Plasma amino acid patterns were studied in sheep receiving varying amounts of DL-or L-methionine (0'6-10·0 g/day) or L-cystine (2·0 and 8·0 g/day) as abomasal supplements or DL-methionine (10 g/day) as a dietary supplement.Total amino acids in plasma decreased when small amounts (0'6-2'5 g/day) of methionine were infused, but increased substantially with the larger amounts of methionine (4'9-10·0 g/day). However, when methionine and taurine were excluded, the remaining amino acids decreased with all amounts of methionine. Cystine supplementation caused smaller changes in total amino acids.Methionine infusions significantly increased the concentration of methionine, cystine, taurine, and cystathionine in plasma. Cystine infusions increased the concention of the latter three compounds, but not that of methionine. Infusion of small amounts of methionine (0· 6-2 . 5 g/ day) produced only small increases in plasma methionine; with the infusion of larger amounts plasma methionine increased rapidly. The relationship between plasma methionine and amount of methionine infused was described by two straight lines which intersected at about 3 . 3 g/ day of methionine. With an infusion of 10 g/day the mean plasma methionine concentration was 235 ",moles/ 100 ml, which represented 64% of the total plasma amino acids. In contrast, an equimolar amount of cystine (8 g/day) produced only a small increase in plasma cystine, and had no effect on plasma methionine.Infusions of both methionine and cystine caused considerable reductions in the plasma concentrations of the branched-chain amino acids (valine, leucine, and isoleucine), and of serine and glycine.Dietary supplements of methionine (10 g/day) caused no change in the total concentration of amino acids in plasma nor in the concentration of any individual amino acid.

SummaryProblems associated with the measurement of changes in the rate of wool growth are discussed. In particular, there are large errors due to the "emergence time" of the wool, that is the time required for newly keratinized portions of fibre to move out of the follicles to the point where they can be removed by clipping. The results show how the emergence time may be estimated with the aid of [35S]cystine and how clipping schedules may be altered to give a more accurate measure of changes in the rate of wool growth.The rates of wool growth in 12 sheep were studied with both clipping and radioautographic techniques. The emergence time varied from 5 to 10 days and was found to decrease by as much as 4 days as a result of increased food intake and faster wool growth.The biggest changes in the rate of wool growth occurred during the first 2 weeks after changing food intake. The mean diameter and mean length growth rate changed together and in about the same proportion in response to the nutritional changes. The ratio of mean length of wool grown per day to mean diameter ranged from 10 to 16 in the sheep studied, but the ratio for each sheep remained relatively constant during large (up to sixfold) increases in growth rate.

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SutrlllnaryWhen sheep were given intradermal doses of 0-5 ml of 0-9% NaCl containing 5-1400 p.g L_[36S]cystine, an area of labelled wool with a much higher specific activity than the rest of the fleece and corresponding to about 7 cm ll of skin was produced. Over this range of mass of cystine, about 21-1 % of the dose of 35S was incorporated into the wool grown by this area.When the 30 8 was injected intradermally as half-cystine residues bound to plasma proteins, a smaller proportion of the dose was incorporated than for similar masses of free cystine, but a larger area of skin (about 11 cro 2 ) produced wool of relatively high specific activity.L-[36S]cystine, Na 13 l!. and the -51Cr complex of ethylenediaminetetra-acetic acid ([51Cr]EDTA) all disappeared from the skin with a half-time of about 10 min, compared with about 10 hr for ovine [131I]albumin. The appearance of radioautograms of individual wool fibres labelled by repeated intradermal doses of L_[35S]cystine showed that the 3bS was incorporated into the growing fibres over a period of many days. It was concluded that there must be a "pool" of cystine, or of keratin precursors containing cystine, in the skin.Intradermal cystine all produced sufficient labelling of the wool fibres to enable rates of growth of individual fibres to be measured by the radioautographic technique. By using a HC-Iabelled amino acid a "permanent" timing mark can thus be imparted to growing wool fibres.After an intradermal dose of L.[3bS]methionine had been given, about 90% of the 35S incorporated into the wool at the injection site was present as cystine. Rougeot (1959) has shown that wool fibres from a small area of the skin of a sheep can be labelled with a subcutaneous dose of 1-10 fLc of ["S]cystine. The same fibres can be labelled repeatedly in this way, and their rates of growth can be accurately measured after the radioactive regions of the fibres have been revealed by radioautography. Fibres growing more than 2 cm from the point of injection show no detectable radioactivity. Rougeot chose [35S]cystine for several reasons, mainly based on the findings of Bern, Harkness, andBlair (1955) andof Ryder (1956): cystine makes up at least 10% of the wool keratin, the asS label rapidly appears in the follicle, only traces of the 35S appear in the wool or hair grown 3 weeks after the dose, and the half-life of asS, 87·1 days, enables the method to be used over periods of many months. ["S]cystine, given intravenously, was also used by Lyne (1959, 1961) in the development and application of a similar technique for the measurements of the rate of wool growth. INTRODUOTION

I . Doses of ~-[~~S]methionine (2 g) and r5S]casein (20 g) were given to sheep in the diet or via the abomasum, and the patterns of 35S-labelling in blood, wool and excreta were studied during the 7 d following administration of the dose.2. Doses given via the abomasum resulted in substantial labelling of the plasma proteins and wool; only small amounts of the dose were recovered in the urine and faeces. In contrast, doses given in the diet resulted in much less labelling of plasma proteins and wool and ingreater losses in excreta. These results provide the basis of a rapid system for testing the effectiveness of various methods of protecting methionine and casein from degradation in the rumen. From the patterns obtained with N-formyl-~~-[~~S]methionine and [36S]polymethionine (mol. wt 7-8 x 104) it appears unlikely that these compounds would stimulate wool growth if given as dietary supplements. 4.[S6S]Casein which had been treated with an 8 % aqueous solution of formaldehyde gave results which showed that the casein had been protected from destruction in the rumen without markedly reducing its subsequent digestibility. Treatment of [35S]casein with excess,formaldehyde (a 40 % aqueous solution) gave a product which was completely indigestible. . It is concluded that the radioisotope technique could be applied to other [35S]amino acids or their derivatives and to other [35S]proteins, and should also be applicable to larger ruminants such as cattle.