Thyroid Circulation in the Rabbit Including Arteriovenous Difference

Publisher Website
Google Scholar
Abstract
Thyroidal I-131 clearance and arteriovenous difference, together with urinary excretion of I-131, were determined in 19 rabbits maintained for varying periods on a low iodine diet. Absolute blood flow was computed by dividing thyroidal I-131 clearance by AV difference. Thyroid cell heights were measured as an independent index of thyroid status. The rabbits were divided into two distinct groups on the basis of acinar cell heights: Group I with mean cell heights of 4.1–5.2 micra and group II with mean cell heights of 6.9–8.9 micra. Group I had a mean clearance of 0.43 gm blood/min. and a mean thyroid/urinary (T/U) ratio for I-131 of 3.1. The mean AV difference was 25%. Absolute and relative blood flows averaged 2.0 gm/min. and 6.1 gm/ min/gm thyroid, respectively. Group II had a T/U ratio of 40 and mean clearance of 4.3 gm/min. Mean AV difference was increased to 57%. Absolute and relative blood flows averaged 7.9 gm/min. and 22 gm/min/gm thyroid, respectively. All of the indices listed were significantly higher (P = 0.02) in group II than in group I. Absolute thyroid circulation was significantly correlated with T/U ratio (r = 0.87), but relative thyroid circulation was not. Relative blood flow was significantly correlated with mean acinar cell height (r = 0.68), but absolute blood flow was not.