Plasma protein distribution and turnover in the female baboon

Abstract

The menstrual cycle of the baboon is associated with marked alterations in the size and protein content of the perineal swelling. The distribution and turnover of I131-labeled plasma protein changes in step with the periodic growth and involution of this tissue. During the follicular phase of the cycle the volume of the perineal swelling increases by about 3 1 and its protein content by approximately 60 g. After the intravenous injection of tracer doses of iodinated plasma, or of albumin alone, the specific activity of circulating protein declines at an approximately constant exponential rate throughout perineal turgescence. Protein synthesis, calculated from plasma specific activity curves, exceeds catabolism estimated from the excretion of I131; the exchangeable protein pool increases in size. Comparison of the specific activities of plasma and perineal tissue fluid and the results of electro-phoretic and ultracentrifugal analyses indicate that the protein which accumulates in the turgescent perineum consists of extravascular plasma protein which is probably lodged predominantly in connective-tissue ground substance. The extravascular plasma protein of the perineum continues to exchange with circulating protein during growth of the perineal swelling. After equilibration, the specific activities of plasma and perineal fluid albumin remain identical. Globulin fractions, on the other hand, attain a higher specific activity in perineal fluid, so that calculations of pool size based on the specific activity of total plasma protein are erroneously high. During perineal involution the decline of the specific activity of plasma protein is very much slower than during the first half of the cycle, indicating a reduced rate of synthesis of plasma protein. At the same time, the size of the exchangeable plasma protein pool becomes progressively smaller.