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Incubation Media (incubation + media)

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Medical Sciences	50%

Selected Abstracts

Effect of bile salts, lipid, and humic acids on absorption of benzo[a]pyrene by isolated channel catfish (Ictalurus punctatus) intestine segments

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2001
Lynn P. Weber
Abstract Dietary absorption of lipophilic contaminants may be a significant route of exposure in aquatic organisms. Bile salts, lipids, and humic acids are important factors that may influence the intestinal absorption of a contaminant such as benzo[a]pyrene (BaP). We hypothesized that bile salts, monoglycerides, and free fatty acids would increase BaP intestinal absorption, while triglycerides, humic acids, and sediment would decrease BaP intestinal absorption. We have established and validated an in vitro model to examine modification of 3H-BaP absorption in everted intestinal segments from channel catfish (Ictalurus punctatus). Uptake of BaP into the everted intestinal segments continued to increase over the times examined in this study (60 min) and apparently occurs passively; thus, fugacity-based models of uptake are supported. Absorption of BaP into intestinal cells was significantly decreased by the addition of monoglycerides and free fatty acids to bile salts in the incubation media. Addition of triglycerides decreased BaP absorption even further. Humic acids may have decreased BaP intestinal absorption, while natural sediment may have increased BaP absorption. The results of this study suggest that all lipids may decrease intestinal uptake of lipophilic contaminants if they remain in unabsorbable excess in the intestinal lumen by retaining BaP in lipid/bile micelles. In contrast, if triglycerides are hydrolyzed into monoglycerides/free fatty acids prior to absorption, lipophilic contaminant uptake will likely be facilitated. Thus, it may be the hydrolytic state of lipids that determines its effects on BaP absorption. Humic acids alone may decrease dietary uptake of BaP, but our results suggest that other components in natural sediment may counteract this effect to cause a slight enhancement of BaP uptake. Further studies are needed to determine the dietary conditions necessary for bio-accumulation to contribute significantly to lipophilic contaminant body burdens in benthivorous fish. Finally, the everted intestinal segment technique has the potential to be used in other species and with different contaminants. [source]

Tyrosine phosphorylation of a 38-kDa capacitation-associated buffalo (Bubalus bubalis) sperm protein is induced by L -arginine and regulated through a cAMP/PKA-independent pathway

INTERNATIONAL JOURNAL OF ANDROLOGY, Issue 1 2008
S. C. Roy
Summary The aim of the present study was to determine the effect of l -arginine on nitric oxide (NO,) synthesis, capacitation and protein tyrosine phosphorylation in buffalo spermatozoa. Ejaculated buffalo spermatozoa were capacitated in the absence or presence of heparin, or l -arginine or N, -nitro- l -arginine methyl ester (l -NAME), an inhibitor of nitric oxide synthase (NOS) for 6 h. Capacitating spermatozoa generated NO, both spontaneously and following stimulation with l -arginine and l -NAME quenched such l -arginine-induced NO, production. Immunolocalization of NOS suggested for existence of constitutive NOS in buffalo spermatozoa. l -Arginine (10 mm) was found to be a potent capacitating agent and addition of l -NAME to the incubation media attenuated both l -arginine and heparin-induced capacitation and suggested that NO, is involved in the capacitation of buffalo spermatozoa. Two sperm proteins of Mr 38 000 (p38) and 20 000 (p20) were tyrosine phosphorylated extensively by both heparin and l -arginine. Of these, the tyrosine phosphorylation of p38 was insensitive to both induction by cAMP agonists as well as inhibition by a protein kinase A (PKA) inhibitor. Further, most of these l -arginine-induced tyrosine phosphorylated proteins were localized to the midpiece and principal piece regions of flagellum of capacitated spermatozoa and suggested that sperm flagellum takes active part during capacitation. These results indicated that l -arginine induces capacitation of buffalo spermatozoa through NO, synthesis and tyrosine phosphorylation of specific sperm proteins involving a pathway independent of cAMP/PKA. [source]

Effect of bile and lipids on the stereoselective metabolism of halofantrine by rat everted-intestinal sacs

CHIRALITY, Issue 2 2010
Jigar P. Patel
Abstract The everted rat intestinal-sac model was utilized to assess the effect of post-prandial conditions on the stereoselective intestinal metabolism of halofantrine to its active metabolite desbutylhalofantrine. Everted intestinal sacs were incubated with (±)-halofantrine HCl in the presence of simulated bile solution (containing lecithin, lipase and cholesterol) and lipids to mimic post-prandial conditions in the small intestine. The halofantrine enantiomer concentrations in intestinal sacs were relatively constant in the presence of bile, but decreased significantly on addition of lipids to the incubation media. Formation of desbutylhalofantrine enantiomers was inversely proportional to bile concentration whereas addition of lipids in the presence of bile caused a significant decrease in desbutylhalofantrine:halofantrine ratio of (,) enantiomers. Pre-treatment of rats with peanut oil had no significant effect on desbutylhalofantrine formation in the incubated sacs or microsomal preparations, nor did it affect the expression of intestinal cytochrome P450. Addition of extra cholesterol to the bile incubations caused a significant increase in tissue halofantrine and desbutylhalofantrine concentrations, which as for lower cholesterol, were diminished on addition of other lipids. The results were consistent with previous in vivo evaluations showing that the desbutylhalofantrine to halofantrine ratio was decreased by the ingestion of a high fat meal. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source]

The release of leptin and its effect on hormone release from human pituitary adenomas

CLINICAL ENDOCRINOLOGY, Issue 6 2001
Márta Korbonits
BACKGROUND Leptin is the protein product of the obese gene, known to play an important role in body energy balance. The leptin receptor exists in numerous isoforms, the long isoform being the major form involved in signal transduction. Leptin expression has recently been demonstrated in the human pituitary, both in normal tissue and in pituitary adenomas. The long isoform of the leptin receptor has also been shown to be present in pituitary adenomas; however, contrasting results have been obtained regarding its expression in the normal human pituitary. AIM The aim of this study was (i) to investigate the presence and pattern of distribution of leptin mRNA and the long isoform of its receptor mRNA in the normal pituitary and in different types of pituitary adenomas with RT-PCR; (ii) to study leptin secretion from human pituitary tumours in culture and (iii) to assess in vitro pituitary hormone release following stimulation with human leptin. RESULTS Leptin receptor long isoform expression was detected in 2/4 GH-secreting adenomas, 12/17 non-functioning adenomas, 5/9 ACTH-secreting adenomas, 1/2 prolactinomas, 2/2 FSH-secreting adenomas and 5/5 normal pituitaries. The receptor long isoform did not segregate with any particular tumour type, and varying levels of expression were detected between the tissues studied. Leptin mRNA was detected at a low level of expression in 2/7 GH-secreting adenomas, 9/14 non-functioning adenomas, 2/3 ACTH-secreting adenomas, 1/3 prolactinomas and 1/3 FSH-secreting adenomas. We were unable to detect leptin mRNA in any of the five normal pituitaries removed at autopsy; however, immunostaining of a non-tumorous pituitary adjacent to an adenoma removed at transsphenoidal surgery showed scattered leptin positive cells. Culture of pituitary adenomas showed that 16/47 released leptin into the incubation media. Leptin release did not correlate with tumour type or with any of the other pituitary hormones released. In vitro leptin stimulation of pituitary tumours caused stimulation of FSH and ,-subunit secretion from a non-functioning adenoma and TSH secretion from a somatotroph adenoma. CONCLUSION We conclude that not only is leptin stored within the pituitary, but it may also be released from pituitary cells and modulate other pituitary hormone secretion. Pituitary leptin may therefore be a novel paracrine regulator of pituitary function. [source]