate and thus has a capability to oppose 297 c…”

“…As arterial BP is a balance between cardiac output and peripheral resistance the sheep with the higher initial BP levels presumably responded to theinitiationofhyperkalaemia with a relatively greater fall in peripheral resistance than the lower BP animals which was not fully compensated for by the increase in heart rate and, since the pulse pressure did not fall, by the increase in cardiac output. Further evidence of increased cardiac output at these levels of hyperkalaemia is provided by measurement of plasma and blood flows through various regional circulations in conscious sheep which have demonstrated that during the early part of a potassium infusion, the hyperkalaemia was associated with increased plasma and blood flows [Beal et al, 1975;Beal, 1976]. In the sheep with the lower initial BP levels the increase in cardiac output as reflected by the increase in heart rate not only compensated for any vasodilation but in many instances was an over-compensation which resulted in the tendency for the arterial BP to rise in these animals.…”

“…Weisfeldt and Mansfield, 1966;Logic, Krotkiewski, Koppius and Surawicz, 1968]. Each of these effects would cause the arterial BP to fall and this has been observed during hyperkalaemia in the intact anaesthetized dog [Emerson, Scott and Haddy, 1970].In the conscious adrenalectomized sheep changes in renal plasma flow and glomerular filtration rate during hyperosmotic potassium chloride infusion were consistent with the vascular resistance of the kidney being lowered by the acute hyperkalaemia [Beal, Budtz-Olsen, Clark, Cross and French, 1975]. In contrast to animals in the anaesthetized state the conscious animal has full neural control of peripheral resistance and cardiac rate and thus has a capability to oppose 297 c…”

Plasma Insulin Concentrations During Infusion of Potassium and Sodium Chloride Solutions Into Conscious Splenectomized Sheep

“…However, previous studies in sheep have shown that acute hyperkalaemia, of the level produced in these experiments, increases cardiac output and blood flow to many tissues and causes diuresis (Beal et al 1975;Beal1976a, 1976b. All of these effects would favour increased clearance of insulin from the circulation and a reduction in plasma concentration rather than the converse.…”

The Effect of High Rates of Vasopressin Administration on Renal Potassium and Sodium Excretion During Potassium Loading in the Sheep

“…By performing the present experiments on adrenalectomized sheep the possible intervention of endogenous adrenal steroids released as a result of the potassium infusion was prevented. As judged from salivary sodium/potassium ratios the effect of the DOCA maintenance injection reaches maximum and returns to sodium-replete ratios within 6-8 h of injection (Beal, Budtz-Olsen, Clark, Cross & French, 1975) so that during these experiments which started 18-20 h after the maintenance injection the concentrations of circulating steroids from exogenous sources would be expected to be low and falling relatively slowly.…”