A. Locatelli

Up regulation of corticotrophin receptors by ACTH1–24 in normal and hypophysectomized rabbits

Abstract The number of ACTH binding sites, in adrenal membranes from adult female rabbits, has been measured at different times after hypophysectomy and after ACTH1–24 treatment. The receptor number was significantly reduced 192 h after removal of the pituitary gland as compared to intact controls. Conversely, ACTH treatment of intact rabbits enhanced the number of ACTH binding sites, or restored these levels to presurgical values in hypophysectomized animals. These results suggest that ACTH, like other hormones, is able to induce an increase in the number of its own receptors; the physiological significance of such variations remains however to be elucidated.

Adrenal maturation of the sheep fetus during late pregnancy

The mechanism by which adrenal growth is achieved and steroidogenesis is stimulated in the fetal lamb during late pregnancy has been studied. Fetal plasma ACTH levels remained roughly constant between 14 and 3 days pre partum (298 +/- 38 pg/ml), then increased to a mean of 634 +/- 89 pg/ml. The rise in ACTH did not occur before the pre partum rise in cortisol. The increase in adrenal weight was achieved in three periods, one of DNA duplication between two phases of cellular hypertrophy. Cellular hypertrophy was accompanied by an important biosynthesis of membrane proteins. This development might partly explain the increased production rate of cortisol by the fetal adrenals during late pregnancy. At the same time, the number of ACTH receptors per 2 adrenals increased 5-fold. There was a close correlation between the levels of fetal plasma corticosteroids and the number of ACTH receptors during late pregnancy. It has been suggested that receptor modulation is one of the factors responsible for the enhanced sensitivity of the fetal adrenals to ACTH just before parturition. Preliminary results on the endocrine regulation of that development are also presented.

Le chimérisme XX/XY ne joue pas de rôle dans la phase initiale du freemartinisme chez les bovins

The XX lymphocytes in peripheral blood of 22 bulls born co-twin with freemartins ranged from 5 to 95%. The difference of 1\m=.\2%between the means of XX percentages at initial and final karyotyping of 14 bulls over periods of 1\p=n-\5years was not significant (P > 0\m=.\25).Seven (58\m=.\3%)of the 12 A.I. chimaeric bulls were reproductive culls as compared to only 5\m=.\4%of their 128 controls (P < 0\m=.\001).The culled chimaeras produced no semen, had a low sperm output or had a high incidence of abnormal spermatozoa. The means for motility, sperm concentration and motile spermatozoa per ejaculate were significantly lower for the 12 chimaeric bulls than for a random sample of 12 controls (P < 0\m=.\025).The 60to 90-day non\x=req-\ return rate for 30 814 services to 8 chimaeric bulls was 70% with a \m=-\0\m=.\1%mean deviation from contemporary breed average (P > 0\m=.\5). The 7 chimaeric bulls culled for poor reproductive performance had larger and more numerous focal areas of testicular degeneration. Areas of lymphocytic infiltration in testes of many of these bulls suggest a rejection phenomenon or the autoimmune response. No XX germ cells were detected in testes of 11 chimaeric bulls, aged 1\p=n-\9years. Differential haemolysis blood typing tests on one bull with 85% XX lymphocytes and 23 of his dam-daughter pairs provided no evidence of germ cell chimaerism. One bull with 33% XX cells sired an excess of daughters (71%) in a progeny group of 48, a significant deviation from a 1:1 ratio (P < 0\m=.\01). A disturbance in normal spermatogenesis in prenatal and postnatal life by transplanted XX primordial germ cells may contribute to the marked reduction in reproductive fitness of many chimaeric bulls.