The concentration of total corticosteroids, corticosteroid binding globulin (CBG) and progesterone were determined in maternal and foetal/neonatal plasma from rats on days 5, 4, 3, 2, 1 before birth and days 0, 1, and 4 after birth. In addition free corticosteroids and adrenal weight/unit body weight were measured on the foetuses/neonates and the foetuses, respectively. Although the concentration of maternal total corticosteroids and CBG ranged from 53.0 ± 12.5 to 31.0 ± 13.1 μg/100 ml (x̄ ± sem) and 26.6 ± 2.2 to 45.1 ± 0.9 μg corticosteroid bound/100 ml plasma, respectively, the changes in the concentration of these constituents were not related to the initiation of either parturition or lactation. The concentration of total corticosteroids in foetal plasma increased significanly (P < 0.05) from day 5 (14.6 μg/100 ml) to reach peak concentrations (44.9 μg/100 ml) on day 3 before birth and then decreased to low levels (7.7 μg/100 ml) at birth. The pattern of change in foetal adrenal weight/unit body weight closely followed the pattern of change in the concentration of total corticosteroids in foetal plasma during the last 5 days of gestation. There was a significant (P < 0.05) daily decrease in the concentration of CBG in the foetuses from 4 days before until 1 day before birth, which resulted in a significant (P < 0.01) increase from 3.08 to 5.94 μg/100 ml of free corticosteroids in the foetal plasma between day 2 and day 1 before birth, respectively. This peak corresponded with a significant fall (P < 0.02) in the maternal progesterone (measured by protein binding assay) from 2.57 μg/100 ml to 0.62 μg/100 ml between day 2 and day 1 before birth. Foetal progesterone (measured by radioimmunoassay) showed the same changes as maternal progesterone but was between 25–50 % of that in maternal plasma. These findings suggest that the changes in foetal free corticosteroids and maternal progesterone are important in the initiation of parturition in the rat.

In this study a pathway for the synthesis of triacylglycerol (TAG) within the lumen of the endoplasmic reticulum has been identified, using microsomes that had been preconditioned by depleting their endogenous substrates and then fusing them with biotinylated phosphatidylserine liposomes containing CoASH and Mg

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The percentage of a-glucan phosphorylase in the active form was measured in the liver of premature rats following surgical delivery. The enzyme is 30°/, active in the late foetal liver and reaches 45O/, activation four hours after birth. Thereafter there is a slow decline to the new-born level. Puromycin and actinomycin D injected at delivery are without effect on the enzyme activity and activation of preformed inactive enzyme therefore occurs. These results are interpreted to mean that there is a transitory increase in the concentration of 3' : 5'-cyclic AMP in postnatal rat liver. Glucose and ergotamine tartrate partially inhibit phosphorylase activation when injected at delivery and their effects are additive, implicating hypoglycaemia and hormonal mechanisms in the postnatal activation. Fructose and galactose also inhibit phosphorylase activation while mannose is without effect. Foetal liver phosphorylase is activated in utero by injection of 3' : 5'-cyclic AMP and in postnatal rats a transitory increase in phosphorylase activity after injection of the cyclic nucleotide indicates a life time of the injected compound of less than S h. These results are discussed in relation to the induction of enzymes in postnatal rat liver by 3' :5'-cyclic AMP.

The objective of this study was to determine whether genotype, age (4, 8, 14 and 22 months), sex (ewe and wether) and muscle type influence ovine (n = 587) muscle metabolic characteristics. The genotypes represented were Poll Dorsetgrowth × Border Leicester Merino, Poll Dorsetgrowth × Merino, Poll Dorsetmuscling × Merino, Merino × Merino and Border Leicester × Merino. Between 4 and 22 months of age, myoglobin concentration within all muscles and all genotypes doubled, with the bulk of this response occurring between 4 and 8 months of age. Levels in the longissimus thoracis et lumborum (LT) and semimembranosus muscles were double those seen in the semitendinosus (ST) muscle, and Merinos had the lowest myoglobin concentrations of all genotypes. The other aerobic indicator, isocitrate dehydrogenase, had lower activity in the ST compared with the LT, was lower in 22-month-old sheep compared with all other ages, and decreased as selection for leanness increased. Both phosphofructokinase and lactate dehydrogenase activity tended to increase with age, were lower in the ST compared with the LT, and had higher activity in the Border Leicester × Merino sheep. The correlation between the percentage of total myofibre area comprising type 2X myofibres and metabolic markers was far higher for the oxidative indicators isocitrate dehydrogenase and myoglobin, which both decreased as relative area of type 2X fibres increased. However, the strongest correlations were with the relative area of type 2A myofibres, which were consistently high for both oxidative and glycolytic metabolic markers implying positive coregulation with both energy producing pathways.

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