ABSTRACT

Specific binding sites for chum salmon growth hormone (sGH) were identified in the membranes obtained from tissues of rainbow trout. Specific binding of ¹²⁵I-labelled sGH (% per mg protein) was found in the liver (37%), ovary (6%), brain (6%), gill (4%), intestine (4%) and posterior body kidney (4%). Specific binding was not significant in head kidney, anterior body kidney, spleen, heart, skeletal muscle or skin. Scatchard analyses demonstrated the presence of a single class of high-affinity low-capacity receptors in the liver, gill, intestine and kidney. The association constants for the membranes from liver, gill, intestine and kidney were of the same order (1 litre/nmol). Chum salmon prolactin did not inhibit the binding of ¹²⁵I-labelled sGH to receptors in the liver, gill, intestine and kidney.

Transfer of rainbow trout from fresh water to 80% seawater evoked a rise in plasma concentration of GH and a significant decrease in the GH binding to the liver membranes after 1 day. Binding in the gill and kidney was not altered significantly. Membranes were treated with 4 mol MgCl₂/l to remove bound GH from the receptors, and the results indicated that the reduction in binding in the liver after transfer to sea-water was probably due to receptor occupancy by increased endogenous GH. The occupancy of liver GH-binding sites was maximal 4 days after transfer. Total (MgCl₂-treated) binding sites in the liver increased significantly 14 days after transfer. Scatchard analysis indicated that receptors were altered in capacity without changes in binding affinity. Although GH may also directly affect osmoregulatory organs through their GH receptors, the present results indicate the likelihood of at least partial mediation by the liver of the seawater-adapting action of GH in the rainbow trout.

Journal of Endocrinology (1991) 130, 425–433

ABSTRACT

The present study was undertaken to investigate the effects of protein kinase C (PKC) activation and calcium mobilization on the release of prolactin from human decidual cells in early pregnancy. Decidua obtained from patients in early pregnancy was enzymatically dispersed and cultured with phorbol myristate acetate (PMA) and calcium ionophore A23187 in a cell culture system. Prolactin in the medium was measured by enzyme-immunoassay.

PMA, a PKC activator, dose-dependently attenuated the release of prolactin from cultured decidual cells, while a PKC inhibitor, H7, significantly (P < 0·001) diminished the effect of PMA on prolactin release. PMA had no effect on cell numbers or DNA synthesis in the decidual cells during culture. It did not significantly increase the generation of inositol phosphate in decidual cells prelabelled with myo[³H]inositol and it had no effect on intracellular calcium concentration ([Ca^{2 +} ]_i). Calcium ionophore A23187, a Ca^{2 +}-mobilizing agent, also significantly (P<0·001) attenuated the release of prolactin and potentiated the PMA-induced suppression of prolactin release from decidual cells.

These findings suggest that activation of PKC and mobilization of Ca²⁺ may be involved in regulating prolactin release from human decidual cells. The PMA-induced suppression of prolactin release is not triggered by phosphoinositide hydrolysis nor by the increase in [Ca^{2 +} ]_i in decidual cells.

Journal of Endocrinology (1993) 137, 335–340

ABSTRACT

The ability of insulin-like growth factor-I (IGF-I), insulin and GH to promote hypoosmoregulatory ability was examined in juvenile rainbow trout (Oncorhynchus mykiss). Following adaptation to 12 parts per thousand (p.p.t.) seawater for 5 days, fish were given a single injection of hormone or vehicle, then exposed to 29 p.p.t. for 24 h and examined for changes in plasma osmolarity, ions and glucose. Ovine GH (oGH; 0·2 μg/g) significantly improved the ability of rainbow trout to maintain plasma osmolarity and sodium levels following transfer to 29 p.p.t. seawater. Recombinant bovine IGF-I (0·01, 0·05 and 0·2 μg/g) also improved the hypoosmoregulatory ability of trout; the effect being dose-dependent and greater than that of oGH. Bovine insulin (0·01, 0·05 and 0·2 μg/g) had no statistically significant effect on plasma ions. The results indicate that IGF-I is a potential mediator of the action of GH in seawater adaptation of salmonids.

Journal of Endocrinology (1991) 130, 87–92

ABSTRACT

We have examined the biological effects of insulinlike growth factor-binding proteins (IGFBPs) on insulin-like growth factor (IGF)-activated glucose consumption in a BALB/c 3T3 subline. The method employed was a colorimetric measurement of glucose consumption, allowing the detection of changes from the initial glucose concentration in conditioned medium, following the addition of IGFs and IGFBPs. Human IGFBP-1, purified from amniotic fluid, inhibited IGF-activated glucose consumption, although it had no effect on insulin-activated glucose consumption. The median effective dose (ED₅₀) of IGFBP-1 to cause inhibitory effects on IGF-activated glucose consumption was 100–200 μg/l and was similar for both IGF-I and IGF-II at a concentration of 1·0 μg IGF/1. Therefore, at IGF concentrations of comparable activity, the inhibitory effects of IGFBP-1 were greater for IGF-I than for IGF-II, because of the higher activity of IGF-I in this assay. Recombinant human IGFBP-3 also inhibited IGF-activated glucose consumption, without affecting insulin-stimulated glucose consumption. The inhibitory effects of IGFBP-3 were greater for IGF-II than for IGF-I when IGFBP-3 was coincubated with either of the IGFs, at both IGF concentrations of comparable activity and equivalent molar concentrations. Thus, it became clear that the inhibitory effects of these IGFBPs on IGF biological action depended primarily upon their affinity for the specific IGF ligand and molar ratio of IGFBP/IGF peptide. Interestingly, when cells were pretreated with IGFBP-3, prior to the simultaneous addition of IGFs and IGFBP-3, the inhibitory effect was higher for IGF-I than for IGF-II. Either no effect or a minor inhibitory effect on IGFactivated glucose consumption was detected with IGFBP pretreatment alone. When the ED₅₀ for inhibition of IGF action by IGFBPs in this in-vitro assay was compared with the physiological concentrations of IGFs and IGFBPs in normal human serum and in amniotic fluid, it was estimated that the IGFBP-1 concentration present in serum was not sufficient to modulate IGF action effectively while the concentration in amniotic fluid was enough for effective suppression. IGFBP-3 exhibited an ED₅₀ low enough to suppress IGF-II and possibly IGF-I action when cells were pretreated with IGFBP-3. Thus, our data suggested that IGFBP-1 in amniotic fluid and IGFBP-3 in serum could be a potent inhibitor for IGF action. IGFBP-1 in serum, however, may not be able to function as a direct inhibitor under physiological conditions but, rather, may modulate IGF action together with other IGFBPs.

Journal of Endocrinology (1993) 136, 457–470

We recently found lumbosacral sympathetic ganglionic galanin neurons innervating the quail uterine oviduct. Galaninergic innervation of the uterine muscle may be essential for avian oviposition, as galanin evoked oviposition through a mechanism of induction of vigorous uterine contraction. The questions arising from these findings are: what changes occur in galanin expression in the sympathetic ganglionic galanin neuron during development, and what is the hormonal factor(s) that induces galanin expression in this neuron? Therefore, the present study examined the developmental changes in galanin of the quail sympathetic ganglionic neuron and uterus, and the effect of administration of ovarian sex steroids on galanin induction. Immature birds reared under long-day photoperiods from 4 weeks of age demonstrated progressive increases in galanin levels both per unit ganglionic protein (concentration) and per ganglia (content) concurrent with ganglionic development during weeks 4--13. The uterine galanin content and uterine weight also increased progressively during the same period, but the galanin concentration in the uterus at 4 weeks was high due to the much smaller tissue mass. Immunocytochemical analysis with anti-galanin serum showed that immunoreactive ganglionic cells were few and small at 4 weeks and increased progressively thereafter. Administration of oestradiol-17 beta to immature birds at 3 weeks of age for 1 week increased both the galanin concentration and content in the ganglia without ganglionic growth. A marked increase in galanin-immunoreactive ganglionic cells was detected following oestradiol treatment. In contrast, progesterone increased ganglionic galanin levels, but the effects were low. Expression of the mRNAs encoding oestrogen receptor-alpha and -beta (ER alpha and ER beta) in the ganglionic tissue was verified by RT-PCR/Southern blot analysis. Immunocytochemical staining with anti-ER serum further revealed an intense immunoreaction restricted to the nucleus of ganglionic neurons. These results suggest that ovarian sex steroids, in particular oestradiol-17 beta, contribute as hormonal factors to galanin induction, which takes place in the lumbosacral sympathetic ganglionic neurons innervating avian uterine oviduct during development. Oestradiol may act directly on this ganglionic neuron through intra-nuclear receptor-mediated mechanisms to induce galanin.

A number of studies on the Atlantic salmon (Salmo salar), have reported changes in plasma GH during parr-smolt transformation, but there is a lack of information about the endocrinology of the GH system during this process. In order to elucidate the mechanisms underlying these changes in plasma GH levels during the parr-smolt transformation of Atlantic salmon, GH mRNA expression in the pituitary was studied together with total pituitary GH content, in vitro GH secretion rate and plasma GH and IGF-I levels. Atlantic salmon were kept in outside tanks, under natural condition from early February until late June. Approximately three times a month fish were killed and pituitaries and blood were sampled for investigation. Further, pituitaries were moved to the laboratory for in vitro GH secretion studies. The results show that the GH system is first activated by an increase in GH secretion rate, which leads to an increase in plasma GH levels and causes a drop in the total GH content of the pituitary. This drop in pituitary GH content is later reversed by an increased GH synthesis seen as an increase in GH mRNA expression. Maximal activation of the GH system is seen to occur in early May, when plasma IGF-I levels reach highest levels, after which a certain deactivation of the GH system takes place. The data show that plasma levels of GH are to a large extent regulated by the secretion rate from the pituitary, although changes in the GH clearance rate are also likely to take place and influence the plasma GH levels. The study further underlines the significant role that the GH-IGF-I axis plays in the parr-smolt transformation of the Atlantic salmon.

We examined the effects of environmental salinity on circulating levels of the two prolactins (tPRL177 and tPRL188) and levels of pituitary tPRL177 and tPRL188 mRNA in the euryhaline tilapia, Oreochromis mossambicus. Fish were sham-operated or hypophysectomized and the rostral pars distalis (RPD) autotransplanted onto the optic nerve. Following post-operative recovery in (1/4) seawater, tilapia were transferred to fresh water (FW), (1/4) seawater (SW) or SW. Serum tPRL177 and tPRL188 levels in sham-operated and RPD-autotransplanted fish were highest in FW and decreased as salinity was increased. tPRL177 and tPRL188 mRNA levels in RPD implants as well as in pituitaries from the sham-operated fish were also highest in FW and decreased with increasing salinity. Serum osmolality increased with salinity, with the highest levels occurring in the seawater groups. We conclude that some plasma factor (probably plasma osmolality), in the absence of hypothalamic innervation, exerts a direct regulatory action on prolactin release and gene expression in the pituitary of O. mossambicus. This regulation is in accord with the actions of the two prolactins in the freshwater osmoregulation of the tilapia.

ABSTRACT

Advances in techniques in molecular biology have facilitated the research into endogenous opioids and related peptides in several ways. The organization and expression of genes and the primary structure of three precursor proteins of opioid peptides have been elucidated. These studies predicted the presence of potentially bioactive peptides, which has been confirmed by later studies. Advances in techniques in protein chemistry have helped to elucidate the distribution and molecular forms of endogenous opioids and related peptides in the body, and the processing of precursor proteins. Studies on the function of these peptides have shown a broad spectrum of actions. Leumorphin, a newly identified peptide, has been shown to exhibit unique biological activities. In spite of extensive studies, the physiological and pathophysiological significance of opioid peptide systems are not yet completely understood. This is mainly due to the paucity of our knowledge about opioid receptors. Further studies on the subtypes of opioid receptors will help to elucidate all aspects of the function of endogenous opioids and related peptides.

J. Endocr. (1985) 107, 147–157