Alteration of the fatty acid composition of monolayer cultures of LM cells grown in chemically defined medium was achieved by supplementation with fatty acids complexed to bovine serum albumin. Phospholipids containing up to 40% linoleate were found in cells grown in medium containing 20 mu g of linoleate/ml. Incorporation of linoleate into phospholipids reached a plateau after 12-24 hr, and cells remained viable for at least 3-4 days. Although linoleic, linolenic, and arachidonic acids were incorporated into LM cells equally well, only the latter was elongated by these cells under these experimental conditions. Nonadecanoic acid was incorporated to a lesser extent than the polyunsaturated fatty acids. Phosphatidylcholine and phosphatidylethanolamine of LM cells had different fatty acid compositions; phosphatidylethanolamine contained more longer chain and unsaturated fatty acids. Cells were also grown in the absence of choline and presence of choline analogs such as N,N-dimethylethanolamine, N-methylethanolamine, 3-amino-1-propanol, and 1-2-amino-1-butanol. The analog phospholipids in these cells had fatty acid compositions which were intermediate between those of phosphatidylethanolamine and phosphatidylcholine of control cells grown in the presence of choline. Linoleate was found in both phosphatidylcholine and phosphatidylethanolamine of cells supplemented with linoleate. The sphingolipid fraction of these cells, however, did not contain significant amounts of linoleate. When linoleate was present in the phospholipids, compensatory decreases in the oleate and palmitoleate content of phospholipids were observed. Lowering of the growth temperature to 28 degrees produced an increase in unsaturate fatty acid content of the phospholipids. When linoleate was supplied to cells grown at 28 degrees, there was no further increase in the unsaturated fatty acid composition of the phospholipids. Using both fatty acid supplementation and lowered growth temperature, LM cell membranes can be produced which have phospholipids with vastly different fatty acid compositions.
Evidence is presented that the apocrine sweat glands of cattle have a temperature-regulating function. Under the stereo microscope, sweat droplets could be observed forming at the openings of the sweat gland ducts in response to intradermal injections of adrenaline, and during exposure to hot conditions. The sweat spots could be stained macroscopically, and prints showing the location of the spots were obtained with bromothymol blue papers pressed onto the skin surface. Quantitative measurements indicate that the evaporation of this sweat is the main source of heat loss in hot environments.
SummaryThe wool growth responses to changes in feed intake are related to the changes produced in body weight. The relation is expressed by the equation W = Ei-kG, where W = wool growth rate, i = feed intake rate, G = rate of body weight change, and E and k are constants. The ratio of E to k in sheep of different productive efficiency was found to be constant.Evidence is presented that this equation indicates a relation between wool growth and metabolic rate, both possibly being responses to changes in endocrine secretion. An alternative interpretation that the equation reflects the effect of body weight change on the supply of amino acids limiting wool growth is also discussed but is considered less likely to be true.The bearing of the results on the evaluation of feedstuffs for wool produc. tion and on the definition of individual productive efficiency is discussed.
SummaryA study has been made of the incorporation at different levels in the developing fibre of 35S into the two main protein fractions of wool. The proteins have been studied as the S-carboxymethyl derivatives rather than as the oxidized derivatives previously investigated. The results obtained give further support for a mechanism of synthesis which involves two stages. However, the incorporation of some 35S into the low-sulphur fraction of the keratinized fibre only 24 hr after the injection of [35S]cystine is somewhat surprising and possible explanations for this have been considered. A detailed comparison has been made of the proteins extracted from the unkeratinized portions of wool roots by 8M urea with those which can be extracted from the keratinized residue with urea-thioglycollate. As might be expected the latter proteins were very similar to those isolated from wool itself. The group of urea-soluble, high-sulphur proteins was different in containing considerable amounts of protein lower in both molecular weight and sulphur content than the comparable fraction from the fully keratinized wool. The possibility is discussed that some of these urea-soluble, high-sulphur proteins may be precursors of those in the fully keratinized fibre, conversion taking place by a process of sulphur enrichment.
SummaryThyroidectomy of the newborn lamb prevents the maturation of secondary wool follicles. The administration of L-thyroxine to thyroidectomized lambs allows normal follicle development.Body growth and wool growth are also depressed by thyroidectomy and most thyroidectomized lambs do not survive more than a few weeks without replacement therapy. The effects on wool growth do not appear to be secondary to the effects on follicle development.The thyroxine requirements for normal wool growth and for normal secondary follicle maturation appear to be greater than the requirements for general body growth. I. INTRODUCTIONThe development of wool follicles in the lamb has been described by Carter (1943), Carter and Hardy (1947), Burns (1949), Fraser (1954, Schinckel (1953Schinckel ( , 1955, and Short (1955). Primary follicles are fully developed and are producing fibres at birth. Development of most if not all secondary follicles commences by the time of birth but in the Merino only about 20 per cent. of secondary follicles are producing fibres at this time. In the first month after birth this proportion increases to 70-80 per cent. Further development then occurs more slowly.The thyroid is well known to affect growth and differentiation. Simpson (1924) found that thyroidectomy of lambs retarded growth and reduced fleece weights at 13-14 months of age by 50 per cent. but no observations were reported on follicle development. The hair cycles of rats are greatly retarded by thyroidectomy (Salmon 1938; Scow and Marx 1945;Scow and Simpson 1945; Dicke 1948), and the administration of throxine to normal rats has been reported to accelerate the hair cycle (Butcher 1937). The lamb does not exhibit several cycles of wool development similar to the hair cycles in the rat, but development of individual follicles appears to be a similar process in both species. This paper reports the results of an experiment carried out to determine the effect of the thyroid on the maturation of the secondary follicles of the lamb. The results show that the thyroid does markedly influence this process.
SummaryFive sheep (two Merinos, two Corriedales, and one crossbred) were subjected to unilateral thoracic sympathectomy. Fleece samples were collected at 28-day intervals, for a period of seven months, from tattooed areas of skin on both the sympathectomized and control sides.The results show a mean increase of 36 per cent. in wool growth rate on the sympathectomized side over the control side for ten weeks after the operation. This effect then disappeared so that no difference between the two sides was observed over the remainder of the experimental period. It is suggested that the initial effect of sympathectomy on wool growth rate was brought about by vasodilation of the denervated vessels and that the subsequent disappearance of this effect was due to the onset of warmer weather causing vasodilation of the control side.Skin surface temperature showed a significant increase on the sympathectomized side immediately after the operation but this effect also disappeared within a few weeks so that no difference was detected during the fleece collection periods. Skin surface temperature may have been depressed on the sympathectomized side during the process of actual measurement due to constriction of the denervated cutaneous vessels caused by nervous excitement.
Since wool-growth rate is strongly influenced by the plane of nutrition, any measure of inherent wool-producing capacity in the sheep must take this into account, and the relation of these three factors to each other must be known. On general grounds, the relation of wool-growth rate to nutrient intake seems likely to follow the familiar law of diminishing returns which introduces the concept that for each sheep there may be an asymptotic value of wool-growth rate characteristic of the individual. From this and other considerations, it was postulated that these relationships could be described by an equation of the form where y = wool-growth rate, x = nutrient intake rate at or above maintenance levels, Xo = the nutrient intake rate for which y = 0, A = the asymptotic value of y, and k' = a constant dependent on the nutritive qualities of the diet employed:
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