I . Changes in total retinol-binding protein (RBP), the holoprotein (holoRBP) and prealbumin (PA) concentrations have been monitored in plasma of thirty protein-and vitamin A-deficient preschool children from within a few hours up to 7 weeks after treatment with retinol and a good-quality protein diet.2. The children were classified into groups according to nutritional status as having either kwashiorkor, marasmus-kwashiorkor or marasmus, and given formula diets whose protein and energy contents increased stepwise from I g and 105 kJ/kg body-weight respectively up to 4 g and 733 kJ/kg body-weight after 4 weeks. Retinol was administered in the forms of retinyl palmitate either orally or intramuscularly.3. PA and total RBP were determined by electroimmunoassay procedures and the holoRBP by its fluorescence after separation from other plasma proteins.4. RBP in plasma of the vitamin A-deficient child is largely denatured and incapable of binding administered retinol, which must first be taken up by the liver before native holoRBP is released. An increased pool of native apoprotein accumulates in the liver during vitamin A deficiency which is released into plasma quickly after retinol uptake to form peak concentrations of total and holoRBP approximately 3 h after dosing intramuscularly and 6 h orally.5. The accumulated pool of RBP was highest in livers from the marasmus group and lowest in those from the kwashiorkor group, reflecting their relative capacities to synthesize plasma proteins.6. The mean plasma concentrations of total and holoRBP for the various groups were minimal 24-48 h after dosing with retinol and then improved almost linearly over the following week.7. Mean plasma PA concentrations of the various groups on admission were also in order of the severity of their malnutrition. There was little or no change in this protein concentration over the first 24 h after dosing with retinol, but thereafter the mean values rose almost linearly over 2 weeks. Albumin on the other hand changed little during the first week. The results show that PA is the more sensitive measurement of protein nutritional status.A number of studies have shown that the plasma concentrations of retinol and its carrier, retinol-binding protein (RBP) and prealbumin (PA) are reduced in protein-energy mal- After treatment with a massive dose of retinol and a better-quality protein diet the concentrations of the various components of the vitamin A transport system recovered to levels within the normal range after 1-2 weeks. None of these studies, however, examined plasma RBP concentration within a few hours after dosing with retinol.(The nomenclature used in this paper for the various forms of retinol-binding protein is as follows : retinol-binding protein (RBP) is total immunoreactive protein ; retinol-binding holoprotein (holoRBP) is native protein with its ligand retinol attached ; retinol-binding

I. Seasonal changes in retinol-binding holoprotein (holoRBP) concentration in plasma of groups of male and female Japanese quail (Coturnir corurnix juponicu) were examined over 18 months. 2.In Expts I and z the birds were maintained under natural lighting conditions and in Expt 3 under artificial-light photoperiods corresponding to the changing daylength at 56" N latitude. All groups were at 18-20" and received Superlayers' (Rank Hovis McDougall) pellet diet.3. The mean plasma holoRBP concentration in all groups changed in an annual cycle with minimal values in September-October and maximal values in February-April, when daylength or light photoperiod increased to more than 10 h.4. The group mean values in the female cycle change 2-to 3-fold from 5~1 0 0 pg/ml in late summer to 220-280pg/ml in the spring, whereas in the male the range is only 1'3-1'5 times, from 140-170 to 186250 ,ug/ml. 5.In the female the rate of egg laying was maximal in April-May and lowest in November-December.6. The spring increase in plasma holoRBP reflects the increased vitamin A requirement of birds for reproduction and it is presumably under hormonal control. The wider amplitude in the female cycle compared with the male probably arises from the additional demand for the transfer of vitamin A into the eggs and hence the need for a higher initial secretion rate from the female liver to meet it.Retinol-binding protein (RBP) is the specific carrier protein for vitamin A in plasma. It is necessary for the distribution of the vitamin to target tissues such as the eye, epithelial tissues and the gonads. Retinol is bound to the protein (approximately 21000 daltons) in a I : I complex in the human (Kanai et al. 1968) and in all other animal species so far examined including the chick (Abe et al. 1975). This material is called holoRBP to distinguish it from the uncomplexed or unsaturated apoRBP. It has been established previously that the absence of vitamin A for completion of the synthesis of the bimolecular complex in the liver inhibits the release of the protein into the bloodstream by as much as 70 % (Muto et al. 1972). Alternatively, deficiency of good-quality protein in the diet of an otherwise vitamin A-replete subject reduces the pool of some essential amino acids for protein biosynthesis in the liver and lowers the plasma RBP concentration by as much as 3 0~ below control values (Muhilal & Glover, 1974). Thus the plasma level of RBP can change as a consequence of nutritional deficiencies. However, in the normal seasonal breeding animal like the sheep, replete with vitamin A and protein, the concentration of holoRBP undergoes annual cyclic changes from a minimum of 25 pg/ml in the summer to a maximum of ~oopg/ml plasma in the autumn and then gradually regresses in the spring to the summer value (Glover et al. 1976).The autumnal surge in RBP concentration occurs in both sexes with decreasing daylength which has also long been known (Yeats, 1949) to effect changes in the sexual development of sheep. This relationship between RBP concentra...

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