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SH Torres, JB De Sanctis, L M de Briceno, N Hernandez, and HJ Finol

An inflammatory process may be involved in nitric oxide production in skeletal muscle of type 2 diabetic patients. Nitric oxide generation in skeletal muscle was assessed in 14 non-complicated type 2 diabetic patients and in 12 healthy subjects. In samples of quadriceps femoris muscle, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), nitrite, nitrate and nitrotyrosine were determined. The macrophage-specific antigen CD163, the T-cell membrane factor CD154 and tumour necrosis factor-alpha (TNF-alpha) were also assayed. In six patients, ultrastructural analysis of muscle was performed. Nitrites and nitrates were increased in patients as compared to controls (22.7+/-4.5 and 32.7+/-7.0 vs 16.0+/-2.9 and 22.8+/-4.0 micromol/mg protein; P<0.001, Mann-Whitney U test). Endothelial NOS was similar in diabetic and control subjects (36.4+/-13.8 vs 36.3+/-6.8 ng/mg protein), contrasting with the significant increase of iNOS recorded in patients (34.3+/-13.0 vs 8.5+/-2.8 ng/mg protein, P<0.00002). Nitrotyrosine levels were higher in the patient than in the control group (42.1+/-24.4 vs 10.3+/-2.5 ng/mg protein, P<0.00002), as were CD163 (10-fold) and TNF-alpha (fourfold) levels. Furthermore, CD154 levels were detectable only in the patient samples (10.2+/-5.3 ng/mg protein). By multiple-regression analysis, changes in glycated haemoglobin values could predict 96% variation in nitrotyrosine. Macrophages were present in all muscle samples analysed by electromicroscopy. The increased levels of CD163, CD154 and TNF-alpha indicate that an inflammatory process occurs in skeletal muscle of type 2 diabetic patients. This may contribute to iNOS induction, muscle damage and insulin resistance.

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L L Hernandez, J L Collier, A J Vomachka, R J Collier, and N D Horseman

Serotonin (5-HT) is a homeostatic regulator of lactation. Selective 5-HT reuptake inhibitors (SSRI) are commonly prescribed pharmaceuticals that inhibit activity of the 5-HT reuptake transporter, increasing cellular exposure to 5-HT. Use of SSRIs has been shown to alter lactation performance in humans and 5-HT has been shown to reduce milk yield in cattle. However, it has not been determined how SSRI treatments affect the bovine mammary gland. We evaluated the effects of SSRI (fluoxetine (FLX)) administration on tight junctions (TJs) and milk protein gene expression in a lactogenic culture model, using primary bovine mammary epithelial cells (pBMEC). Additionally, we evaluated the effects of intramammary infusions of FLX and 5-hydroxytryptophan on milk production and TJ status in multiparous Holstein cows at dry-off. Treatment of pBMEC cultured on permeable membranes disrupted TJs, as measured by transepithelial resistance and immunostaining for zona occludens 1. Correspondingly, treatment of ‘3D’, collagen-embedded lactogenic cultures of pBMEC with FLX suppressed milk protein gene expression (α-lactalbumin and β-casein) in a concentration-dependent manner. Finally, intramammary treatment of Holstein cows with FLX resulted in an accelerated rate of milk decline. Additionally, TJ permeability increased in FLX-treated animals, as measured by plasma lactose and milk Na+ and K+ levels. Results of these experiments imply that SSRI administration accelerates the rate of mammary gland involution through disassembly of TJs and inhibition of milk protein gene expression in vitro and in vivo, leading to reduction of milk yield.