Histochemical demonstration of steroidogenic activity in preimplantation bovine embryos

Abstract

Summary. 3p-HSD activity has been demonstrated histochemically in bovine Day [6][7][8] late-morulae and early blastocysts recovered non-surgically from 12 superovulated Friesian heifers. In some embryos grown in vitro from late-morula to enlarged blastocyst in Eagle's enriched medium, this key enzyme in steroidogenesis was clearly demonstrable during all the period of their survival in culture (96 hrs).These findings are in favour of the capacity of the bovine embryo to synthesize steroids at least in some stages of early development.In recent years there has been an increasing interest in embryonic endocrinology in the initial stages of development, i.e. bofore implantation on the uterine wall. One of the most important factors justifying such an interest is the need to know when and by which processes the fertilized ovum signals its presence to the maternal organism in order to establish the pregnancy. The rapid diffusion of embryo transfer methodology both in laboratory and in farm animals has further stimulated investigations on this and on other important metabolic functions of the early embryo.At present, numerous findings prove the presence in the preimplantation blastocyst of steroid hormones and of enzymes involved in their metabolism and interconversion. However, the data reported by various workers on this subject are not univocal, and are often difficult to correlate because they are the result of investiga- Further biochemical investigations have evidenced the presence of progesterone, oestrogens and other steroids in the blastocyst and/or in the blastocele fluid of the rabbit (Seamark and Lutwak-Mann, 1972 ; Eik-Nes et al., cit. by Lutwak-Mann, 1971 ;Fuchs and Beling, 1974 ;Borland et al., 1977 ;Fujimoto and Sundaram, 1978 ;Singh and Booth, 1978) and of the pig (Perry et al., 1973 ;Heap et al., 1975).On the other hand the uterine fluid contains large amounts of progesterone (Seamark and Lutwak-Mann, 1972 ;Fuchs and Beling, 1974 ;Cowman et al., 1976 ;Borland et at., 1977 ;Fowler et al., 1977) and oestrogens Borland et al., 1977). This has induced many workers to assume that the hormones found in the preimplantation blastocyst have an uterine origin (Seamark and LutwakMann, 1972 ;Borland et al., 1977 ;Fujimoto and Sundaram, 1978 ;Singh and Booth, 1978). This hypothesis seems to be confirmed also by the scarcity of smooth endoplasmic reticulum and tubular mitochondria (Borland et al.,1977) and by the marked pinocytotic activity (Beier and Maurer, 1975) Dey, 1973, 1974a, b ;Dey and Dickmann, 1974a ;, mouse (Dey and Dickmann, 19746), rabbit and hamster (Dickmann and Gupta, 1974 ;Niimura and Ishida, 1976). According to the autonomous production by the preimplantation embryo of steroid hormones plays an important role in the regulation of embryonic metabolism, in the transformation of the morula to blastocyst, in the loss of the zona pellucida and in implantation.The data on this subject in the literature on bovines are scarce, relating mostly to the endocrine processes regulating implantation. In p...