A RETROSPECTIVE STUDY OF INCREASED PLASMA PROGESTAGEN CONCENTRATIONS IN COMPROMISED NEONATAL FOALS

Plasma progestagen concentrations were measured daily by radioimmunoas say (RIA) in 35 sick foals for the duration of their illness. The foal s were divided into three groups on the basis of time to stand after b irth. Foals were given intensive care treatment according to the sever ity of their illness. Plasma and urine concentrations of pregnenolone (P5) and pregnenediol (P5 beta beta) were measured by gas chromatograp hy-mass spectrometry; plasma cortisol concentrations were measured by RIA and the foals' renal and respiratory status were assessed by creat inine clearance ratios and arterial oxygen concentrations respectively . Five patterns of plasma progestagen concentrations were identified; in general, values increased when the feat's clinical condition deteri orated and decreased as the foal improved. Median progestagen concentr ations decreased over the first three days post partum in Group 1 foal s but remained elevated in foals from Groups 2 and 3. Similar changes were observed in plasma P5 and P5 beta beta concentrations. Plasma cor tisol concentrations were highest in foals from Groups 2 and 3 (P < 0. 01) compared with foals from Group 1. Regardless of foal group, mean c ortisol concentrations were highest (P < 0.001) in those foals treated with adrenocorticotrophic hormone compared with those treated with de xamethasone or with neither drug. There was no relationship (r(2) = 0. 21) between plasma cortisol and progestagen concentrations. Results fr om renal clearance, steroid conjugation and respiratory status suggest that these factors did not play a significant role in elevating proge stagen concentrations in sick foals. It is hypothesized that there may be a relationship between adrenal stimulation and an enzyme block res ulting in overproduction of P5 and P5 beta beta in the sick neonatal f oal.