Involvement of hypothalamic dopamine in the regulation of prolactin secretion

The neuroendocrine control of prolactin (PRL) secretion is known to be a multifactorial process, but dopamine (DA) secreted by the tuberoinfundibular dopaminergic (TIDA) neurons of the hypothalamus is believed to exert a predominant inhibitory control on the secretion of PRL. The secretory activity of the TIDA neurons, including the rate of biosynthesis of DA and the rate of release of the neurohormone into hypophysial portal blood, can be readily evaluated in the rat. In most conditions in which an altered secretion of PRL has been documented, an altered secretory activity of the TIDA neurons has been found. When an acute reduction in the secretion of DA is observed, an increased secretion of PRL is associated, with an inverse relationship between DA and PRL concentrations in hypophysial portal and systemic blood, respectively. However, the secretion of PRL can be regulated by PRL itself through stimulation of the secretory activity of the TIDA neurons, and consequently hyperprolactinemia can be observed concomitantly with a sustained high secretion of DA, as seen after treatment with estrogen. The short loop feedback of PRL secretion seems to be impaired in the aging rat, since a sustained reduced hypothalamic secretion of DA is observed in spite of long-term hyperprolactinemia.     

Enucleation of CHO cells by means of cytochalasin B and centrifugation: the topography of enucleation.

The lanthanum colloidal technique has been used for studying in electron microscopy the modifications occurring during blast transformation in the composition and the amounts of the lanthanum-retaining surface components of human blood T and B lymphocytes. The transformation event has usually been followed by a slight decrease in the surface labeling of the T-line lymph cells. Conversely, in the B-derived lymphocyte population various important staining alterations have been observed.The biochemical meaning of the above-mentioned differential alteration occurring in the lanthanum-staining of the stimulated lymphocyte's surface as a function of their T or B origin is further discussed.     

Androgen receptor in rat liver: characterization and separation from a male-specific estrogen-binding protein

Many liver processes are sexually dimorphic. In particular, the microsomal content of specific enzymes and the synthesis of specific proteins are under sex steroid hormone control. Because the liver of male rats is strikingly androgen responsive, we sought evidence for an androgen receptor in this tissue. We detected and characterized both cytosolic and nuclear androgen-binding proteins. Both forms bind [3H]R1881 (methyltrienolone, 17 beta-hydroxy-17 alpha-methyl-4,9,11-estratriene-3-one) with the high affinity, low capacity, and specificity for androgens and antiandrogens characteristic of androgen receptors. No high-affinity binding of [3H]DHT could be detected in unfractionated cytosol because of the rapid metabolism of this ligand; however, binding of a DHT metabolite to the high-capacity male-specific estrogen binder (MEB) of cytosol was observed. Both gel filtration and heparin-Sepharose affinity chromatography separate the cytosolic androgen receptor from MEB. Incubation of cytosol in the absence of sodium molybdate resulted in androgen-binding activity which was retained by DNA-cellulose. Castration of male rats results in a time-dependent loss of both cytosolic and nuclear androgen binding, as well as a loss in MEB activity. Androgen-binding activity is low in livers from female rats, but can be induced by testosterone treatment. An intact pituitary is necessary for maintenance of androgen-binding activity, as hypophysectomy results in complete loss of activity.     

Application of nitrous acid deamination of hexosamines to the simultaneous GLC determination of neutral and amino sugars in glycoproteins

A method is described for simultaneous gas chromatographic analysis of neutral sugars and hexosamines in glycoproteins. Sugars are hydrolyzed with the aid of Dowex 50-X2 (H⁺) resin and the resin bound glucosamine and galactosamine are deaminated with NaNO₂ to the coresponding neutral 2,5-anhydrohexoses. Hexoses and 2,5-anhydrohexoses are then quantitated as the corresponding alditol acetates. Application of the procedure to several different glycoproteins is presented.     

A comparison of the growth-promoting, lipolytic, diabetogenic and immunological properties of pituitary and recombinant-DNA-derived bovine growth hormone (somatotropin).

The physiological mechanisms by which growth hormone (somatotropin) exerts its several metabolic activities remain poorly understood. In particular, there is disagreement as to whether the diabetogenic and lipolytic activities of the hormone are intrinsic properties of the molecule or are the result of contamination with other pituitary components. The availability of recombinant-DNA-derived bovine growth hormone (rebGH) presented an opportunity to compare the biological activities of rebGH and pituitary bGH in the absence of pituitary contaminants. Pituitary bGH and rebGH were immunologically identical in the radioimmunoassay for bGH, and good agreement was obtained for the potency of the latter measured by radioimmunoassay (1.6 units/mg) and the dwarf-mouse bioassay (1.4 units/mg). The lipolytic activity in vitro was examined by measuring the release of glycerol from rat epididymal fat maintained in the presence of dexamethasone (0.2 microgram/ml) and the material to be tested (0.1 and 0.2 mg/ml). Although two preparations of pituitary bGH stimulated a significant (P less than 0.01) increase in glycerol production, neither rebGH nor recombinant-DNA-derived chicken GH was lipolytic. However, when rebGH was intravenously injected into three sheep (0.15 mg/kg), the increase in plasma nonesterified fatty acids was similar to that measured with the same dose of pituitary bGH. Insulin-tolerance tests were conducted in sheep before and after treatment with rebGH and pituitary bGH (four subcutaneous injections of 0.15 mg/kg). Although the effect of rebGH was less than that of the pituitary hormone, both significantly impaired the ability of insulin to lower the concentration of plasma glucose. These data suggest that the lipolytic and diabetogenic activities of bGH are intrinsic properties of the molecule. However, the lipolytic activity may only become apparent after either modification of the molecule in vivo or activation of a lipolytic intermediate.