Comparative biochemistry and physiology. Part C, Pharmacology, toxicology & endocrinology最新文献

Eggshell thinning in ducks was induced by administration of p,p'-DDE in the diet (40 mg/kg food) for 45 days. This treatment resulted in a 19% reduction of the Eggshell Index (EI). Shells from calcifying eggs obtained at the time of slaughter showed a 36% reduction of EI. Prostaglandin synthesis by a homogenate of eggshell gland mucosa from p,p'-DDE-treated ducks was reduced by 24%. HCO3(-)-stimulated ATPase activity by a homogenate of eggshell gland mucosa from p,p'-DDE-treated ducks was not significantly changed. The calcium content of eggshell gland mucosa was increased to 127% in p,p'-DDE-treated ducks. p,p'-DDE-treated ducks showed profound changes in the shell gland luminal content of several ions. Calcium (-43%), sodium (-15%), potassium (-15%), bicarbonate (-33%) and chloride (-29%) were all significantly reduced in p,p'-DDE-treated ducks. The content of phosphate was unchanged. These findings are discussed in relation to a proposed mechanism for p,p'-DDE-induced eggshell thinning that involves inhibition of prostaglandin synthesis in eggshell gland mucosa.

Immunoblots (Western blot) of mullet liver microsomes revealed the presence of multiple forms of P-450 that appear to be structurally related to rainbow trout CYP1A1 and CYP2K1 and to P-450 LMC1 and LMC4, but not to LMC5. 3-Methylcholanthrene but not beta-naphthoflavone induced a major 58 kDa liver protein and a minor 56 kDa protein in mullet that both cross-reacted with anti-trout CYP1A1 IgG. The levels of immunodetectable P-450s and the activities of microsomal lauric acid hydroxylase, DMBA hydroxylase and progesterone 6 beta-hydroxylase were several times lower in mullet liver than in rainbow trout liver; however, progesterone 16 alpha-hydroxylase and progesterone 20 alpha-hydroxylase activities were 4-fold and 6-fold higher, respectively, in mullet than in trout liver.

The effects of new hypothalamic peptides, PACAP-27 and PACAP-38, and secretin and VIP on the interdigestive pancreatic secretion and duodenal myoelectric activity during the asecretory phase of the pancreatic interdigestive cycle, compared with the milk ingestion phase, were examined in five calves. Peptides were infused for 5 min into the external jugular vein (0, 3, 10, 30 and 100 pmol/kg body wt during the asecretory phase of the pancreatic interdigestive cycle, and the pancreatic secretory response was compared with that obtained during milk ingestion. Intravenous infusion of PACAP-27 caused dose-related stimulation of pancreatic juice flow and bicarbonate and protein output; this effect was identical to infusion of secretin. The effect of PACAP-38 was less pronounced, and that of VIP was the weakest. Pancreatic juice volume and bicarbonate responses during milk ingestion were similar to responses obtained with the highest doses of hypothalamic peptides and secretin, whereas postprandial protein secretion was much greater than the secretion stimulated with peptides. It was concluded that PACAP from the VIP/secretin family may stimulate pancreatic exocrine secretion in conscious calves and a part of the pancreatic response to food intake can be mediated by PACAP.

The pulsatile secretion of the hypophyseal luteinizing hormone (LH) is induced by the pulsatile secretion of the hypothalamic neurons secreting gonadotrophin-releasing hormone (GnRH). Seasonal variations in the pulsatility of LH were studied in the adult male mink (Mustela vison), reared under natural environmental conditions. Twenty-one animals were studied according to five critical phases in the breeding season: (1) the terminal phase of sexual quiescence, which precedes renewal of gonadal activity (October-November); (2) renewal of gonadal activity (December); (3) maximum gonadal activity at the height of the breeding season (February); (4) reduction of testicular activity (April); and (5) the initial phase of testicular quiescence (June). Levels of gonadal growth and activity were used to define each phase. A second animal group was studied after being reared for 2 months in an experimental gonado-inhibitory photoperiod, which, necessarily for the mink, was of the "long-day" type: 20L:4D regimen in the present study. Results, obtained with fully conscious animals, provide evidence for the pulsatile secretion of gonadotrophic hormone in this species. In spite of inter-individual differences in pulse patterns, particularly in phases 1 and 2, the pulsatile character of LH secretion is seen to vary markedly as a function of gonadal activity. The variations reflect an increase of hypophyseal activity as early as the preparative phase to the breeding season, and a decrease of activity during the testicular regression phase, which is followed by the onset of gonadotrophic quiescence in June. The main parameter affected statistically by these seasonal fluctuations is pulse frequency; variations in pulse frequency correlated with variations in mean plasma concentrations of LH. In the experimental gonado-inhibitory photoperiod, which led to a severe reduction in gonadal activity, all hormonal pulsatility parameters were statistically reduced; this confirms the importance of photoperiodic control of reproduction in Mustela vison. Several possible mechanisms are proposed for photoperiodic control.

The effect of tea extract on the intestinal absorption of glucose and sodium was studied in rats. Tea extract reduced the mucosal uptake of glucose and its portal plasma concentration, but was without any effect on its serosal transport. The mucosal uptake of sodium was similarly inhibited. The tea extract reduced also the in vitro activity of the Na(+)-K+ ATPase in an intestinal mucosal homogenate. These data are consistent with the hypothesis that an active ingredient in tea reduced sodium extrusion from the enterocytes by inhibiting the Na(+)-K+ pump, thus destroying the gradient needed for the mucosal transport of glucose.

The basal levels of mu and pi class glutathione S-transferases RNA were 18-fold higher in the male mouse liver as compared with the female. When 0.75% (w/w) BHA was included in the diet it altered the RNA levels of alpha, mu, pi GST classes and mGSTA4-4 in a tissue and sex specific manner. The most marked induction of RNA was seen for the mu class GSTs of female liver, lung and kidney (52, 10 and 8-fold, respectively), and of male liver and kidney (25 and 3.5-fold, respectively), the pi class GSTs of female liver, lung, and kidney (11, 10, and 5-fold, respectively), and mGSTA4-4 of female liver (4-fold). The effect of BHA on the induction of the mu and pi class GST RNA was 2-9 fold greater in female as compared with male tissues. The degree of induction of GST RNA did not correlate directly with changes in GST protein indicating that post-transcriptional events regulating GST expression may be affected by BHA particularly for GST mu and mGSTA4-4.

The dihydropyrazole RH-3421 inhibits veratridine- and K(+)-induced rises in synaptosomal free Ca2+ with IC50s of 0.2 and 1 microM, respectively. The K(+)-induced rise in free synaptosomal Ca2+, which requires external Ca2+, is also blocked by RH-3421 in the presence of tetrodotoxin. The K(+)-stimulated 45Ca2+ uptake by synaptosomes is unaffected by tetrodotoxin, blocked by cobalt ions and inhibited by RH-3421 both alone (IC50 = 11 microM) and in the presence of tetrodotoxin. RH-3421 does not influence the level of free Ca2+ or basal 45Ca2+ uptake in non-depolarized synaptosomes. The results suggest RH-3421 inhibits voltage-sensitive calcium channels in nerve endings.

Membrane-bound neuropathy target esterase (NTE) and associated phenyl valerate carboxylesterases were solubilized from chicken embryo brain by phospholipase A2. Phospholipase A2 from bee or cobra (Naja) venoms were the most effective preparations in solubilizing brain NTE and other phenyl valerate carboxylesterases. Phospholipase C and several proteinases (endoproteinase, pronase E, proteinase K, thermolysin, trypsin) did not solubilize brain membrane-bound carboxylesterases but reduced their activity. NTE solubilization by phospholipase A2 did not affect its apparent Km and Vmax for the substrate phenyl valerate or the susceptibility of phenyl valerate carboxylesterases to inhibition by paraoxon and mipafox. NTE thermal stability diminished after the treatment of brain membrane fragments with phospholipase A2.

The effect of Misoprostol (an analog of PGE1) on the biochemical changes in the small intestine of suckling rats was studied. Misoprostol increases sucrase activities in the proximal and the distal small intestine. Jejunal aminopeptidase N activity is higher in Misoprostol-treated rats than in the control rats. This drug also modifies the relative weight of the small intestine and the mucosal ratio of DNA to RNA. Misoprostol effects appear to be mediated by corticosterone release.

The DNA and amino acid sequences of the membrane-spanning region of the GABA receptors of the German cockroach have been identified along with information on the nature and the specific site of mutation in the cyclodiene-resistant strains. In this resistant strain, the mutation has occurred at the most conserved, lower M2 cylinder region involving a G to T conversion, resulting in an amino acid change of alanine (GCC) residue to serine (TCC). The site, furthermore, coincides with the most conserved region of all GABA receptor subunits and the expected Cl- transporting segment constituting the innermost surface of the channel opening. The deduced sequence of the German cockroach GABA receptor differs from that of Drosophila mainly in the connecting region between M3 and M4.