Increase during lactation of RNA synthesis b isolated liver nuclei

Comparative localization of prolactin-binding sites in different rat tissues by immunohistochemistry, radioautography and radioreceptor assay

Prolactin was localized in various rat tissues, using two different histological approaches: immunohistochemistry and autoradiography. Following injection of ovine prolactin (oPRL) to intact rats, oPRL was localized in the proximal convoluted tubules (PCT) of the kidney using an immunoperoxidase technique. Diffuse and weak staining was observed in the liver while no staining was observed on sections of adrenal, testis and brain. Incubation of [125I]oPRL on frozen cryostat tissue sections followed by radioautographic processing revealed specific radioautographic grains on cells of convoluted tubules of the kidney. Specific grains were also seen on hepatocytes of the liver, cells of the adrenal cortex, interstitial cells of the testis and epithelial cells of the choroid plexus of the brain. The amount of specific radioautographic grains seen per tissue agreed well with in vitro binding values of [125I]oPRL to crude membrane preparations in the same tissues. Our observations clearly show that in the rat specific binding sites for prolactin are present on cells of the proximal convoluted tubules of the kidney, hepatocytes of the liver, glandular cells of the zona reticularis, zona fasiculata and zona glomerulosa of the adrenal, interstitial cells of the testis and epithelial cells of the choroid plexus. These studies demonstrate the necessity of using more than one morphological approach in the identification of prolactin-binding sites in different tissues at the cellular level.

The effects of pregnancy and lactation on the activities of trypsin and alpha-chymotrypsin in the rat pancreas

1. The food intake, pancreas weight and trypsin (EC 3.4.21.4) and alpha-chymotrypsin (EC 3.4.21.1) activities in the pancreas were measured in rats during pregnancy and lactation and after the young were weaned. 2. All the quantities measured increased significantly during lactation and had returned to their original values by 4 weeks after weaning. Food intake and pancreas weight were highest after the second week of lactation. Total trypsin and alpha-chymotrypsin activity, and the activity per g tissue, fell during pregnancy and rose during lactation, reaching a maximum 1 week after weaning. 3. From these and other results it is suggested that the hypertrophy and hypersecretion of pregnancy and lactation are initiated by changes insulin secretion and mediated by the trophic effects of gut hormones, and that differences in the nature and timing of the response may be controlled by nutrient availability.

Pituitary hormones and the small bowel: effect of hypophysectomy on intestinal adaptation to small bowel resection in the rat

The influence of pituitary hormones on intestinal adaptation to small bowel resection was studied by examining jejunal and ileal structure and function in control and in sham-operated rats, and in animals with 50% proximal or distal resection which were divided into three main groups: normally-fed, hypophysectomized. and pair-fed. The pituitary was removed 2 weeks before intestinal surgery and gut structure and function were studied 4 weeks later. The effectiveness of hypophysectomy was confirmed by histological examination of the aspirated pituitary, and by showing a significant subsequent reduction in weight of the testes and adrenals. Food intake and body weight fell significantly after removing the pituitary; intestinal surgery caused a transient further decrease in food intake. Measurements of intestinal villus height and crypt depth, indices of mucosal mass (mucosal wet weight, protein and DNA content/cm intestine), measurements of mucosal alpha-glucosidase activity, and in vivo galactose absorption/unit length of intestine all showed comparable results. In rats with an intact intestine, resection resulted in mucosal hyperplasia and increased segmental absorption. Following hypophysectomy, there was marked mucosal hypoplasia and hypofunction which seemed to be due largely to associated hypophagia since comparable changes were found in the pair-fed, sham-operated rats. However following pituitary removal, both distal jejunum and proximal ileum retained their capacity to regenerate though the magnitude of this adaptive change was much greater in the resected, pair-fed rats suggesting that hypophagia alone cannot explain the diminished adaptation to resection after hypophysectomy. By inference, pituitary hormones do influence the adaptive response to resection.

RNA synthesis in nuclei isolated from early embryos of Xenopus laevis

1. Rates of RNA synthesis in isolated Xenopus embryo nuclei decrease from blastula through gastrula and neurula stages to hatching tadpoles. 2. In blastula and gastrula nuclei, net synthesis of RNA continues for over 30 min, both in the presence of KCl at 0.4 M and in its absence. In nuclei from later stages, net synthesis continues for only about 10 min in the absence of KCl. 3. At low ionic strength, RNA synthesis in all nuclei is greater with optimum Mg-2+ (6 mM) than with optimum Mn-2+ (1 mM). At high ionic strength the reverse is true. 4. An unusual feature, which gradually disappears as development proceeds, is that curves relating RNA synthesis to KCl concentration show a peak at 0.1 M KCl. In blastula nuclei, RNA synthesis is more rapid at 0.1 M KCl than at 0.4 M. 5. This peak at low ionic strength is not observed in the presence of the initiation inhibitor rifamycin AF/013. It is concluded that the peak arises from initiation of RNA synthesis by an excess of RNA polymerases bound non-specifically to the isolated nuclei. The residual synthesis, representing elongation of chains that were initiated in vivo, still declines as development progresses. 6. In blastula nuclei, over half of the RNA synthesis is effected by polymerase II (inhibited by alpha-amanitin), the proportion remaining roughly constant with increasing ionic strength. In neurula nuclei, the proportion rises from about one-half to three-quarters. The initiation-dependent peak in blastula and gastrula nuclei is contributed by both alpha-amanitin-sensitive and alpha-amanitin-resistant enzymes.

Induction of a lactogenic receptor in rat liver: influence of estrogen and the pituitary

A receptor exists in female rat liver with high specificity for lactogenic hormones. Previous work showed the receptor level increased at the time of puberty in female but not male animals. Pregnancy caused a further substantial increase. Here we show that estrone (50 mug/day) administration to male rats induced a 10- to 30-fold increase in specific binding of ovine prolactin and human growth hormone after 8-12 days with a significant increase first seen after 4 but not 2 days of injection. In females, this regimen increased binding to pregnancy levels. In prepuberal (20-days-old) male and female rats, estrone was also markedly stimulatory. The binding sites for ovine prolactin and human growth hormone were of high affinity in liver membranes from both female and estrone-treated male rats (K(a) = 0.6 to 1.4 x 10(9) M(-1)). Estrone and estradiol were equally effective in inducing the lactogenic receptor. Estriol (50 mug/day), progesterone (500 mug/day), human placental lactogen (1 mg/day), and testosterone (100 mug/day) were without influence. Hypophysectomy drastically decreased the levels of lactogenic receptor in mature female rats, and estrogen treatment failed to restore receptor levels to normal. Hypophysectomized male rats were also unresponsive to estrogen. Throughout these studies the specific binding of (125)I-labeled insulin remained relatively constant. This work demonstrates estrogen induction of a lactogenic receptor. The pituitary gland appears to have a critical, though presently undefined, role in the induction process.