Studies on the carbohydrate metabolism of sheep. XI. The role of the adrenals in ovine pregnancy toxaemia

Abstract

Plasma cortisol levels in fed and fasted non-pregnant and in undernourished pregnant ewes were consistently less than 1.5 µg per 100 ml. Most values were considerably above this level in 20 field cases of pregnancy toxaemia, 31 of 52 values being greater than 3 µg per 100 ml. These levels must be regarded as abnormally high in sheep. Pregnancy toxaemia was induced in two experiments by fasting after a period of severe under nutrition and in two by fasting previously well-nourished ewes in the presence of severe psychological stresses. The onset of clinical signs was associated with marked increases above normal in plasma cortisol. In three experiments involving a total of 23 previously well-nourished ewes, 11 of which carried twins or triplets, only one mild case of pregnancy toxaemia was induced by complete fasting in late pregnancy for up to 6 days, in the absence of any additional environmental stress. Pregnancy toxaemia was readily induced in 24 of 38 ewes in three experiments when severe psychological stresses accompanied fasting in late pregnancy. Adrenal hypertrophy, indicating sustained adrenal hyperactivity, was most pronounced in field cases of pregnancy toxaemia induced primarily by sustained under nutrition. Fresh adrenal weights (total of two adrenals) averaged 6.7 g compared to 3.8 g in normal non-pregnant ewes. Mean plasma cortisol levels in ewes with pregnancy toxaemia were significantly correlated with fresh adrenal weight. The suggestions that abnormalities of carbohydrate and fat metabolism in ewes with pregnancy toxaemia are those of adrenal steroid diabetes, and that cerebral depression may be largely a consequence of a cortisol-induced inhibition of glucose utilization, are discussed in the light of the probable metabolic effects of cortisol in the undernourished pregnant ewe.