Potassium Exchange in the Dog Heart in Situ

Coronary perfusion with constant flow and constant specific activity permitted an estimate of the transmembrane fluxes of potassium in both directions in the dog heart in situ. The determination of efflux was based on the washout characteristics. Perfusion pressure and coronary flow within the limits studied have little influence on efflux. The estimate of influx involved correction of experimental data using the efflux from the same experiment and is therefore less accurate; it is subject to changes due to alterations in collateral blood supply of the perfusion area. The efflux varies by 50% from heart to heart, averaging 0.68 mEq K + /kg and min at an average heart rate of 130 beats/min. Changes in heart rate reveal that 1.65 µEq K + /kg are exchanged per beat above the resting flux of the nonbeating heart; the latter was estimated by extrapolation to be 0.55 mEq K + /kg and min.

Gamma-Emitting Radionuclides in Newborns, Infants, and Children

During the period April 1962 to April 1963, 28 newborn infants, 7 stillborns, and 21 children from 4 to 15 years of age were examined for emission of gamma activity in a low-background, high-sensitivity, total-body counting facility. The 21 children contained traces of combined Zr(95) and Nb(95), Ru(103), (106), and Cs(137) in addition to the normal K(40). The greatest concentration of Cs(137) observed was 80 picocuries per kilogram of body weight, or about 4 percent of the natural K(40) radioactivity. Four of the seven stillborns, each counted for 10 hours, shoWed K(40) and traces of Zr(95), Nb(95), and Ru(103), (106). The ratios of Zr(95) to Nb(95) were lower in the stillborns than in their placentas which suggested placental discrimination against Zr(95). The ratios of Cs(137) to K(40) were lower in infants than in children or adults. Thyroid glands obtained atautopsy from 24 infants during April to September 1962 contained no detectable radioiodine ( less than 30 pc).

Validation of insorption by blood analysis with comparisons of systemic and portal venous disappearances of D2O, Na24, and K42

The rates of disappearance D2O, Na22/24 and K42 from the arterial blood were determined in 17 dogs following rapid injection of the isotopes into the femoral and portal veins. Differences between systemic and portal venous injections were significant during the early phases of the disappearance of the isotopes (P < 0.05). Systemic insorption was simulated by continuous intravenous injection of D2O, Na22, and K42 at known rates into the femoral vein. The appearance of the isotopes in the arterial blood was determined repeatedly during and after their injection. The rate of injection (simulated insorption) was calculated using the mean systemic arterial disappearance rate. The differences between the calculated and actual rates of injection were insignificant. When portal insorption was simulated by constant injection of the isotope into the portal vein, the calculated rate of injection was not significantly different from the actual rate if the mean portal arterial disappearance curve was used in the calculation. When the systemic arterial disappearance curve was utilized, the calculated rate of injection was slightly faster than the actual rate.

Submitted on July 11, 1962

Body Composition: Relative in vivo Determinations from Potassium-40 Measurements

Measurements of body composition from serial, in vivo determinations of potassium-40 were made on 51 obese human subjects who were placed on a low calorie diet. Weight losses in the group averaged from 12 to 36 pounds. There was no change in potassium content or in lean body weight. Weight loss resulted from the loss of excess body fat.