Protein binding of plasma cortisol in the foetal lamb near term.
Binding of cortisol to plasma proteins was studied in the foetal lamb by equilibrium dialysis at 37 degrees C. At 122 days of pregnancy the mean level of transcortin expressed as cortisol-binding 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 x 10(8) 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.
D000818:Animals; D005260:Female; D005312:Fetal Blood; D005865:Gestational Age; D006854:Hydrocortisone / Q000097:blood*; D011247:Pregnancy; D011485:Protein Binding; D012709:Serum Albumin / Q000032:analysis; D012756:Sheep / Q000097:blood*; D014156:Transcortin / Q000032:analysis
D012709:Serum Albumin; D014156:Transcortin; D006854:Hydrocortisone