Disappearance of plasma radioactivity after injection of H³- or I¹³¹-labeled arginine vasopressin

¹ Medical Research Center, Brookhaven National Laboratory, Upton, Long Island, New York

Tritiated and iodinated arginine vasopressin (AVP) were administered intravenously to human beings and to dogs. The level of plasma radioactivity was measured with time and showed a single exponential function in all cases, except with I¹³¹ vasopressin in human beings, where two exponential components were evident. In the dog, the half-time for the disappearance of radioactivity from plasma ranged from 3.5 to 7 min after administration of I¹³¹ AVP and from 4 to 5 min after H³ AVP. In similar experiments in man, I¹³¹ AVP gave a fast component with a half-time ranging from 0.3 to 2 min and a slow component with a half-time ranging from 1.6 to 6.5 min, whereas H³ AVP gave a single component with a half-time ranging from 2.3 to 5.5 min. The similarity in the disappearance curve of antidiuretic activity and the disappearance curve of radioactivity suggests that the latter reflects the rate of degradation of the biologically active hormone. Therefore, these labeled hormones appear to be useful tools for evaluation of vasopressin turnover in physiological and clinical conditions alleged to be associated with increased levels of circulating antidiuretic hormone or with abnormal rates of vasopressin production, release, or inactivation.

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