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SUMMARY
Binding of cortisol to plasma proteins was studied in the foetal lamb by equilibrium dialysis at 37 °C. At 122 days of pregnancy the mean level of transcortin expressed as cortisolbinding capacity was 28 ± 6 (s.d.) ng cortisol/ml plasma. During the last 14 days of pregnancy there was a progressive increase in transcortin-binding capacity to 85 ± 14 ng cortisol/ ml plasma. A sharp increase in the concentration of both protein-bound and unbound cortisol was observed over the same period. A rise in the concentration of total cortisol from around 3 to 42 ng/ml was associated with an increase in unbound cortisol from 0·2 to a maximum of 2·1 ng/ml. The concentration of albumin-bound cortisol was approximately equal to that of unbound cortisol. The mean value for the transcortin–cortisol affinity constant was 1·15 × 108 l/mol.
It is concluded that an increase in transcortin-binding capacity is partly responsible for the prepartum increase of corticosteroid levels observed in normal foetal lambs.
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Ministry of Agriculture and Fisheries, Ruakura Agricultural Research Station, Private Bag, Hamilton, New Zealand
(Received 23 August 1974)
The foetal adrenals are important in initiating parturition in sheep (Liggins, Fairclough, Grieves, Kendall & Knox, 1973) and goats (Thorburn, Nicol, Bassett, Shutt & Cox, 1972). Indirect evidence suggests that the foetal adrenals may be involved in the termination of pregnancy in the cow. Such evidence includes prolongation of pregnancy when foetal pituitary function is impaired (Kennedy, Kendrick & Stormont, 1957; Holm, 1958), and the induction of parturition by administering either corticotrophin (Welch, Frost & Bergman, 1973) or dexamethasone (Hunter, Welch, Fairclough, Barr & Seamark, 1974) to the foetal calf.
Comline, Silver, Nathanielsz & Hall (1973) have noted a two- to threefold increase in foetal cortisol levels in prematurely calving cows. These authors conclude that this comparatively small rise in foetal cortisol levels casts doubt on whether the foetal adrenal cortex is
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ABSTRACT
The effect of immunizing against somatostatin (SRIF), with SRIF conjugated to bovine thyroglobulin, was examined in cross-bred sheep fed either cut pasture or lucerne pellets. Plasma concentrations of GH were unaffected by SRIF immunization, but were lower in pellet-fed sheep. Plasma concentrations of insulin-like growth factor I (IGF-I) increased after immunization in sheep on both diets. Pasture-fed sheep had lower plasma concentrations of IGF-I than those on pellets. Sheep showed a small increase in growth rate in response to immunization. Immunization had no effect on carcass composition and did not affect plasma concentrations of IGF-II, free fatty acids or glucose. The results show that even though SRIF immunization increases plasma concentrations of IGF-I, it does not necessarily result in a large increase in growth rate.
J. Endocr. (1987) 112, 27–31
