IODINE TRANSFER TO MILE asma was deter, 1:1 slurry of to 3 ml of the itle mixing, the precipitate the 1 after washing t was taken to d subtraction of for the milk or ue to the bound of these experi- 79% of a daily bout 1% of the and a milk-I™/ 5% of the I™ und to the milk of the control » periods when ) the cows. For m this chemical er day the milk m 1.7 to 0.4% decrease is ap'; however, the | by a faetor of the milk/plasma " times imerease [ of perchlorate »tein-bound [™ were 0.06 and 0.09% of a daily dose per liter of plasma and milk duringthe control period. of the total Iin the plasma and inereased The administration of 10 g of Nal per day protein I” proportions by a factor of 2.8, but Administration of perchlorate did not change these concentrations. Because of the changes in the nonprotein-bound I™ the proportion of protein-bound I™ decreased from 9.1 to 7.2% from 6 to 23% in the milk. en we tn oO Oo on oa—_— 2 on be It it oo had relatively little effect on milk protein- bound I. During the thyroxine studies it was noted that levels of 5 to 10 mg of thyroxine per day inereased milk production and pro- vided evidence that the thyroxine preparation was active. To supplement these observations two cows were given daily doses of p-thyroxine and 2-4 dinitrophenol intravenously (Table 1) and the milk/plasma ratio. These data are in general accord with observations made with cows given levels of milk and plasma Ifollowed. The 2 and 4 ¢ of NaI daily (6). No fractionation p-thyroxine did not cause a decrease in the experiment. It was of interest to compare the effect of was evident. Similarly, 2-4 dinitrophenol did not produce a decrease in the milk I™ levels. of milk or plasma I was made in this transfer of Ito the milk; in fact, an inerease another halide upon the transfer of I" into milk. For this, 60 g of NaCl were given daily to a cow in addition to the 50 g customarily supplied in the commercial mixed feed. Data in Table 1 show that the high level of sodium chloride deereased the amount of radioiodine in milk. This decrease was not as marked as that observed with 10 g¢ of Nal. The milk/ plasma ratio was lowered, however, and thus suggests that sodium chloride can affect the iodide-coneentrating mechanism of the mammary gland. An inerease in the levels of thyroxine cireulating in the blood can reduce the uptake of I™ by the thyroid gland. Premachandra and Turner (7), moreover, have shown that increases the amount of I" found in milk; no explanation of the mechanism was offered. With this in mind, four cows were given daily intravenous injections of L-thyroxine and the blood and milk levels of I" followed (Table 1). The data show that 10 mg of exogenous L-thyroxine per day reduced both the concen- mS em bo tom be bo a0 oe Thyroxine administration thus reduced plasma to milking cows resulted in an increase of plasma I" of 1.5 times, a decrease in milk I by a factor of three, and a lowering of the milk plasma ratio by five. Again, the plasma I™ increased markedly during the period of administration of the test substance, therefore, the decrease in milk I’ was less than expected on the basis of the change observed in the creasing of the thyroxine levels in blood de- m/p these levels decreased to 0.032 and 0.027% of a daily dose per liter for the plasma and milk, in that order. Expressed on the basis of proportions the plasma protein-bound I™ deereased from 17.6 to 6.4%, whereas the milk protein-bound I™ changed from 5.4 to 4.5% as the result of the administration of thyroxine. Figure 1 plots the changes in milk, plasma, urine, and thyroid I™ of two eows before and after the start of daily oral administration of 10 g of KCIO,, It should be noted that the crdinate on the left refers to the I coneentration in morning milk and blood plasma, whereas the ordinate on the right is the per cent of I in the thyroid and in the urme. In these experiments KC1O, was first admin- istered at 4 pm; the next morning’s milk sample showed the reduced I™ concentration and the o MILK tration of I? in milk and the milk/plasma [™ ratio by about two. Since no change in the blood Ilevel was noted while the milk I” level decreased, it is possible that this action of the thyroxine was directly upon the mammary gland. In these experiments the average levels of protein-bound Iwere 0.088 and 0.059% of a daily dose per liter for plasma and milk, re- spectively, during the control period. When the 10 mg of thyroxine were being given daily, rot r a 1% o PLASMA o URINE a« THYROID No et Fd din 4 3S00 AUvd 1NI9N3d n that simulated PERCENT DAILY DOSE PER LITER ‘the I capsules el 4 BAYS Fic. 1. Effect of KCIO, upon the milk, plasma, urine, and thyroid I™ levels, The left ordinate refers to the I™ concentration in milk plasma and urine. The right ordinate indicates the I” aceu- mulation in the thyroid. All values are expressed as a pereentage of the daily intake of radioiodine. Day 0 on the baseline ig the day administration of perchlorate began. [3 |